Simulation of eccentric photorefraction images.

Photorefractive (PR) screening of children is currently used for detection of specific vision problems. We have used three-dimensional ray tracing and several published models of the human eye to investigate the ability to predict photorefractive results. Specifically, by using the optical design of an actual photorefractive instrument and using a monochromatic source as an example, we demonstrate the methodology of computing the relative spatial irradiance at its detector surface. The variation of the irradiance at the detector is computed for several eye models for a range of refractive errors. The results showed that the basic physics of photorefraction is described simply using the width and the center of the dark zone (CDZ) of retinal reflex images. Refractive parameters of a subject can be directly determined from these values of CDZ, and the contribution of monochromatic and chromatic aberrations upon the CDZ is derived.