A topographical relationship between visual field defects and optic radiation changes in glaucoma

PURPOSE. To investigate the topographic relationship between glaucomatous retinal ganglion cell loss and changes in the optic radiation (OR) using diffusion tensor imaging (DTI).

METHODS. A cross-sectional study was completed on nine patients with primary open angle glaucoma and nine age- and sex-matched controls. Glaucoma patients with binocular, symmetrical superior, or inferior visual hemifield defects were selected. A comparative DTI analysis was conducted between OR fibers connected to the affected and unaffected visual hemifield in the glaucoma group and corresponding OR in the control group.

RESULTS. There was a significantly lower number of fiber bundles in the affected OR compared with unaffected OR and controls (P < 0.01). Radial diffusivity was similar between the affected and unaffected OR (P = 0.39), but higher in both groups compared with controls (P < 0.01). There was no difference in axial diffusivity among all groups. As a consequence, fractional anisotropy was lower and mean diffusivity was higher in the affected and unaffected OR compared with controls.

CONCLUSIONS. A significant loss of OR fibers connected to the severely damaged part of the optic nerve head, but not the fibers connected to the relatively spared retinal hemifield shows a direct relationship between retinal neuronal damage and functionally connected OR fibers in glaucoma. However, OR fibers connected to the relatively preserved visual hemifield in the glaucoma subjects still showed changes in radial diffusivity compared with controls, suggesting possible early dysfunction. Our results support the notion that glaucoma is a neurodegenerative disease involving the posterior visual pathway.