Neuroimaging Findings in Glaucoma (Proton Magnetic Resonance Spectroscopy Study)

Abstract

The aim of the research is to determine metabolic changes in brain tissue by magnetic resonance spectroscopy (MRS) for patients who had primary open angle glaucoma (POAG) and to reveal a correlation between morphometric and functional alterations in the optic nerve and retina with basic MRS data. Methods: The study involved 24 patients with a diagnosis of POAG aged 58 to 80 years (mean age 73.2 ± 9.5 years). All patients underwent verification of the diagnosis of POAG, quantitative static perimetry (indexes were evaluated: MD - mean deviation), optical coherence tomography of the retina (assessment of the area of the neuro-retinal rim (NRR) and the thickness of the nerve fibers’ layer of the retina (RNFL)). The 2D-PRESS (Point RESolved Spectroscopy) volume-selection method was used for multivoxel MRS, TE (Time Echo) = 144ms TR (Time Repetition) = 2s, the size of each voxel was 10 * 10 * 15mm. The region of interest included thalami (4 voxels in each thalamus) and occipital cortex; Cho/Cr, NAA/Cr and NAA/Cho were evaluated. Results: According to analysis of variance, the ratio of NAA/Cr in the right thalamus was associated with the POAG stage of the right eye (F = 5.006; p = 0.0173) and decreased with increasing of the disease stage. At the same time, there were no significant differences in different stages of POAG of the left eye (F = 1.337; p = 0.285). The ratio of NAA/Cr in the left thalamus did not differ depending on the POAG stage of the right eye (F = 1.337; p = 0.285) but depended on the stage of POAG of the left eye (F = 6.245; p = 0.0074). Thus, the eye POAG stage affected the ratio of NAA/Cr in the ipsilateral thalamus, but not in the contralateral one. It was also revealed that the ratio of NAA/Cr in the right occipital cortex correlated positively with the area of the NRR and MD of the left eye (r = 0.54; p = 0.0069 and r = 0.54; p = 0.0260, respectively). Conclusions: The decline of NAA/Cr ratio in thalamus and occipital cortex is observed in patients with primary open-angle glaucoma, which confirms the impairment of functional state of these brain structures and may indicate the neurodegeneration in the central part of visual system in patients with POAG. The correlations of the stage of primary open-angle glaucoma and the Cho/Cr ratio and NAA/Cr ratio in thalamus were revealed, which could have diagnostic and prognostic value in POAG. The dependence of the ratio of NAA/Cr in the thalamus and occipital cortex and morphometric data of the optic disc and the functional state of the retina was determined, which confirms the involvement of the optic tract in the POAG progression and its possible development.