HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Alexander, K. R. Articles by Fishman, G. A. Search for Related Content PubMed PubMed Citation Articles by Alexander, K. R. Articles by Fishman, G. A.

Contrast Response Properties of Magnocellular and Parvocellular Pathways in Retinitis Pigmentosa Assessed by the Visual Evoked Potential

¹From the Department of Ophthalmology and Visual Sciences and the ²Department of Psychology, University of Illinois at Chicago, Chicago, Illinois; the ³Department of Ophthalmology, New York University School of Medicine, New York, New York; and ⁴Ferkauf Graduate School, Yeshiva University, Bronx, New York.

PURPOSE. To evaluate the contrast response of the visual system in retinitis pigmentosa (RP) under conditions designed to emphasize the parvocellular (PC) and magnocellular (MC) pathways.

METHOD. Visual evoked potentials (VEPs) were measured in 10 patients with RP and in 10 age-equivalent control subjects with normal visual acuity and color vision, by using an array of isolated checks that were presented against a steady yellow background. The checks were modulated sinusoidally, either in isoluminant chromatic contrast (5.6 Hz), to favor the chromatic PC pathway, or in luminance contrast (5.6 and 11.2 Hz), to favor the MC pathway. Response amplitude and phase at the stimulus (fundamental) frequency were derived from Fourier analysis, and contrast response functions were fit with a Michaelis-Menten equation to derive R_max, the maximum response amplitude, and , the contrast necessary to produce R_max/2.

RESULTS. In the control subjects, the mean amplitude function for chromatic modulation increased approximately linearly with increasing contrast, whereas the function for luminance modulation increased sharply at low contrasts and saturated at contrasts above approximately 30% for both temporal frequencies, as expected. The patients with RP showed primarily a reduction in R_max with little change in in all testing conditions. The reduction in R_max was equivalent for chromatic modulation and luminance modulation at 5.6 Hz, but was substantially lower for luminance modulation at 11.2 Hz.

CONCLUSION. Contrast processing was impaired within both the MC and PC pathways in these patients with RP, but the degree of impairment within the MC pathway depended on temporal frequency. These VEP results are in general agreement with recent psychophysical studies of contrast sensitivity losses in patients with RP, and further they characterize contrast processing deficits in these patients at suprathreshold levels.

This article has been cited by other articles:

				S. Maia-Lopes, E. D. Silva, M. F. Silva, A. Reis, P. Faria, and M. Castelo-Branco Evidence of Widespread Retinal Dysfunction in Patients with Stargardt Disease and Morphologically Unaffected Carrier Relatives Invest. Ophthalmol. Vis. Sci., March 1, 2008; 49(3): 1191 - 1199. [Abstract] [Full Text] [PDF]