Age-related changes in gray and white matter microstucture of patients with macular dystrophies and healthy controls as revealed by DTI.

Previous research has shown that loss of central vision resulting from macular degeneration not only affects functional processing but also the macroscopic structure of the visual pathway. In particular, magnetic resonance imaging (MRI) showed volumetric reductions of the gray and white matter of patients with macular degeneration in portions of the calcarine sulcus that represent the central visual field. However, the basis of these macrostructural alterations due to partial vision loss is still unclear. Diffusion tensor imaging (DTI) based on MRI is a technique that allows inferences about the microstructure of brain tissue. Here, 25 patients with hereditary and 13 patients with age-related macular degeneration and an equal number of age-matched healthy controls (age range from 19 to 85 years) were examined with DTI. Patients and controls were compared on several diffusion-based quantitative indices including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD). A surface-based analysis approach was adopted. In healthy people, diffusivity increased with age in the medial occipital cortex, the cingulate cortex, the temporal cortex, the insular, and the frontal cortex. However, dissociations between AD and RD were observed in several brain regions: Age-related increases of RD were primarily observed in the white matter of the medial occipital cortex, whereas age-related increases of AD were primarily observed in the gray matter of the temporal cortex. Compared to age-matched healthy controls, young but not elderly patients with vision loss showed increased RD in two distinct regions of the posterior calcarine sulcus and the inferior frontal cortex. No reduction in AD was observed. This finding suggests that fiber connections of afferent visual pathways are still preserved in patients with vision loss. However, the white matter microstructure of the visual cortex may be affected by changes in local connectivity or the extra-axonal structure. Meeting abstract presented at VSS 2015.