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Corneal high order aberrations after standard LASIK with the mechanical microkeratome Moria One Use-Plus SBK: effect of flap thickness on corneal aberrometric profile

Session Details

Session Title: Refractive

Session Date/Time: Sunday 16/02/2014 | 08:30-11:00

Paper Time: 09:16

Venue: Kosovel Hall (Level -2)

First Author: : Maria LuisaColaco PORTUGAL

Co Author(s): :    Mónica Franco   Cristina Pereira   Hugo Nogueira   António Folgado   Ana Maria Carvalho   José Maia Seco

Abstract Details

Purpose:

To study corneal wavefront changes associated with standard LASIK surgery using MORIA mechanical microkeratome, accessed with Galilei G2; secondarily we investigated if flap thickness had any influence on the postoperative corneal aberrometric wavefront profile.

Setting:

Currently refractive surgery focuses on the importance of corneal aberrometry after LASIK and how these changes can cause significant visual complaints, halos, glares and decreased contrast sensitivity, despite a 20/20 vision on the Snellen chart.

Methods:

Retrospective study of 33 patients, 60 eyes, from the refractive surgery department of a tertiary hospital in Lisbon, that underwent LASIK between January 2012 and July 2013. Galilei dual Scheimpflug analyzer was performed pre and postoperatively obtaining the corneal aberrometry in the central 6 mm. We studied the root mean square of global high order aberrations (total HOA), spherical aberration (SA), coma, trefoil and 4th and 5th order indexes. For practical reasons we used the module of Zernike polynomials. Afterwards the sample was divided into two groups consisting of patients who had undergone LASIK with a 130 microns flap thickness (group A) or a 90 microns flap (group B), and studied if there were significant differences in corneal aberrometry between the two groups.

Results:

Mean age of our sample was 32.7 +/- 5.5 years. Mean uncorrected visual acuity in the postoperative period was 0,85 +/- 0,22. Mean postoperative total HOA was significantly higher than the preoperative 1.93 +/- 0.73 vs. 1.68 +/- 0.81 (p=0.038). Spherical aberration, coma, trefoil and 4th order HOA were all higher postoperatively relative to the preoperative values. The differences were all statistically significant (p<0.05) and more marked in terms of spherical aberration, coma and 4th order HOA (0.51 +/- 0.20 vs. 0.23 +/- 0.11, 0.24 +/- 0.18 vs. 0.18 +/- 0.14, and 0.64 +/- 0.29 vs. 0.31 +/- 0.21 respectively). The increase in coma was essentially in the horizontal coma (p=0,009). For groups A and B although a trend towards higher postoperative values was kept in both groups, no significant differences between the Zernike polynomials was found except for horizontal coma. In fact we found significantly higher horizontal coma levels in group B, with a thinner flap, 0,30 +/- 0,19 vs. in group A 0,19 +/- 0,14 (p=0,007). Although not statistically significant we found a tendency towards higher spherical aberration values in group A, with a thicker flap.

Conclusions:

LASIK significantly alters the wavefront profile of the human cornea, particularly inducing more spherical aberration and coma. The 5th order HOA do not change significantly with this surgery. In our study flap thickness was not associated with significant differences in corneal aberrometric profile post-LASIK, however there was a higher horizontal coma in thinner flaps (90 μm) and a tendency to induce more spherical aberration in the group with a thicker flap (130 μm). This may suggest that shallower cuts induce surface anomalies whilst deeper cuts induce more stromal remodelling and loss of keratocytes. The later may eventually lead to higher postoperative wavefront aberrations and poorer visual outcome. FINANCIAL INTEREST: NONE