Optical Analysis for Light Intensity Distribution in EPR with Different Light Sources

摘要

Eccentric photorefraction is an objective refraction technique that, by taking a picture of the pupil of the subject, can measure refractive errors in human eyes. The method assessing the refractive errors is mainly from the size and orientation of the crescent of the pupil image. Because of the effects of the light source and the vignetting of the optical system's aperture, the boundary of the crescent is not sharp so as to accurately determine its size. This uncertainty reduces the accuracy of the EPR system and limits its extensive application. In this paper, analysis on the light intensity distribution across the pupil is presented. It aims to determine the size of the crescent based on the profile of the intensity. Point light source, line light source and extended line source are discussed, and camera aperture opening in the form of straight edge, rectangle and slit are also included in discussion. The analysis shows that the EPR system with a line source and a rectangular aperture opening will give a good linear light distribution profile across the pupil, which may be helpful to automatically determine the size of the crescent. The method will effectively improve the measurement accuracy of EPR.