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M.F. L. Silva, S. Maia–Lopes, M. Guerreiro, P. Faria, L. Duarte, M. Castelo–Branco; Visual Perception Asymmetries Within the Magno– and Parvocellular Pathways in Normal Subjects . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4746.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Available evidence regarding spatial anisotropies of retinal function has been previously documented based on anatomical and electrophysiological findings, but their consequences on visual performance are still poorly understood. We aimed to explore visual field perceptual asymmetries in a a normal population. Methods: We used different contrast sensitivity (CS) tasks to probe retinal visual pathways. The magnocellular task was based on the frequency doubling illusion (FD perimetry) and was performed by means of 2 standard and 1 custom–made tests (Test1: Humphrey C20, n= 48 eyes; Test2: Matrix N30–F, n=174; Test3: C20–custom, n = 81). For parvocellular assessment we used 2 custom–made CS tests (Test4: C20Photopic, n = 39; Test5: C20Mesopic, n=40), where the stimulus was a sinusoidal grating with high spatial frequency and 0 temporal frequency. We performed comparisons between superotemporal (ST), inferonasal (IN), inferotemporal (IT) and superonasal (SN) visual quadrants. Statistical analysis was performed using factorial ANOVA with post hoc Fisher’s PSLD correction. Results: Different patterns of functional disadvantage were found with the parvo– and magnocellular tasks. With the former, CS thresholds were comparatively higher in all tested locations, as expected. Furthermore an inferonasal pattern of disadvantage was observed: all comparisons were significant under photopic conditions (p<0.0123; in all comparisons). A similar effect was seen under mesopic conditions. Multivariate analysis showed significant effects both in terms of naso–temporal and left–right asymmetries (p<0.0001). With the magnocellular task a superotemporal disadvantage was observed (all comparisons significant for all tests, p = 0.0358). Multivariate analysis showed significant effects both in terms of naso–temporal and up–down assymetries (p<0.0001 and p= 0.0006; left–right comparison, ns). Conclusions: The main finding of our study is that spatial perceptual anisotropies occur across different visual pathways. The magnocellular system shows a pattern of retinal disadvantage corresponding to the superotemporal visual field. A parvocellular based inferonasal disadvantage was also found, especially under photopic conditions. The pattern of naso–temporal and left–right bias in the latter task suggests that in this case both retinal and cortical mechanisms contribute to perceptual asymmetries.
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