wavefront sensing of the human eye jim schwiegerling, phd & jochen straub, phd
TRANSCRIPT
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Wavefront Sensing of the Human Eye
Jim Schwiegerling, PhD
&
Jochen Straub, PhD
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Introduction
• Want to examine the effects of Conventional Refractive Surgery (LASIK) on the aberrations of the eye.
• Need to separate the effects of surgery from the effects of healing.
• Measured wavefront error, visual acuity, contrast sensitivity and pupil size prior to and at multiple time points during a one year time frame following surgery.
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Lasik
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Design of the study
• 89 LASIK patients
• Measurements pre-op, 1 week, 1 month, 3 months, 6 months, and 12 months post-op
Visit Eyes
Pre-op 158
1 week post-op 154
1 month post-op 145
3 months post-op 131
6 months post-op 105
12 months post-op 132
• Manifest Refraction
• Corneal Topography
• Aberrations
• Pupil Diameter
• Contrast Sensitivity
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Manifest Refraction
Manifest Refraction: Sphere
-7
-6
-5
-4
-3
-2
-1
0
1
-50 0 50 100 150 200 250 300 350 400
Days after surgery
Sph
ere
in d
iopt
ers
Manifest Refraction: Cylinder
-2
-1
0
1
2
3
-50 0 50 100 150 200 250 300 350 400
Days after surgery
Cyl
inde
r in
dio
pter
sNo statistically significant change in average manifest refraction is seen
during the healing period between the 1 week and any following exam.
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Scanning Slit
Technique uses white lightscatter from cornea and crystalline lens.
By refracting through eachsurface, this technique canmeasure anterior and posterior corneal shape, aswell as anterior crystallinelens shape.
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Corneal Topography
Radius of Curvature of the Anterior and Posterior Corneal Surface
5
5.5
6
6.5
7
7.5
8
8.5
9
-2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13
Months After Surgery
Rad
ius
of C
urva
ture
(m
m)
Anterior
Posterior
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Shack-Hartmann Wavefront Sensor
Plane WavefrontsEye
Lenslet Array
Aberrated Wavefronts
Eye
Lenslet Array
Perfect wavefronts give a uniform grid of points, whereas aberratedwavefronts distort the grid pattern.
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Example Images
Low Aberrations High Aberrations
No Refractive Surgery Post-LASIK with VISX Star S2
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Wavefront Reconstruction
PSF
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Aberrations
The change in aberrations due to surgery is statistically significant for pupil diameters of 5.0 mm and larger. The change in aberrations during healing at 6
months is significant.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
3.5 4 4.5 5 5.5 6 6.5 7 7.5
Pupil Diameter (mm)
Abe
rrat
ions
(m
icro
ns)
pre-op
1 week post-op
6 months post-op
12 months post-op
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Pupil Diameter
A statistically significant increase in dark-adapted pupil diameter is measured 1 week after surgery. The pupil diameter returns to its pre-op size after 6
months.
4.5
5
5.5
6
6.5
7
7.5
pre-op 1 weekpost-op
1 monthpost-op
3 monthspost-op
6 monthspost-op
12monthspost-op
Pup
il D
iam
eter
(m
m)
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Aberrations & Contrast Sensitivity
m=98% m=85% m=70% m=55% m=40%
m=25% m=10%
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Contrast Sensitivity
Contrast Sensitivity Pupil Diameter Aberrations
1 week Decreases Increases Increase
6 months Increases to pre-op
Decreases to pre-op
Decreases to pre-op
12 months Decreases slightly No change Increase
Changes in Contrast Sensitivity
-0.1
0
-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13
Months After Surgery
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Discussion
• The posterior surface of the cornea changes shape as a result of the flap incision and laser ablation, most likely due to a weakening of the mechanicla strength of the cornea.
• Conventional LASIK reduces refractive error (defocus and astigmatism), but introduces higher order aberrations (mainly spherical aberration).
• Pupil size is enlarged by surgery and slowly returns to normal during the healing phase. Decreases in visual performance cannot be solely attributed to larger pupil size.
• Contrast sensitivity is decreased by the higher order aberrations.