Changes in Posterior Corneal Surface After Laser Surface Ablation for Myopia Sun Woong Kim, M.D.1, Hae Jung Sun, M.D.1, Tae Im Kim, M.D.2, Eung Kweon Kim, M.D., Ph. D.2 Department of Ophthalmology, Soonchunhyang University Hospital, Bucheon, Korea 1, The Institute of Vision Research, Department of Ophthalmology, College of Medicine, Yonsei University, Seoul, Korea 2

The authors have no financial or proprietary interest in any materials or methods mentioned.

Purpose To evaluate the changes in posterior corneal surface before and after laser surface ablation using a rotating Scheimpflug camera, the Pentacam (Oculus Inc, Wetzlar, Germany).

Methods 30 myopic eyes (14 PRK, 16 LASEK) of 20 patients were evaluated preoperatively and postoperatively (1-6months) with the Pentacam Main outcome measures Posterior central corneal curvature change the average in central 4mm zone in tangential curvature map Posterior corneal elevation change determined by subtracting the preoperative elevation data from the postoperative elevation data based on the maximum difference at the center of the difference map BFS determined by preoperative measures Anterior chamber depth (ACD) change determined by subtracting the preoperative central ACD data from the postoperative central ACD data

Results Table 1. Patient demographics Sex M : F = 12 : 18 Age 28.43±6.61 yrs Preoperative SE -4.80±1.80 D Ablation depth 58.37±20.83 μm Follow up period 2.80±1.94 months SE : Spherical equivalent

Results Table 2. Comparison of changes in posterior corneal measurements Preop. Postop. Difference ∆ P 95% CI ACD (mm) 3.22±0.22 3.16±0.23 -0.06±0.08 0.000* 0.03~0.08 Posterior elevation (µm) 0.47±4.23 0.551 -1.11~2.05 Posterior curvature (mm) 6.14±0.18 6.12±0.17 -0.02±0.07 0.106 -0.004~0.04 * P < 0.05 by paired t-test

Results A paradoxical decrease in ACD was seen after laser ablation. No significant differences were seen in the posterior curvature after laser ablation.

Results The amount of forward shifting of posterior corneal surface had no correlation with residual corneal thickness or ablation depth (Pearson correlation, P > 0.05)

Conclusions There was no significant protrusion in posterior corneal surface after laser surface ablation.