TEMPORAL PROPERTIES OF LETTER IDENTIFICATION IN RETINITIS-PIGMENTOSA

The effect of stimulus duration on the visual acuity of individuals wi th retinitis pigmentosa (RP) was assessed by using Sloan letters of 10 0% contrast and durations ranging from 15 ms to 3.8 s. In addition, co ntrast thresholds for identifying Sloan letters (0.7 log minimum angle of resolution; 20/100 Snellen equivalent) were measured over the same range of durations in the same subjects with RP. Compared with result s from a control group of subjects with normal vision, the subjects wi th RP showed losses in visual acuity at all stimulus durations, with a slightly though significantly greater reduction in visual acuity at s hort durations. The letter-contrast thresholds of the subjects with RP were elevated above the normal range to the same degree at all durati ons. Analysis of the results in the format of letter contrast sensitiv ity functions indicates that temporal summation for letter identificat ion was normal for these subjects with RP and that their relatively gr eater acuity loss at short exposure durations was most likely related to their elevated letter contrast thresholds.