GALILEI Map Interpretation Guide UG - ADAPT · 4 GALILEI Interpretation Guide Software version 5.2 FOrEwOrd “After working in corneal topography for more than 10 years, I was the

Map Interpretation GuideMap Interpretation GuideSoftware Version 5.2

Map Interpretation GuideSoftware Version 5.2

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Foreword .................................................................................................................................................................................. 4 Introduction ............................................................................................................................................................................ 5 Getting Started ..................................................................................................................................................................... 6

1 The Refractive Report ...................................................................................................................................... 6 1.1. Importance of color scale and step size in maps .................................................................. 6 1.2. Indices displayed with the Refractive Report ........................................................................... 7 1.3. Evaluation of Refractive Reports ......................................................................................................... 10

2. The Keratoconus Report ................................................................................................................................. 14 2.1. Importance of Instantaneous map and Keratoconus Indices ..................................... 14 2.2. Evaluation of Keratoconus Reports ................................................................................................... 15

3. The Wavefront Report ...................................................................................................................................... 19 3.1. Zernike coefficients, higher order aberrations and shape of the cornea ......... 19 3.2. Understanding the relationship between HOAs, refraction, quality of vision, corneal shape and curvature ...................................................................... 20 3.3. Evaluation of Wavefront Reports .......................................................................................................... 22

4. The IOL Power Report ...................................................................................................................................... 27 4.1. About how GALILEI’s Total Corneal Power is improving

the IOL power calculation .......................................................................................................................... 27 4.2. Evaluation of IOL Power Reports ........................................................................................................ 32

5. The Map x1 ............................................................................................................................................................... 34 5.1. Importance of the pachymetry map ................................................................................................. 34 5.2. Other Map x1 options ................................................................................................................................... 36 5.3. Evaluation of the Map x1 display ....................................................................................................... 37

6. The Map x4 ............................................................................................................................................................... 41 6.1. Importance of the Anterior BFTA Elevation map .................................................................. 49 6.2. Evaluation of the Map x4 display ....................................................................................................... 53

7. Axial and Instantaneous Anterior-Posterior Topography ..................................................... 55 7.1. Importance of the topography of both corneal surfaces ................................................ 56 7.2. Evaluation of the topography of both corneal surfaces ................................................. 57

8. BFS and BFTA Elevation maps ................................................................................................................... 62 8.1. Importance of the BFS Elevation map ............................................................................................ 62 8.2. Importance of the BFTA Elevation map ......................................................................................... 63 8.3. Evaluation of the Display showing BFS & BFTA Elevation maps of both surfaces .................................................................................................................................. 64 9. The American Style Display ........................................................................................................................ 68 9.1. Evaluation of the American Style Display .................................................................................... 70

10. The German Style Display ............................................................................................................................ 72 10.1. Evaluation of the German Style Display ........................................................................................ 72 11. Differential Maps ................................................................................................................................................ 75

Appendix .................................................................................................................................................................................. 79

cONTENTS

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GALILEI Interpretation Guide Software version 5.2

FOrEwOrd“After working in corneal topography for more than 10 years, I was the first user of a GALILEI system in Brazil in 2007. I am grateful to the Department of Ophthalmology, Federal University of São Paulo that accepted to receive my unit for research. If at that time I was passionate about the possibility to integrate Placido and Scheimpflug technologies, now I am delighted to see that the GALILEI is much more than a topographer. It is a multifunctional analyzer of the anterior segment of the eye with features and applications that serve more than only refractive surgery. More sophisticated and complete than other equipment, it gave us the opportunity to provide more accurate data in a simple to use device with easy to interpret exams. The CGA color scales and the Alternate Profile were developed to fulfill such a target. The CGA color scales and Alternate Profile use the strategy of establishing a fixed guide value that focuses on the yellow step of the best available color scale for each magnitude. This color scale guide is designed to ease the perception of borderline cases – those cases we want to discover before and not after problems appear. This Map Interpretation Guide reflects my opinions on corneal tomography and how to use the GALILEI. I hope it is useful for all GALILEI users, especially those who are just beginning to use it.

Carlos G. Arce, M.D.

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INTrOducTIONThe purpose of this guide is to facilitate the interpretation of GALILEI reports and displays and highlight how the choice of color scales can help guide interpretation.

This guide provides example cases to help the user to understand relevant clinical patterns in maps included in the GALILEI reports and displays, focusing on three common cases:

Example 1: Normal Spherical CorneaExample 2: Normal Astigmatic Cornea with Initial Posterior Surface ChangesExample 3: Keratoconus (KC) with Irregular Astigmatism

Maps of the Alternate Profile included in this guide correspond to my suggestions reported in the manual software (SW) version 5.2 update notes. The Alternate Profile was optimized to use the best available scale for each magnitude and incorporates the universal meaning of traffic light colors for all maps (Refer to the Appendix: Arce CG. SW version 5.2 update notes 2010 for more information). Maps of the Default Profile are those available in all GALILEI units in former SW versions. The Default Profile uses one default distribu-tion of colors for all maps. Although the same data are used to pro-duce maps of both profiles, the map patterns and colors may look different due to the scales used. Numerical values are shown only in the Alternate Profile and could be displayed on all maps.

Note: These cases were acquired with SW version 5.0, which did not include the indices for KProb and Instantaneous Curvature that are included in later versions. Therefore these indices are reported as N/A in the reports.

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GETTING STarTEd 1. The refractive report

The basic Refractive Report contains the four standard maps that are displayed by other tomographers. These maps include Anterior Axial Curvature, Pachymetry, Anterior Elevation and Posterior Elevation (BFS) maps, shown in clockwise order.

1.1. Importance of color scale and step size in maps

The Anterior Axial Curvature map is displayed in the Alternate Profile (Figure 1A) with the Default CGA 1 D color scale and is calculated with a keratometric refractive index of 1.3375. The Default Profile (Figure 1B) of the same map is presented with the Default Type I 1.5 D color scale.

There are reasons why Anterior Axial maps with one diopter (D) scale are recommended and easier to understand. First, it is faster and simpler to count color steps one-by-one in 1 D increments. For example it is easier to quantify the difference between the flatter and steeper zones and to observe the asymmetry of dioptric profiles in different meridians or the increased number of diopters in multifocal corneas.

Second, larger steps may mask typical patterns of asymmetry and astigmatism. Normal, predominantly spherical surfaces (with astigmatism less than 1 D) will not display the trade-mark bow-tie pattern. In fact, other devices are set up with smaller steps to accentuate the bow-tie pattern so they are more easily observed. Smaller steps (< 1 D) are not necessary because slight astigmatism is not a problem and usually is a good sign of normality. In fact, very small differences in curvature add unnecessary “noise” on the maps. Furthermore, the intuitive universal meaning of colors is lost when extreme red or blue colored regions are achieved producing false positive patterns.

Third, vertical or horizontal asymmetries larger than 1.4 D are usually considered risk factors for refractive surgery. Since the GALILEI Default CGA 1 D color scale has 6 green steps ranging from 41 D to 46 D, any asymmetry larger than 1 D will be evident, even if the surface has a curvature within the normal range. The appearance of a yellow region indicates that the surface curvature is on the border-line of being abnormally steep and any orange region indicates that the surface has already an abnormally steep curvature.

The German CGA 20 µm scale used in the Pachymetry map of the Alternate Profile is much better, in my opinion, than the Default Type II 25 µm scale of the Default Profile or the ANSI Type III 10 µm used by other equipment. Although I would prefer to have only 5 or 6

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green steps instead of 7 green steps, the thickness progression and distribution are more apparent when the yellow step is located in the middle of the color scale. The German style has 15 thicker steps of 20 µm each instead of only 11 steps as displayed with the Default style.

The Anterior BFS Elevation (8-mm-diameter central zone) and Posterior BFS Elevation (7.8-mm-diameter central zone) maps have the ANSI CGA 5 µm scale in the Alternate Profile. Within a 5-mm-diameter central region of interest (ROI), the normal maximum peak of Anterior Elevation BFS was preliminarily established to be less than 10-12 µm and of the Posterior Elevation BFS to be less than 15-16 µm (Arce CG. Data not published; Blanco C, Nuñez X. Elevation and pachymetry values in normal corneas obtained by GALILEI. Boston, USA. ASCRS 2010). These values can be seen when the numbers are overlaid on the map or measured quickly using the mouse on any map location. To facilitate map interpretation, the Alternate profile provides 3 green steps in the maps to show the normal ± 5 µm values and 2 yellow steps to indicate such borderline values. The Default Profile uses the Default Type III 5 µm scale with the zero value in the second of 6 green steps, which may make it more difficult to detect any abnormality in the two elevation maps.

1.2. Indices displayed with the refractive report

In addition to maps, relevant numerical indices corresponding to the maps are shown in the right column of the Refractive Report. The indices are presented in mm and diopters, when available. The average SimK values, K Steep, K Flat and steeper Astigmatism with angle are calculated and displayed at the top. Several indices from other maps (Anterior Instantaneous, Posterior Axial Curvature, and Total Corneal Power by ray tracing) and the anterior and posterior squared eccentricity (e2 = -Q) are also displayed in the Refractive Report.

The average normal anterior axial curvature has a 7.8 mm radius, which corresponds to an equivalent power of 43.27 D (range: 41 D to 47 D) using the 1.3375 keratometric refractive index (or 48.21 D using the 1.376 physiologic refractive index). The average normal posterior axial curvature has a 6.5 mm radius, which corresponds to an equivalent power of -6.15 D (range: -5.50 D to -6.8 D).

The shape is reflected in the eccentricity (e) value. Normal corneal surfaces vary from a sphere (e2 = 0) to a prolate (steeper at the center and flatter at the periphery) toric ellipsoid asphere (+1 > e2 > 0). The anterior surface (mean value e2 = +0.20 ± 0.16) is less prolate than the posterior surface (posterior e2 > anterior e2, mean value e2 = +0.25 ± 0.16) in agreement with the normal corneal thickness distribution where the cornea is thinner at the center (Arce CG. Corneal shape

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and HOAs may be used to distinguish corneas with keratoconus. Poster. Paris, France. ESCRS 2010). Although there are corneas with KC and e2 < +1, and corneas with PMD that may achieve e2 < 0, it seems there are no normal untouched corneas with e2 < 0 or e2 ≥ +1 (Arce CG, Trattler W, Dawson DG. Keratoconus and Keratoectasia. In Atlas of Corneal Pathology and Surgery. Boyd S. Editor-in-Chief. Jaypee Highlights Medical Publishers. Panama. 2010).

The mean Total Corneal Power (TCP) by ray tracing, TCP steep, TCP flat and steeper Astigmatism with angle are also calculated automatically for a similar zone than the Sim K. The Axial Anterior Curvature in diopters calculated with a 1.3375 refractive index is also shown from the central (0 – 4 mm), mid-peripheral (4 – 7 mm) and peripheral (7 – 10 mm) regions. Other indices displayed are the central (0 – 4 mm), mid-peripheral (4 – 7 mm) and peripheral (7 – 10 mm) corneal thickness averages; the thinnest point thickness and location; the pupil size and location of pupil center, and the limbus-to-limbus distance from Superior-Inferior and Temporal-Nasal. Missing indices may indicate that an earlier SW version was used to acquire the images or the result of poor quality data input. For example, when the pupil and/or limbus indices are not shown, the user can review the images in the Verify panel to verify the top view (TV) image focus and alignment to the fixation marks.

The Refractive Report is the most commonly printed report used for preoperative refractive surgery screening around the world. The Refractive Report contains the traditional maps that have been standardized by previous topography devices. However, the Refractive Report may be insufficient for some cases because it compares anterior and posterior corneal surfaces using only BFS elevation maps. The posterior surface curvature map is not shown in this popular report and can be more instructive to aid early detection of pathology and screening for corneal disease. For this reason I suggest reviewing routine cases using two separate reports. A new customized report containing the curvature and elevation topography of both anterior and posterior corneal surfaces (refer to N°7 of this guide: Axial and Instantaneous Anterior-Posterior Topography). A second report using the Map x1 option and containing only the pachymetry map (refer to N°5 of this guide: Map x1). This is my preference in my Eye Clinic in Brazil and my suggestion for countries where pachymetry and topography exams are reported separately in order to fulfill independent codes used by health systems. We must remember that pachymetry is a different measurement and this exam deserves a separate consultation report from topography.

