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Ian P Conner, Terry L Schwartz, James V Odom, Janine D Mendola; Monocular retinotopic mapping in amblyopic adults. Journal of Vision 2003;3(9):112. doi: 10.1167/3.9.112.
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© ARVO (1962-2015); The Authors (2016-present)
The visual abilities in humans with amblyopia have been well studied using psychophysical measures, but neurological characterization is incomplete. Prior fMRI investigation of visual cortex in amblyopia provided retinotopic boundaries from stimulation of the nonamblyopic eye only. This study seeks to determine whether the apparent retinotopic organization of visual cortex in amblyopic subjects is dependent upon the eye stimulated for the mapping. We used the fMRI BOLD technique at 1.5T and high contrast, chromatic eccentricity and polar angle stimuli to map retinotopic organization in 8 control, 7 anisometropic, and 9 strabismic amblyopic adults. Each eye was stimulated separately while the other eye viewed an isoluminant gray screen, and fixation stability was monitored with the Avotec-SMI system. Despite slightly worse fixation stability in the amblyopic population, this factor does not explain our results. The major abnormality seen for anisometropic subjects is decreased and disorganized signal from the amblyopic eye, including loss of foveal representation in eccentricity maps. For strabismic eyes, eccentricity representation appears normal, with some expansion of peripheral field representation. Polar angle maps indicate a bias favoring the ipsilateral hemisphere for strabismic eyes and even fellow eyes, i.e., temporal better than nasal retina. In a separate analysis making a specific comparison of nasal and temporal retina stimulation, we further revealed a surprising representation of temporal retina in the hemisphere contralateral to the amblyopic eye in a subset of the strabismic amblyopes. This abnormal representation may originate from transcallosal connections. We conclude that large scale changes in visual field representation occur in amblyopia, and distinguish the major subtypes.
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