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Page 1: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University
Page 2: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Does Size Matter?Does Size Matter?

Arthur Bradley, PhD,

Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng,Ph.D.

Indiana University School of Optometry

Susana Marcos, Ph.D.,Instituto de Optica, Madrid, Spain

The impact of ablation zone and pupil size

Page 3: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Typical Soft CL: Lens diameter 14 mm

Typical Soft CL Optical Zone 9-11 mm

Spectacle Lens isalways much

larger than pupil

Most Spectacle and Contact Lens corrections employ opticalcorrections larger than the pupil, thus ensuring full correctionof the entire wavefront that creates the retinal image.

Page 4: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Newer refractive optical corrections, however, employ opticalzones that may be smaller than the pupil, and thus onlycorrect part of the wavefront creating the retinal image.

Phakic IOLs

Artisan anteriorchamber IOL5 or 6 mm OZ

NuVita anteriorchamber IOL

5mm OZ

PhotoablativeRefractive Surgery

Visian ICLposterior chamber4.65-5.5 OZ

Current AZ sizes rangefrom 5.5 - 7 mm

Page 5: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

What are the consequences of pupils that arelarger than the optical correction?

Does size really matter? Surely it must!

Should a patient with a > 8 mmdiameter pupil choose RS?

Page 6: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Concern about pupil size and refractive surgery: an unresolved issue

1990: Applegate and Gansel, “The importance of pupil size in optical qualitymeasurements following RK”1996: Pop “The complicated laser -Large pupils cause a devilish problem:halos” (LASIK) Claimed that patients with >8mm pupils are 100% dissatisfied.1998: Nixon (patient letter to JCRS), 9mm pupils, 5.5 mm LASIK suffers lossof contrast, halos, star bursts that make it impossible to drive at night.1998: Davidorf “Measurement of pupil size may be the most frequentlyneglected facet of the refractive surgery evaluation…Clearly, a patient withpupils that dilate to 8 or 9 mm in low light is likely to suffer from visualaberrations following refractive surgery”2003: Freedman et al, identifies and “empirical rule” that “It is generallyaccepted that the transition zone between ablated and unablated cornea must lieoutside the measured pupil size by 0.5 to 1.0 mm to minimize…..halos, glare,ghosting and desaturation”.2004: Pop and Payette, “Pupil size at any month postoperatively was notstatistically predictive of postoperative NVC”2004: Klyce, in editorial following Pop’s article “The pupil proclaimsinnocense”

Page 7: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

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Example of pre- and post-LASIK wavefronts(Marcos IOVS 2001), 6 mm AZ, 9mm transition.

Myope

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3LASIK

50m mrange

6m mrange

HO“corr”

HO&LO“uncorr”

PRE POST

RMS0.8 mm

RMS2.7 mm

6.5 mm pupil

PRE POST

Sample Eye

RMS12.5 mm

RMS5.7 mm

Page 8: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Increased HO aberrations in post-LASIK eye are exaggerated with increasing pupil size.Unknown for very large pupils.

2 3 4 5 6 70

0.5

1

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4.5

3.5

Treatment Zone

Measured Aberrations

Note that this anexample of poorpost-op correctedoptics. Largestlevel of HOaberrations inMarcos study

Pre

Post

HO RMS analysis of same eye as a function of pupil sizeR

MS

mm

Size of large pupils

?

Deq=1.7D

Page 9: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

How large are pupils at low light levels?

=low mesopic

Winn et al, 1994, who tookgreat care to remove othercues which might result inpupil constriction.

Periman et al,2003 usingColvardpupillometerreplicate Winnet al.

Mean=7 mm inyoung adults,significantproportionhave >8 mmpupils

Page 10: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

FOZ<Ablation Zone

AZ=6mm

Partal and Manche, 2003

AZ=6.5, Effective TZ=5.5

Pre-op Rx -5.25DTZ5.5

AZ6.5

Pupil8 mm

In this example, <50% of areaof night-time pupil is treated

Boxer et al 2002

Successful treatment zone (TZ) generallyappears smaller than planned ablationzone (AZ)

How large is the ablation zone?