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1.3. Evaluation of refractive reports

Example 1: Normal Spherical Cornea

The Alternate Profile (Figure 1A) of the Refractive Report shows a normal almost spherical anterior surface. There is an anterior axial curvature map without a bow-tie pattern (0.22 D of astigmatism and e2 = 0.09) that tends to blue because the surface is uniformly flat (SimK Avg 41.09 D). The thinnest thickness value is 560 µm and there is asymmetric thickening of the peripheral cornea well observed by the change of color from green to blue (more nasal blue steps than temporal). There is an almost completely green anterior BFS map as should be expected when the surface uniformly fits the same radius of best fit sphere (±5 µm). The normal green horizontal bridge pattern on the posterior BFS map suggests that the posterior surface is toric, prolate and elliptical (the indices report 0.25 D of astigmatism and e2 = 0.29).

In the Default Profile (Figure 1B) there is an asymmetry of colors on the posterior BFS map with an orange zone at the temporal side of the central yellow (zero value) bridge. Despite a possible correlation with the asymmetric pachymetry map, this apparent asymmetry in elevation could be a mistaken “hot zone” since it is not observed in the respective map of the Alternate Profile. It also does not appear in the posterior curvature maps that will be shown later in this document (refer to N°7 of this guide: Axial and Instantaneous Anterior-Posterior Topography).

Example 2: Normal Astigmatic Cornea With Initial Posterior Surface Changes

This report shows a normal anterior prolate elliptical surface (e2 = 0.31) with a typical steeper vertical (warmer) bow-tie representing a 1.5 D with-the-rule astigmatism. A normal horizontal green bridge pattern is found in the anterior BFS map of the Alternate Profile (Figure 2A). There is a false-positive orange zone in the anterior BFS map of the Default Profile (Figure 2B). The posterior surface is also elliptical but more prolate (e2 = 0.72) than the anterior surface. The posterior BFS map also shows a normal horizontal bridge pattern with a yellow “hot zone” (border line values ≤ 15 µm) at the temporal side. Notice that this yellow hot zone is orange in the Default Profile in the posterior BFS map.

There is a completely green pachymetry map indicating a normal thickness distribution and normal thinnest thickness value of 545 µm. There is a normal symmetric thickness progression (fewer than 10 steps of 20 µm per step).

Border line yellow hot zones in the Alternate Profile are important to detect early topographic signs as they are indicators to search for risk factors in other maps. When these hot zones are temporal or nasal,

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Figure 1B

Figure 1A

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Figure 2B

Figure 2A

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it usually announces an asymmetric bow-tie (irregular astigmatism) in the respective curvature maps. In this case such asymmetries will be described later (refer to N°2 of this guide: The Keratoconus Report and to N°7: Axial and Instantaneous Anterior-Posterior Topography). When they are located at the center of the bridge, they may correlate with steeper curvatures as with example N°3 that follows. Despite the differences in color distribution with the Default Profile, it is important to remember that each map represents the same surface and it is originated from exactly the same numeric values.

Note: The astigmatism or cylinder value calculated from the axial map is relative to the center of the map. Misalignment of the device red-cross to the center of the fixation marks (four white dots) can change the magnitude and angle of the axial curvature (related to the K steep and K flat values). The instantaneous curvature astigmatism values are less sensitive to decentration. Also the axis is less stable for lower magnitude cylinder values, e.g. when K steep = K flat.

Example 3: KC with Irregular Astigmatism

There are several clear indicators of KC and abnormal corneal deformation in maps and indices of this Refractive Report:

a) Despite a SimK Avg of 46.86 D that is within normal range, there is an irregular with-the-rule astigmatism in both the anterior (3.28 D cylinder) and the posterior (-0.48 D cylinder) surfaces.

b) The anterior curvature has a steep (red), very asymmetric vertical bow-tie appearance that resembles a doll-like pattern with a small head and a big colored skirt.

c) The anterior surface has an inferior steepening of more than 52 D and a superior flattening less than 40 D (≈ 12 D of inferior-superior (I-S) dioptric difference).

d) Both anterior and posterior surfaces (e2 = 1.17 and e2 = 1.23, respectively) are prolate with an asymmetric hyperbolic shape (e2 > 1.0).

e) The central corneal thickness (CCT) is 471 µm and the thinnest point is 467 µm (2nd orange step). Both thicknesses are less than 500 µm, which is the borderline of the Alternate profile guide value that I use.

f) The thinnest point is located 0.8 mm from the pupil centroid. Despite that this dislocation is less than 1 mm, its location induces a slight asymmetry of thickness progression and distribution reflected by 7 temporal steps and 11 nasal steps. For comparison, using the Alternate Profile, the normal progression profile is fewer than 10 steps (Arce CG, Use of optical pachymetry in diagnosis of keratoconus. Boston, ASCRS 2010).

g) Since normal maximum values on BFS elevation maps should be below 16 µm, no more than 2 yellow steps are expected in the Alternate Profile (Figure 3A). Here however both anterior and posterior BFS maps already have yellow-orange horizontal bridge patterns.

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Figure 3B

Figure 3A

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h) There is an abnormal central hot zone in both BFS elevation maps achieving almost 20 µm (third yellow step) in the anterior surface and 30 µm (already orange) in the posterior surface.

i) When viewed in the Default Profile (Figure 3B), these same anterior and posterior surface hot zones are both displayed as orange-red hot zones.

2. The Keratoconus report

In the Keratoconus Report, the traditional Anterior Axial Curvature map is replaced by the Anterior Instantaneous (tangential) Curvature map. The other maps are the same shown in the Refractive Report and include the Pachymetry, Anterior Elevation and Posterior Elevation (BFS) maps, shown in clockwise order.

2.1. Importance of Instantaneous map and Keratoconus Indices

The Anterior Instantaneous Curvature map concentrates on the localized curvature and every point correlates better with its real anatomical location on the corneal surface. As a consequence, smaller details are accentuated in the Instantaneous Curvature map. Such details are smoothed out in the Axial map of the same data.

This Instantaneous map is calculated with the keratometric refractive index of 1.3375 and is displayed with the Default CGA 1.5 D scale in the Alternate Profile. In the Default Profile it is shown with the Default Type I 1.5 D scale. As we have seen, selecting different scales for the axial and instantaneous maps increases the chances of observing different curvature patterns. Sometimes one display appears normal whereas the other appears suspicious.

The numerical indices of axial curvature and limbus measurements are replaced by the anterior surface Keratoconus Indices. Among these indices, the Inferior-Superior (I-S) index and the Standard Deviation of Corneal Power (SDP) are often increased in KC. The “at risk” I-S index based on GALILEI data has not been formally defined. Although usually an I-S index of more than 1.4 D is considered a risk factor for post-LASIK ectasia based on data from other devices, an I-S index found in KC suspects of 1.20 D has also been reported (Li X, Yang H, Rabinowitz YS. Keratoconus: classification scheme based on video-keratography and clinical signs. J Cataract Refract Surg 2009; 35:1597–1603). On the other hand the Surface Regularity Index (SRI) approaches zero in spherical surfaces.

The Keratoconus Prediction Index (KPI) is a compilation index that simulates the percent probability of KC based on the anterior surface analysis (Maeda N, Klyce SD, Smolek MK, Thompson

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HW. Keratoconus Prediction Index. Invest Ophthalmol Vis Sci 1994; 35:2749–2757 and Mahmoud AM, Roberts C, Lembach R, etal. Simulation of machine-specific topographic indices for use across platforms. Optometry and Vision Sc 2006; 83:682–693). KPI and other indices are guide numbers reflecting the probability of keratoconus based on the anterior surface curvature features. Since this is a probability relying on topographic data from one dataset, it should not be the sole assessment tool in the diagnosis of KC and should be confirmed by clinical diagnosis. Based on my experience, GALILEI’s KPI from 0 to 10% seems to correspond to normal or suspicious corneas; KPI from 10 to 20% to suspicious or borderline keratoconic corneas; KPI from 20 to 30 % to keratoconic or perhaps still suspicious corneas, and KPI more than 30% should be considered pellucid marginal degeneration (PMD) or KC (Arce CG. Data not published). The Keratoconus Probability (KProb) refers to a specificity and sensitivity validation of the reported KPI value based on the statistical analysis of a series of normal corneas and corneas with KC (Refer to the Roberts C. SW version 5.2 update notes for more information).

2.2. Evaluation of Keratoconus reports


The Keratoconus Report either in the Alternate (Figure 4A) or the Default (Figure 4B) Profile shows maps with similar patterns described for the Refractive Report. I-S index is 0.61 D indicating a small asymmetry within normal range. SDP is only 0.36 D and SRI is 0.41 D suggesting a regular and spherical anterior surface. ACP is 40.99 D confirming the tendency towards a flat surface. The KPI is 0%.


In the Alternate Profile (Figure 5A) the Anterior Instantaneous Curvature map shows a “D-shaped” pattern reflecting asymmetry in the horizontal meridian. This “D-shaped” sign has been already reported as a risk factor for ectasia (Abad JC, Rubinfeld RS, Del Valle M, Belin MW, Kurstin JM. Vertical D: A novel topographic pattern in some keratoconus suspects. Ophthalmology 2007; 114:1020–1026). The I-S index is 1.29 D also indicating some inferior-superior asymmetry. The SDP index is 0.91 D, SRI is 0.93 D, ACP is 43.87 D and KPI is 0.9%, which are all within normal range.

The aforementioned curvature asymmetry observed in the Alternative Profile display of the anterior surface is less pronounced in the Default Profile, as shown in Figure 5B.

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Figure 4B

Figure 4A

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Figure 5B

Figure 5A

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Figure 6B

Figure 6A

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Example 3: KC with Irregular Astigmatism

The Keratoconus Report shows similar patterns in maps found in the Refractive report in both the Alternate (Figure 6A) and the Default (Figure 6B) profile. However in the Anterior Instantaneous Curva-ture map (in the upper left panel) there is more than 54 D of inferior steepening and less than 36 D of superior flattening (≈ 18 D of diop-tric difference). The I-S index is 10.18 D indicating significant inferior-superior asymmetry. The SDP index is 3.67 D, SRI is 1.81 D, ACP is 47.62 D and KPI is 100%, which are well within the typical abnormal range indicating KC.

3. The wavefront report

3.1. Zernike coefficients, higher order aberrations and shape of the cornea

The Wavefront Report of GALILEI’s SW 5.2 shows the total corneal higher order aberrations (HOAs) in microns (at left) and in diopters (at right). The Wavefront map in microns is similar to the Wavefront map in diopters, however the colors are inverted. The pie distributions of indices for both maps are exactly the same. Thus, I prefer to present the map of HOAs in microns (at left) and the pie distribution in diopters (at right). The GALILEI allows one to search the amount of corneal HOAs in any region of interest (ROI) from 3 to 6 mm. I normally initiate my evaluation with a 6-mm-diameter ROI and all Zernike coefficients active (when all indice symbol tabs are highlighted). It is important to mention that HOAs found in normal corneas have a different distribution and lower magnitude values than in KC, PMD or after corneal surgeries (Alió JL, Shabayek MH. Corneal higher order aberrations: a method to grade keratoconus. J Refract Surg 2006; 22:539–545).

The first row of the Wavefront Report shows the Zernike coefficients for astigmatism and defocus. These second-order corneal aberrations are related to the corneal components of the patient’s manifest refraction, thus they are often better understood in diopters instead of microns.

The second row contains third-order corneal aberrations. Vertical (at left) and horizontal (at right) trefoil is very close to zero in normal corneas. In corneas with penetrating (PKP) or lamellar keratoplasty (Pesudovs K, Coster DJ. Penetrating keratoplasty for keratoconus: the nexus between corneal wavefront aberrations and visual performance. J Refract Surg 2006; 22:926–931), radial keratotomy (RK), paracentral scars, advanced PMD or corneas modified by edema, the trefoil terms are larger than ±0.20 µm due to paracentral and/or peripheral irregularities (Arce CG. Data

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not published). The vertical (center left) and horizontal (center right) coma term may be used to evolve the progression of KC and PMD. Coma is one of the most important HOAs and a strong sign reflecting deformation of corneal surfaces (Gobbe M, Guillon M. Corneal wavefront aberration measurements to detect keratoconus patients. Cont Lens Anterior Eye 2005; 28:57–66). Asymmetric astigmatism, an asymmetric change of aspheric curvature of the anterior surface and/or asymmetry of thickness progression usually correlates with increased coma (Arce CG. Data not published).

Third row has the quatrefoil and 4th order astigmatism. Both terms tend to increase more than ±0.30 µm when the cornea has paracentral or peripheral deformation. As a rule of thumb, as the cornea is more deformed, the higher the 5th to 8th HOAs the system calculates. The most important fourth-order aberration is the spherical aberration (SA), located at the center of the third row. The normal SA value is in the range +0.15 µm to +0.30 µm and should be stable throughout life, when the cornea is not progressively deformed, surgically altered or diseased.

