Letter contrast sensitivity in retinitis pigmentosa patients assessed by Regan charts.

Regan Contrast Sensitivity Letter Charts were used to assess the effects of reduced contrast and luminance on visual acuity in retinitis pigmentosa (RP) patients. Letter acuity was measured monocularly in 17 RP patients and in 14 age-similar normals using charts of three different contrast levels presented at each of four levels of illumination. Despite visual acuities of 20/40 or better under standard clinical test conditions, an appreciable number of RP patients were unable to identify any letters on the intermediate- and/or low-contrast Regan charts. For example, even at the recommended test luminance, 5 patients could not read any letters on the intermediate (11%) contrast chart, and 9 could not be scored on the low (4%) contrast chart. Consequently, the Regan charts were found to have limited usefulness in quantifying the exact extent of visual impairment in this group of RP patients. Nevertheless, our results document the degree of visual acuity loss that can be experienced by RP patients under conditions of low contrast and luminance.