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W. Wittich, D. H. Watanabe, M. A. Kapusta, J. Faubert, O. Overbury; Does Brain Laterality Influence Cortical Plasticity in Patients with Retinitis Pigmentosa?. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3627.
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© ARVO (1962-2015); The Authors (2016-present)
The majority of research on visuocortical plasticity in the presence of ocular disease has focused on central visual field loss due to macular degeneration. However, preliminary data have indicated that similar cortical reorganization may occur in the presence of peripheral field loss as well, for example due to retinitis pigmentosa (RP), Poggel et al. (ARVO 2007, # 935). What remains elusive is whether such cortical adjustments result in measureable behavioural changes, specifically the perception of visual space. The present study examined whether spatial interval discrimination in RP patients differed as a function of eccentricity and extent of field loss.
12 patients with RP were asked to judge the relative horizontal distance of a central circular dot between two flanker dots, one of which was at fixation. Stimulus presentation was asymmetrical, whereby all targets appeared in either the right (RVF) or left (LVF) visual field. Monocular and binocular performance accuracy was measured using the method of constant stimuli, using 7 locations within ±30% of stimulus eccentricity. Visual field diameters (Goldman III/4e target) in the right and left visual hemifield were expressed as a ratio in order to indicate visual field asymmetry.
Pearson’s correlation coefficients revealed a systematic relationship between binocular error and field asymmetry in the left visual field, r2= .59. This was not the case in the right visual field (r2= .02) or in any of the monocular conditions. This result indicated that if the LVF was larger than the RVF, error scores in the LVF were shifted away from fixation (spatial magnification) while, if the LVF was smaller, error scores in the LVF were shifted towards fixation (spatial contraction).
Spatial judgments in RP patients were related to the extent to which their remaining visual field was asymmetric, resulting in distorted perception. However, this effect was only present in the left visual field under binocular viewing. The right visual cortex has previously been associated with superior accuracy and speed involving spatial vision tasks. This specialization has not yet been considered in the context of cortical plasticity of the visual system. Future investigations of the functional consequences of visual plasticity should consider brain laterality when choosing test paradigms.
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