Analysis of the BOLD signal along colour-opponent pathways in LGN and V1 and microstructural alterations of the optic radiation in POAG and OHT patients

Purpose Primary open angle glaucoma (POAG) is associated with retinal ganglion cell loss and atrophies in the lateral geniculate nucleus (LGN) and visual cortex (V1). The causes and pathogenesis of glaucoma are unclear; with increased risk of progression to glaucoma in patients with ocular hypertension (OHT). To investigate this further the current study applied Magnetic Resonance Imaging (MRI) in a matched sample of POAG and OHT patients. Method We recruited 53 patients (POAG n = 32; OHT n = 21) and applied functional-MRI (fMRI) to a sub-group of POAG (n = 9) and OHT (n = 9) patients to test differences in LGN and Primary Visual Cortex (V1) BOLD response to differential chromatic modulations. Tract Based Spatial Statistics (TBSS) was applied to Diffusion weighted images (DWI) to compare fractional anisotropy (FA) values across the whole-brain between patient groups. Probabilistic tractography along the optic radiation (OR) tested for differences in microstructural alterations associated with POAG compared to OHT patients. Behavioural deficits associated with POAG on LGN activity was also investigated. Results Findings showed behavioural deficits in POAG in the three major cardinal directions (magno- parvo- and koniocellular pathways), reflecting deficits in post-receptoral processing. Strong correlations were observed between LGN and V1 activity in OHT which was significantly reduced in POAG. Activity in LGN is increased in POAG, whereas V1 activity is slightly lower in POAG compared to OHT. DWI showed significantly reduced FA in sagittal striatum and associated visual WM pathways, primarily of the left hemisphere. Reduced FA along the OR was observed in POAG compared to OHT patients with results indicating enhanced structural asymmetries in POAG. Conclusion We present evidence novel differences in chromatic contrast sensitivity and microstructural WM between POAG and OHT patient groups. Our findings reveal evidence for asymmetry within the visual system associated with POAG, opening several avenues for further investigation.