Spatial and temporal variations in contrast are a fundamental source of information about the visual environment. Therefore, the disruption of contrast processing due to retinal disease can potentially have a profound effect on the quality of life of persons afflicted with retinal degenerations. Because relatively little is known about the nature of contrast processing deficits in retinal diseases, the proposed studies will evaluate contrast coding through the use of innovative and sophisticated testing methods, including psychophysics, electroretinography (ERG), and the visual evoked potential (VEP), that are intended to target specific visual subsystems that can be affected differently by retinal pathology. The studies are focused on retinitis pigmentosa (RP), a group of hereditary retinal dystrophies that are the most frequent genetic cause of blindness in adults. Parallel investigations of control subjects will better define mechanisms of contrast processing in visually normal persons. The specific aims are: (1) to define the origin and relative contribution of postreceptoral processes to implicit time delays in the ERG of the cone system of patients with RP; (2) to identify the mechanisms underlying deficits in foveal contrast sensitivity in RP within the framework of magnocellular (MC) and parvocellular (PC) pathways; (3) to determine whether deficits in suprathreshold contrast discrimination in RP represent changes in response scaling or changes in effective contrast within the MC and PC pathways; and (4) to establish whether letter optotypes and grating stimuli provide equivalent measures of contrast sensitivity deficits in retinal disease. These aims will be accomplished through a series of studies that will test subjects recruited from a cohort of more than 1,200 well-categorized patients with RP, available through the University of Illinois Research Center of The Foundation Fighting Blindness. Given recent developments in understanding the molecular genetic basis for sight-threatening hereditary retinal dystrophies, and with clinical trials of therapeutic intervention being planned, the proposed studies are intended to provide a rational basis for developing new, more sensitive testing methods that will be of clinical value in monitoring the visual status of persons with eye disease and in assessing the outcome of potential treatment regimens.