Abstract

Optotype acuity was measured as a function of chart illumination in patients with retinitis pigmentosa (RP) to characterize more completely the degree of foveal impairment in this night-blinding disorder. Acuity-luminance functions were obtained from twenty RP patients who had 20/40 or better Snellen acuity, minimal or no posterior subcapsular cataracts, and no observable foveal lesions, as well as from ten age-similar normal observers. Subjects viewed modified Bailey-Lovie charts through an artificial pupil and an appropriate correction in a phoropter with illumination ranging from −1.1 to 5.2 log Td. Results were analyzed with a hyperbolic equation: in which MAR is the measured minimum angle of resolution, A is the asymptotic value of MAR, I is the chart retinal illuminance, s is a semisaturation parameter, and m is a slope parameter. The RP patients showed normal values of logs but had increases in logA and logm that were correlated significantly (r = 0.65). These findings indicate that (1) the greater the acuity loss of the RP patients at high luminances, the proportionately greater their acuity deficit at low luminances; (2) the patient’s acuity reductions result from a mechanism other than a decreased quantal catch.

© 1988 Optical Society of America