The Aberration Structure of theKeratoconic Eye

Geunyoung Yoon, Ph.D.

Department of OphthalmologyCenter for Visual Science

Institute of OpticsDepartment of Biomedical Engineering

University of Rochester

Wavefront Congress 2007

Optical quality of the keratoconic eyecompared with normal

Totalaberration

Cornealtopography

Keratoconus Normal

15

0

-10

µm

Theoretical visual benefit when corrected thehigher order aberration.

Visual benefit in keratoconic eyesAdvanced

KC

0

2

4

6

8

10

12

FE SC SM SM KB JP JP MB SL SG SG JF Avg.

Normals

Subject

Visu

al B

enef

it

Statistical significance (p<0.01) of each Zernikemode from zero for normal and keratoconic

population Pantanelli S et al., Ophthalmology, in press (2007)

-4

-2

0

2

4

6

8

10

1 2 3-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Lower order Higher order

Normal myopiaKeratoconus

Zern

ike

coef

ficie

nt (m

icro

ns)

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*

*

* *

*

Defocus Verticalcoma

Sphericalaberration

Vertical 2ndastigmatism

Why negative vertical coma?Corneal curvature causes relative phase advances and phase delays.

Phase

advance

Phase

delay

Resultantwavefront

MB

Keratoconiccornea

Aberrationfree cornea

superior

inferior

-2

0

2

4

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12

1 2 3-0.5

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0.5

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1.5

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Normal myopiaKeratoconus

Zern

ike

rms (

mic

rons

)

3 4 5 87 96 1211 1310 1615 1714 201918

Coma, Z3-1and Z3

1, is the most significant higherorder aberration in keratoconic eyes

Lower order Higher order

Except for defocus, all the Zernike rms values are significantly differentfrom normal eyes.

Abnormal eyes have a significantly greaterproportion of higher order aberration

compared to normal eyes.

HO Variance

Total Variance=

Normal: 1 ± 1 %

KC: 16 ± 20 %

Coma (Z3-1 & Z3

1)HO Variance

Trefoil (Z3-3 & Z3

3)HO Variance

Spherical Aberration (Z40)

HO Variance

= 62 ± 30 %

= 18 ± 27 %

= 6 ± 13 %

Proportion of HOA to HO variance in keratoconic eyes

Early detection of keratoconus suspect usingcorneal first surface higher order aberration

B_hren J et al., Am. J. Ophthal., in press (2007)

Moderate KC KC suspect (felloweye of the KC eye) Normal eye

11 Zernike modes, totalHOA RMS, coma RMS andthird-order RMS

2 Zernike modes, Z3-1 and Z5

-1

Optical and surgical options to improvevision of keratoconic eyes

- Spectacles- Contact lenses

Hard and rigid gas permeable lensesSoft lensesHybrid lenses (hard in the center + soft skirt)Piggyback lens (rigid gas permeable over soft)Other specialized lenses (Rose K, multi curve aspheric, scleral)

- Cornea transplants- Intrastromal corneal ring segments- Corneal cross linking with Riboflavin

- Adaptive optics- Customized soft contact lenses

Front surface customizedBack surface customizedBoth surface customized

Large stroke adaptive optics makes it possible tocorrect large amounts of the higher order

aberration of keratoconic eyes

Total rms = 1.7 µm

Higher order rms = 1.3 µmTotal rms = 0.1 µm

Higher order rms = 0.04 µm

Without AO With AO

50 100 150 200 250

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100

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250 -5

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50 100 150 200 250

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250 -5

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50 100 150 200 250

50

100

150

200

250 -5

-4

-3

-2

-1

0

1

2

3 Wavefront height (m

icrons)

Front surface customized soft contact lenses

Blurredimage

Sharpimage

With conventional contact lens

With customized contact lens

Correcting the higher order aberration withcustomized soft contact lenses

Sabesan R et al., Optics Letters, in press (2007)

HO rms = 3.07 µm

HO rms = 1.05 µm

Withconventionallens

Withcustomizedlens

6 mm pupil

20 40 60 80 100 120

20

40

60

80

100

120

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20 40 60 80 100 120

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20 40 60 80 100 120

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20 40 60 80 100 120

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20 40 60 80 100 120

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120

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20 40 60 80 100 120

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120

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20 40 60 80 100 120

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80

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120

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0

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6

8

3.74 µm

1.07 µm

1.74 µm

0.52 µm

Keratoconic eyes

Wavefront height (µm

)

High contrast letter (100%)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1 2 3

Subject

Visu

al a

cuity

(log

MA

R)

Series1

Series2

Improving visual acuity with customizedcontact lenses in keratoconus

High contrast letter (100%)

Subjects

Visu

al a

cuity

(log

MA

R)

Conventionallens

Customizedlens

2.1 lines improved

SC MX MB

6 mm pupil

RGP

Back surface customized soft contact lens

Laser beam

Residual aberration

Irregularcornea

Ablating backsurface of the lens

Better fittingBetter optics

Laser beam Best qualityvision

Surface ablation of conventional soft contactlens with an ArF excimer laser

Excimerlaser

Two axissteering mirror

Soft contactlens

Beam delivery optics

Wavefrontsensor

Laser ablation of the back surface of softcontact lens with an Excimer laser

Soft contactlens

Lens mount

Excimer laserbeam

Two axis steeringmirror

Back surface of softcontact lens

An arbitrary back surface profile of softcontact lenses can be generated precisely

with excimer laser ablation.

-1

-0.5

0

0.5

1

1.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

DesignMeasurement

Zernike mode

Zern

ike

coef

ficie

nts (

mic

rons

)

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Scatter effects caused by surface roughness afterablation

Optical zone (5 mm in diameter)

Before ablation After ablation

SH sensor spot patterns with intensity saturated

Conclusion

1. Wavefront data from both wavefront sensor andcornea topography can be used as an objective tool todiscriminate keratoconus from normal eyes.

2. Back surface customized soft contact lenses have thepotential to correct higher order aberrations ofkeratoconic eyes and to provide better lens fitting.