Scheimpflug Imaging

ORBSCAN & PENTACAM

THE SCHEIMPFLUG PRINCIPLE• 1ST described by Theodor Scheimpflug, a

cartographer of the Austrian navy

• 1ST introduced in ophthal

by Drews, Niesel, Brown,

Dragomirescu and Hockwin

• obliquely tilted object can be documented with

maximal possible depth of focus and minimal

image distortion

HOW DO THEY DO IT???• 3 imaginary planes -film, lens and focal

plane(non-parallel ).

• Tilt the lens plane of the lens intercept the

planes of the film and focus in a line of

intersection known as Scheimpflug linedepth

of focus,sharpness of image points located on

different planes are high.

• 1 Rotating camera and monochromatic slit light

source rotate around the optical axis of the eye

perpendicular to each other to obtain slit

images of cornea from 0 to 180° .

• each photograph belongs to a specific angle of

corneal section.

• A 2nd center placed static camera captures and

corrects eye movements pupil diameter &

corrects,

• Software :construct 3D model of AS from

25,000 data points

• calculates data for corneal

topography,thickness,ACD,lens opacification

and thickness,corneal wavefront of the anterior

and posterior corneal surface using Zernike

polynomials .

THE SCHEIMPFLUG SYSTEM • Images the anterior eye with a camera at an angle to a

slit-beam creating an optic section of the cornea and

lens.

• USES• For the assessment of :

keratoconus

cataract

IOL tilt

IOL decentration

corneal clearance

posterior subcapsular opacification

shape changes with accommodation,corneal implants

corneal thickness and anterior chamber depth

• NONCONTACT IMAGING OF AS

a and p surface topography of the cornea .

anterior chamber biometry.

keratometry.

pachymetry mapping.

• PRE OP EVALUATION IN REFRACTIVE SX

Cases @ risk of ectasia.

planning & evaluation of results of sx .

• IN FEMTOSECOND LASER-ASSISTED

CATARACT Sx

• corneal thickness, elevation, curvature, anterior

chamber depth, or refractive power in color

map of the physician’s choice

SCHEIMPFLUG SYSTEMS• 4 devices using the Scheimpflug principle &

camera:

• TMS-5 (Tomey, Nagoya,Japan),

• Pentacam® HR (OCULUS, Wetzlar, Germany),

• Sirius® (CSO,Florence, Italy),

• Galilei® (Ziemer, Port, Switzerland)

ORBSCAN(ORBTEK, INC.) 1995

• slit-scanning corneal topographer

• true elevation maps of A & P corneal surfaces.

• pachymetry of the entire cornea.

• Anterior change depth.

• Pupil size and white to white measurement.

ORBSCAN II (BAUSCH & LOMB).

• placido system to give conventional

topographical maps + orbscan.

• IMAGING:slit scanning /cobble stone

methodology with 40 slits of h8 12.5 mm & 0.3

mm width ,schleimflug angle 45⁰.

Advantages of orbscan

• quantity of information superior.

Disadvantages of orbscan

• it is more expensive than placido systems.

• It has a slower image capture (2-3 s vs 0.5 s).

• orbscan II is not validated against a gold standard.

Indications

1. Detect KC ,ectatic corneal diseases.

2. Screen forme fruste KC,CL warpage b4 refractive sx.

3. Measure regular and irregular astigmatism.

4. Aid in planning refractive surgery.

5. Measure optical zone sizes, centration,changes

after keratorefractive sx & orthokeratology.

6. Aid suture removal after PK.

7. Guide CL fitting in advanced KC .

8. Pachymetry.

• Interpretation of Orbscan Maps

• printout :quad map ( 4 maps).

1. elevation maps

-anterior float & posterior float.

-the measured surface vs reference sphere .

-cornea tissue above reference sphere :warm colors

while those below :cooler colors.

-uses:RCL fitting, assess severity of KC ,screen FFKC.

-BFS

2.REFRACTIVE MAP:

• measures the local corneal D overlying the

pupil .

• useful for identifying central islands in

PRK/LASIK patients.

• The Orbscan II : Axial, Tangential,Optical, Mean

& Astigmatic power maps.

4.pachymetry map

• 30 um ≥ USG pachymetry as value from tear

film endothelium and indentation of tissue by

usg prob.

• Provides thickness across whole cornea .

• Orbscan and usg pachymetry measurements

are not comparable & should not be used

interchangeably

• overlays.

• The circular lines at 3 mm, 5 mm,7 mm,9 mm

areas.

• The pupil centre and outline as well as the k-

lines (steepest and flattest axis of astigmatism)

applied.

PENTACAM• Trade name of comprehensive AS analyser.

• combines a rotating Scheimpflug camera with a static

camera.

• Scheimpflug camera:corneal scan from o to 180°

each of the photographs is an image of the cornea at

a specific angle.

• The static camera :placed in the center to detect the

pupil’s contours and control fixation.

• The light source :UV-free blue LED (475 nm).

• Ultra fast digital signal Processor : utilizes a ray

tracing algorithm to construct and calculate the AS.

• 50 scans in 2 s with 500 true elevation points / scan

surface(25,000 measured ,analyzed true elevation

points.

