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K.R. Alexander, C.S. Barnes, G.A. Fishman, J. Pokorny, V.C. Smith; Contrast Processing Deficits in Melanoma-associated Retinopathy (MAR) . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4965.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Patients with the MAR syndrome are night blind and have a selective reduction of the ERG b-wave amplitude of both rod and cone systems. Wolf and Arden (Vision Res., 36, 2369-2379, 1996) proposed that MAR patients also have a selective functional loss within the magnocellular (MC) pathway, with sparing of parvocellular (PC) pathway function. The purpose of this study was to evaluate this hypothesis further by measuring the contrast sensitivity of MAR patients using a new technique designed to assess the functional integrity of the MC and PC pathways across a broad range of spatial frequencies (Leonova et al., ARVO, 2002). Methods: Two MAR patients, ages 57 and 61 years, with normal Snellen acuity, participated in the study. The sera of both patients produced strong, specific immunolabeling of retinal bipolar cells. Contrast sensitivity was measured at spatial frequencies ranging from 0.25 to 8 c/deg, using two paradigms of contrast sensitivity: 1) a steady-pedestal paradigm, in which there was a brief presentation of the test stimulus against a continuously presented adapting field (favoring the MC pathway), and 2) a pulsed-pedestal paradigm, in which there was a simultaneous brief presentation of both the test stimulus and adapting field (favoring the PC pathway). Results from the MAR patients were compared with those of 10 visually normal control subjects, ages 23 to 57 years. Results: Both MAR patients showed a substantial loss of contrast sensitivity compared to normal for each of the two testing paradigms. For the steady-pedestal paradigm (presumed MC-pathway mediation), the patients’ sensitivity loss was greatest at the lowest spatial frequency, and the magnitude of the loss decreased systematically with increasing spatial frequency. For the pulsed-pedestal paradigm (presumed PC-pathway mediation), the sensitivity loss was greatest at an intermediate spatial frequency, with sensitivity approaching the normal limits at the highest spatial frequency, consistent with their normal visual acuity. Conclusions: Visual deficits in MAR patients are not limited to the MC pathway, but are also apparent under test conditions that favor the PC pathway. Our results illustrate the usefulness of measuring steady-pedestal and pulsed-pedestal contrast sensitivity across a broad range of spatial frequencies in order to distinguish mechanisms of vision loss in retinal disease, and to identify visual impairment that may not be evident through the clinical measurement of Snellen acuity alone.
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