1. Wavefront Sensing of the Human Eye
Jim Schwiegerling, PhD
&
Jochen Straub, PhD

2. 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.

3. Lasik

4. Design of the study 89 LASIK patients
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
89 LASIK patients
Measurements pre-op, 1 week, 1 month, 3 months, 6 months, and 12 months post-op
Manifest Refraction
Corneal Topography
Aberrations
Pupil Diameter
Contrast Sensitivity

5. Manifest Refraction
No statistically significant change in average manifest refraction is seen during the healing period between the 1 week and any following exam.

6. Scanning Slit Technique uses white light scatter from cornea and
crystalline lens.
By refracting through each
surface, this technique can
measure anterior and
posterior corneal shape, as
well as anterior crystalline
lens shape.

7. Corneal Topography

8. Shack-Hartmann Wavefront Sensor
Plane Wavefronts
Eye
Lenslet Array
Aberrated Wavefronts
Eye
Lenslet Array
Perfect wavefronts give a uniform grid of points, whereas aberrated
wavefronts distort the grid pattern.

9. Example Images No Refractive Surgery Post-LASIK with VISX Star S2
Low Aberrations
High Aberrations

10. Wavefront Reconstruction
PSF

11. 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.

12. 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.

13. Aberrations & Contrast Sensitivity
m=98%
m=85%
m=70%
m=55%
m=40%
m=25%
m=10%

14. Contrast Sensitivity Contrast Sensitivity Pupil Diameter Aberrations
1 week
Decreases
Increases
Increase
6 months
Increases to pre-op
Decreases to pre-op
12 months
Decreases slightly
No change

15. 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.