Page 11: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Increased aberrations in post-RS central pupil definitelyassociated with decreased visual function.

But what of highly aberrated periphery?

Marcos, 2001, 3 mm pupil

Post RS Aberrations and VisionP

ost

/pre

Oshika et al, 2002, post-LASIK eyes who lost > 2lines of BSCVA had moreinduced SA and coma incentral 3 mm than eyesthat did not lose BSCVA.

Examples

Page 12: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

E.g. Atchison et al 1979: Effect of pupil size on VA in normal eyes

MAR

Pupil Diameter (mm)1 2 3 4 5 6 7 8

1

2

2-3 mm pupil is bestAberrationeffect

Diffractioneffect

Does increased pupil size, which should universally lead toincreased aberrations, also lead to decreased vision?

Approach #1: vary pupil size and measure impact on vision

Page 13: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Holladay et al, 1999, post-LASIK loss in BSCVA

Montes-Mico and Charman, 2002

Emmetropic control

Post PRK

12 c/deg

Decrease light level

Conclusion #1: Increased pupil sizesassociated with low light levels reducedvisual function in post RS eyespresumably to the recruitment of thehighly aberrated marginal optics.

Surrogate test of pupil size effect is examine the impact of light level.

Page 14: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Approach #2: Look for correlations between patient pupilsize and and post-RS vision problems.Note that this approach lacks an internal control, requires adequaterange of pupil sizes, clincial relevance requires inclusion of eyeswith large pupils, need to have measurement technique thatsimulates pupil sizes experienced during night driving.

2001 Haw and Manche, pre-op pupil size did correlate with anypost-PRK visual symptoms or measured visual performance.

2003 Lee et al, Surveyed LASIK patients and reportedsymptoms of glare and halos did not significantly correlatedwith pupil size.

2004 Pop and Payette find that pupil size is not a risk factor forNVC after LASIK.

Conclusion #2: Increased pupil sizes associated with low lightlevels did not reduced visual function in post RS eyes.

Page 15: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Without data, resort to modeling refractive correctionsthat are smaller than the pupil.

Develop a theoretical model of eye that is emmetropic in thecentral region of the pupil, but still myopic in the outeruncorrected region of the pupil (a bifocal eye). Analogous toCharman and Walsh’s (1986) bifocal model, originally developedto examine retinal images in eyes with bifocal SVCL.

Data Summary:Mesopic/Scotopic pupils measured up to 9 mm, with a mean ofabout 7 mm for most young adult eyes.Can find no published aberration data for pupils larger than 7 mm.We know little about the peripheral optics and vision of post RSpatients with larger than normal pupils.Large pupil are/are not associated with vision problems.Patients with large pupils should/should not have RS.

Page 16: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Charman and Walsh (1986) Model

B=TZ x Rx=70 arc min

B=P x RxE.g. 110 min

plano

myopic

Simulated PSF For a -4 D Myope with 8 mmpupil, 5 mm TZ

Halo?

Page 17: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Lackner et al 2003, using same argument as Charmanand Walsh proposed that light outside of TZ causesHalos experienced by LASIK patients.

Page 18: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Charman et al, 2002 a, b argue that small TZ in RS cause problemsfor peripheral vision due to increases likelihood of rays entering thepupil that do not pass through the TZ.

Dramatic increase in in mid-periphery RMS, and accompanyingreduction in visual sensitivity

TZ

Simulated PSF

TZ=6mm

pre

post

Page 19: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Experimental Evidence to support/reject this bifocal model of post-RS eye

1. Fan Paul et al 2002:Patient description of PSF

Note that no abruptappearance of Halos for P>TZ

“”Halos may be attributed topupil a diameter that is greaterthan the optical zone diameter”BUT observed halos not thesame as bifocal modelpredictions!

Hal

o s

core

2. Schallhorn et al, 2003, 1 month after LASIK

TZ

Page 20: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

3. Lackner et al, 2003:Glare and halo phenomena afterLASIK. “only patients whose measured pupil diameter wassmaller than the ablation zone were included.”