Total root mean square (RMS) in diopters and microns is also shown at the bottom right of the numerical indices.

Squared eccentricity (e2) is equivalent to negative asphericity (e2 = -Q). e2 and Q are average values representing the shape of corneal surfaces. Prolate anterior surfaces have positive e2 and oblate surfaces have negative e2. When e2 = 0, then the surface is spherical. An elliptical surface has e2 from zero to < ±1. A parabolic surface has e2 = ±1.0. A hyperbole has e2 > ±1.0. The shape of anterior corneal surface correlates well with the amount of HOAs. More prolate anterior surfaces have less positive SA. When e2 ≈ 0.55, the SA is ≈ zero.

3.2. understanding the relationship between HOas, refraction, quality of vision, corneal shape and curvature

Regardless of the cause, corneas with increased HOAs show a quantifiable decrease in visual performance that is pupil size dependent. The amount of coma has been corelated with the quality of vision in patients with asymmetric progression of KC or PMD. Trefoil, coma and quatrefoil have been correlated with the presence of glare and halos after corneal surgeries and IOL implantation. The amount of SA has a direct influence in the quality of vision and focusing of images by the eye. An SA of zero will produce a sharper image but shallow depth of focus. A larger SA (negative or positive) allows larger depth of focusing. Corneas after hyperopic or presbyopic surgery and with KC are more prolate and have negative SA, which partially explains their loss of sharp vision but their facility to focus near and far.

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Corneas with KC become progressively steeper (positive Rabinowitz index when > 47.2 D), multifocal, and more prolate. Often steeper anterior surfaces with zones of > 50 D and clear topographic KC signs have eccentricity values higher than +0.80. And typically the posterior surface will precede the anterior surface to show a parabolic shape (e2 = +1). The anterior surface initially has a symmetric (regular) with-the-rule (vertical, steeper (“warm” or yellow/orange/red color) bowtie) astigmatism that increases (normal astigmatism < 3 D), showing larger difference of curvature values from the periphery to the center. Such multifocal corneas have more color steps on curvature maps. With the steepening of both surfaces, a nipple-, sagging- or globe-shaped cone appears depending on the size of the steeper central zone. The SA becomes less positive or is shifted to a negative value (SA ≤ 0 typically when the anterior e2 > 0.60).

In a practical view and for screening or diagnostic purposes, although there are corneas with KC with ellipsoid symmetric shape and e2 < 1 in either anterior or posterior corneal surfaces, there are no normal untouched corneas with either anterior or posterior corneal surfaces with a parabolic symmetric shape and e2 ≥ 1 (Arce CG. Data not published). This observation supports e2 = 1 to be an important cut-off value in KC diagnosis. Furthermore, when the anterior surface already has a hyperbolic shape (e2 > +1), the cone peak is beginning to be dislocated temporal-inferiorly.

Hyperopic or presbyopic surgery with excimer laser generates an anterior surface with e2 ≥ 1 and a posterior surface with e2 < 1. After intracorneal femtosecond presbyopic surgery, we expect the e2 of both surfaces to increase. It has been suggested that the best combination after hyperopic or presbyopic surgery is a SA of around -0.50 µm and a plano or a very low positive residual refraction. This is one of the reasons why these eyes may accept subjectively a variety of refractive corrections and remain with an unchanged visual acuity. On the other hand, the combination of a negative residual refraction with a negative corneal SA seems to be rejected by these patients. Therefore it is better not to recommend mono-vision or multifocal vision with negative refraction after corneal refractive surgery or intraocular lens (IOL) implantation in eyes with such prolate corneas.

On the other hand, when a myopic LASIK or PRK ablation is required, the anterior surface becomes more oblate and flatter with more positive SA. The ideal combination in these eyes for best mono-vision, better near focus than far focus, or multifocal vision seems to be achieved by leaving a moderate negative (myopic) residual refraction. I understand that this concept explains partially why spherical IOLs (with SA between +0.18 to +0.25 µm) were so successful after being implanted in normal eyes (with SA between +0.20 to +0.30 µm), when a small myopic residual refraction was programmed. Similarly, it explains why mono-vision after incomplete myopic LASIK correction is better tolerated and accepted than mono-vision after hyperopic LASIK correction.

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These concepts open the possibility to customize IOL implants according to the residual refraction that the surgeon and patient want to keep after surgery. After cataract extraction, the SA from the lens is removed. Therefore pseudophakic eyes will remain with an SA produced by the cornea and the IOL implanted. Spherical IOLs have positive SA, most of them between +0.18 to +0.25 µm. Currently available aspheric IOLs may have either negative SA (e.g. -0.20 µm for the Alcon Acrysoft® IQ or -0.27 µm for the AMO Technis® Multifocal IOL) or neutral SA (e.g. zero for the Bausch & Lomb SofPort®, hydrophilic Rayner C-flex Aspheric or hydrophobic Mediphacos IOLs). Although one could compensate the normal positive corneal SA with the negative SA of certain IOLs, the policy to leave all eyes with zero or close to zero SA may not always be the best solution. There are very satisfied patients with larger positive or negative SA that would like to preserve their previous good multifocal quality of vision after IOL implantation. Their total SA should not be modified. Although we presently have one-size-fits-all IOLs, I foresee a time where corneal wavefront measured by the GALILEI would guide the manufacturing of better IOLs.

3.3. Evaluation of wavefront reports


The e2 of the anterior surface is 0.09, i.e. almost spherical. This value correlates well with the low 2nd order astigmatism (0.19 @ 29.8°, shown in the flatter axis) and 4th order astigmatism (-0.01 µm), the slightly increased positive spherical aberration (+0.30 µm), and the low trefoil and quadrefoil in an ROI of 6 mm.

Differences among total corneal wavefront-derived, SimK-derived (0.22 D @ 100°, shown in the steeper axis), and ray-traced total corneal power-derived (0.12 D @ 141°, shown in the steeper axis) astigmatisms reflect differences in the calculations of each value, differences in reference planes, and different sensitivities to measurement decentration. The size of the data zone or region of interest (ROI) can also change the astigmatism value. The wavefront region of interest can be selected to be between 3- to 6-mm-diameter central ROI. The region size is shown above the map. The SimK and the ray traced total corneal power astigmatism values are calculated from a 1- to 4-mm-diameter ring ROI.

The horizontal coma is +0.42 µm suggesting some asymmetry in asphericity on this meridian. Although there is a relatively low total RMS (0.74 µm or 0.57 D), the pie chart confirms that defocus, coma and spherical aberrations are the most prominent aberrations in this cornea.

The Wavefront Report is shown in the Alternate Profile, which I recommend for printing, in Figure 7A and in the Default Profile in Figure 7B.

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Figure 7B

Figure 7A

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Figure 8B

Figure 8A

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Example 2: Normal Astigmatic Cornea with Initial Posterior Surface Changes (Figure 8)

As expected, the e2 of the anterior surface (0.31) is smaller than the e2 of the posterior surface (0.72), thus the posterior surface is more prolate than the anterior surface.

The 2nd order astigmatism (1.15 D) is responsible for 93.5% of the total corneal aberrations. The coma term is less than ± 0.16 µm despite the slight “D-like” asymmetry found in the Instantaneous Anterior Curvature map. The defocus term is -0.18 D and other HOAs are less than ± 0.1 µm. SA is + 0.15 µm. Smaller SA would mean there is a tendency towards a steeper more multifocal prolate surface and therefore a sign of change in corneal shape. The total RMS is 1.19 D or 1.55 µm.

The report, shown in the Alternate Profile, which I recommend for printing, is in Figure 8A and the Default Profile in Figure 8B.

Example 3: KC with Irregular Astigmatism (Figure 9)

The anterior (1.17) and posterior (1.23) e2 reflect very prolate already hyperbolic corneal surfaces. Keratoconic corneas typically have an e2 value close to +1.0 or higher.

Defocus in this case is very low (+0.04 µm), vertical trefoil is higher than normal (+0.45 µm), and SA is already negative as expected (-0.15 µm). Other HOAs have low values.

The 2nd order astigmatism (1.56 D, 36.7%) and both vertical coma (-2.47 µm) and horizontal (-0.52 µm) coma (58.5%) together are responsible for most corneal HOAs.

The vertical coma is probably the most important HOA to monitor KC. Vertical coma is also a numerical expression of corneal deformation. GALILEI may also show the total corneal coma either in µm or D. The amount of irregular astigmatism with a significant dioptric difference between the steeper and flatter curvatures and the Kranemann-Arce index (below) also reflect quantitatively the deformation of the corneal surfaces. The Kranemann-Arce index is the differential between the minimum negative and the maximum positive BFTA elevation values in microns within the 5-mm-diameter central zone. The normal Kranemann-Arce index was 10.72 ± 5.72 µm (maximum BFTA limit 25–30 µm) for the anterior surface and 22.49 ± 9.29 (limit 40–45 µm) for the posterior surface (Arce CG. Corneal shape and HOAs may be used to distinguish corneas with keratoconus. Poster. ESCRS; Paris, France. 2010). Qualitatively, the deformation indicative of corneas with KC is shown by (1) the irregular pattern of astigmatism found in

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Figure 9B

Figure 9A

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the curvature maps, (2) the asymmetric pattern of aspheric change found on the BFTA elevation maps, and (3) the asymmetric pattern of thickness distribution found in the pachymetry maps (refer to N°5 of this guide: Map x1).

The report, shown in the Alternate Profile, which I recommend for printing, is in Figure 9A and in the Default Profile in Figure 9B.

4. The IOL Power report

Both the Alternate (Figure 10A to 12A) and the Default Profile (Figure 10B to 12B) of the IOL Power Report show the Anterior Axial curvature map and the Total Corneal Power map by ray tracing from an 8-mm-diameter data zone, the Total Wavefront HOA map from a 6-mm-diameter data zone, and a top view of the Placido ring pattern reflected on the cornea.

This report shows all indices including the SimK values required for standard IOL formulas. The average simulated keratometry (SimKavg) is actually the average of the flatter SimKf and the steeper SimKs. The astigmatism is the difference between SimKf and SimKs. The Anterior Instantaneous Curvature and the Total Corneal Power (ray traced) from a 1- to 4-mm-diameter ring zone are also shown. The Total Corneal Power (ray traced) is also calculated as the average of a central zone (0 to 4-mm-diameter), paracentral zone (4 to 7-mm-diameter), and peripheral zone (7 to 10-mm-diameter).

Also shown are the RMS HOA, the SA, the central anterior chamber depth (ACD) or distance from the corneal endothelium to the anterior lens, the anterior chamber volume for an 8-mm-diameter central zone, the chamber angles in degrees at the superior, temporal, inferior and nasal direction, the nasal-temporal (horizontal) and superior-inferior (vertical) limbus diameter, the pupil diameter (approximately mesopic) and the Cartesian location of the pupil centroid relative to the center of the map. The average anterior segment length (ASL) or distance to the posterior lens requires measurement with a dilated pupil.

4.1. about how GaLILEI’s total corneal power is improving the IOL power calculation

The most important value in this window is the 4-mm central average Total Corneal Power (TCP). This is the value that is used in the ASCRS-supported IOL calculator (iol.ascrs.org). The TCP is calculated by ray tracing the refractive power of the cornea using the anterior surface, the pachymetry and the posterior surface. Unlike the SimKavg, the TCP considers the pachymetry and the posterior surface curvature, as well as the actual index of refraction of each interface. The challenge in

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Figure 10B

Figure 10A

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Figure 11B

Figure 11A

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Figure 12B

Figure 12A

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comparing the SimK to TCP is that both values’ calculations also have different reference planes and index of refractions. The SimK is based on the anterior surface curvature data however it uses an adjusted or keratometric index of refraction to estimate the pachymetry and posterior curvature, assuming an untouched, standard corneal shape and Gullstrand eye model. The TCP uses the actual pachymetry and posterior curvature, and standard index of refraction for the cornea and aqueous humor. The power depends on the method of calculation and the chosen reference plane, which is different for both values. The TCP values were calculated with the index of refraction of the cornea in version 5.2 and of the aqueous in version 5.2.1. Both values are referenced to the anterior corneal surface. The TCP map did not change appearance (and is still different from the SimK map) however the magnitude of TCP changed slightly, corresponding to the change in index of refraction. The ASCRS IOL calculator offers two formula depending on the software version used (pre-version 5.2.1 and version 5.2.1 and newer).

