FEMTOLASER CATARACT SURGERY

FEMTOSECOND LASER CATARACT SURGERYRevolution, Evolution, or No Solution?Making Sense of the Literature

Ken Lipstock, M.D.Richmond, Virginia1emtosecond laser provides an ultrafast burst of energy.

Argon, excimer, and Nd: YAG lasers: nanosecond (10 ) pulses

Femtosecond: 10 second

Excimer: photoablates

Argon: photocoagulates

Nd: YAG and Femtosecond: photodisrupt. Their light energy can be absorbed by optically clear tissue and create microcavitation bubbles that cause an acoustic shock wave that incises the target tissue.

F-9-15Femtosecond lasers ultrafast pulse allows smaller amounts of energy to provide similar power output to the NdYag. This results in much smaller cavitation bubbles therefore reduced collateral damage to adjacent tissues.Femtosecond laser first FDA approved for LASIK flaps in 2001 and then approved for cataract surgery in 2010.

With guidance systems (OCT or Scheimpflug-like technology) it is used to make: Cataract clear corneal incisions and limbal relaxing incisions

Capsulorhexis

Lens fragmentation/softening; a pretreatment prior to phacoemulcification and/or irrigation/aspiration.Mistrust but VerifyWe are witnessing one of the most intense marketing campaigns ever in Ophthalmology.And this is a sentence from a scientific study in a respected peer reviewed journal!

Is Femtolaser Cataract Surgery the most important evolution since the transition to phacoemulsification?

Much has been claimed but how much is substantiated?

In the following presentation I will review the literature to try to shed some light on the subject. Since the vast majority of journal articles are written by those with financial ties to the femtosecond companies, the authors of the journal articles will be color coded red for financial ties and green if not. (The lead author will be in red if at least one of the authors has financial ties.)It has automated, computer-guided laser precision with minimal collateral tissue damage......with emerging evidence of ......greater precision and accuracy of the anterior capsulotomy, and more stable and predictable positioning of the intraocular lens.CompanyMode of dockingImagingLensSxAlcon, Ca.Curved glass at first, now uses soft contact interfaceOCT

LensARPrivately HeldOrlando, Fl.2 piece non contact interfaceScheimpflug-likeCatalysAMO, Ca.Liquid-optics interfaceOCTVictusB & LCurved glass interfaceOCTCapsulorhexisHypothesis: a capsulorhexis (rhexis) should overlap the IOL optic approximately .5 mm symmetrically 360 degrees and be larger than 4 mm . This will give a better and more consistent effective lens position (ELP) because of less asymmetric contractile force from the fibrosing anterior capsule on the IOL. The IOL should then not position more anteriorly or posteriorly than anticipated or with decentration or tilt. A better ELP leads to:

Closer to targeted spherical equivalent and less cylindera. Better uncorrected distance vision (UCDVA)

2. Less higher order aberrations like spherical aberration and tilta. Better corrected distance vision (CDVA)b. Better quality of vision with less glare, halos, and better contrast sensitivity.1,2,37Claim of the Femtolaser Companies:The femto anterior capsulotomy is more precise (consistent) and more accurate than a manual curvilinear capsulorhexis (CCC).Better size, more circular, better centered thus better overlap of the IOL. And better overlap yields less IOL decentration and tilt and better anterior-posterior position. 4,5

45Assymetric OverlapDecentered IOLCCC vs. Femto ButtonsFriedman; JCRS; 2011Kranitz; JRS; 2011 Continuous curvilinear capsulorhexis (CCC) technique was developed simultaneously by Neuhann in Germany and Gimbel in Canada around 1987. 6,7 Prior rhexis techniques (eg. can opener) led to 100% anterior capsular tears during cataract surgery and CCC tear rate approached 0%. 8 Prior to CCC capsular tears led to IOLs with haptics commonly with one in the bag and one in the sulcus or with both in the sulcus. Scientific BackgroundContinuous Curvilinear Capsulotomy: A Revolutionary Change for IOL Positioning9Assia, Apple (Oph 1993) showed:

Bag-Sulcus Fixation mean Decentration= .64 .39mm (range up to 1.76mm)Note: 1 SD =66.6% thus: 1.0mm decentration was common

Bag-bag Fixation mean Decentration= .18 .09IOLMean dec.Mean tiltAkkin (1994)0.151.1Hayashi (1997)MZ60BD0.27 .152.62 1.33SI30NB.30 .162.53 1.36MA60BM.30 .152.71 1.84Mutlu (1998)0.28 .142.83 .89Kim (2001)MZ60BD0.31 .152.67 .84SI-30NB0.32 .182.61 .83AcrySof MA60BM0.33 .192.69 .87Taketani (2004)AcrySof MA30BA0.30 .173.43 1.55Baumeister (2005)CeeOn 911A0.24 .133.03 1.79PhacoFlex SI-400.23 .133.26 1.69CeeOn 911A0.29 .212.34 1.81AcrySof MA60BM0.24 .102.32 1.41Mutlu (2005)AcrySof SA30AL0.34 .082.70 .55AcrySof MA30BA0.39 .132.72 .84Rosales (2006)UNKNOWN0.25 .28.87 2.16de CastroUNKNOWN0.34 .192.34 .97Baumeister (2009)AR40C0.19 .122.89 1.46Z90000.27 .162.85 1.36Hayashi (2014)H60M0.25 .174.88 1.45MA60BM0.28 .164.85 1.5210Mean IOL decentration 0.28 .16 mm and tilt 2.61 1.2Mean follow-up= 12.2 months Range= 3 to 48 months

