Aberrations caused by Aberrations caused by decentrationdecentrationin customized laser refractive in customized laser refractive

surgerysurgeryDiana C. Lozano1,2

Advisors: Jason Porter2,3a, Geunyoung Yoon2,3b, and David R. Williams2,3a

San Diego State University, San Diego, CA1

Center for Adaptive Optics, Santa Cruz, CA2

Center for Visual Science3a and Department of Ophthalmology3b

University of Rochester, Rochester, NY.

August 11, 2003

OutlineOutlineWhat are refractive errors in the eye?What are refractive errors in the eye?What happens during refractive surgery? What happens during refractive surgery? How does refractive surgery (LASIK) correct myopic How does refractive surgery (LASIK) correct myopic errors?errors?Effectiveness of LASIK treatmentsEffectiveness of LASIK treatmentsSources of aberrations in LASIK: Sources of aberrations in LASIK: DecentrationDecentrationDecentration Decentration of the laser ablation treatmentof the laser ablation treatmentProject goalsProject goalsMethodsMethodsResultsResultsConclusionConclusion

Refractive errors in the human eyeRefractive errors in the human eye

Focal Point

Retina

Light rays from adistant star.

CorneaNormal Eye

Myopic Eye

Light rays from adistant star.

Retina

Focal Point Cornea

Eye’s also suffer from higher order aberrationsEye’s also suffer from higher order aberrationsAberrations prevent us from having perfect vision and blur images on the retina, especially when the pupil size is large (such as at night).

Aberration Map Retinal Image

0.5 deg

Perfect Eye

5.7 mm pupil

Normal EyeBest Corrected

• Most of these aberrations cannot currently be corrected with glasses, contact lenses, or laser refractive surgery.

What happens during refractive What happens during refractive surgery?surgery?

• Eye is numbed using anesthetic drops.

• Eyelid holder prevents blinking.• Microkeratome creates a flap. • Corneal flap is held back.• Excimer laser removes predetermined

amount of corneal tissue to re-sculpt the cornea.

• Flap placed back into position and naturally re-adheres.

Information taken from Strong Vision http://www.stronghealth.com/services/strongvision/LASIK.cfm

How does refractive surgery correct myopic How does refractive surgery correct myopic errors?errors?

Before Correction Before Correction -- Myopic EyeMyopic EyeCornea

Perfectly centeredlaser ablation

After Perfect CorrectionAfter Perfect Correction

Ideal Focal PointLight rays

from adistant star

Effectiveness of LASIK treatmentsEffectiveness of LASIK treatments

Conventional refractive surgery corrects the eye’s Conventional refractive surgery corrects the eye’s refractive errors (myopia, refractive errors (myopia, hyperopiahyperopia and and astigmatism)astigmatism)Customized refractive surgery: also attempts to Customized refractive surgery: also attempts to correct the eye’s higher order aberrationscorrect the eye’s higher order aberrations

Refractive surgery increases higher order aberrations.Refractive surgery increases higher order aberrations.There are several potential sources for the these There are several potential sources for the these induced higher order aberrations:induced higher order aberrations:–– Cutting of the flapCutting of the flap–– Healing processHealing process–– DecentrationsDecentrations due to eye and head movementsdue to eye and head movements–– Decentrations Decentrations due to shift in ablation treatmentdue to shift in ablation treatment

DecentrationDecentration of the laser ablation treatmentof the laser ablation treatment

Before Correction Before Correction -- Myopic EyeMyopic Eye

Cornea

DecenteredLaser Ablation

Light rays from a

distant star

Decentered focal point

After After DecenteredDecentered CorrectionCorrection

Ideal focal point

Project GoalsProject Goals

To determine what percentage of the overall To determine what percentage of the overall amount of aberrations created after surgery amount of aberrations created after surgery are due to static shifts of the customized are due to static shifts of the customized ablation treatmentablation treatment

To find ways to reduce higher order To find ways to reduce higher order aberrations caused by aberrations caused by decentrationsdecentrations in in refractive surgery.refractive surgery.

What we mean by shift of a customized What we mean by shift of a customized ablation treatment.ablation treatment.

Aberrations are measured over center of a dilated Aberrations are measured over center of a dilated pupil (2.5%pupil (2.5% neosynephrineneosynephrine).).

LASIK is performed over an LASIK is performed over an undilated undilated pupil.pupil.–– Patients more sensitive to lights when dilatedPatients more sensitive to lights when dilated–– Easier for surgeon to center Easier for surgeon to center undilatedundilated pupilpupil–– Eye tracking easier with Eye tracking easier with undilatedundilated pupilpupil

Shift of treatment occurs because the center of the Shift of treatment occurs because the center of the dilated and dilated and undilatedundilated pupils are not in the same pupils are not in the same location in the eye.location in the eye.

This This decentration decentration will induce additional higher order will induce additional higher order aberrations.aberrations.

