Foveal cone involvement in retinitis pigmentosa progression assessed through psychophysical impulse response parameters.

PURPOSE To compare psychophysical impulse response parameters in retinitis pigmentosa (RP) patients and healthy controls using a temporal contrast sensitivity threshold paradigm, and to measure changes in these parameters with RP progression. METHODS Sixty-six RP patients and 10 healthy control subjects were tested, and the amplitude and timing parameters of the psychophysical impulse response function were computed through time-domain transformation under assumption of minimum-phase properties. RESULTS/CONCLUSIONS The initial rise time of the impulse response, ta, was significantly lengthened in RP patients compared to controls, as was the fall time from peak to trough, tp-->t. The log peak-to-trough amplitude, log R, was significantly reduced. With disease progression, all impulse response parameters continued to move away from the normal range. Only minor distinctions according to RP pathophysiologic subtype or mode of inheritance were found, supporting the hypothesis of a common course of the secondary retinal degeneration across different RP subcategories.