Clinical Studies in the CCC Era Measuring IOL Decentration and TiltHow Much Does 0.28 .16mm Decentration and 2.6 1.2 Tilt Effect Vision?Let`s look at the Non-Femto Literature first.Would even less decentration and tilt provide better UCVA and CDVA?Would even less decentration and tilt provide better contrast sensitivity and less glare and halos?Would even less decentration and tilt have more or less effect depending on whether the IOL is spherical, negative aspheric, neutral aspheric, accommodating, multifocal?Remember: Femto Companies Claim Better Rhexis Better ELP Better Vision

Better Vision can mean both smaller refractive error and better quality of CDVA.

Okada has shown that a better rhexis does NOT lead to a Smaller Refractive Error (spherical equivalent or cylinder.)

Okada (Oph 2014) : Does the Rhexis Circularity or Centration effect Post-op Refractive Error? 93 eyes Phaco mostly by residents Pre-op spherical equivalent -7.75 to +4.50 Alcon Spherical IOL (SN60AT)Results for One Month and 1 yearMeasurements: Rhexis Circularity (comparison to perfect circle; ratio 1.0=perfect) Rhexis (not IOL) Decentration from pupil center Complete Overlap of Rhexis (360 over the IOL Optic) yes or no

111 Monthmean1 Yearmean from 1 month 1 yearCircularity.83 .01.87 .03p < .001Decentration (mm).30 .14.23 .13p < .001360 overlap (% of eyes)88%90%p = .02Okada Results (Contd):(StabilizationChange from 1 Month to 1 Year)Over time the rhexis became more circular, less decentered and with more overlap.Circularity of Rhexis NO significant correlation of circularity with post-op target spherical equivalent at 1 month or 1 year

NO significant correlation of circularity with post-op cylinder at 1 month or 1 yearOkada Results (Contd)Decentration of Rhexis

NO correlation with change in cylinder from 1 month to 1 year. It did correlate with the change in spherical equivalent between 1 month and 1 year (p=.03).

But Bottom Line:

NO significant correlation of Decentration with post-op target spherical equivalent at 1 month or 1 year.

NO significant correlation of Decentration with post-op cylinder at 1 month or 1 year.

Okada Results (Contd)16360 Overlap vs. Incomplete Overlap

NO correlation with change in spherical equivalent between 1 month and 1 year. It did correlate with change in cylinder between 1 month and 1 year.

But Bottom Line:

NO significant correlation of Overlap with post-op target spherical equivalent at 1 month and 1 year

NO significant correlation of Overlap with post-op cylinder at 1 month and 1 year

Okada Results (Contd) Rhexis Centration and Circularity and Overlap do not correlate with Post-op Refractive error.

Rhexis Centration and Overlap do play some role in stability of refraction but not enough to effect the average post-op refractive error at one year.Conclusion:Effect of IOL Position on Quality of Vision

Remember, Femto companies hypothesize: Better Overlap Better IOL Position Better Vision

Okadas Study Showed: Better Overlap Does Not Better Refractive Error

Question: Could Better Overlap Better Quality of Vision

Lower order Aberrations: myopia, hyperopia, astigmatism

Higher Order Aberrations (HOAs): coma, spherical aberration, trefoil, etc. can effect the quality of vision. These are measured with a wavefront analyzer.

Decentration and Tilt may effect Aspheric IOLs more than spherical IOLs so we will spend some time reviewing this subject now.

19Remember this:

The larger the pupil the more HOAs there are.

The pupil size increases in dim light and decreases with age.

55 years old (cataract age) pupil diameter:Bright mesopic=3.2mmMesopic=4.0mmLow Mesopic= 5.0mm12Effect of IOL Position on Quality of Vision (Contd) The First Negative Aspheric IOL was Tecnis (Pharmacia now AMO). Holladay and Piers did the early theoretical research for Pharmacia. Basic Idea:

A. The amount of total eye spherical aberration could be manipulated with an IOL because spherical aberration unlike other HOA`s like coma and trefoil is not very sensitive to the position of the IOL (rotation, decentration and tilt). However decentration and tilt could still possibly effect the results.

B. The cornea has positive asphericity and this is stable despite aging. It is approximately +.27. The lens has negative asphericity to balance the cornea so the total eye spherical aberration is minimized. The lens becomes more positively aspheric after age 40 causing more total eye positive asphericity.