Pupil and Limbus Centers:Dilated Eye

Subject ML, OS

S

ITN

LimbusDilatedPupil

Pupil and Limbus Centers:Undilated Eye

Subject ML, OS

Decentration of ablation

S

IT

Dilated Pupil

Limbus

Undilated Pupil

N

Example Example -- Perfect Perfect CentrationCentration

Pre-op: Spherical

Perfect correction and alignment

Post-op:No aberrations

=+

6 mm pupilRms = 1.0 µm

Example Example -- DecentrationDecentration

Pre-op: Spherical

Post-op: Vertical Coma

Correction decentered by 0.2 mm

+ =

Rms = 1.0 µm Rms = 1.05 µm6 mm pupil

Aberrations induced by decentration!

ProcedureProcedureTook pictures of the pupil and iris of 7 preTook pictures of the pupil and iris of 7 pre--LASIK subjects (13 LASIK subjects (13 eyes) when eyes) when undilated undilated and dilated (and dilated (neosynephrineneosynephrine).).

Pupil center found for both conditions relative to the Pupil center found for both conditions relative to the limbus limbus center center

Decentration Decentration = shift in pupil center from a dilated to = shift in pupil center from a dilated to undilated undilated pupilpupil

ShackShack--HartmannHartmann wavefrontwavefront sensor used to measure the wave sensor used to measure the wave aberrations over the dilated pupil for each patient aberrations over the dilated pupil for each patient preoperatively.preoperatively.

Calculated aberrations induced solely due to a shift in the Calculated aberrations induced solely due to a shift in the location of the center of the pupil in a location of the center of the pupil in a customizedcustomized LASIK LASIK procedure (procedure (GuiraoGuirao et al., JOSA A, 18(5), 2001).et al., JOSA A, 18(5), 2001).

Measured 6Measured 6--month postmonth post--operative wave aberrationsoperative wave aberrations

Magnitudes of pupil center shiftMagnitudes of pupil center shift• Range of vector magnitudes: 0.08 mm to 0.631 mm• Average vector magnitude: 0.33 mm ± 0.165 mm

0

0.1

0.2

0.3

0.4

0.5

0.6

X-Shift Y-Shift Vector

Vector

Horizontal Shift Vertical Shift

Mag

nit

ude

of

Pu

pil C

ente

r S

hif

t (m

m)

Vector

Vertical

Horizontal

Shifts in pupil centerShifts in pupil center• Pupil center tended to shift in the inferior-nasal direction

when the pupil dilated.

Right Eye Left Eye

Center of Center of undilated undilated

pupil

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8TN

S

I

Center of dilated pupils

• Decentration of ablation is in the superior-temporal direction.

pupil

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8NNT

S

I

Aberrations theoretically induced due Aberrations theoretically induced due to to decentrationsdecentrations

• Calculated ratio of theoretically induced higher order Rms to pre-and post-op higher order Rms

• Range of % of post-op: 7% to 119.3%• Average % of post-op: 33 ± 30.9 %

0

10

20

30

40

50

60

70

Percent of Pre-HO RMS Percent of Post-HO RMSPerc

enta

ge o

f Ind

uced

Rm

s rel

ativ

e to

Pre

/Pos

t-op

Rm

s

6.0 mm pupil

Induced / Pre-op Induced / Post-op

Per

cen

tage

(%

)

ConclusionsConclusionsShift in pupil center from dilated to Shift in pupil center from dilated to undilatedundilated::–– Average magnitude: Average magnitude: 0.33 mm ± 0.165 mm0.33 mm ± 0.165 mm–– Range of magnitudes: 0.08 mm to 0.631 mmRange of magnitudes: 0.08 mm to 0.631 mm–– Tended to be in the superiorTended to be in the superior--temporal directiontemporal direction

DecentrationDecentration of customized ablation induces higher order of customized ablation induces higher order aberrationsaberrations

Percentage of aberrations that could theoretically be Percentage of aberrations that could theoretically be accounted for by accounted for by decentrationdecentration::–– Average percentage of postAverage percentage of post--op: 33 ± 30.9%op: 33 ± 30.9%

Potential solution to reduce induced aberrations:Potential solution to reduce induced aberrations:–– Reference the customized treatment with respect to the Reference the customized treatment with respect to the

limbuslimbus and NOT the center of the pupil.and NOT the center of the pupil.

AcknowledgementsAcknowledgementsFunding provided through a Research Experiences for UndergraduatFunding provided through a Research Experiences for Undergraduates (REU) es (REU) Supplement to the Center for Adaptive Optics, a National ScienceSupplement to the Center for Adaptive Optics, a National Science Foundation Foundation

Science and Technology Center (STC), ASTScience and Technology Center (STC), AST--987683987683

Thanks to Dr.Williams Lab, Antonio Thanks to Dr.Williams Lab, Antonio Guirao Guirao and and CfAOCfAO

Special thanks to:Special thanks to:Jason PorterJason Porter

Dr.Dr.GeunyoungGeunyoung Yoon Yoon Dr.David R. Williams

Special thanks to:Special thanks to:Lisa HunterLisa Hunter

Malika MoutawakkilMalika MoutawakkilHilary Hilary O’BryanDr.David R. Williams O’Bryan