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Editors Selection IGR 10-4
Magnetic Resonance Imaging: Functional MRI
Comment by Neeru Gupta on:
16936 Retinotopic organization of primary visual cortex in glaucoma: Comparing fMRI measurements of cortical function with visual field loss, Duncan RO; Sample PA; Weinreb RN et al., Progress in Retinal and Eye Research, 2007; 26: 38-56
16991 Retinotopic organization of primary visual cortex in glaucoma: a method for comparing cortical function with damage to the optic disk, Duncan RO; Sample PA; Weinreb RN et al., Investigative Ophthalmology and Visual Science, 2007; 48: 733-744
In this pair of innovative and carefully performed studies by Duncan et al. (67, 68) functional magnetic resonance imaging (fMRI) was used to assess changes in the primary visual cortex of subjects with primary open angle glaucoma. Six subjects with well characterized glaucoma in one eye and a less affected fellow eye were selected among patients recruited for a longitudinal study designed to evaluate the optic nerve structure and visual function in glaucoma.
The Blood Oxygenation Level Dependent (BOLD) fMRI signal was used to detect changes in brain neural activity. In patients with well defined asymmetrical visual field loss, point-wise comparison indicated that the differences in sensitivity of standard automatic perimetry between both eyes corresponded to the differences in local BOLD signal differences in a previously selected region of interest driven by the most affected eye (Paper 1). Optic disk damage was thoroughly characterized in these patients using GDx, HRT and OCT measurements. The fMRI responses to visual stimulation were found to be related to differences in parameters such as RNFL thickness or mean height contour between eyes (Paper 2).
FMRI is a method by which visual cortex functional changes are measurable in vivo and can be compared to optic disk and visual field changes in glaucomaIt is possible that in addition to neural degeneration, BOLD signal changes are related to neural activity changes caused by reduced retinal input. It is not known whether functional compensatory changes occur in cortical areas driven by the less affected eye. Comparison to normal patients may provide exciting information regarding plasticity in the adult visual system with glaucoma.
These seminal studies demonstrate a method by which visual cortex functional changes are measurable in vivo and can be compared to optic disk and visual field changes in glaucoma. The approach used by the authors offers a valuable and unique opportunity to understand specific cortical changes in response to selective visual pathway stimulation in glaucoma. It is a genuine multi-disciplinary effort to further understand vision losses in glaucoma patients.
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