Binocular integrated visual field deficits are associated with changes in local network function in primary open-angle glaucoma: a resting-state fMRI study

Recent brain imaging studies have shown that the degenerative eye damage generally observed in the clinical setting, also extends intracranially. Both structural and functional brain changes have been observed in glaucoma participants, but we still lack an understanding of whether these changes also affect the integrity of cortical functional networks. This is relevant, as functional network integrity may affect the applicability of future treatments, as well as the options for rehabilitation or training. Here, we compare global and local functional connectivity between glaucoma and controls. Moreover, we study the relationship between functional connectivity and visual field (VF) loss. For our study, 20 subjects with primary open-angle glaucoma (POAG) and 24 age-similar healthy participants were recruited to undergo a complete ophthalmic assessment followed by two resting-state (RS) (f)MRI scans. For each scan and for each group, the ROIs with EC values higher than the 95th percentile were considered the most central brain regions ("hubs"). Hubs for which we found a significant difference in EC in both scans between glaucoma and healthy were considered to provide evidence for network changes. In addition, for each participant, behavioural scores were derived based on the notion that a brain regions hub function might relate to the: 1) sensitivity of the worse eye - indicating disease severity, 2) sensitivity of both eyes combined - with one eye potentially compensating for loss in the other, or 3) difference in eye sensitivity - requiring additional network interactions. By correlating each of these VF scores and the EC values, we assessed whether VF defects could be associated with centrality alterations in POAG. Our results show that no functional connectivity disruptions were found at the global brain level in POAG participants. This indicates that in glaucoma global brain network communication is preserved. Furthermore, a positive correlation was found between the EC value of the Lingual Gyrus, identified as a brain hub, and the behavioural score for the VF sensitivity of both eyes combined. The fact that reduced local network functioning is associated with reduced sensitivity of the binocular VF suggests the presence of local brain reorganisation that has a bearing on functional visual abilities.