1. Corneal Biomechanical Changes Following Surface Keratorefractive Surgery Teeravee Hongyok, MD, Christopher J. Rapuano, MD, Ajoy Virdi, MBBS, Elisabeth J. Cohen, MD, Kristin M. Hammersmith, MD Cornea Service, Wills Eye Institute Jefferson Medical College, Thomas Jefferson University Philadelphia, PA The authors have no financial interest in the subject matter for this poster. World Cornea Congress VI, Boston, MA, USA, April 7-9, 2010

2. Ocular Response Analyzer (ORA) Pictures from http://www.ocularresponseanalyzer.com/ The ORA is the only machine that can perform direct clinical assessment of corneal biomechanical properties. 4 main parameters are measured by ORA: Corneal Hysteresis (CH) is the difference in inward and outward applanation pressures (P1 and P2). CH may reflect viscoelasticity of cornea. Corneal Resistance Factor (CRF) may reflect elasticity of cornea Goldmann Correlated IOP (IOP G ) Corneal Compensated IOP (IOP CC ) The signal peak height and multiple oscillations are changed in post-laser in situ keratomileusis (LASIK) keratectasia eyes compared to the normal post-LASIK eye (Glass DH, et al., ARVO 2008; E-abstract 646). Using the new ORA software (version 2.04) launched in 2009, the device can mathematically describe the ORA waveform characteristics with 38 new parameters including height, slope, area-under-the curve and waveform score.

3. Corneal Biomechanics in Keratoconus and after Refractive Surgery CH and CRF have been found to be significantly reduced in patients with keratoconus 1,2 and post-LASIK corneal ectasia 3 LASIK was also found to decrease CH and CRF. 4-8 The significant alteration of corneal biomechanics may play a critical role in development of this serious ectatic complication after refractive surgery. We hypothesized that surface ablation, which has no stromal flap and leaves a thicker residual stromal bed, would result in less change in corneal biomechanics than LASIK. 1 Luce JCRS 2005, 2 Kirwan Ophthalmologica 2008, 3 Kerautret JCRS 2008, 4 Pepose AJO 2006, 5 Ortiz JCRS 2007, 6 Chen JCRS 2008, 7 Hamilton JCRS 2008, 8 Kirwan JCRS 2008

4. Purpose To evaluate pre- and post-operative changes in corneal biomechanical properties using the Reichert Ocular Response Analyzer (ORA) in patients who undergo surface keratorefractive surgery.

5. Methods Prospective, non-randomized clinical trial Inclusion: patients over the age of 18 who planned to undergo surface keratorefractive surgery on the Cornea Service at Wills Eye Institute from November 2008 to February 2009 IRB approved Data collection: before surgery, 1 and 3 months after surgery –Corneal thickness: U/S (Accupach V) and optical (Galilei) –Corneal topography: and Galilei (Ziemer) –Corneal topography: Atlas 995 (Carl-Zeiss) and Galilei (Ziemer) –Reichert ORA hardware version 3.0, software version 2.04 Basic biomechanics parameters and new waveform parameters were analyzed.

6. Results 9 eyes of 5 male patients underwent custom off-flap myopic epi-LASIK and completed 3 month F/U (age: 36 ± 7.8 years). PreoperativePostoperative 1 month 3 months UCVA [logMAR ± SD] (Snellen) 1.20 ± 0.17 (20/316) -0.01 ± 0.1 (20/20+) -0.06 ± 0.05 (20/17) MRSE (D) -4.4 ± 1.25 +0.18 ± 0.31 -0.21 ± 0.36 Mean keratometry (mean ± SD, D) Atlas 43.80 ± 0.44 40.07 ± 1.03 40.50 ± 0.99 Galilei 43.39 ± 0.44 39.64 ± 1.16 39.96 ± 1.08 Laser ablation depth (μm) 60.67 ± 17.2 60.67 ± 17.2 Pachymetry (mean ± SD, μm) U/S (Accupach V) 549 ± 31 467 ± 37 495 ± 27 Optical (Galilei) 560 ± 29 495 ± 32 503 ± 34

7. Basic Corneal Biomechanics Parameters Changes after Epi-LASIK * P < 0.05 (Wilcoxon Signed Rank Test) * * * * ** *

8. Corneal Hysteresis Changes after Laser Refractive Surgery: compared to other studies No. of Eyes 66 65 43 90 32 32 33 35 9

9. Corneal Resistance Factors Changes after Laser Refractive Surgery: compared to other studies No. of Eyes 66 65 43 32 32 33 9

10. New Waveform Parameters: Significant Changes in 9 of 38 (p<0.05) Sample of Signal Overlay of Preoperative ORA and Postoperative ORA Decreased overall Waveform Score Decreased Peak 2 parameters Uslope2) Upslope of peak2 (Uslope2) Maximum single step increase in rise of peak1 (Mslew2) Maximum single step increase in rise of peak1 (Mslew2) Aspect ratio (height/width)of peak 2 (Aspect2) Aspect ratio (height/width) of peak 2 (Aspect2) Aspect ratio of downslope (height/width)(Slew2) Aspect ratio of downslope (height/width) (Slew2) Decreased Peak 1 parameters Height of peak1 (H1) Height of peak1 (H1) Height of peak1 at 50% applanation peak (H11) Height of peak1 at 50% applanation peak (H11) Absolute value of monotonic decrease on downslope part of peak1 starting at the peak value (Dive1) Absolute value of monotonic decrease on downslope part of peak1 starting at the peak value (Dive1) Area under the P1 curve (P1area) Area under the P1 curve (P1area) Preoperative ORA signal Postoperative ORA signal

11. Conclusions Epi-LASIK, a surface ablation procedure, significantly reduced corneal hysteresis and corneal resistance factor. Unexpectedly, the magnitude of reduction seems to be similar to LASIK from previous publications. –It appears that corneal thickness is more important than the flap creation on the corneal biomechanics. Waveform analysis also found significant changes in both peak 1 and peak 2 and a decrease in overall waveform score after surface ablation.

12. Conclusions A marked decline in these parameters may reflect changes in the viscous and elastic qualities of the cornea after surface ablation. Future work is needed to determine whether differences in these corneal biomechanical parameters are useful in detecting patients who are at risk to develop post-refractive surgery ectasia, even after surface ablation.