41 y.o. 6.0mm pupil mean s.a.=.1065 y.o. 6.0 pupil mean s.a=.1913Effect of IOL Position on Quality of Vision (Contd)

Aspheric IOLsA spherical IOL has positive asphericity which increases the spherical aberration of the eye. Pharmacia developed a -.27 negative aspheric IOL (Tecnis) to eliminate total eye spherical aberration and thereby improve the quality of vision eg., contrast sensitivity. Tilt and decentration can induce HOA`s but much more in a negative aspheric IOL than a spherical IOL.

Question: Would tilt and decentration be a problem with negative aspheric IOL`s?Holladay and Piers (JRS 2002)

They calculated the Modular Transfer Function (MTF) at different amounts of tilt and decentration. MTF is a mathematical/theoretical calculation of contrast (the contrast of an image relative to the contrast of the object traveling through an optical medium). This relates to quality of vision.

Amount of tilt and decentration of Tecnis where the MTF (quality of vision) becomes worse than a spherical IOL:

Decentration= 4mm Tilt= 7

Holladay used monochromatic light for his calculations. In 2007 Piers corrected the calculations based on the more physiologic polychromatic light we experience:

14Decentration= .8mmCompare to 0.28 .16mm actual mean decentration of IOLs with a CCCTilt= 10Compare to 2.6 1.2 actual mean tilt of IOLs with a CCC1516

Ignore top dotted line (theoretical IOL with all HOAs corrected)Solid line= TecnisDashed line= Spherical IOLlawlesslawlessDecentrationTiltPolychromatic MTFPolychromatic MTF.28

.442.63.8Decentration .28 .16 .44mmNote: Minimal effect on MTF for most patients.0.8Tilt 2.6 1.2 3.8 Note: Tilt effects MTF even less than decentration.10Piers GraphSpherical aberration was less with Tecnis at all pupil sizes (the bigger the pupil the larger the difference).

Total HOA`s were lower with Tecnis only if pupil 6.0 mm (most cataract patients pupils are smaller) and coma and trefoil were no different at all pupil sizes.

Even though spherical aberration was less, Tecnis gave no improvement in CDVA photopic with high contrast charts or mesopic low contrast charts.

Tecnis gave no improvement in Contrast Sensitivity photopic or mesopic.

Kohnen`s team in Germany 17,18,19A series of intraindividual studies (same patient with one eye spherical IOL and other eye Tecnis).Aspheric IOL Clinical Studies5. Were these less than expected results with Tecnis due to tilt and decentration?

a) The Kohnen group measured it: Tecnis: decentration= 0.27 .16mm (as expected from other studies)tilt= 2.9 1.5 (as expected from other studies)(Decentration and Tilt of Spherical IOLs studied were almost exactly thesame.)

b) Multiple Regression Analysis showed no statistically significant correlation between decentration or tilt with the HOAs. ie, Decentration and Tilt were not the reason why Tecnis performed worse than expected.

c) This is consistent with the Piers graphs: Decentration and Tilt with a CCC are too small to significantly effect HOAs even with negative aspheric IOLs.

Kohnen (Contd)So why didnt Tecnis eyes see better? They had significantly less spherical aberration and we know decentration and tilt were too small to effect that impact. Puzzling.

Possible explanations:

a) Pupil size: average pupil in the study in mesopic conditions was 3.8mm. Negative spherical correcting IOLs have a much larger effect in pupils 6.0mm.

b) Interactions with other HOAs. It is not just spherical aberration we are dealing with. Some HOAs may interact with others in a negative or positive way.

Take home message: Factors effecting quality of vision are complex. (Marketing companies may use that to their advantage.) Negative aspheric IOLs are not significantly effected by decentration and tilt for most patients.20Neutral Aspheric IOL StudiesDeveloped Several Years Later

Concept 1. Do not add or subtract from the total eye spherical aberration.

2. Neutral aspheric IOLs may not actually decrease the total eye spherical aberration but they are less effected by decentration and tilt than negative spherical IOLs.

Model Eye Study calculation of MTF with Decentration; comparing Aspheric, Neutral Aspheric, & Spherical IOLs.Two pupil sizes and three types of IOLs. Verticle lines = .3 and .4mm decentration from the literature. (Mean and with one standard deviation.) Monochromatic light (Holladay) was used. Slope should be less narrow as per Piers/ Polychromatic light.Decentration has no effect on neutral aspheric and spherical IOL.. Tecnis is more beneficial in larger pupil.21

ModulationTecnisNegative AsphericModulationSoft PortNeutral AphericModulationSpheric.4.4.4.4Eppig (JCRS 2009) 21Modulation Modulation ModulationTilt has minimal effect on Tecnis even with monochromatic MTF calculations.22

Swedish Multicenter Double masked study of 80 patients with Tecnis in one eye and Neutral aspheric Akreos in the other.

Results (3 months post-op): Total HOA`s less for Tecnis for 4, 5 and 6mm pupils (p