The TCP is the average of every detected point in the selected ROI. This average was initially described for the total-mean (equivalent or Gaussian power) and total-optical (ray-traced following Snell law) Orbscan II corneal powers (Sónego-Krone S, López-Moreno G, Beaujon-Balbi O, Arce CG, et al. A direct method to measure the power of the central cornea after myopic laser in situ keratomileusis. Arch Ophthalmol 2004; 122:159–166), later coined as quantitative area topography (QAT).

The SimKavg is an assumed or approximate “total corneal power” (Simulated K) calculated from the anterior surface curvature data. On the GALILEI, the SimK value was determined to be calculated from a 1- to 4-mm diameter ring-shaped ROI and is the mean of two values, the flat SimK and the steep SimK. Similar assumed or approximate “total corneal powers” are based on the anterior curvature (Axial and Instantaneous Curvatures) and the corneal power is then calculated using a keratometric refractive index of 1.3375. All corneal powers based only on anterior surface data require correction factors when used for altered corneas, including those that have undergone refractive surgery.

The equivalent power of the cornea (thick lens formula) is the addition of the anterior and posterior curvatures including the ratio thickness/refractive index of the cornea. It follows the thick lens formula of Gaussian optics. The size of the best central data zone for this total corneal power calculation has been established to be 2-mm diameter. These values can be used in IOL power calculations for untouched corneas, which have good congruency between both surfaces. Although GALILEI does not presently show the equivalent corneal power, it has been already used successfully for IOL power calculation after refractive surgery (Arce CG, Soriano ES, Weisenthal RW, Hamilton SM, et al. Calculation of intraocular lens power using Orbscan II quantitative area topography after corneal refractive surgery. J Refract Surg 2009; 25:1061–1074).

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Presently, there is more evidence that IOL power calculation using the ray traced Total Corneal Power from a central 4-mm-diameter data zone is more accurate for eyes that have undergone refractive surgery. This is the value that can be used to adjust the SimK values used in IOL formulas to calculate IOL power (Weikert MP, Shirayama M, Wang L, Koch DD. Role of posterior corneal power using the GALILEI dual Scheimpflug analyzer in standard IOL power calculation. San Francisco, 2008 ASCRS; Raju L, Wang L, Koch DD. Comparison of IOL power calculations using different average corneal power readings in post radial keratotomy patients. San Francisco 2009 ASCRS; Savini G, Hoffer KJ, Carbonelli M, Barboni P. Corneal power measurements by a dual-Scheimpflug analyzer for IOL power calculation in unoperated eyes. Boston 2010 ASCRS; Sandoval HP, Guenena MA, Solomon KD. Accuracy of a dual-Scheimpflug analyzer to calculate post-LASIK corneal power cataract surgery patients. Boston 2010 ASCRS).

The use of SimKf and SimKs to calculate toric IOLs is a common practice around the world. However these values are derived from only the anterior surface and therefore they do not take into account the curvature of the posterior surface. Recently it was proposed to use the astigmatism and axis derived from the Total Corneal Power in order to avoid residual postoperative surprises (Barraquer R. Personal communication 2009). Although the SimK and ray-traced astigmatism values can be similar, there are corneas with different magnitudes and axis. The astigmatism value calculated from the entire cornea (including both anterior and posterior surfaces) should be more accurate in eyes that have undergone excimer laser refractive surgery and in eyes with incongruent corneal surfaces, i.e. “crossed” curvatures with against-the-rule astigmatism in the anterior surface and with-the-rule astigmatism in the posterior surface.

4.2. Evaluation of IOL Power reports


The SimKavg is 40.99 D, SimKf 40.88 D, SimKs 41.09 D, and the SimK astigmatism in the steeper axis is 0.22 @ 100°. The Anterior Instantaneous Curvature value is not displayed since it was not available at the time of acquisition, using SW 5.0. The Anterior e2 is 0.09. The Mean Total Corneal Power (Ray Traced) based on Software 5.0 is 40.45 D, which is almost 0.50 D smaller than the SimKavg. The ray traced flatter power is 40.39 D and the steeper 40.51 D with a smaller steep axis cylinder value of 0.12 D @ 141°.

This eye had an axial length of 24.60 mm measured by immersion ultrasound biometry. From the GALILEI data it is possible to calculate the central average distance from the epithelium to the anterior surface of the lens: 3.29 mm (anterior chamber depth from the corneal endothelium to the anterior lens surface) + 0.577 mm (central average pachymetry in a 4-mm-diameter ROI) = 3.867 mm.

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The Central Average (0-4 mm) of Total Corneal Power (ray traced) based on Software 5.0 is 40.38 D. With an SA of +0.30 µm, a little still positive postoperative total SA after cataract surgery may be predicted if an aspheric monofocal IOL with negative SA (between -0.20 and – 0.27 µm) is implanted in this eye. Using the SRK-T IOL formula, the power of an IOL with 118.7 of A constant for emmetropia will be +20.25 D with the SimKavg. The ray traced Total Corneal Power of SW 5.0 and SW 5.2 are not referenced to SimK and cannot be used directly in SimK formulae.

Example 2: Normal Astigmatic With Initial Posterior Surface Changes

The SimKavg is 43.63 D, SimKf 42.88 D, SimKs 44.37 D, and the SimK astigmatism in the steeper axis is 1.49 @ 85°. The Anterior Instantaneous Curvature does not appear because exams were made with former SW 5.0. The Anterior e2 is 0.31. The Mean Total Corneal Power (Ray Traced) from a 1-4-mm-diameter ROI is 43.34 D, a little smaller than the SimKavg. The ray traced flatter power is 42.63 D and the steeper 44.04 D with almost the same axis and cylinder of 1.41 D @ 87°.

This eye had 25.40 mm of axial length measured by immersion ultrasound biometry. From GALILEI data it is possible to calculate the central average distance from the epithelium to the anterior surface of the lens: 3.12 mm (anterior chamber depth from endothelium) + 0.554 mm (central average pachymetry in 4-mm-diameter ROI) = 3.674 mm.

The Central Average (0-4 mm) of Total Corneal Power (ray traced) is 43.32 D. With an SA of +0.15 µm, an already negative postoperative total SA after cataract surgery may be predicted, if an aspheric monofocal IOL with negative SA is implanted in this eye. Using the SRK-T IOL formula, the power of an IOL with 118.7 of A constant for emmetropia will be +14.84 D with the SimKavg.

Example 3: KC With Irregular Astigmatism

The SimKavg is 46.86 D, SimKf 45.22 D, SimKs 48.50 D, and the SimK astigmatism in the steeper axis is 3.28 @ 95°. The Anterior Instantaneous Curvature does not appear because exams were made with former SW 5.0. The Anterior e2 is 1.17. The Mean Total Corneal Power (Ray Traced) from 1-4-mm-diameter ROI is 46.31 D, almost 0.50 D smaller than the SimKavg. The ray traced flatter power is 44.68 D and the steeper 47.94 D with almost the same axis and cylinder of 3.26 D @ 96°.

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This eye had 26.30 mm of axial length measured by immersion ultrasound biometry. From the GALILEI data it is possible to calculate the central average distance from the epithelium to the anterior surface of the lens: 2.30 mm (anterior chamber depth from endothelium) + 0.483 mm (central average pachymetry in a 4-mm-diameter ROI) = 2.783 mm.

The Central Average (0-4 mm) of Total Corneal Power (ray traced) is 46.54 D. With an SA of -0.15 µm, more than -0.35 µm of postoperative total SA after cataract surgery may be predicted, if an aspheric monofocal IOL with negative SA is implanted in this eye. If a spherical IOL with positive SA (between +0.18 and +0.20 µm) is used the final total SA would be slightly positive or close to zero. In this eye a surgical correction of the astigmatism might be possible with a spherical toric IOL or an aspheric toric IOL with neutral SA (SA = 0). Using the SRK-T IOL formula, the power of an IOL with 118.7 of A constant for emmetropia will be +8.14 D with the SimKavg.

5. THE MaP x1

The Alternate profile shows as a first option the same pachymetry map with the German CGA 20 µm scale, numerical values and overlays already described before (refer to Figure 1A from the Refractive Report). The Default Profile shows the Anterior Axial curvature map with the default Type I 1.5 D scale and without overlays as it was also described before (refer to Figure 2A from the Refractive Report).

5.1. Importance of the pachymetry map

Although any available map may be shown, the Map x1 presentation is useful to report the pachymetry map separated from the topography study. The Pachymetry map of GALILEI gives much more information than ultrasound pachymetry. It shows the value and location of central corneal thickness (CCT) and the thinnest corneal pachymetry, the central, paracentral and peripheral average thickness. Pachymetry maps have a classical pattern with a uniform and symmetric distribution and progression, from a thinner central zone with the thinnest corneal point located at the center of the map within 1 mm from the pupil centroid. The pachymetry profile extends from the center with concentric rings and progressively thicker pachymetry towards the periphery. Since the normal difference between CCT and the thinnest corneal point thickness should always be less than 25 µm, both mark points have to be located within the same color step on a pachymetry map with the German CGA 20 µm scale. A borderline (Δ = 20–25 µm) or an already abnormal pachymetry difference would occur when the thinnest corneal point is located within the next warmer color

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step. Changes in this basic pachymetry pattern may be related to surgical modification, progressive deformation or variation in the biomechanical properties of the cornea and/or its water content (edema). The distribution and the rate of thickness progression are easily perceived by counting the number of color steps on the map along a meridian. Setting the map with the German CGA 20 µm scale on the Alternate Profile further allows one to evaluate the symmetry or asymmetry of the thickness distribution and progression from the center to the periphery. Normally there is less than 200 µm of thickness difference between the CCT or thinnest corneal point and the periphery of the map at 4.5 mm of distance. Therefore, a normal thickness progression should have less than 10 color steps with a 20 µm scale as used in the Alternate Profile. More steps would mean thinning of the center and would be expected in a stretched or forward bulging cornea, or thickening of the periphery as occurs with edema and a camel sign (a double corneal densitometry peak corresponding to an endothelial defect) at the periphery (Arce CG. Data not published).

Thinning and dislocation, usually temporal-inferior, of the thinnest point are signs of corneal deformation inducing more asymmetric thickness distribution and progression according to the severity of the disease. In a series of patients, all corneas with a thinnest point thinner than 500 µm and dislocated 1 mm or more from the pupil centroid had KC. Interestingly, in advanced KC the thinning and dislocation of the thinnest point may coexist with a thickening of the inferior or nasal-inferior periphery. Such an extreme asymmetric pachymetry pattern is described now as the “pitch drop” sign (also called the “Venetian glass” sign) and has been related to a possible “glide down” of corneal collagen lamella and loss of corneal viscosity (Arce CG. Use of Optical Pachymetry in Diagnosis of Keratoconus. Boston 2010 ASCRS).

Accurate corneal pachymetry has other clinical applications. Irregular thick pachymetry patterns may be found in older patients or eyes with glaucoma and subclinical or clinical corneal edema. In these cases the endothelial edge may show an abnormal second peak (camel sign) on corneal densitometry as reviewed in the Diagnostics>Densitometry panel. When such a camel sign is seen in thick corneas at the center, it seems to be a very early indication of endothelial failure, Gutatta or Fuchs’ disease. Since the posterior surface is more susceptible to changes in the corneal homeostasis, another early sign of a central thickening by subclinical central edema is the modification of the posterior curvature and shape. The posterior surface becomes less prolate and consequently with a reduced posterior e2 closer to or even smaller than the anterior e2. The inversion of the anterior/posterior e2 ratio may not be observed when the thickening happens more at the periphery than at the center.

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Therefore central thick corneas with a camel sign and inversion of the anterior/posterior e2 ratio, and with or without dislocation of the thinnest point requires investigation for subclinical corneal edema. This is especially critical in patients undergoing intraocular surgery such as cataract extraction or refractive surgery with excimer laser. In this last case the secondary modification of the posterior surface shape may compensate and hide early steepening induced by KC progression.

It was recently suggested that glaucoma screening should consider the assessment of these parameters and the study of the chamber angle with the GALILEI (digital goniometry and goniography). Ocular pressure measurements vary in sensitivity to corneal pachymetry, curvature and biomechanics. The modification of corneal biomechanical variables, thickness and curvature do not affect Pascal dynamic contour tonometry (DCT), however they may cause errors in Goldmann applanation tonometry (GAT).

Interestingly, after myopic refractive surgery the thinnest corneal point is typically located at the center of the ablation zone, along either the line of vision or the pupil centroid. Separation of the thinnest point from these landmarks is the best way to diagnose an off-centered laser treatment. On the other hand, after a hyperopic laser treatment, the thinnest point is usually paracentral.

5.2. Other Map x1 options

Another option for Map x1 is the Refractive map. The Refractive map may also be aligned to the pupil. A misaligned Refractive map will be shown later when the Map x4 display is described.