Hal

o s

ize

in s

qu

are

deg

rees

Although the model is compelling, the experimental data do notsupport a bifocal model as a cause of NVC following RS.

Page 21: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

WF from -3D Myope, 8.4 mm Same eye with 2ndorder fully corrected

Myopic peripheral optics Emmetropiccentral optics

+ =

Simulated bifocalpost-RS eye

Wavefront Version of Bifocal Model of post-RS eye

Page 22: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Wavefront Version of Bifocal Model of post-RS eye

Can we represent this bifocal model withZernike Polynomials (10th order)

Cross-sections through Myopicand Emmetropic wavefronts

Myope

Pupil diameter = 8.4 mm-5051015202530354045

Pupil diameter = 8.4 mm

Zernike Polynomials do not adequately fit bifocal model

Challenge #1

Emmetrope

Page 23: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Vis

ual s

ensi

tivity

Challenge #2: Due to waveguide optics of photoreceptors, humanpupil behaves as though it contains an apodizing function

cone

Axial ray

Marginalray

Apodization filter

h x( ) = hmax ¥10-r x-xmax( )2

Page 24: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Impact of Apodization on bifocal model PSF

PS

F i

nte

nsi

ty

w/ SCE

w/o SCE

00.20.40.6

0.81

0 1 2 3 4 55 4 3 12

For example, the visualintensity of the halogenerated by the rayspassing through theedge of an 8 mm myopicpupil will be attenuatedby approximately 20%

Apodization will reduce thevisual impact of highlyaberrated rays passingthrough the uncorrectedmargins of a dilated pupil.

BUT: as emphasized byAtchison, pupil apodization isabsent under scotopicconditions.

Page 25: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Challenge #3 Can we predict NVC from aberrometry data?

Cheng, et al, 2004:Experimentally introducecontrolled levels of aberrationsinto the retinal image andmeasure the impact on VA.

LogMAR

0

0.5

1

1.5

2

-0.3-0.2 -0.1 0 0.1 0.2 0.3 0.4

RM

S w

avef

ront

err

or RMS

0

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ual S

treh

l rat

io

LogMAR

VSR

LogMAR

Pup

il fr

actio

n

0

0.2

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0.8

1

-0.3-0.2 -0.1 0 0.1 0.2 0.3 0.4

PF

RMS which weights each part ofthe pupil equally was one of theworst predictors of VA loss due toelevated aberrations

Page 26: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Marechal

PF = HiQ areaPupil area

Image Quality Metrics that predictvisual impact of HO aberrations aregenerally unaffected by the highlyaberrated rays passing through themargins of a large pupil.

VisuallyweightedStrehlRatio

The highly aberrated marginal rays are notsignificant contributors to the PF or SR evenbefore RS, and therefore increasing theiraberrations is unlikely to have much impact on thecentral spike in the PSF.

Page 27: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Summary:

Understanding the visual impact of marginal rays entering thepost-RS eyes with pupils larger than the TZ is largely unknown.We lack the empirical data and an accurate model.

We need to examine the aberrations post-RS eyes over ( mmpupils. We need to systematically examine the visual impact ofpupil size.

Such data will lead to improved recommendations to patients withlarger pupils, and will also lead to blend strategies that arefunctionally optimized.

Such data will also help resolve the intriguing question of whyNVC seem to disappear in many post-RS patients (e.g Schallhornet al, 2003, Lackner et al 2003). Is it neural adaptation (Webster etal, 2002; Artal et al, 2003), pupil adaptation (Woodhouse, 1975) orstructural/optical adaptation (Klyce, 2004)?

Page 28: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University

Sample data fromliterature showingeffect of pupil size inpost RS eyes.

Failed to find data beyond 7 mm,and most for smaller pupils.

Miller et al, 2002

Seiler et al, 2000

6+mm AZ

Pre

PostPRK

LASIK

Page 29: Does Size Matter?voi.opt.uh.edu/VOI/WavefrontCongress/2004/... · Does Size Matter? Arthur Bradley, PhD, Pete Kollbaum, OD, Larry Thibos, Ph.D., Xu Cheng, Ph.D. Indiana University