Prediction of flap response

Abstract

Purpose: To find predictors of the induced biomechanical and optical effects of lamellar flap creation on the cornea. Setting: Optimed Eye and Laser Clinic, Pretoria, South Africa, and the Department of Ophthalmology and Biomedical Engineering Center, The Ohio State University, Columbus, Ohio, and Bausch & Lomb Vision Research Laboratory, Rochester, New York, USA. Methods: This prospective study monitored the refractive, wavefront aberration, and corneal topographic changes in 29 eyes of 15 patients for 3 months after the creation of a corneal lamellar flap. The main outcome measures for statistical analysis were refraction, total corneal thickness, residual corneal bed thickness, horizontal white-to-white corneal diameter, horizontal flap diameter, topography data, and wavefront data. Results: Statistically significant changes were seen in the autorefraction mode. Wavefront data showed significant change in 4 Zernike modes—90/180-degree astigmatism, vertical coma, horizontal coma, and spherical aberration. The topography data indicated the corneal biomechanical response was significantly predicted by stromal bed thickness in the early follow-up period and by total corneal pachymetry and flap diameter in a 2-parameter statistical model in the late follow-up period. Conclusions: Uncomplicated lamellar flap creation is responsible for systematic changes in corneal topography and induction of higher-order optical aberrations. Predictors of this response include stromal bed thickness, flap diameter, and total corneal pachymetry.