GEOMETRICAL-THEORY TO PREDICT ECCENTRIC PHOTOREFRACTION INTENSITY PROFILES IN THE HUMAN EYE

In eccentric photorefraction, light returning from the retina of the e ye is photographed by a camera focused on the eye's pupil. We use a ge ometrical model of eccentric photorefraction to generate intensity pro files across the pupil image. The intensity profiles for three differe nt monochromatic aberration functions induced in a single eye are pred icted and show good agreement with the measured eccentric photorefract ion intensity profiles. A directional reflection from the retina is in corporated into the calculation. Intensity profiles for symmetric and asymmetric aberrations are generated and measured. The latter profile shows a dependency on the source position and the meridian. The magnit ude of the effect of thresholding on measured pattern extents is predi cted. Monochromatic aberrations in human eyes will cause deviations in the eccentric photorefraction measurements from traditional crescents caused by defocus and may cause misdiagnoses of ametropia or anisomet ropia. Our results suggest that measuring refraction along the vertica l meridian is preferred for screening studies with the eccentric photo refractor.