• available in three models:

• Pentacam BASIC – the individual model

• Pentacam CLASSIC – the versatile model

• Pentacam HR – the professional model

INTERPRETATION OF A PENTACAM MAP

• corneal tomography has two parts:

• corneal parameters on the left side

• 4-view refractive composite map on the right

side.

• Qs:

• Quality specification.

• specifies the quality of the tomography.

• “OK”,else computer extrapolates.

• Q-val:

• asphericity of anterior corneal surface.

• The ideal value:measured in 6-mm central zone. In ().

• N/l :–1 to 0.

• Q >0 :oblate corneas(>–3Dphotoablation & RK.

• Q <-1 :hyperprolate corneas(>+3Dphotoablation & KC).

• K1= (Kf)

• power of the flat meridian of the anterior surface of cornea measured within the 3-mm central zone (Sim-K) in diopters (D).

• N/l: > 34 D

• K2=(Ks):

• Curvature power of the steep meridian of the

anterior surface of the cornea measured within

the 3-mm central zone (Sim-K) in D.

• N/l : < 49 D.

• Km=(K-avg):

• Mean curvature power of the anterior surface

of cornea within the 3-mm central zone (Sim-K)

and expressed in D. It should be considered to

avoid flap complications.

• Km < 40 D, free-flap complications

• Km > 46 D ,button-hole complication

• K-max:

• Maximum curvature power of the whole anterior surface of cornea in D.

• N/l Kmax < 49 D,

• Kmax (od) - K-max(os) = < 2 D,

• Kmax (od) - K2(od) = < 1 D.

• If ≥ 1D, K-max instead of K2 used for hyperopic correction to avoid post PRK irregularities.

• Astig:

• Amount of corneal astigmatism on anterior surface

• (K2 – K1) within 3-mm central zone (Sim-K)

• Axis:

• The axis of anterior corneal astigmatism within the 3-mm central zone.

• Pupil center

• for the decentration technique for hyperopia, astigmatism or corneal irregularity treatment.

• to evaluate angle kappa

• Pachy Apex:

• thickness at the apex of the cornea.

• APEX:the origin of the coordinates,

• X and Y are horizontal and vertical meridians

• 0 : both pachy apex coordinates.

• X axis : p/t’s right left(p/t seated opp to physician).

• Y axis :bottom up.

• “+0.2,–0.4” :0.2 mm temporal and 0.4 mm inferior to corneal apex.

• Pupil diameter:

• diameter of pupil in photopic, mesopic or scotopic.

• for adjusting optical zone diameter & ICRS implantation

• Thinnest location (TL):

• thinnest point of the cornea.

• thin cornea <470 μm with n/l OR 500 μm with

Abn/l tomography.

• between both eyes n/l difference:< 30 μm.

• TL - pachy apex ≤ 10 μm.

• minus indicates inferior displacement of the TL.

Anterior Chamber Volume (ACV), Angle

(ACA)Depth (ACD):

• ACV < 100 mm3, ACA < 24° or ACD < 2ACG

• 4 phakic IOL:ACD≥ 3.0 mm,ACA>30°,ACV

≥100 mm3.

FUNCTION (OUTPUTS1.Scheimpflug image+Densitometry :

• entire anterior segment from cornea posterior

lens surface,

• Densitometry of the lens :

i. The evolution of a cataract can be made visible

even at an early stage

ii. It makes classification of the cataract easy

iii. Long-term controls of cataracts are possible

iv. The extension of the cataract can be measured

• Densitometry of cornea :

Useful 4 evaluation of corneal haze, progression/

regression(post viral keratitis, corneal scars,Post

C3R)

2.Corneal topography map :

• The Anterior Sagital/tangential Map

• anterior surface dioptric power measured by

sagittal method.

• Steep areas :hot (red,orange),flat areas :cold

(green,blue).

• The cross point of this segmentation :apex

• parameters are studied on the steep axis at the

5-mm central circle.

• The n/l pattern :symmetric bowtie (SB)

SB WTR ast. 2 SEGMENTS (A) AND (B) ARE

EQUAL IN SIZE

n/l : I>S, I -S < 1.5 D.

IF S >I ,S-I < 2.5 D

• ABNORMAL PATTERNS

• better seen on the tangential map.

1.Round (R);

2.Oval (O)

3. Superior Steep (SS)

4. Inferior Steep (IS)

5. Irregular (Irr);

6. Abnormal Symmetric Bowtie (SB).

7. Symmetric Bowtie with Skewed Radial Axis (SB/SRAX). The angle

between the axes of the two lobes is >22°

8. Asymmetric Bowtie/Inferior Steep (AB/IS); the I-S >1.5 D,

9. Asymmetric Bowtie/Superior Steep (AB/SS); the S-I >2.5 D;

10. Asymmetric Bowtie with Skewed Radial Axis (AB/SRAX). angle between the axes of the two lobes is >22°

11. Butterfly (B);

12. Claw pattern (C);

13. Junctional (Vertical D);

14. Smiling face (SF);

15. Vortex (V). The steep & flat segments are distributed in a vortex pattern

• The Anterior Tangential Map

• morphologic patterns of the cone in ectatic corneal disorders.(nipple, oval and globus).