A new feature of SW 5.2 was the possibility to align the data to the pupil in any Map x1 presentation. Excimer lasers and corneal surgeries are centered to two main landmarks. The first landmark is the pupil centroid that may shift after dilation. Since GALILEI exams are always made under similar mesopic conditions, the pupil diameter should be comparable between exams in the same patient. The second landmark is the line of vision intersecting the anterior surface that is usually found with a coaxial light (from the microscope) reflected on the cornea. In the GALILEI it corresponds to the center of the four dots reflected on the cornea. This landmark tends to shift downwards in the keratoconic cornea when the geometrical apex of the cornea is also dislocated (Miháltz K, Kránitz K, Kovács I, Takács A, et al. Shifting of the line of sight in keratoconus measured by a Hartmann-Shack sensor. Ophthalmology 2010; 117:41–48).

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The Map x1 presentation is also useful showing the top view of the eye with any map in the background. This overlay feature is a nice method to localize the map to the pupil and to determine the position of corneal scars and lesions, shunts, intracorneal segments (rings) or inlays, and anterior or posterior chamber IOLs, including multifocal and torics (Fuentes MV, Galvis V, Tello A, Arce CG. Restor esférico vs Restor asférico. Calidad visual. Buenos Aires, 2009 ALACCSA Meeting).

5.3. Evaluation of the Map x1 display


The pachymetry map (Figure 13A) shows some asymmetric thickness distribution with thicker blue steps at the nasal periphery. The thickness progression is also asymmetric with 10 steps of 20 µm each to the nasal side (40.89 µm/mm from the map center) and only 5 steps to the temporal side (17.56 µm/mm). Unfortunately peripheral data is not shown when the map is aligned to the pupil (Figure 13B) so the asymmetry of pachymetry distribution is less apparent. The TCP (560 µm) is located at 0.4 mm @ 334° temporal inferior from the pupil centroid. This exam was relatively well centered as verified with the top view image (Figure 13C), thus the asymmetric thickness pattern is real and not an artifact produced by a misaligned examination. The uniform pattern without a bow-tie of the Refractive map (with German CGA 1 D scale) when the map is re-aligned to the pupil (Figure 13D) has an opposite color distribution than the curvature maps. Realignment of this map to the pupil produces a shift on the axis of the small astigmatism in this surface. The original astigmatism of 0.22 D @ 100° found when the exam was taken (Figure 13E) shifted to 0.26 D @ 87° when this map was centered to the pupil (Figure 13D). The Refractive map of the Default Profile (Figure 13F) shows a similar pattern with the Default Type I 1.5 D color scale.

This Map x1 option may be used to see the top view of the eye with or without values (Figure 13G) and maps with faded or transparent colors to study the location and centering of intracorneal implants or inlays and monofocal, multifocal, or toric IOLs.


There is a complete green pachymetry map (Figure 14A) indicating a normal thickness range, as well as symmetric and normal thickness distribution and progression (less than 10 steps with 20 µm each). The thinnest corneal pachymetry is 545 µm and located at 0.7 mm @ 316° temporal inferior from the pupil centroid (Figure 14B).

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Figure 13B

Figure 13A

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Figure 13D

Figure 13C

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Figure 13F

Figure 13E

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The exam was fairly well centered (Figure 14C). The Refractive map aligned to the pupil (Figure 14D) showed a partially formed “cool” bow-tie and a dioptric difference of 3 D within the 5 mm central data zone related to the 1.57 @ 85 of astigmatism, which is close to the 1.49 @ 85° calculated before realignment (Figure 14E). Refractive map of the Default Profile (Figure 14F) shows a similar pattern despite the different scale used.

This Map x1 option may be used to see the several top view of the eye, in this case without values (Figure 14G).


The asymmetry and faster rate of thickness progression (Figures 15A and 15B) are manifested by the thinning of the thinnest thickness (467 µm), the dislocation temporal inferior of 0.8 mm @ 262° of the thinnest point from the pupil centroid and the larger number (11) of color steps to the nasal side (49.78 µm/mm from the map center) and only 7 steps to the temporal side (27.11 µm/mm). The exam was only slightly misaligned horizontally (Figure 15C) probably influencing some perception of asymmetric thickness distribution in the original map (Figure 15A) that is absent when the map is realigned to the pupil (Figure 15B). In this last map, there is a clear perception of the temporal-inferior dislocation of the thinnest orange zone.

The Refractive map aligned to the pupil (Figure 15D) shows much more inferior refractive power (warmer colors) and less focused light rays at the top (blue steps) explaining the large vertical coma (-2.47 µm) found in the Wavefront report. The dioptric difference between the superior and inferior regions is 14 D (14 color steps) within the 5 mm central data zone. The astigmatism changed from 3.28 D @ 95° before alignment (Figure 15E) to 2.01 D @ 85° after alignment (Figure 15D). Notice that the reported astigmatism in SimK is different than the dioptric differential because the cylinder values were obtained from a different and smaller data zone (Sim-K is obtained from a 1 to 4 mm central ring). The Refractive map of the Default Profile (Figure 15F) shows a slightly different pattern with the Default Type I 1.5 D color scale.

This Map x1 option may be used to see several top views of the eye, in this case without overlaid values (Figure 15G).

6. THE MaP x4

The GALILEI’s great versatility allows the user to customize this Map x4 with any four available maps. The Alternate Profile (Figures 16A, 17A and 18A) uses the Map x4 for evaluating only the anterior surface of the cornea with the Anterior Axial curvature map, Anterior Instantaneous curvature map, Anterior BFS elevation map and

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Figure 14B

Figure 14A

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Figure 14D

Figure 14C

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Figure 14F

Figure 14E

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Figure 15A

Figure 14G

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Figure 15C

Figure 15B

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Figure 15E

Figure 15D

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Figure 15G

Figure 15F

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Anterior BFTA elevation map. An alternative version would have the Refractive map (not aligned to the pupil) instead of any of the two curvature maps mentioned above (Figures 16B, 17B and 18B). A third option would be to set the anterior surface maps with similar scales to other Placido topographers.

The Default Profile (Figures 16C, 17C and 18C) shows the Anterior Axial Curvature map, Anterior Instantaneous Curvature map, the Refractive map and the Anterior BFS Elevation map with Default settings (refer to the GALILEI manual).

6.1. Importance of the anterior BFTa elevation map

All maps presented in this display have already been described, except for the Anterior Best Fit Toric Aspheric (BFTA) elevation map. This map is very useful to study the symmetry or asymmetry of aspheric variation of corneal surfaces. The aspheric variation is defined as the change of curvature from the center to the periphery in different meridians. When there is a symmetric change, all meridians in all directions have a uniform color. When it is green, there is a good fit between the surface elevation and the BFTA ideal surface that was used as a reference (Figures 16A and 16B of Example 1 at bottom-right). An asymmetric aspheric variation is represented by different color zones at both sides of a meridian. Typically there are two main meridians (as in astigmatism), i.e. the most symmetric meridian is located at 90° from the most asymmetric meridian (Maps 18A and 18B of Example 3 at bottom-right). A tendency towards yellow zones (positive elevation) means a slower rate of change than the change the BFTA referential surface has. A tendency to bluer zones (negative elevation) means a faster rate of change.

The BFTA referential surface has recently been considered to be a qualitative representation of the corneal symmetry to assess the degree of corneal deformation. Asymmetry of curvature (irregular astigmatism), HOAs (coma), or pachymetry (pitch-drop sign) are also representations of corneal deformation. The correlation among these parameters is a new field of study that may help to understand the natural history of diseases like KC and PMD (Arce CG, Trattler W, Dawson DG. Keratoconus and Keratoectasia. In Atlas of Corneal Pathology and Surgery. Boyd S. Editor-in-Chief. Jaypee Highlights Medical Publishers. Panama. 2010. In Press).

KC at any stage usually has a regular or irregular with-the-rule astigmatism. Similarly, PMD has an against-the-rule astigmatism. Oblique astigmatism may happen in either or both. Both advanced, very asymmetric eccentric KC and PMD have in common a steepening in the lower hemisphere and a relative flattening in the upper hemisphere producing an important dioptric difference between both sides. Both diseases also show an inferior dislocation of the TCP

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Figure 16B

Figure 16A

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Figure 16C

Figure 17A

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Figure 17C

Figure 17B

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with asymmetry of the thickness distribution and progression. Due to these reasons the BFTA elevation maps in both diseases show the greater asymmetry of their aspheric variation in the vertical meridian. In my opinion this is a major differential sign between KC and PMD. KC has the asymmetric aspheric meridian coincident with the steeper axis of astigmatism while PMD has it coincident to the flatter axis of astigmatism (Arce CG. Data not published).

Monofocal or multifocal IOLs with symmetric aspheric surfaces may be well centered with a perfect surgery and a patient may have 20/20 of visual acuity and still perceive halos, glare or a loss of contrast sensitivity in that eye. The aspheric quality of corneal surfaces may be important to establish why patients may have these visual symptoms after implantation of aspheric intraocular lenses (IOL). GALILEI is the first device that allowed me to study the quality of corneal surfaces in a comprehensive way using the BFTA elevation maps.

We began with the observation and classification of which surface pattern is present in cases with visual complaints and which are present in very satisfied patients. This analysis is a step forward toward customization of cataract surgery and IOL implantation. However it is still necessary to verify the hypothesis that fewer complaints will be more frequent in the corneas that have symmetric aspheric surfaces, i.e. completely green BFTA maps, and a lower Kranemann-Arce index (differential between the minimum negative and the maximum positive BFTA elevation value in microns within a 5-mm-diameter central zone).

6.2. Evaluation of the Map x4 display


The Anterior BFTA Elevation map is completely green indicating that data of this cornea fit very well with the toric aspheric ideal surface. There is a symmetric change of curvature from the center to the periphery (aspheric variation) at all meridians (360°). The Kranemann-Arce index is only 4 µm.

The other maps were already described before.


The Anterior BFTA Elevation map is within a ± 5 µm normal range and has a Kranemann-Arce index of 12 µm. Although this elevation curvature has a completely green map, the steeper (vertical) axis of astigmatism has more symmetric aspheric variation than the flatter (horizontal) axis.

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Figure 18B

Figure 18A

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Figure 18C



The Anterior BFTA Elevation map clearly shows asymmetry in the vertical meridian, the same meridian where the astigmatism is steeper and more asymmetric with larger dioptric difference. The Kranemann-Arce index is 50 µm. The flatter axis of astigmatism (horizontal) is almost always correlated with a more symmetric aspheric meridian in corneas with KC.


7. axial and Instantaneous anterior-Posterior Topography

These displays are only available in the Alternate Profile. They follow my suggestion to modify the traditional policy of printing the common Refractive Report. Instead, I suggest printing the Anterior-Posterior Topography display with either the Axial (Figure 19A, 20A and 21A) or Instantaneous (Figure 19B, 20B and 21B) curvature map instead of the Pachymetry map, and print a separate Pachymetry map as a Map x1 display.

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7.1. Importance of the topography of both corneal surfaces

Early topography allowed only analysis of the the anterior surface curvature. Later, scanning-slit technology allowed analysis of BFS elevation maps to compare the shape of the anterior and posterior surfaces. Topography by elevation progressed using both surfaces but topography by curvature remained focused on the anterior surface. In my opinion, the simple display of the curvature of the posterior surface as a routine and essential diagnostic exam is a step forward in our continuous learning of corneal pathology.

The additional information that the Anterior-Posterior Topography can supply is not restricted to the characteristics of the posterior surface only but also to the relationship between the two surfaces. Both will appear congruent when they behave similarly to the forces that modulate their shape and curvature. In such a case the appearance and patterns found in the anterior and posterior curvature maps shall be similar according to the selected color scale even with differences in the size of steps. In fact, such congruency is expected in normal corneas as a sign of the also normal relationship of curvature and shape of both surfaces. Although the concept is clear, the normal variation of this relationship and the limits of its normal range have not been completely established.

Both surfaces become incongruent when they are very different in shape or curvature. It is accepted that the normal posterior surface was more prolate than the normal anterior surface. Preliminary research has shown that a certain grade of incongruence of both surfaces is not necessarily a sign of abnormality and may still be a deviation within normality. Changes may happen either on the anterior or on the posterior corneal surface. Additional factors like laser refractive surgery would affect the anterior surface. On the other side, the initial signs of keratoectasia (and indeed thinning of the center) and corneal edema (producing central thickening) would affect first the posterior surface.

