LIGHT-INTENSITY DISTRIBUTION IN ECCENTRIC PHOTOREFRACTION CRESCENTS

We try to improve the accuracy of eccentric photorefraction by taking more information into account than just the size and tilt of the cresc ent. Based on Gaussian optics and the assumption of an isotropic scatt ering retina, a theoretical analysis of the light-intensity distributi on in the pupils of astigmatic eyes is presented. The method is applie d to different photorefractor setups (point light source, long linear light,source, knife-edge aperture, and circular aperture). In the case of a knife-edge aperture the crescent structure can be formulated ana lytically. In the case of a circular aperture an analytic description is possible only for spherical refractive errors, but astigmatic refra ctive errors can be determined from crescent parameters with neural ne tworks. (C) 1998 Optical Society of America.