Optic Nerve and Optic Radiation Neurodegeneration in Patients with Glaucoma: In Vivo Analysis with 3-T Diffusion-Tensor MR Imaging

Abstract

To evaluate, with high-field-strength diffusion-tensor (DT) magnetic resonance (MR) imaging, the axonal architecture of the optic nerves and optic radiations in patients with glaucoma and determine whether DT MR imaging-derived parameters correlate with disease severity. The study was approved by the institutional review board. All participants provided written informed consent. Sixteen patients with primary open-angle glaucoma were examined. Glaucoma severity was clinically assessed with use of a six-stage system based on static threshold visual field parameters. Ten healthy individuals served as control subjects. DT MR imaging was performed with a 3-T MR unit. Mean diffusivity (MD) and fractional anisotropy (FA) maps were automatically created. Regions of interest were positioned on the MD and FA maps, and mean MD and mean FA values were calculated for each optic nerve and each optic radiation. The optic radiations and optic nerves of patients with glaucoma, as compared with control subjects, had significantly higher MD and significantly lower FA. The mean MD values for the optic nerves and the glaucoma stages varied consistently (r = 0.8087, P < .0001). A negative correlation between mean FA for the optic nerves and glaucoma stage (r = -0.7464, P < .0001) was observed. Glaucoma is a complex neurologic disease that affects optic nerves and optic radiations. The finding that DT MR imaging-derived MD and FA in the optic nerves correlate with glaucoma severity suggests that these parameters could serve as complementary indicators of disease severity.