Abstract

The Stiles-Crawford function (Stiles, 1937) is a psychophysical measure of photo receptor orientation and directional sensitivity. It is found that the Stiles-Crawford functions are affected in various pathologies. Birch and his group (Birch, Sandberg, and Berson, 1982) found in patients with different genetic types of retinitis pigmentosa (RP; visual acuity of 20/40 or better, no visible opacities in the media) that parafoveal Stiles-Crawford Effect of the first kind (SCE I) functions were either significantly flattened or have displaced peak positions. Morphological changes have been found in photoreceptors of RP patients (post-mortem). These morphological changes could lead to an increase in the numerical aperture of the cones (acceptance angle hypothesis) and result in reduced directional sensitivity. Alternatively, patients with RP may show increased variation in the alignment of photoreceptors (with normal acceptance angles) due to fractional forces on the retina, loss of supporting structures, and/or alterational forces maintaining alignment (splaying hypothesis). If the peak of the SCE I remains near center in the pupillary aperture, one assumes that photoreceptor alignment mechanism(s), perse, are still functional even if affected. Of course, both options, changes in optical properties, and splaying can occur concurrently.

© 1988 Optical Society of America