Morphometric analyses of the visual pathways in macular degeneration

Introduction. Macular degeneration (MD) causes central visual field loss. When field defects occur in both eyes and overlap, parts of the visual pathways are no longer stimulated. Previous reports have shown that this affects the grey matter of the primary visual cortex, but possible effects on the preceding visual pathway structures have not been fully established. Method. In this multicentre study, we used high-resolution anatomical magnetic resonance imaging and voxel-based morphometry to investigate the visual pathway structures up to the primary visual cortex of patients with age-related macular degeneration (AMD) and juvenile macular degeneration (JMD). Results. Compared to age-matched healthy controls, in patients with JMD we found volumetric reductions in the optic nerves, the chiasm, the lateral geniculate bodies, the optic radiations and the visual cortex. In patients with AMD we found volumetric reductions in the lateral geniculate bodies, the optic radiations and the visual cortex. An unexpected finding was that AMD, but not JMD, was associated with a reduction in frontal white matter volume. Conclusion. MD is associated with degeneration of structures along the visual pathways. A reduction in frontal white matter volume only present in the AMD patients may constitute a neural correlate of previously reported association between AMD and mild cognitive impairment. Keywords: macular degeneration - visual pathway - visual field - voxel-based morphometryComment: appears in Cortex (2013

Automated Morphometry of the Visual Pathway in Primary Open-Angle Glaucoma

PURPOSE. To establish whether primary open-angle glaucoma (POAG) is associated with a change in volume of the visual pathway structures between the eyes and the visual cortex. METHODS. To answer this question, magnetic resonance imaging (MRI) was used in combination with automated segmentation and voxel-based morphometry (VBM). Eight patients with POAG and 12 age-matched control subjects participated in the study. Only POAG patients with bilateral glaucomatous visual field loss were admitted to the study. The scotoma in both eyes had to include the paracentral region and had to, at least partially, overlap. All participants underwent high-resolution, T(1)-weighted, 3-T MRI scanning[b]. Subsequently, VBM was used to determine the volume of the optic nerves, the optic chiasm, the optic tracts, the lateral geniculate nuclei (LGN), and the optic radiations. Analysis of covariance was used to compare these volumes in the POAG and control groups. The main outcome parameter of the measurement was the volume of visual pathway structures. RESULTS. Compared with the controls, subjects with glaucoma showed reduced volume (P <0.005) of all structures along the visual pathway, including the optic nerves, the optic chiasm, the optic tracts, the LGN, and the optic radiations. CONCLUSIONS. POAG adversely affects structures along the full visual pathway, from the optic nerve to the optic radiation. Moreover, MRI in combination with automated morphometry can be used to aid the detection and assessment of glaucomatous damage in the brain. (Invest Ophthalmol Vis Sci. 2011;52:2758-2766) DOI:10.1167/iovs.10-568

Changes in cortical grey matter density associated with long-standing retinal visual field defects

Retinal lesions caused by eye diseases such as glaucoma and age-related macular degeneration can, over time, eliminate stimulation of parts of the visual cortex. This could lead to degeneration of inactive cortical neuronal tissue, but this has not been established in humans. Here, we used magnetic resonance imaging to assess the effects of prolonged sensory deprivation in human visual cortex. High-resolution anatomical magnetic resonance images were obtained in subjects with foveal (age-related macular degeneration) and peripheral (glaucoma) retinal lesions as well as age-matched controls. Comparison of grey matter between patient and control groups revealed density reductions in the approximate retinal lesion projection zones in visual cortex. This indicates that long-term cortical deprivation, due to retinal lesions acquired later in life, is associated with retinotopic-specific neuronal degeneration of visual cortex. Such degeneration could interfere with therapeutic strategies such as the future application of artificial retinal implants to overcome lesion-induced visual impairment.