Psychophysical studies of cone optical bandwidth in patients with retinitis pigmentosa.

Estimates of variation in the alignment of cones with the pupil were obtained from the fovea and parafovea in normal subjects and in patients with retinitis pigmentosa known to have reduced directional sensitivity. The degree of cone disarray was inferred from differences in sensitivity between Stiles-Crawford functions obtained with a stimulus alone and with the stimulus superimposed on a background entering the pupil at a point corresponding to the peak of the Stiles-Crawford function. The magnitude of the selective effect of the background in normals was consistent with previous estimates of variations in photoreceptor alignment in the macula. In contrast, the selective adaptation effect was not present in patients with retinitis pigmentosa. These results exclude increased disarray among cones with normal optical bandwidths, but rather, suggest that morphological abnormalities increasing the optical bandwidths of individual cones underlie reduced directional sensitivity in these patients.