By Linda Conlin, Pro to Pro Managing Editor
There’s yet another connection to the eye as a window to the brain. Research earlier this year found plaques that compromise brain function in the retinal ganglion cells of patients with mild cognitive impairment and Alzheimer’s disease (AD). Now, new research from Boston Medical Center found a significant correlation between biomarkers in the vitreous humor of the eye and confirmed cases of AD and Chronic Traumatic Encephalopathy (CTE) in post-mortem brain and eye tissue. (Vig, Viha et al. ‘Vitreous Humor Biomarkers Reflect Pathological Changes in the Brain for Alzheimer’s Disease and Chronic Traumatic Encephalopathy’. 1 Jan. 2023 : 1181 – 1193.)
Currently, the definitive diagnoses of AD and CTE are made by postmortem neuropathological examination. In AD, neuropathological changes occur decades before symptom onset, so by the time a patient is diagnosed, the effects of treatment may be limited. Similarly, CTE associated with repeated traumatic brain injuries, including concussions and repeated blows to the head, is also associated with the development of dementia, and patients would benefit from early detection and treatment. The findings of this study build on the authors' previous work that biomarkers in vitreous fluid are linked to cognitive function in live patients with both normal cognition and mild cognitive impairment.
Vitreous fluid, or vitreous humor, is the transparent gelatinous tissue filling the eyeball behind the lens. Tau protein biomarker levels were measured both in the vitreous humor of postmortem eyes and cortical tissue of the brain. Abnormal Tau proteins are associated with both AD and CTE. Tissue and fluid examination revealed that vitreous levels of Tau were significantly elevated in AD and CTE groups when compared to control groups and correlated to cortical brain levels. These eye-based protein biomarkers could be a more accessible and cost-effective supplement for diagnosis or prognosis in neuropathological disease. Vitreous fluid sampling may be potentially safer, quicker, and more accessible to obtain with a potentially lower risk of adverse events and may be done as an outpatient office procedure.
Patients with eye disease have shown an increased risk for developing neurodegenerative disease, and several studies have established a link between neurodegenerative diseases and ophthalmic conditions like glaucoma, diabetic retinopathy, age-related macular degeneration, and cataracts. Investigating biomarkers in this at-risk population is important in order to study their role in early diagnosis. While the eye provides images of what’s around us, they also provide a glimpse inside into age-related or disease-related changes that occur in the brain and neural structures.