TH-CD-207-08: Neurodegeneration of the Visual Pathway in Mild Glaucoma Assessed by MRI

Abstract

Purpose: Glaucoma is a leading cause of irreversible blindness characterized by progressive degeneration of the retinal ganglion cells. The glaucomatous effects on the visual pathway in the brain remain largely unknown. This study explores the use of quantitative white matter MRI and cortex segmentation methods for the assessment of neurodegeneration in early stage glaucoma. Methods: Four mild primary open-angle glaucoma patients (60.2±4.0 y.o) and six age-matched normal control subjects (60.6±3.4 y.o) were scanned using T1-weighted spoiled gradient echo for high resolution anatomy, diffusion-weighted echo planar MRI for diffusion tensor imaging (DTI) to measure fractional anisotropy (FA) and apparent diffusion coefficients (ADC). Cortical statistics are calculated with Brodmann area maps in Freesurfer. Multiple-echo gradient echo imaging was used for quantitative susceptibility mapping (QSM). The Laplacian-based approach and V-SHARP method will be applied to unwrap phase, and an iterative least squares approach will be used to estimate the magnetic susceptibility. Group comparisons of structural MRI indices were performed using unpaired t-tests with significance threshold p<0.05. Results: The primary visual cortex (V1) area was significantly reduced (p<0.05) in the glaucoma group (L:2234±126mm2 R:2414±223mm2) and the visual area MT (L:1489±171mm2 R:1328±32mm2) compared to normal control (V1 L:2716±203mm2 R:2910±377mm2; MT L:1520±322mm2 R:1570±62mm2). The V1 cortical thickness showed a slight but nonsignificant trend of thinning in glaucoma. FA values of the optic radiation were significantly lower in the glaucomatous right hemisphere (0.434±0.017) compared to age-matched controls (L: 0.499±0.019; R: 0.503±0.010). Higher ADC and lower magnetic susceptibility values of optic radiation in disease group are noticeable but not statistically significant. Conclusion: MRI revealed significant occipital cortical layer (V1, MT) area decreases and optic radiation degeneration using DTI and QSM in early stage glaucoma. These results suggest that multimodal MRI may provide clinically useful makers for early detection of glaucoma.