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Deficits in Temporal Integration for Contrast Processing in Retinitis Pigmentosa

¹From the Department of Ophthalmology and Visual Sciences and the ²Department of Psychology, University of Illinois at Chicago, Chicago, Illinois.

PURPOSE. The purpose of this study was to evaluate the properties of foveal temporal integration in patients with retinitis pigmentosa (RP) within the framework of contrast processing by the magnocellular (MC) and parvocellular (PC) pathways.

METHODS. Temporal integration functions were measured in eight patients with RP whose visual acuities ranged from 20/25 to 20/63. Contrast thresholds were obtained at durations ranging from 15 to 480 ms, using steady-pedestal and pulsed-pedestal paradigms to bias performance toward the MC and PC pathways, respectively. The patients’ results were compared with those of 10 age-similar control observers with normal vision. For both paradigms, contrast thresholds as a function of duration were fit with a two-limbed function to derive the critical duration for temporal integration (t_c) and the asymptotic threshold at long durations (L).

RESULTS. The log t_cs of the patients with RP were significantly longer than those of the control subjects for the steady-pedestal paradigm (presumed MC-pathway mediation; t = 3.67, P < 0.001), but not for the pulsed-pedestal paradigm (presumed PC-pathway mediation; t = 0.76, P = 0.45). Further, the patients with RP showed a significant correlation between log t_c and log L for the steady-pedestal paradigm (r = 0.72, P < 0.05) but not for the pulsed-pedestal paradigm (r = -0.37, P = 0.36).

CONCLUSIONS. The patients with RP in this study showed greater deficits in contrast sensitivity and a more prolonged critical duration under test conditions that favor the MC rather than the PC pathway. A likely explanation is a high-frequency response attenuation at the level of the cone photoreceptors that has a differential effect on contrast-processing tasks that emphasize different postreceptoral mechanisms.

This article has been cited by other articles:

				K. R. Alexander, A. S. Rajagopalan, W. Seiple, V. M. Zemon, and G. A. Fishman Contrast Response Properties of Magnocellular and Parvocellular Pathways in Retinitis Pigmentosa Assessed by the Visual Evoked Potential Invest. Ophthalmol. Vis. Sci., August 1, 2005; 46(8): 2967 - 2973. [Abstract] [Full Text] [PDF]

				K. R. Alexander, C. S. Barnes, G. A. Fishman, J. Pokorny, and V. C. Smith Contrast Sensitivity Deficits in Inferred Magnocellular and Parvocellular Pathways in Retinitis Pigmentosa Invest. Ophthalmol. Vis. Sci., December 1, 2004; 45(12): 4510 - 4519. [Abstract] [Full Text] [PDF]