• elevation maps

• a and p surfaces of the cornea,

• H8 of cornea vs BFS.

• 4 refractive sx screening, the ideal diameter of RS is 8 mm and mode is the float mode.

• Shape : n/l: symmetric hourglass

• Abnormal shapes :

a. Skewed hourglass :large angle Kappa and misalignment during taking the capture,abn/l distorted cornea.

b. Tongue-like extension and irregular hourglass :abn/l distorted corneas.

c. Isolated island :abnormal distorted corneas with central/ paracentral protrusion.

• Parameters (BFTE float mode): Look at the

highest plus values within central 5-mm zone

• Abnormal > 12 μm and > 15 μm on the a and p

elevation maps respectively.

• Cone can be quantified in ectatic corneal d/s

• Parameters (BFS float mode): Another

method of quantification done by pointing with

the cursor at the TL symbol on the elevation

maps and left click on the mouse to display the

values.

• cone can be localized In ectatic corneal d/s.

3.The Pachymetry Map

• The corneal thickness is displayed as a colour image over its entire area from limbus to limbus.

• 3 main landmarks

– cornea apex (orange arrow),

– TL (red arrow),

– 2 opposing points on the vertical meridian at the central 5-mm circle(white dotted arrows)

• S- I ≤ 30 μm n/l.

• Shape: normal:concentric shape

• Abnormal shapes include:

a. Horizontal displacement of the TL .

b. Dome shape. The TL is vertically displaced .

c. Bell shape. There is a thin band in the inferior part of the cornea(PMD).

d. Keratoglobus. A generalized thinning reaching the limbus

• 2 pachymetry profiles:

• corneal thickness spatial profile (CTSP)

average progression of thickness starting from the TL to corneal periphery in relation to zones concentric with the TL

• percentage thickness increase (PTI).

• the percentage of progression of the same

• The normal profile is a curved line plotted in red, parallel to the course of the normative black dotted curves,

• Abnormal profiles include:

a. Quick Slope . The red curve leaves its course before

the 6-mm zone. forme fruste keratoconus

b. S-shape :The red curve has a shape of an “S”. FFKC and ectatic disorders.

c. Flat shape :The red curve takes a straight course. oedematous corneas

• applications

a. Keratoconus detection

b.Preoperative planning for any corneal refractive

sx

c. Progression control after corneal surgery

d. Improved IOL calculation for post-LASIK

patients

e. IOP modification with regard to corneal

thickness

4.IOL calculation map

• corneal sx cat sx accurate IOL power

calculation.

ADVANTAGES OF PENTACAM• automatic initiation of measurement

• reproducibility

• non contact measuring

• <2 s

• pachymetry accurate & 4 entire cornea

• easy,efficient,time saving

• STEPS OF READING CORNEAL

TOMOGRAPHY

1. Display the 4-view refractive composite map

and take an overview to scan for any irregular

shapes.

2. Study the corneal parameters and focus on the

parameters of anterior corneal surface, corneal

thickness and anterior chamber. Mention all the

parameters in your report

3. Study each map separately:

4. Scoring the Case

-accumulative score

-the risk of developing iatrogenic ectasia

after

“Overall, the anterior sagittal

map, both elevation maps, and pachymetry map have

regular

shapes.”

• Overall, the elevation maps show some

irregularities more obvious on the posterior

one.Other maps look regular.

• “Quality of the image (QS) is OK for both

surfaces. K-readings are within the normal

range; both K2 and K-max are < 49 D and (K-

max—K2) is < 1 D. The amount and axis of TA

should be compared with MA. Q-value of both

surfaces is within the normal range [–1 , 0]. TL

is > 500 μm. Difference in thickness between

the TL and pachy apex is < 10 μm. There is no

vertical displacement of the TL. Angle kappa is

not significant; x-coordinate is < 200 μm in

absolute value. ACV is > 100 mm3, ACA is

normal and > 30°, ACD is normal (> 2.1 mm)

but < 3.0 mm.

• “The anterior sagittal map:SB, no SRAX, I-S = 1

D, which is normal.”

“The posterior

elevation map shows tongue-like extension in BFS mode

and

abnormal values (> 15 μm) within the central 5-mm zone in

BFTE mode.”

• The pachymetry map:concentric pattern, I-S

is normal (< 30 μm), and there is no

horizontal or vertical displacement in the TL.”

• GALILEI DUAL SCHEIMPFLUG ANALYZER

• integrates a Placido disc and a dual rotating Scheimpflug system for corneal topography 4 3D analysis of the AS.

• covers the cornea, anterior chamber and lens .

• Placido disc and Scheimpflug images are simultaneously acquired to obtain the information on the curvature and elevation of the cornea respectively.

• The Pentacam and Galilei are interchangeable contrary to Sirius

SIRIUS SCHEIMPFLUG ANALYZER • integrates a Placido disc and a mono rotating

Scheimpflug system for corneal topography 4 3D analysis of AS.

• elevation maps are displayed in Sirius in a special