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Research further links Alzheimer's with eye disease

31/10/2018By Richard Chiu • Staff Journalist
Researchers have discovered a link between degenerative eye conditions, thin retinas and Alzheimer’s disease, in separate studies potentially leading to early diagnoses and new treatments for the brain disorder.

A groundbreaking study by researchers from the University of Washington, School of Medicine found a “significant link” between diabetic retinopathy (DR), age-related macular degeneration (AMD), glaucoma and Alzheimer’s disease.

In another study, published weeks later, the Washington University School of Medicine in St Louis revealed thinning at the centre of the retina found in eye exams may help detect Alzheimer’s in otherwise older, symptomless patients.

In the first study – published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association – scientists analysed data from 3,877 randomly selected patients from the Adult Changes in Thought database.

The participants were aged 65 and older and, crucially, not diagnosed with Alzheimer’s disease at the start of the research.

"Our hope is to use this technique to understand who is accumulating abnormal proteins in the brain that may lead them to develop Alzheimer’s."
Bliss O’Bryhim, Department of Ophthalmology and Visual Sciences' resident physician

During the five-year study, an expert committee diagnosed 792 of those cases with Alzheimer’s disease. Patients with AMD, DR or glaucoma were at 40–50% greater risk of developing Alzheimer’s disease compared with similar study participants without these eye conditions. Cataract diagnosis was not an Alzheimer’s disease risk factor.

“We don’t mean people with these eye conditions will get Alzheimer’s disease,” UW School of Medicine lead researcher Dr Cecilia Lee said.

“The main message from this study is that ophthalmologists should be more aware of the risks of developing dementia for people with these eye conditions and primary care doctors seeing patients with these eye conditions might be more careful on checking on possible dementia or memory loss.”

Despite saying more research was needed, Lee said anything detected in the eyes may relate to what is happening in the brain and that a better understanding of neurodegeneration in the brain and the eyes could be critical in the early diagnosis and treatment of Alzheimer’s.

Thin retinas

The second study, published in JAMA Ophthalmology, discovered OCT-angiography (OCTA) may be used as another potential method for screening patients for Alzheimer’s disease during an eye exam. The small study detected the presence of Alzheimer’s damage in older patients with no symptoms.

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“This technique has great potential to become a screening tool that helps decide who should undergo more expensive and invasive testing for Alzheimer’s disease prior to the appearance of clinical symptoms,” study author Dr Bliss O’Bryhim, a resident physician in Washington University’s Department of Ophthalmology and Visual Sciences, said.

“Our hope is to use this technique to understand who is accumulating abnormal proteins in the brain that may lead them to develop Alzheimer’s.”

The researchers used OCTA to examine the retinas in the eyes of 30 study participants with an average age in the mid-70s, none of whom exhibited clinical symptoms of Alzheimer’s.

Around half of those in the study had elevated levels of the Alzheimer’s proteins amyloid or tau as revealed by PET scans or cerebrospinal fluid, suggesting that although they didn’t have symptoms, they likely would develop Alzheimer’s.

“In the patients with elevated levels of amyloid or tau, we detected significant thinning in the centre of the retina,” co-principal investigator Dr Rajendra Apte said.

“All of us have a small area devoid of blood vessels in the centre of our retinas that is responsible for our most precise vision. We found that this zone lacking blood vessels was significantly enlarged in people with preclinical Alzheimer’s disease.”

Of the patients studied, 17 had abnormal PET scans and/or lumbar punctures, and all of them also had retinal thinning and significant areas without blood vessels in the centres of their retinas.

The researchers believed the changes detected in these eye tests can be used as markers for Alzheimer’s and could someday be developed to use a screening tool for detecting the disease early on.

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