BLUE AND GREEN CONE MECHANISMS IN RETINITIS PIGMENTOSA

Abstract

Pronounced abnormalities in the increment threshold curves for the blue and green cone mechanisms only 10.degree. above the fovea, and in some cases also in the fovea, were found with a 2.5.degree. stimulus in different genetic types of retinitis pigmentosa [in man]. Whenever cone thresholds were abnormal, thresholds determined by the blue cone mechanism (.pi.1 and .pi.3) were more elevated than those determined by the green cone mechanism (.pi.4). Thresholds determined by the green cone mechanism were consistently more elevated at low background intensities than at intermediate and high background intensities. Threshold elevations for the blue and green cone mechanisms relative to each other in the perifovea in a given patient tested with the 2.5.degree. stimulus could be simulated in normal observers tested with a single small stimulus. The summation pools for blue and green cone mechanisms are apparently proportionally reduced below normal in retinitis pigmentosa, at least in the perifovea, and both mechanisms may be comparably involved at the photoreceptor level.