A COMPUTER-MODEL FOR PREDICTING IMAGE QUALITY AFTER PHOTOREFRACTIVE KERATECTOMY

BACKGROUND: Accurately predicting visual performance remains a concern in refractive surgery. The effects of the eye's optics on retinal ima ge quality were investigated using computer ray tracing to model the h uman eye after photorefractive keratectomy (PRK). METHODS: Ray-tracing analysis was used with an anatomically realistic model of the human e ye including aspheric surfaces and crystalline lens gradient index dis tributions, The contribution of corneal curvature to refractive error was investigated using data of axial length, corneal power, anterior c hamber depth, and lens power from 318 eyes from the literature, The co mputer interface was specifically designed for use with PRK and provid es graphical plots of the remodeled eye, ray paths and retinal image f ormation. RESULTS : Modeling the optical contribution of corneal curva ture resulted in an improvement in predicted refractive state of the e ye as a function of axial length expressed as the R(2) value of the re gression analysis from 0.88 to 0.96. Subsequently, analyses were condu cted for single and multizone treatment areas of differing diameter an d with varying pupil size, Retinal image quality following PRK for the human cornea was found to be affected by not only the corneal paramet ers of anterior curvature and thickness, but also by axial length, pup il size, and anterior chamber depth. CONCLUSIONS: The inclusion of mul tiple interdependent optical parameters showed differences from conven tional methods in predicting refractive outcome following PRK and reve aled factors affecting image quality may account for some imperfection s in visual performance based on simpler optical modeling.