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C. Nucci, A. Cerulli, F. Bolacchi, M. Melis, A. Spanò, R. Floris, G. Simonetti, F. Garaci; Axonal Architecture of Optic Nerve and Optic Radiations in Glaucomatous Patients. An in vivo Analysis With 3 Tesla MR Diffusion Tensor Imaging. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4403.
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© ARVO (1962-2015); The Authors (2016-present)
Diffusion tensor imaging (DTI) is a magnetic resonance (MR) technique for studying white matter structures. Quantitative information on water diffusion within these structures, including its preferential direction within a voxel (fractional anisotropy, FA) and its magnitude independent of directionality (mean diffusivity, MD), can be derived from MR-DTI to characterize axonal architecture. The aim of the present study was to evaluate optic nerves and optic radiations of glaucomatous patients in vivo by using MR-DTI.
16 patients with primary open-angle glaucoma were included (9 males and 7 females, mean age 63 ±13 years, range 53-71 years). The glaucomatous eyes were stratified by the severity of the visual field defects into 6 stages according to the Hoddapp-Anderson-Parish system. Ten healthy subjects, matched for age and sex, served as controls. MR-DTI was performed with a 3 Tesla MR scanner. Diffusion-weighted SENSE-sshEPI sequences with a maximum b value of 800 s/mm2 were carried out along 15 directions. DTI trace images were created by averaging 15 diffusion-weighted images. Mean diffusivity and fractional anisotropy maps were automatically created. Three regions of interest (ROIs) were manually drawn over the reference SE-EPI images of both the optic nerves and the optic radiations. The ROIs were electronically superimposed over the MD and FA maps and the mean MD and mean FA values were calculated.
The mean MD values of the optic nerve and the glaucoma stages varied together consistently (r=0.8087, 95% CI: 0.6686-0.8934, p<0.0001). A significant difference in mean MD values was achieved between glaucoma stage 1 vs. 2 and between stage 3 vs. 4. A negative correlation was found between the mean FA values and the glaucoma stages (r=-0.7464, 95% confidence interval -0.8440 to -0.601, p<0.0001). A significant difference in FA values was achieved between stage 0 vs. stage 1, stage 1 vs. 2 and between patients with glaucoma stage 4 vs. 5. A significant elevation of MD and reduction of FA were observed in the optic radiations of patients with glaucoma with respect to control subjects.
We found that the MD and FA of glaucomatous optic nerves correlates with disease severity. In addition, the optic radiations of glaucoma patients presented diffusion abnormalities that distinguished them from healthy controls. MR-DTI seems to have a potential role as a complementary tool for evaluating the severity of glaucoma and its response to treatment.
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