Widespread Structural and Functional Brain Connectivity Changes and Associations with Balance in Glaucoma

Abstract

Purpose : Although recent studies showed that glaucoma affects not only the eye but also the brain, the behavioral relevance remains unexplored. In addition, glaucoma patients often present an increased risk of falls apart from visual impairments, yet the underlying mechanisms remain unclear. In this study, we investigated the changes in structural and functional brain connectivity in glaucoma, and the associations with patients’ ability for postural control.

Methods : Early glaucoma subjects (n=32) and healthy controls (n=10) underwent 3-Tesla anatomical MRI, diffusion tensor imaging (DTI) and task-free functional connectivity MRI (tf-fMRI) with eyes closed at rest. tf-fMRI data and DTI data were analyzed using CONN toolbox and tract-based spatial statistics, respectively after co-registration to anatomical MRI data. Additionally, a subset of 7 glaucoma subjects underwent dynamic posturography using the Equitest posture platform (Neurocom, Inc) to assess postural stability, specifically the multisensory integration abilities relevant for balance.

Results : There were significant differences in clinical ophthalmic assessments between glaucoma patients and healthy controls while no apparent age or gender difference was observed (Figure 1). In tf-fMRI, the left supramarginal gyrus (SMG) showed lower functional connectivity with the visual occipital area (VO) and superior sensorimotor area (SSM) in glaucoma patients compared to healthy controls (Figure 2A, B). Furthermore, negative associations were found between sway velocity during posturography and functional connectivity between SMG and VO in glaucoma patients (Figure 2C, D). In DTI, lower fractional anisotropy was observed in the optic tracts and optic radiations of the primary visual pathway, as well as the superior longitudinal fasciculus (SLF) around the left SMG in glaucoma patients compared to healthy controls (Figure 2E, F).

Conclusions : The current findings suggest the involvement of brain areas responsible for vision and balance in early stages of glaucoma. Glaucoma patients present reduced structural integrity in the white matter around SMG, as well as reduced functional connectivity between SMG and VO or SSM compared to healthy controls. Furthermore, decreased functional connectivity between SMG and VO may negatively impact postural control. Altered brain coordination may be a potential mechanism behind increased fall risk in glaucoma.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.