Sensitivity losses in a long wavelength sensitive mechanism of patients with retinitis pigmentosa.

the foveal vision of certain patients afflicted with retinitis pigmentosa may be mediated solely by a long wavelength sensitivity (lws) mechanism, because (1) increment threshold data could always be fitted to a single template curve with unity slope, (2) test and field sensitivities differ only by a proportionality constant over the visible spectrum, (3) intense background fields have additive (quantum catch) effects on thresholds, and (4) wavelength differences of bipartite foveal stimuli could not be distinguished. Both test and field sensitivities were appreciably lower than the lws sensitivity values for unaffected deuteranopes. The action spectrum was similar (but not identical) to estimates of the erythrolabe absorption spectrum. The results provide a better understanding of the photopic vision of patients with retinitis pigmentosa and further evidence that their effective optical density of residual cones is reduced.