Close up photo of older male patient undergoing a sight examination to assess eye diseases which can be linked to Alzheimer's disease
Credit: Inside Creative House/Getty Images

Research led by Boston Medical Center has uncovered a link between biomarkers found in the vitreous humor of the eye and Alzheimer’s disease.

As reported in the Journal of Alzheimer’s Disease, the research team also found a link with chronic traumatic encephalopathy (CTE) suggesting the biomarkers could “serve as a proxy for neuropathological disease.”

The number of Americans with Alzheimer’s disease (AD) is predicted to reach 13.2 million by 2060 and already impacts more than six million North American individuals over the age of 65 years. A problem with both AD and CTE, a related tauopathy that shares common characteristics with AD, is that diagnosis is often delayed, which can limit the benefit of available treatments.

Previous research has shown people with eye diseases such as glaucoma, diabetic retinopathy, age-related macular degeneration, and cataracts are at higher risk of neurodegenerative disease.

In this study, Manju Subramanian, an ophthalmologist at Boston Medical Center and an associate professor at Boston University, and colleagues assessed whether biomarkers in eye fluid could predict whether an individual had a neurodegenerative disease such as AD.

The researchers tested vitreous humor fluid from 41 postmortem eyes and brains from people with AD (n=7), CTE (n=15), both AD and CTE (n=10) and those without signs of neurodegenerative disease (n=9). The team measured levels of amyloid-β, total tau, phosphorylated tau, neurofilament light chain, and eotaxin-1, all of which are known to be linked to neurodegeneration, in the eye fluid samples.

Subramanian and team found that levels of total tau were significantly higher in the eye fluid from those with AD and those with CTE compared with controls. Levels of total tau were also higher in those with AD or CTE versus individuals with both conditions.

When the researchers assessed the samples based on disease stage, they found that people with early stage CTE had higher levels of neurofilament light chain compared with controls and those with later stage disease.

“To our knowledge, this is the first study to investigate the role of vitreous fluid biomarkers and link it to confirmed post-mortem brain tissue pathological examination of AD,” said Subramanian in a press statement.

“In addition, this is the first study to find a link between vitreous fluid biomarkers and confirmed CTE. Our findings provide further evidence to support the potential role of vitreous biomarkers in early diagnosis and prognostication of diseases like AD and CTE.”

The authors note that the sample was small and plan to do further studies with greater numbers of patients and controls to confirm their results and assess other vascular and white matter pathologies.

Also of Interest