Wavefront-guided Ablation Retreatment in Myopic Eyes

1. Wavefront-guided Ablation Retreatment in Myopic Eyes Engy M Mohamed MD, Orkun Muftuoglu MD, R.Wayne Bowman MD, V. Vinod Mootha MD, H. Dwight Cavanagh MD,PhD, Gamal A Radwan MD PhD, James P.McCulley MD, FRCOphth Dr. McCulley receives consultant reimbursement from Alcon. No financial interest of any of the other authors Supported in part by an unrestricted research grant from Research to Prevent Blindness, Inc., New York, New York.

2. Introduction • Retreatment rates for primary myopic keratorefractive surgery range from 5.5% to 8.3%. • Persistence of residual refractive error is one of the most frequent causes of retreatment after LASIK. • Standard refractive surgeries also induce high order optical aberrations (HOA). • For some patients, HOA induction causes visual symptoms such as halos, starburst, glare, and double vision with a decrease of BCVA and/or contrast sensitivity. • Theoretically, correction of HOA may yield better quality of vision. • Wavefront technology is used for measuring and treating optical aberrations that could not be addressed previously with standard refractive surgery. It offers an additional potential benefit for successful retreatment in patients who had not achieved initial satisfactory outcomes with traditional keratorefractive surgery. • Iris registration provides the data and system to control the variable of ocular cyclotorsion associated with the changes occurring in body position changes from upright to supine in some subjects in addition to the following functions: 1) IR allows images taken by different cameras with different illumination sources to be aligned 2) enables images of the eye taken after the LASIK flap has been lifted to be used. 3) compensates for variations in pupil size between the diagnostic and treatment conditions.* *Chernyak DA. Iris-based cyclotorsional image alignment method for wavefront registration. IEEE Trans Biomed Eng 2005;52:2032-40.

3. Purpose of the study • Determine the efficacy, predictability, and safety of the Visx S4 IR wavefront platform are evaluated in cases of LASIK retreatment. • Our analyses sought to detect any differences between the visual outcome between eyes that had no prior retreatment after their initial keratorefractive surgery and those with multiple previous retreatment procedures. Methods • A retrospective analysis was carried out on 77 consecutive eyes of 57 patients undergoing LASIK retreatment at University of Texas Southwestern Medical Center at Dallas at the Laser vision center. • All had undergone initial LASIK procedure from August 2005 to September 2008. • Institutional Review Board approval was obtained for this retrospective analysis.

4. Inclusion criteria : 1) previous LASIK surgery with residual myopia, hyperopia or mixed astigmatism 2) no intraoperative complications in the initial procedure 3) stable refractive error for at least 3 months before surgery 4) sufficient residual central corneal thickness (> 250μm) 5) no contact lens wear for two weeks before the baseline retreatment examination. . Exclusion criteria : 1) corneal ectasia, keratoconus suspect or decentration 2) marked pupillary decentration 3) eyes that undergone ≥ 3 previous retreatments 4) previous keratoplasty or intraocular surgery such as cataract surgery or scleral buckle 5) ocular or systemic disease likely to affect corneal wound healing 6) pregnancy or nursing Based on the number of previous retreatments eyes were divided into 2 groups: Group 1 (n=63) included eyes with no previous retreatments; Group 2 (n=14) included eyes with previous retreatments. 11 eyes (79%) 3 eyes (21%) with one previous retreatment with 2 previous retreatments

5. Initial surgery *All eyes had myopia or compound myopic astigmatism before initial refractive surgery.*The eyes were retreated by their initial surgeons. All flaps were lifted by careful dissection with a Sinskey hook*The initial surgery was with several laser platforms

6. Results

7. On comparing both groups as regards their initial data and post-operative data the following differences were found

8. There was statistical difference between preoperative and post operative visual function in both groups

9. The efficacy index (ratio of postoperative UCVA and preoperative BCVA) 0.97 in group 1 0.85 in group 2 The safety index (ratio of postoperative and preoperative BCVA) 1.001 in group 1 0.96 in group 2

10. Predictability Attempted versus achieved At 6 months correction 6 month after LASIK retreatment

11. Graph showing the mean value of spherical equivalent (SE) before surgery and 1, 3 and 6 months after LASIK retreatment In a subset of 22 eyeson comparing preoperative to postoperative HOA, there was no significant difference between preoperative and postoperative HOA

12. Conclusion • These outcomes support the use of wavefront guided ablation in conjunction with iris registration for achieving excellent success in situations where the initial procedures have failed to do so. • There is statistically significant difference between both groups in: -Age (p=0.008) -Initial SE (p=0.03) -Interval between initial LASIK and retreatment (p=0.01) -Initial keratometric power (p=0.038). • We can conclude that the higher the initial spherical equivalence and initial keratometric readings, the higher the number of retreatments required to reach the aimed emmtropia will be. In addition, the shorter the interval is between the initial LASIK treatment and the retreatment, the more likely eyes will require several retreatments. • Other results yield some trends; although statistically insignificant yet they can be further investigated which is : Group 2 had a higher initial corneal thickness, 12 eyes (86%) had initial conventional LASIK and 13 eyes (93%) flaps were cut with a microkeratome ; which indicates that these two parameters may have a higher risk of increased number of retreatments.