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D. A. Poggel, L. J. Toth, D.-S. Kim, J. F. Rizzo, III; Brain Activation Maps in Patients With Retinal Degeneration. Invest. Ophthalmol. Vis. Sci. 2007;48(13):935.
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© ARVO (1962-2015); The Authors (2016-present)
Retinotopic mapping in functional Magnetic Resonance Imaging (fMRI) has recently been applied to patients with different forms of partial blindness, albeit with contradicting results. We wanted to investigate how different patterns of visual field loss as induced by age-related macular degeneration (ARMD) or retinitis pigmentosa (RP) influence the topography of brain activation.
We performed retinotopic mapping in patients with age-related macular degeneration (ARMD, n=5) and retinitis pigmentosa (RP, n=6). FMRI data (T2*-weighted images) were acquired with a 3T Philips Intera MR Scanner. Retinotopic mapping stimulation consisted of a clockwise rotating wedge and an expanding annulus (5 cycles, 32s per cycle, 8Hz flicker, black-and white checkerboard). Data were analyzed with Brain Voyager software (General Linear Model and linear correlation maps). Statistical activation maps were projected onto an anatomical T1-weighted image of the brain and compared to results from 10 healthy subjects.
In healthy subjects, early visual cortical areas were strongly activated, comparable to results from literature. ARMD patients mostly showed normal maps in anterior visual cortex, but posterior regions representing the central (blind) visual fields were silenced. RP patients responded with activation across large parts of the visual cortex, even though visual stimulation was delivered only to a small central intact retinal region.
Blindness in the central visual field (ARMD) leads to silencing of projection areas of the scotoma, whereas in RP activation is spreading into cortical areas representing the blind periphery. This suggests a reorganization of visual cortex activity in response to blindness.
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