This study investigated the retinotopic functional representation in the visual cortex of mild to moderate primary open-angle glaucoma (POAG) participants and age-matched normal volunteers, using wide-view visual presentation, high-resolution retinotopic stimuli, and high-resolution blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI). fMRI was performed on nine POAG participants (61±11-years-old) and nine age-matched controls (58±5-years-old). A wide-view visual presentation (±55 degrees) was used to evaluate central and peripheral vision. Cortical magnification factors and BOLD% changes were calculated and plotted as a function of eccentricity. Correlation analysis between BOLD% changes and visual field loss and also between BOLD% changes and retinal nerve fibre layer thicknesses were performed. Comparison of BOLD% changes for individual visual field quadrants between POAG subgroups and normal group was performed and evaluated. The authors found that BOLD% changes of POAG participants in peripheral visual regions were significantly reduced compared to normal controls but similar in central visual regions, consistent with the notion of peripheral vision being affected first and more so in comparison to the central vision. fMRI retinotopic mapping revealed enlarged representation of the parafoveal region in the visual cortex of POAG participants compared to normal controls. Cortical magnification of the central, but not peripheral, visual representation in the visual cortex was larger in POAG participants, suggesting functional remapping. BOLD% changes of individual visual field quadrants were significantly correlated with visual field scores and with retinal nerve fibre layer thickness in the corresponding quadrants. The study group concluded that their results support the hypothesis that there are both functional alteration and remapping in the topographic representation of the visual cortex in POAG participants, and these changes are correlated with disease severity. 

Retinotopic fMRI reveals visual dysfunction and functional reorganization in the visual cortex of mild to moderate glaucoma patients.
Zhou W, Muir ER, Nagi KS, et al.
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Chrysostomos D Dimitriou

Essex County Hospital, Colchester, Essex, UK.

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