Corneal elastic response after photorefractive keratectomy for asymmetrical topographies: long-term follow-up

Session Details

Session Title: Corneal Biomechanics

Session Date/Time: Tuesday 13/09/2016 | 16:30-18:00

Paper Time: 17:36

Venue: Auditorium C6

First Author: : A.Renna SPAIN

Co Author(s): :    J. Alio   L. Brenner                 

Abstract Details

Purpose:

To evaluate corneal elastic response of photorefractive keratectomy (PRK) in eyes with asymmetrical topographies, and to compare such outcomes with a control-matched group of normal topographies.

Setting:

Vissum, Alicante, Spain.

Methods:

Thirty eyes with asymmetrical topographies, with superior-inferior dioptric difference (SI) > 1.40 D, were compared to 30 eyes with normal topographies. Both groups were matched for age, spherical equivalent (SE), keratometry, corneal astigmatism, pachymetry, residual stromal bed, ablation depth (AD), and Percentage Tissue Altered (PTA). Biomechanical outcomes were evaluated 3- and 12-months postoperatively after PRK retrospectively and after more than 3 years postoperatively in those patients that continued the follow-up prospectively.

Results:

The mean preoperative SI index in the asymmetrical group was 2.06 ± 0.56 D vs. 0.09 ± 0.75D in the control group (P<0.001). From 3- to 12-months postoperatively, the asymmetrical group presented a significant mean re-steepening of 0.51 ± 0.40 D (P<0.001) vs. 0.19 ± 0.40 D (P=0.002) in the control group (P=0.015). Mean PTA of 14.56% generated an elastic modulus reduction of 9.96% in the asymmetrical group vs. 2.13% in the control group (P<0.001). The elastic modulus reduction correlated with the preoperative SE (ρ=0.331, P=0.020) and SI (ρ=-0.374, P=0.008). These trends were confirmed after more than 3 years postoperatively.

Conclusions:

Asymmetrical topography corneas presented an increased stress relaxation, with keratometric re-steepening, shift towards prolateness, and reduction of the elastic modulus. The long-term follow-up demonstrated the usefulness of PRK for asymmetrical topographies despite an amplified biomechanical elastic response showing no progressive pathological process.

Financial Disclosure:

NONE