Three-dimensional reconstruction of surfaces by automated infrared photoretinoscopy

A photoretinoscope with infrared light-emitting diodes (LED) operating simultaneously from different eccentricities creates an almost linear change in brightness across the pupillary meridian perpendicular to the knife edge (Schaeffel et al., 1993a). The slope of the brightness profile, in turn, is almost linearly related to refractive error over a range of +5 to -5D. Using digitized video images, the procedures to find the pupil and to measure the slope can be fully automated and run at 25/30Hz (Schaeffel et al., 1993b). The precision of detection of differences in refraction are comparable to the depth of focus of the eye (0.25 D).