Posters

Validation of corneal power changes as measured by Scheimpflug analysis following corneal laser surgery

Poster Details

First Author: A.Gyldenkerne DENMARK

Co Author(s):    A. Ivarsen   T. Olsen   J. Hjortdal        

Abstract Details

Purpose:

To study whether the Pentacam can measure and predict corneal power changes following small-incision lenticule extraction (SMILE) for high myopia or astigmatism.

Setting:

Department of Ophthalmology, Aarhus University Hospital, Denmark

Methods:

The study included 828 eyes from 414 patients with myopia and/or astigmatism undergoing uncomplicated ReLEx SMILE-procedures on both eyes in the period 2011-2012. The study protocol included Pentacam HR measurements and conventional auto-keratometry (K-reading) before and three months after surgery. The aim was to compare the recorded subjective refractive change with different measures of changes in corneal power: (1) Sagittal Power (2) True Net Power (TNP) and (3) Total Corneal Refractive Power (TCRP), calculated by ray tracing. Measurements were recorded with ring and zone diameters from 1.0-8.0 mm, centered on the corneal apex or pupil. Calculations were performed by converting refractive values to power vectors. One eye (the model eye) was randomly selected from each patient, and used to find the type of power measurement that best predicted the change in manifest refraction (SE). P-values were calculated using paired t-tests.

Results:

The conventional K-reading was found to underestimate the change in SE by -1.21 D ± 0.53 (± SD) (significantly different from zero; p<0.001). The best Sagittal Power calculation (pupil-centered 3-mm ring) underestimated the change in SE by -1.11 D ±0.45 (p < 0.001); the best TNP calculation (pupil-centered 3-mm ring) underestimated the change in SE by -0.52 D ± 0.41 (p < 0.001); and finally, the difference between changes in SE and the 3-mm ring TCRP measurement was found to be 0.0015 D ± 0.40 (range -1.11 D to 1.10 D, p=0.94).

Conclusions:

The 3-mm ring TCRP measurement, which is based on ray-tracing, was found to be the best method to predict the observed subjective refractive change induced by the SMILE procedure. FINANCIAL INTEREST: One of more of the authors... receives consulting fees, retainer, or contract payments from a company producing, developing or supplying the product or procedure presented