The appropriate interpretation of the congruence or incongruence of corneal surfaces is a new powerful tool in corneal diagnostics. It is a great help to make decisions especially in border line corneas. It is interesting to notice that congruence of both surfaces is typical in corneas with advanced KC and PMD, or after few corneal surgeries like radial keratotomy (RK) or penetrating keratoplasty (PKP). Congruent patterns in these cases mean that whatever produced the corneal change or deformation, it influenced both surfaces and not only one. Corneas with KC have congruent surfaces either with or without irregular astigmatism and inferior steepening. The simultaneous steepening and increased prolate shape of both surfaces are typical findings in KC and might be the reflection of how the whole cornea (and not only the anterior surface) was stretched forward.

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Presently, we do not know if the strain on both corneal faces is similar or different. The denser collagen distribution at the anterior 1/3 of the stroma proper and the patterns found when both surfaces are incongruent are evidence supporting that the posterior surface is more prone to deformation. This surface is usually steeper and more prolate. In virgin corneas the posterior surface may become much more prolate and steeper before any modification on the anterior surface is detected. Surgeons want to discover these borderline or initial cases (also called frustrous or suspicious) before and not after problems are obvious. These cases are rejected for refractive surgery due to their potential risk of ectasia. Similarly, the posterior curvature and elevation maps may identify earlier signs of postoperative ectasia in corneas that have already undergone refractive surgery.

On the other hand, when the sodium-potassium endothelial pump begins to fail, the accumulated water within the cornea seems to push backward the posterior surface producing a thicker CCT and thinnest corneal point, sometimes with the anterior surface maintaining typical KC patterns, ie. cases with KC and Fuchs’.

This improved and comprehensive method to compare anterior segment corneal topography is one of the most important features of the GALILEI, which many other devices do not offer in such an appropriate way.

7.2. Evaluation of the topography of both corneal surfaces


This is a good example (Figures 19A and 19B) of an apparent incongruence still within normal range. Evidently the anterior surface is not only less steep (SimK Avg = 8.23 mm) but also less prolate (e2 = 0.09; almost spherical) than the posterior surface (K Avg = 6.77 mm and e2 = 0.29). The posterior astigmatism is usually smaller than the anterior astigmatism, however in this cornea the anterior surface has 0.22 D @ 100° and the posterior surface has 0.25 D @ 86°. The warm (steeper axis) bow-tie appears in the posterior curvature maps because these maps use a 0.25 D color step. It does not appear in the anterior curvature maps because these maps use a 1 D or 1.5 D steps in axial or instantaneous maps respectively.

The relative difference of these two surfaces may also be observed by analyzing the patterns of both BFS elevation maps already described before. While the anterior surface (8.27 mm of radius) is flatter than the posterior (6.88 mm of radius), the anterior BFS elevation map is the expression of an almost spherical shape, i.e. the values are close to zero and a complete green map. On the other side, the posterior surface has a normal typical elliptical shape (classical horizontal bridge pattern of a with-the-rule astigmatism).

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Figure 19B

Figure 19A

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Figure 20B

Figure 20A

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Figure 21B

Figure 21A

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This is another example (Figures 20A and 20B) of an apparent incongruence between surfaces however in this case due to an initial abnormal change on both surfaces. Curvature asymmetries were more evident in the Instantaneous curvature maps. As expected, the anterior surface is less steep (SimK Avg = 7.74 mm) and less prolate (e2 = 0.31) than the posterior surface (K Avg = 6.45 mm and e2 = 0.72).

The yellow “hot zone” (already described) in the posterior BFS elevation map correlates with the asymmetry of posterior curvature maps. There is a borderline inferior steepening of this surface. Although with some incongruence in the maps, there are few signs suggesting that both surfaces tend to change together. First, there are more color steps toward the meridian at 10 o’clock (superior-nasal) in both curvature maps. Second there is a lighter temporal green zone (+ 5 µm range) on the horizontal bridge pattern of the anterior BFS elevation map that correlates with the yellow hot zone of the posterior BFS map.

This cornea is not KC. Despite the normal Anterior Axial map, the comparative analysis of other maps, including those from the posterior surface, found initial asymmetries that suggest caution for refractive surgery.


In Figures 21A and 21B, the anterior surface has a steeper axis with more than 47 D (<7.18 mm of radius). As expected it is less steep (Sim-K Avg = 7.20 mm) and less prolate (e2 = 1.17) than the posterior surface (K Avg = 5.73 mm and e2 = 1.23). There is a central yellow hot zone in the anterior BFS elevation map (with maximum elevation of 18 µm) that is much more evident and has already orange steps in the posterior BFS elevation map (with maximum elevation of 32 µm). While most of the horizontal bridge has yellow steps (> 10 µm), there is still a green nasal zone in both maps. On the other hand, there is a difference of maximum negative elevation at the top (-33 µm and -57 µm) and at the bottom (-46 µm and -68 µm) of the anterior and posterior BFS maps, respectively. These vertical and horizontal asymmetries on BFS elevation maps seem to be related to the asymmetry of curvature and/or aspheric variation of shape in both surfaces.

In this example, both surfaces have a hyperbolic shape (e2 > 1.0). In corneas with KC like this example, the anterior astigmatism is larger (3.28 D @ 95° or Δ=0.5 mm of radius) than the posterior (-0.48 @ 89° or Δ=0.39 mm of radius).

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8. BFS and BFTa Elevation maps

8.1. Importance of the BFS Elevation map

While BFS elevation maps have been extensively studied for almost two decades, BFTA elevation maps are a relatively new and valuable feature introduced by the GALILEI with improved quality and new applications.

BFS maps compare the shape of corneal surfaces against an ideal averaged sphere (the referential surface) calculated from the measured corneal data. Values shown on these maps are the result of such a comparison and the elevations shown are relative to the Best Fit Sphere. The radius of the Best Fit Sphere for a surface depends on the zone or area of data analyzed, i.e. the region of interest (ROI). Values that are below (negative elevation) or above (positive elevation) the referential BFS surface will appear as blue or yellow zones, respectively. Recent statistical studies found that the maximum positive BFS elevation (within a 5-mm-diameter data zone) is around 12 µm for the anterior surface and 16 µm for the posterior. The GALILEI is very precise and the ANSI CGA 5 µm scale further improves the perception of borderline values because its 2 yellow steps correspond to 10 µm and 15 µm.

Corneal surfaces usually have an elliptical shape (0 < e2 < +1). If we imagine that an ellipse is like an egg shape, the flatter axis is on the largest meridian of the ellipse (egg), i.e. corresponding with the axis of the typical central bridge (band or strip) pattern observed on BFS maps. Most normal corneas have such bridge patterns within green steps (±5 µm). The flatter axis and such a central bridge pattern are horizontal in a with-the-rule astigmatism, vertical in an against-the-rule astigmatism, and tilted in an oblique astigmatism. The classical bridge pattern means the cornea is not spherical but toric. However it is not always present and if the surface is spherical, then the data will fit the radius of curvature of the BFS. There will be small elevation values on the map (±5 µm) and therefore the BFS map will be completely green

Interestingly, asymmetries in BFS elevation maps are easily observed as temporal-nasal or superior-inferior differences in the values and colors. Since BFS asymmetries have been correlated with asymmetries on the aspheric curvature of the surface, the finding of any central or paracentral yellow zone is a strong and reliable sign of warning. These yellow “hot zones” were coined as “bulls eye” or “fried egg” pattern. They correlate well with a steepening and/or asymmetry of curvature and their occurrence forces a more detailed search of risk factors in other GALILEI maps.

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Another sign of asymmetry happens when the bridge pattern transforms into a peninsula pattern. Usually one side remains green (±5 µm) and the other is depressed achieving values below -10 µm with blue color steps. On the other hand, stretching, and indeed central steepening of surfaces, may render the island pattern, i.e. a yellow or warmer hot zone with positive elevation (>15 µm) that becomes isolated surrounded by a blue zone with negative elevation (<-10 µm). Analogies of the island pattern would be an egg tip, a peak of an iceberg or a volcanic island. In this last analogy, the green zones would be the sea level, the yellow zones would be the earth above the sea level and the blue zones would be under the sea. The warmer or more red the zone, the more altitude (height) the volcano will have. If it is darker or towards the violet, then it will be deeper in the sea.

8.2. Importance of the BFTa Elevation map

BFTA maps are more complex than BFS maps because they compare the shape of corneal surfaces against a toric aspheric surface, i.e. the symmetric or asymmetric egg-like shape of normal corneal surfaces versus another ideal, always symmetric and regular egg-like shape of the referential surface.

The patterns of BFTA maps are also typical but they have different patterns than seen in the BFS maps. A symmetric aspheric variation of curvature happens when there is a similar rate of curvature change from the center to the periphery at both sides. A symmetric aspheric variation of curvature means that the elliptical corneal surface matches the BFTA referential surface and therefore the elevation values are small (± 5 µm) and always in the green range. When the entire surface fits the BFTA well, then the maps tend to be completely green. It may also be coincident with one of the main axes (steep or flat) of astigmatism. In such a case, maps show a green meridian from side of the map to another, dividing two hemispheres of the map with different color. When the rate of curvature change is greater at one side, then the map points are below the BFTA surface and have negative values (blue). When the rate of curvature change is less than the BFTA referential surface, then the map points are above the BFTA surface and have positive values (yellow).

Asymmetry of aspheric variation of curvature may be quantified by the difference between the maximum negative elevation at one side of the symmetric meridian and the maximum positive elevation at the other side. We recently referred to this difference, measured within a 5-mm-diameter central data zone, the Kranemann-Arce index of asphericity (Kranemann C, Arce CG. Data not published). Although a Kranemann-Arce index lower than 15 µm is a clear sign of symmetry, the limit value between normal and abnormal asymmetry has not been established yet.

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There are at least 17 combinations of Anterior and Posterior BFTA Elevation map patterns. They are shown in the Table 1 (below).

This large variety of patterns is evidence that corneal surfaces are not necessarily uniform and symmetric. There are studies in progress about the relationship of these patterns with respect to the amount of HOAs originated in the cornea and the visual complaints after refractive and cataract surgery, especially when aspheric multifocal IOLs are implanted. The use of the GALILEI’s BFTA maps to preoperatively recognize irregular or asymmetric corneal patterns that may not fit with the symmetric uniform surfaces of such IOLs may further improve our customization of cataract surgery and our selection of patients suitable for Premium IOLs (Arce CG. Qualitative and Quantitative analysis of aspheric symmetry and asymmetry on corneal surfaces. Boston ASCRS 2010).

A BFTA map totally green indicates a symmetric prolate or oblate toric surface. The amount of asymmetry of surface on BFTA maps is related to the amount of coma. When a BFTA map has randomly distributed yellow, green and blue zones, it is reflecting a wrinkled surface that should generate trefoil and quadrefoil.

8.3. Evaluation of the display showing BFS & BFTa Elevation maps of both surfaces

Example 1: Normal Spherical Cornea (Figure 22)

The anterior surface shows an almost complete green (±5 µm) BFS and BFTA Elevation maps indicating that data fit well with both sphere or toric aspheric referential surfaces. These patterns are in agreement with a low Kranemann-Arce index of 4 µm and the e2 of 0.09.

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The posterior BFS map shows the typical green bridge pattern of a normal toric elliptical surface. Despite the small peripheral blue and yellow zones, it also shows an almost completely green BFTA Elevation map with a Kranemann-Arce index of only 10 µm. The posterior e2 is 0.29.

Combination of BFTA patterns matches the Pattern 1 of Table 1, i.e. both surfaces have a symmetric aspheric variation of curvature in 360°. Considering that the SA is 0.30 µm, there are no significant HOAs (trefoil, quadrefoil, secondary astigmatism and coma). Theoretically, this is a good case for aspheric monofocal or multifocal IOL implantation expecting a residual refraction as close to plano as possible. In case of selection of a spherical IOL, I would recommend leaving this eye slightly myopic in order to improve its depth of focus. The pupil diameter of 5.45 mm concerns me about the selection of pupil-dependent or pupil-independent IOLs.

