Investigating the topographic effect of epithelium in myopic eyes with and without topographic preoperative abnormalities

Session Details

Session Title: Advanced Tools for Outcome Assessment

Session Date/Time: Tuesday 17/09/2019 | 08:30-10:30

Paper Time: 09:26

Venue: Free Paper Forum: Podium 4

First Author: : I.Salah Mabed FRANCE

Co Author(s): :    A. Saad   D. Gatinel                          

Abstract Details

Purpose:

To Explore the shape of Bowman layer in normal (Group N) and keratoconus suspected (Group KCS) classified corneas having low to moderate myopia corrected by photorefractive keratectomy (PRK).

Setting:

Rothschild Foundation, Paris, France.

Methods:

Anterior corneal specular Placido topography using OPD-Scan® II (NIDEK, Gammagori, Japan) was performed in 97 eyes of 55 patients (Group N; 77 eyes, Group KCS; 20 eyes) undergoing PRK for myopia, before and after epithelium removal. The differences in axial keratometry, asphericity and astigmatism were computed in different central corneal zones in Normal and KCS groups. After epithelial peeling, some normal classified corneas became KCS. Therefore, we have subdivided the group N into two groups: one of normal classified corneas which stayed normal after epithelium removal (group N), and one of normal classified corneas that became KCS classified (Group Nb).

Results:

The mean difference in axial mean keratometry in the third central millimeter rings was +0.50 ± 0.24 D, 0.69 ± 0.31 D and 0.49 ± 0.35 D respectively in Group N, group Nb and group KCS. The mean difference in the magnitude of epithelial induced astigmatism was 0.37 D x 89° (positive cylinder), 0.54 D 86° and 0.52 D 86° in the first central millimetre rings respectively in Group N, group Nb and group KCS. These differences were significant (p< 0.0001). Preoperative keratometry was the only predictive factor differentiating eyes of group N from those of Nb (p<0.001).

Conclusions:

The epithelial layer tends to reduce the magnitude of the Bowman layer’s astigmatism and prolateness and irregularities. In KCS group we found a similar trend than in normal eyes for epithelial steepening (~0.50 D). Besides, our results suggest that in KCS diagnosed corneas, the contribution of the epithelium to corneal refractive power is less pronounced than in normal corneas with subtle deformations (Group Nb). The epithelium would be able to mask Bowman layer’s irregularities until a certain degree of severity.

Financial Disclosure:

None