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 Age Preoperative SE Ablation depth Follow up period SE : Spherical equivalent M : F = 12 : 18 28.43

± 6.61 yrs -4.80

± 1.80 D 58.37

± 20.83

μ

m 2.80

± 1.94 months

Results

Table 2. Comparison of changes in posterior corneal measurements Difference Preop.

Postop.

∆ 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) Posterior curvature (mm) 6.14

± 0.18

* P < 0.05 by paired t-test 0.47

± 4.23

0.551

-1.11~2.05

6.12

± 0.17

-0.02

± 0.07

0.106

-0.004~0.04

Results

A paradoxical decrease in ACD was seen after laser ablation.

3.35

3.30

3.25

3.20

3.15

3.10

3.05

ACD1 ACD2 No significant differences were seen in the posterior curvature after laser ablation.

6.20

6.15

6.10

6.05

PreopCurvature PostopCurvature

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) 8       4 -4 0                    -8 440  480 520 Residual thickness 560    8  -4 4 0                        -8 25  50 75 ablation depth 100  

Conclusions

There was

no significant protrusion

in posterior corneal surface after laser surface ablation.