Table 1. Possible combinations of patterns of anterior and posterior BFTA elevation maps

Pattern Anterior Surface Posterior Surface Axis of Asymmetry

1 Symmetric Symmetric Both maps are green with values ± 5 µm

2 Symmetric Asymmetric Same of steeper axis of astigmatism

3 Symmetric Asymmetric Same of flatter axis of astigmatism

4 Symmetric Asymmetric Different than steeper or flatter axis of astigmatism

5 Asymmetric Symmetric Same of steeper axis of astigmatism

6 Asymmetric Symmetric Same of flatter axis of astigmatism

7 Asymmetric Symmetric Different than steeper or flatter axis of astigmatism

8 Asymmetric Asymmetric Same of steeper axis of astigmatism for both surfaces

9 Asymmetric Asymmetric Same of flatter axis of astigmatism for both surfaces

10 Asymmetric Asymmetric Same for both surfaces but different than steeper or

flatter axis of astigmatism

11 Asymmetric Asymmetric Different for both surfaces but one in same flatter or

steeper axis of astigmatism

12 Asymmetric Asymmetric Different for both surfaces and both different than axis

of astigmatism

13 Symmetric Irregular At any axis. Several undefined yellow (≥ +10 µm)

and/or blue (≤ -10 µm) zones

14 Irregular Symmetric At any axis. Several yellow and/or blue zones

15 Irregular Asymmetric At any axis. Several yellow and/or blue zones

16 Irregular Irregular At any axis. Several yellow and/or blue zones

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Example 2: Normal Astigmatic Cornea With Initial Posterior Surface Changes (Figure 23)

The anterior BFS map shows a typical green bridge of a normal elliptical toric surface (e2 = 0.31). The anterior BFTA map is almost completely green indicating that the data fit a toric aspheric shape well, reflected in a Kranemann-Arce index of 12 µm.

The posterior BFS map also shows a typical bridge pattern of an elliptical surface however with a hot yellow temporal zone. The posterior e2 is 0.72. The posterior BFTA map shows a more symmetric meridian at 45°–225° axis and a more asymmetric meridian at 135°–315° axis with a Kranemann-Arce index of 33 µm.

A combination of BFTA patterns match pattern 4 of Table 1, i.e. the anterior surface has a symmetric aspheric variation of curvature in 360° however the posterior surface has an asymmetric aspheric variation of curvature at a different axis than the astigmatism. Considering that the SA is 0.15 µm, there are no significant HOAs (trefoil, quadrefoil, secondary astigmatism and coma), and the astigmatism from the Total Corneal Power (ray-traced) is 1.41 D. Theoretically this is a good case for aspheric monofocal or multifocal IOL implantation with cylinder compensation by corneal incisions. I would expect a residual refraction close to plano or with a spherical equivalent as close to zero as possible. In case of a selection of a toric aspheric IOL, I would recommend leaving this eye close to plano. However if a toric spherical IOL is chosen, I would leave a very little negative spherical equivalent. The pupil diameter of 3.12 mm gives freedom to choose between pupil-dependent and pupil-independent IOLs.

Example 3: KC With Irregular Astigmatism (Figure 24)

The anterior and posterior BFS maps show typical bridge patterns with yellow hot central zones in surfaces with already hyperbolic shapes. The posterior surface is more prolate (e2 = 1.23) than the anterior surface (e2 = 1.17). Both BFTA maps show increased asymmetry of asphericity with an anterior Kranemann-Arce index of 52 µm and a posterior index of 102 µm. Interestingly, despite the higher asymmetry of the posterior surface (i.e. the colors achieve red and dark blue steps), there is a good congruence (similar meridians) with the asymmetry of anterior surface. As expected in KC the asymmetric variation of aspheric curvature on both surfaces is also coincident (similar meridians) with the steeper axis of astigmatism. It has been my observation that most corneas with KC have this combination of BFTA patterns matching the pattern 8 of Table 1.

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Figure 23

Figure 22

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Figure 24

Considering that the SA is -0.15 µm, there is significant trefoil and coma with an astigmatism of 3.26 D from the Total Corneal Power (ray-traced). Theoretically, this is not a good case for implantation of an aspheric monofocal or multifocal IOL with negative aspheric aberration. A spherical monofocal IOL is a good option, however an astigmatic compensation by corneal incisions may further weaken this cornea.

I would consider the possibility to implant in this eye a spherical toric IOL or an aspheric toric IOL with neutral aspheric aberration. In such a case, I would expect a residual refraction close to plano or with a spherical equivalent as close to zero as possible, however I believe a little negative spherical equivalent might be tolerated. I cannot predict how trefoil or coma may influence the final quality of vision of this eye, however the small pupil diameter of 2.30 mm gives me more freedom to choose these options with toric IOLs.

9. The american Style display

This custom presentation of 4 maps resembles well the classical quad map of a commonly used scanning-slit device. The custom scales I used are not identical, but close to those suggested by the manufacturer in Brasil following our previous work at the

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Department of Ophthalmology, Paulista School of Medicine, Federal University of São Paulo that introduced the concept of color distribution and intuitive meaning of traffic lights (Schor P, Arce CG. Aspectos básicos do Orbscan. Em: Alves MR, Chamon W, Nosé W, eds. Cirurgia Refrativa. Rio de Janeiro, Brasil: Editora Cultura Médica Ltda; 2003:28–37; Stillitano I, Alzamora JB,. Arce CG, Schor P, Campos MSQ. Quantitative area pachymetry of corneas with keratoconus. World Ophthalmology Congress, São Paulo, Brasil. Fevereiro 2006; Alzamora JB, Arce CG, Schor P, Campos MSQ. Quantitative area topography: a new concept applied to study normal and pathologic corneas. World Ophthalmology Congress, São Paulo, Brasil. Fevereiro 2006; Arce CG, Kashiwabuchi RT, Campos M, Schor P. Traffic light sign meaning of Orbscan II and GALILEI color scales. Submitted for publication).

The two BFS Elevation maps at the top are displayed with the American Type III 5 µm scale, the axial (sagittal) curvature map with ANSI CGA 1D scale and the pachymetry map with ANSI CGA 15 µm scale, at the lower left and right, respectively. Observe that this strategy allows one to have the borderline guide values of 47 D and 500 µm in the first yellow step as presently suggested by the GALILEI in the Alternate Profile.

However, it is important to notice that the original BFS elevation maps from the other scanning-slit device are calculated from 10 mm-diameter data zones. Furthermore, this device also calculates the posterior BFS value using the same refractive indices of anterior BFS (1.0 for the air and keratometric 1.3375 for the cornea). The GALILEI has smaller fixed data zones and for the posterior BFS value uses the physiologic refractive indices (1.376 for the cornea and 1.336 for the aqueous humor). Anterior and posterior elevation maps are derived from 8.00 mm and 7.80 mm of diameter, respectively. This apparent 0.2 mm difference between anterior and posterior data zones is due to the convergence of light rays when crossing the cornea. GALILEI‘s smaller data zone avoids peripheral zones without data and comparison of exams always with the same data zone. The larger the data zone, the larger the BFS radius (and flatter the curvature) will be. There is approximately 1 D to 2 D difference between a BFS calculated from 10 mm and 8 mm data zone. If comparison of the values between both devices is required, I recommend reducing the data zone size or the region of interest (ROI) in the other device by using its view menu.

This presentation may also be compared to the GALILEI’s Refractive Report, as the traditional way to present topography of the whole cornea. This Map x4 does not include the posterior curvature map and introduces a different parameter (pachymetry) that is presented well separately.

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9.1. Evaluation of the american Style display

Examples 1: Normal Spherical CorneaExamples 2: Normal Astigmatic Cornea With Initial Posterior Surface ChangesExamples 3: KC With Irregular Astigmatism

I used the same examples of normal spherical cornea (Figure 25), normal astigmatic cornea with initial posterior surface changes (Figure 26) and KC with irregular astigmatism (Figure 27). Several features and patterns already described for these cases are lost in these maps and few are preserved. The alert sign represented by the yellow steps in BFS elevation maps is lost due to the fact that the American scale style has only one green step (zero value). This reasoning is similar to the argument against the Default scale where the zero value is only in the yellow step. Blue colors are more easily achieved and predominant in curvature and pachymetry maps because there are only three green steps in the ANSI scale style. Despite the first yellow step is in the guide value, established as a limit of normality, the blue color steps show flatter and thicker values, and the perception of normal range values is practically lost.

Figure 25

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Figure 26

Figure 27

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10. The German Style display

This custom presentation of four maps resembles map presentations found in a commonly used rotating Scheimpflug device and may also be compared to the GALILEI’s Refractive Report, which is a traditional Map x4.

A recent study (Belin MW, Khachikian SS. An introduction to understanding elevation-based topography: how elevation data are displayed – a review. Clin Experimental Ophthalm 2009; 37: 14–29) suggested a variable data zone for the BFS elevation maps. However there are users who prefer a fixed 8- or 9-mm-diameter data zone. Since GALILEI always uses 8 mm for the anterior BFS maps and 7.8 mm for the posterior BFS maps, comparison of the values between both equipments would require a reduction of the data zone size in the other device.

Anterior and posterior BFS elevation maps at the top and bottom right, respectively, are shown with the American Type IV 2.5 µm scale. The axial curvature map at the top left is displayed with the ANSI Type II 0.5 D scale and the pachymetry map at the lower left is displayed with the ANSI Type III 10 µm scale.

Observe that no borderline values are fixed at any color step because the color scales do not allow such an option. Smaller steps for elevation, pachymetry and curvature are a common practice by users to increase the sensitivity of maps. Although perceiving patterns like asymmetric bow-ties, from the practical point of view, such practice also increases the noise on maps. On the other hand, small asymmetries between superior and inferior hemispheres (I-S index) below 1 D do not seem to be risk factors for post-operative ectasia. Some doctors are less strict and use 1.50 D. Therefore, any apparent improvement or facility to diagnosis using steps with smaller size actually increase the occurrence of false positive alert signs. Furthermore, when smaller steps are used, extreme colors at both sides are achieved faster in the maps because the values are closer at the center. Colors lose their intuitive meaning when normal values such as 46 D, 10 µm or 500 µm appear with orange or red colors.

10.1. Evaluation of the German Style display

Examples 1: Normal Spherical CorneaExamples 2: Normal Astigmatic Cornea With Initial Posterior Surface ChangesExamples 3: KC With Irregular Astigmatism

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I used the same examples of normal spherical cornea (Figure 28), normal astigmatic cornea with initial posterior surface changes (Figure 29) and KC with irregular astigmatism (Figure 30). These maps require the user to read the numeric values on the maps in order to perceive normal and abnormal values. Although the intuitive meaning of colors partially remains, normal values are included in the orange and red range. Perhaps the most important loss with American and German Style Map x4 would be on the pachymetry maps. Having only three green steps of the ANSI scale and a larger number of blue steps make it more difficult to perceive the symmetry or asymmetry of the thickness distribution and progression, which are important signs of KC progression.

Although the original values are exactly the same, maps shown with the American and German Styles are different than those shown with the Alternate Profile, which I suggested and which were introduced in the software version 5.2.

The GALILEI is an excellent device for customizing color scales and step size. This feature enables users to select which map representation (including color, range and step size) allows easier, faster and more logical interpretation of maps.

Figure 28

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Figure 29

Figure 30

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11. differential Maps

The manual and documents released for the SW 5.2 have good explanations of the differential maps. New features allow aligning maps to the same reference centers or multiple marks. The most common preference is realignment to the pupil center, which is possible in the Display>Map x1 and Diagnostics>Difference display, as well as in the IOL Power Report total corneal wavefront map.

In my opinion the best scale for differential maps is the American scale with the green step at the zero value. In this case all yellow steps will represent positive change and all blue steps negative change. The size of the step may also be selected. My suggestion is to use 5 µm steps for height and pachymetry maps, 1.0 D steps for anterior curvature, refractive and total corneal power maps and 0.25 D steps for posterior curvature maps.

Figure 31A shows the anterior axial curvature differential map using the autodetect alignment of exams taken in January and August 2009 on the right cornea of a 38-year old male patient with marginal pellucid degeneration. Figure 31B shows the pachymetry differential map and Figure 31C the posterior axial curvature. Please observe that all maps A and B are shown in their original color scales but the differential map is in the American Style.

Figure 31A

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Figure 31C

Figure 31B

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Private PracticeRua Expedicionarios 427, Sousas, Campinas, SP 13106-028, [email protected]

Associate Researcher & OphthalmologistOcular Bioengineering and Refractive Surgery Sectors,Department of OphthalmologyPaulista School of Medicine, Federal University of São Paulo, Brazil

Carlos G. Arce, MD

This guide represents the opinions of Dr. Carlos Arce, M.D. This map in-terpretation guide is intended to be an instructive and helpful reference for use with the GALILEI. Clinical decisions derived from GALILEI mea-surements remain the decision and sole responsibility of the physician.

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Appendix

Color Scales and Report Formats

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GALILEI™ Color Scales and Reports Formats Appendix

intRoduCtionThis document is a supplement to the GALILEI Map Interpretation Guide. The new, additional color scales and the reports introduced with GALILEI software release 5.2 are described in more detail.A selection of GALILEI reports and the Alternate Profile (CGA) are presented in this document.

