Glaucoma and the Brain: How One Eye's Trouble Affects Your Vision Center
"New research sheds light on the surprising stability of the brain's visual cortex, even when glaucoma affects one eye. Discover what this means for understanding and treating vision loss."
Glaucoma, a leading cause of blindness, is projected to affect over 80 million people worldwide by 2020. This condition damages the optic nerve, leading to vision loss that often starts with blind spots in the affected eye's field of view. While glaucoma's primary impact is on the eye, increasing evidence suggests that the effects of this neurodegenerative disease extend to the brain.
Specifically, research has shown that glaucoma can lead to decreased cell density and activity in the brain's visual processing centers, such as the lateral geniculate nucleus (LGN) and the primary visual cortex. These changes are thought to be due to the degeneration of nerve connections between the eye and the brain. However, it's been unclear whether this loss of input from the affected eye causes the visual cortex to functionally reorganize itself.
To investigate this, a recent study used functional magnetic resonance imaging (fMRI) to examine the brains of individuals with glaucoma in only one eye. The goal was to see if the visual cortex regions that had lost input from the glaucomatous eye showed an increased response to input from the unaffected eye. The results offer valuable insights into the brain's response to vision loss and the potential for therapies.
Glaucoma’s Reach Beyond the Eye
A 2025 literature review examines how glaucoma affects the central nervous system, cognitive function, and quality of life, noting that vision loss from the disease is irreversible. A separate study reports bidirectional causal relationships between glaucoma and brain functional networks, suggesting potential diagnostic biomarkers and neurotherapeutic targets. Research on cortical plasticity and perceptual learning asks whether the brain can adapt to gradual visual-field loss, while a 2026 article describes long-term studies planned to test whether imaging markers of plasticity translate into better vision after therapy.
How Glaucoma Impacts the Visual Cortex: What the Study Revealed
The study compared nine participants with unilateral primary open-angle glaucoma (POAG) to a control group of four individuals without glaucoma. Participants with glaucoma had visual field defects in one eye, specifically in the central area of vision. Researchers used fMRI to measure brain activity while participants viewed visual stimuli with each eye separately.
- No Increased Response: The study found no evidence that the brain areas corresponding to the vision lost from the glaucomatous eye showed an increased response to the unaffected eye.
- Reduced Activation: Consistent with previous studies, there was a noticeable reduction in brain activity in both the primary (V1) and extrastriate (V2) visual cortex when participants viewed the stimuli through their glaucomatous eye. This confirms that fMRI can detect the impact of glaucoma on brain function.
- Stability in the Adult Brain: The results suggest a remarkable level of stability in the adult visual cortex, even in the face of nerve degeneration caused by glaucoma. This indicates that the adult brain may not reorganize itself as much as previously thought in response to this type of vision loss.
Connectivity Changes Along the Visual Pathway
A 2018 systematic review reports altered functional connectivity in both visual and nonvisual systems in early primary open-angle glaucoma (POAG). In contrast, gray-matter atrophy was consistently found in more advanced or severe POAG, but not in every early-stage group analyzed. A 2021 study examined early visual-cortex dynamics using drifting grating patterns and uniform-gray intervals during passive viewing and a one-back task. A related 2020 preprint included those tasks plus a fixation-dot task.
Evidence and Limits in Visual-Pathway Findings
Research on posterior visual pathways reports reduced fractional anisotropy in underlying white matter, with effects in fiber bundles projecting to both central and peripheral representations in early visual cortex. This finding suggests that white-matter deficits may extend more broadly than a single visual-field region. A 2018 review says its findings may prompt further investigation of brain plasticity later in life and strategies to prevent cortical degeneration. An editorial describes glaucoma as a neurodegenerative disease that also involves cognitive aspects and quality of life.
Comparing Eyes With and Without Field Defects
A comparison of eyes from patients with primary open-angle glaucoma and normal-tension glaucoma examined peripapillary atrophy (PPA) in eyes with unilateral visual-field defects. Alpha-zone PPA area was significantly larger in eyes with a field defect than in the fellow eyes with normal fields (t=3.02, P=0.0045). The study found no significant difference between the eyes in beta-zone area. These results describe a difference in one PPA measure, not a difference in both zones.
What This Means for Understanding Glaucoma and the Brain
This research suggests that in adults with unilateral glaucoma, the visual cortex maintains a surprising level of stability, without significant reorganization, as the primary and extrastriate visual cortex regions responding to the fellow eye were equivalent within the LPZ and the control ROIs.
Pressure, Retinal Cell Loss, and Treatment
A 2015 framework article states that glaucoma-related vision loss is associated with the death of retinal ganglion cells. It identifies high intraocular pressure as a major risk factor for vision loss from glaucoma. Lowering eye pressure is the goal of all available medical and surgical treatments, according to the article.
A Growing Public-Health Concern
A Frontiers research-topic overview describes glaucoma as one of the leading causes of irreversible visual impairment worldwide among older adults and calls it a public-health problem. It characterizes glaucoma as a social disease and estimates that its prevalence could grow to 112 million people by 2040. The overview also reports that studies have identified important similarities between primary open-angle glaucoma and other neurodegenerative diseases.
The study indicates that the adult human visual cortex may not be as plastic as once believed in response to optic nerve neurodegeneration. Although there was a reduction in BOLD change in the LPZ ROIs for glaucomatous eye viewing, considerable residual activation was still evident for the high and medium contrast stimuli.
Further research should focus on examining the residual cortical responses near the LPZ to fully understand the origin of these signals. This is important for advancing new approaches, such as retinal prostheses, which may rely on the presence of functioning cortical cells even after extended visual deprivation.