Impact of percent tissue altered and other surgical and corneal parameters on regression after refractive lenticule extraction (ReLEx) SMILE

Session Details

Session Title: Small Lenticule Extraction I

Session Date/Time: Sunday 15/09/2019 | 08:00-10:00

Paper Time: 09:18

Venue: Free Paper Forum: Podium 1

First Author: : L.Beckers GERMANY

Co Author(s): :    D. Breyer   K. Klabe   H. Kaymak   T. Ax   F. Kretz   G. Auffarth              

Abstract Details

Purpose:

Former studies showed comparable visual recovery after ReLEx SMILE and Femto-LASIK. For Femto-LASIK, however, there is evidence that high PTA (Percent Tissue Altered) values can lead to regression after the procedure. Especially values above 40% are seen as a contributing factor to the development of late keratectasia. We argue that the PTA concept cannot be applied to ReLEx SMILE without alterations. Instead we consider ETAF (Effective Tissue Alteration Factor) values and further form and deformation observables in order to quantify the surgical impact on postoperative corneal stability.

Setting:

All ReLEx SMILE (VisuMax, CZM) surgeries were performed by one surgeon (BY) at the Breyer-Kaymak-Klabe Eye Surgery & Premium Eyes in Duesseldorf, Germany, which is part of the International Vision Correcton Research Center Network (IVCRC.net).

Methods:

We only included ReLEx SMILE eyes with existing pre- and postoperative (3 month and 1-5 years after surgery) data for CDVA, manifest refraction, and Scheimpflug tomography (Pentacam, Oculus). If available, data from deformation analysis (Corvis ST, Oculus) was also considered. Eyes with prior surgery were excluded. Parameters that were analyzed as potential regression-inducing factors were age, surgery parameters (relative lenticule thickness, PTA, ETAF, etc.), as well as corneal shape/deformation parameters (Bad-D, CBI, TBI, etc.). Based on these parameters, a linear model was set up in order to explain the variation in postoperative regression.

Results:

The rate of statistically significant (p<=0.05) coefficients in the linear model was 6%, which is comparable to the significance level alpha=5% itself. PTA had no significant impact on corneal regression. With respect to all the above-mentioned regression observables, the slope coefficients did not display any systematic behavior. For instance, the relative lenticule thickness appeared to influence the regression of the spherical equivalent but not that of Kmax or Kmean. In addition all R^2 were below 0.1, meaning that any of the significant coefficients could only explain less than 10% of the observed total variation.

Conclusions:

Neither from a theoretical point of view nor from its actual impact on observed postoperative regression PTA is a proper concept for predicting long-term corneal stability after ReLEx SMILE. Instead, other surgical quantities have to be defined. However, from our linear model approach we conclude that there is no consistent dependency between the postoperative regression after ReLEx SMILE and considered surgical parameters as well as shape/deformation parameters. Thus, ReLEx SMILE yields equally stable long-term results over the full parameter range and no subgroup with increased risk for regression could be identified.

Financial Disclosure:

None