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1 Analyzing the Results ............................................................................................................................... 84 1.1 Color scales – additional options .................................................................................................... 84 1.2 Personalized layout profiles and Alternate Profile ........................................................... 85

2 Repor ts ................................................................................................................................................................... 87 2.1 Refractive Report – Alternate Profile ............................................................................................ 87 2.2 Keratoconus Report – Alternate Profile ...................................................................................... 88 2.3 Wavefront Report – Alternate Profile ........................................................................................... 89 2.4 IOL Power Report – Alternate Profile ........................................................................................... 90

3 Display .................................................................................................................................................................... 90 3.1 Five Custom Reports, and Alternate Reports ....................................................................... 91 3.2 Map x4 – Alternate Profile ..................................................................................................................... 91 3.3 Map x1 – Alternate Profile ..................................................................................................................... 92 3.4 Axial Anterior-Posterior Topography Report ......................................................................... 93 3.5 Instantaneous Anterior-Posterior Topography Report .................................................. 94 3.6 BFS & BFTA Elevation Report ........................................................................................................... 95 3.8 The American Topography Report ................................................................................................ 96 3.9 The German Topography Report ..................................................................................................... 97

4 Diagnostics ......................................................................................................................................................... 98 4.1 Difference maps – Alternate Profile .............................................................................................. 98

ContentS

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1 AnAlyzing the ReSultS

1.1. Color scales – additional optionsIn any map with a color scale anywhere in the GALILEI software, you have a choice of four different color scales: Default is based on the color schemes as recommended by Klyce and Wilson. Default style has only one yellow and 6 green steps. “ANSI style” has two yellow and 3 green steps. “German style” has one yellow and 7 green steps. “American style” has 3 yellow and only one green step.

New in 5.2: In addition to previously available scales, an alternate option is now also available using a strategy proposed by Dr. Carlos G. Arce. These scales are identified by the initials CGA and their color distribution follows an intuitive meaning. The universal code of traffic light signs is used: red for stop surgery, yellow for caution, look for more risk signs and green for going ahead. Blue remains for additional information.

Since the CGA distribution of colors is relative to an accepted still normal borderline value fixed on a yellow step of each color style, it allows easier interpretation of maps. The green range is used for normal values. The yellow step is used to guide borderline values still within normal range. Orange and red steps are used for values beyond the normal range representing risk factors for refractive surgery. Blue steps are used for values representing the opposite of risk factors and usually mean an uncommon or modified pattern. The table summarizes these color options.

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Limit guide values suggested by the Alternate Profile are 47.00 D, -6.75 D, 500 micron and 10-15 micron. However, these numbers may be modified according to the surgeon’s criteria by going to Settings menu and Scales.

1.2 personalized layout profiles and Alternate profile

To preserve the preferred look and feel of the GALILEI software, you can create your own customized layout profile where your settings will be stored. First you will need to create a profile: do this by going to the menu at the top of the screen and select [Options] and then [Profile] and finally [New profile]. You can give it any name you want and this will then be listed as is shown below for the profile “My Profile”. Note that “Default Profile” cannot be deleted since it contains the profile with the factory settings.

After creating your profile, change the settings to the layout of the maps to your preferred settings and once this is done, return to [Options] and [Profile] and click [Save Selected Profile].

New in 5.2: GALILEI remembers the profile last used. When re-starting the program, the same profile will automatically be selected.

New in 5.2: Besides the Default Profile, now there is the option of an Alternate Profile with settings suggested by Dr. Carlos G. Arce. Since the normal range of each map is variable, the proposed Alternate Profile uses CGA scales with the best combination of color steps and styles.

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Thus, the (anterior) axial curvature map has 47.00 D in the yellow step of a 1.0 D Default style scale. The (anterior) instantaneous curvature map has 47.00 D in the yellow step of a 1.50 D Default style scale. Posterior axial and instantaneous curvature maps have -6.75 D in the yellow step of a 0.25 D inverted Default style scale. The corneal pachymetry map has 500 micron in the yellow step of a 20 micron inverted German style scale. Anterior and Posterior BFS, BFA and BFTA Elevation maps have the zero value in the second green step and 15 micron in the second yellow of a 5 micron ANSI style scale. Both differential and wavefront maps have the zero value in the only green step of a 5 micron or a 0.25 D American Style scale. Consequently all positive values are in the yellow to red range and all negative values are in the blue to violet range.

Caution: The Alternate Profile may be changed. Once you have modified the Alternate Profile, it will not be possible to revert to the original settings of the Alternate Profile (other than undoing all your modifications one by one). It is therefore strongly suggested to make a note of any changes you make.

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2 RepoRtS

2.1 Refractive Report – Alternate profile

The Refractive report consists of 4 fixed maps and a set of parameters that provide a comprehensive overview of the cornea.

The Alternate Profile has the Refractive Report with all Settings (Numeric Values, Thinnest Location, Pupil and Axis) included in the following maps:

• Anterior Axial Curvature map with CGA 1.0 D Default style scale. • Corneal Pachymetry map with CGA 20 micron German style scale.• Anterior Elevation (Best Fit Sphere) map with CGA 5 micron ANSI style scale.• Posterior Elevation (Best Fit Sphere) map with CGA 5 micron ANSI style scale.

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2.2 Keratoconus Report – Alternate profile

The Alternate Profile has the Keratoconus report with all Settings (Numeric Values, Thinnest Location, Pupil and Axis) included in the following maps:

• Anterior Instantaneous Curvature map with CGA 1.50 D Default style scale.• Corneal Pachymetry map with CGA 20 micron German style scale.• Anterior Elevation (Best Fit Sphere) map with CGA 5 micron ANSI style scale.• Posterior Elevation (Best Fit Sphere) map with CGA 5 micron ANSI style scale.

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2.3. Wavefront Report – Alternate profile

The Alternate Profile has the Numeric Values included and the Total Corneal Wavefront Pie Chart in diopters displayed. (The pie chart must be selected manually by clicking on the “Pie“ button just above the chart.)

The wavefront map uses a 6mm diameter map display with American style colors and 0.5µm steps.

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2. 4 ol power Report – Alternate profile

The most important features of this report are the ray-traced total corneal power indices. The Central Average TCP assessed by quantitative area topography from the 4-mm-diameter central zone (highlighted) is the value to be used in IOL formulas of unmodified corneas or after refractive surgery.

The Alternate Profile has the Axial Curvature, the Total Corneal Power (Ray Traced), and the Total Corneal Wavefront HOA maps with all settings (Numeric Values, Thinnest Location, Pupil, or Axis) included.

3 diSplAyTo help you make an in-depth analysis of specific cases there are 6 options under the [Display] tab: [Custom Reports], [Map x4], [Map x1], [Scheimpflug] and [Overview].

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This Map x4 report is designed to show the topography data of the anterior surface.

3.1 Five Custom Reports and Alternate Reports

In addition to the five custom reports that can be defined by the user, several new custom reports have been added. They can be selected under the [Display] tab, below the 4 standard reports.

The Alternate Profiles have all Settings (Numeric Values, Thinnest Location, Pupil, and Axis) included in the following Custom Reports.

3.2 Map x4 – Alternate profile

The Alternate Profile has the Map x4 with all Settings (Numeric Values, Thinnest Location, Pupil and Axis) included in the following maps:

• Anterior Axial Curvature map with CGA 1.0 D Default style scale.• Anterior Instantaneous Curvature map with CGA 1.50 D Default style scale.• Anterior Elevation (Best Fit Sphere) map with CGA 5 micron ANSI style scale.• Anterior Elevation (Best Fit Toric Aspheric) map with CGA 5 micron ANSI style scale.

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3.3 Map x1 – Alternate profile

The Alternate Profile has the Map x1 showing the corneal pachymetry with the CGA 20 micron German style scale and with all settings (Numeric Values, Thinnest Location and Pupil).

This scale allows a clear inspection of thickness distribution and progression, searching if thickening from center to periphery is symmetric or asymmetric. Please notice that normal differential thickness between the center and periphery is less than 200 micron, i.e. less than 10 steps of 20 micron each. Therefore, progression of pachymetry is easily observed by simply counting the number of steps, without the need of additional graphics.

A recent study found that when the thinnest point is thinner than 500 micron and dislocated, usually temporal inferior, further than 1 mm from the pupil centroid, the cornea is already deformed enough to be diagnosed as keratoconus.

The corneal pachymetry map alone is can be printed separately as an independent report of thickness besides the topography reports.

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3.4 Axial Anterior-posterior topography Report

The Axial Anterior-Posterior Topography Report shows the axial curvature and the BFS elevation of both corneal surfaces.

• Anterior Axial Curvature map with CGA 1.0 D Default style scale.• Anterior Elevation (Best Fit Sphere) map with CGA 5 micron ANSI style scale.• Posterior Axial Curvature map with CGA 0.25 D Default style scale.• Posterior Elevation (Best Fit Sphere) map with CGA 5 micron ANSI style scale.

This report is designed to show qualitatively and quantitatively the congruency between axial curvature and elevation of both corneal surfaces.

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3.5 instantaneous Anterior-posterior topography Report

The Instantaneous Anterior-Posterior Topography Report shows the instantaneous curvature and the BFS elevation of both corneal surfaces.

• Anterior Instantaneous Curvature map with CGA 1.50 D Default style scale.• Anterior Elevation (Best Fit Sphere) map with CGA 5 micron ANSI style scale.• Posterior Instantaneous Curvature map with CGA 0.25 D Default style scale.• Posterior Elevation (Best Fit Sphere) map with CGA 5 micron ANSI style scale.

This report is designed to show qualitatively and quantitatively the instantaneous curvature and elevation congruency between both corneal surfaces.

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3.6 BFS & BFtA elevation Report

This report shows the Best Fit Sphere and the Best Fit Toric Aspheric Elevation maps of both corneal surfaces.

• Anterior Elevation (Best Fit Sphere) map with CGA 5 micron ANSI style scale.• Anterior Elevation (Best Fit Toric Aspheric) map with CGA 5 micron ANSI style scale.• Posterior Elevation (Best Fit Sphere) map with CGA 5 micron ANSI style scale.• Posterior Elevation (Best Fit Toric Aspheric) map with CGA 5 micron ANSI style scale.

This report is designed to show how both corneal surfaces compare against an ideal sphere and an ideal toric aspheric surface. It qualitatively demonstrates if both toric aspheric surfaces are symmetric (as the all green Anterior BFTA Elevation map of example above) or asymmetric (as indicated by the yellow-blue zones on the posterior BFTA elevation map).

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3.7 the American topography Report

The American Topography Report shows the BFS elevation maps of both corneal surfaces, the axial curvature map and the corneal pachymetry map.

• Anterior Elevation (Best Fit Sphere) map with Type III 5 micron American style scale.• Posterior Elevation (Best Fit Sphere) map with Type III 5 micron American style scale.• Anterior Axial Curvature map with CGA 1.0 D ANSI style scale.• Corneal Pachymetry map with Type III 10 micron (or CGA 15 micron) ANSI style scale.

This report has a different layout of maps and color scales than the GALILEI Default or Alternate Profiles. The layout of maps are more similar to those generated by other devices.

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3.8 the german topography Report

The German Topography Report shows the axial curvature map, the BFS elevation maps of both corneal surfaces, and the corneal pachymetry map.

• Anterior Axial Curvature map with Type III 0.50 D ANSI style scale.• Anterior Elevation (Best Fit Sphere) map with Type IV 2.5 micron American

style scale.• Corneal Pachymetry map with Type III 10 micron ANSI style scale.• Posterior Elevation (Best Fit Sphere) map with Type IV 2.5 micron American

style scale.

This report has a different layout of maps and color scales than the GALILEI Default or Alternate Profiles. The layout of maps is more similar to those generated by other devices.

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4 diAgnoStiCS

4.1 difference maps – Alternate profile

Note: See GALILEI Manual for details on new functionalities for aligning maps before subtraction.

The Alternate Profile has the maps A and B with their original selected scale and the differential map A–B with a 5 micron or 0.25 D American style scale.

Author: Carlos C. Arce, MD [email protected]

Your Customer Support contact address for installations in the USA and Canada:

ziemer uSA, inc.a Ziemer Group Company Phone: 866-708-4472321 Ridge St. e-mail: [email protected] Alton, Illinois 62002, USA

Your international Customer Support contact address for installations in Europe and anywhere else around the world:

ziemer ophthalmic Systems Aga Ziemer Group Company Phone: +41 848 943 637Allmendstrasse 11 e-mail: [email protected] Port, Switzerland

www.ziemergroup.com

Ziemer Ophthalmic Systems AGAllmendstrasse 11

CH-2562 Port, Switzerlandwww.ziemergroup.com

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