The presence of a particular peptide in the retina, able to be detected by fluorescence, could present an opportunity for a non-invasive diagnosis of Alzheimer’s disease.
Amyloidbeta (amyloid β) is overexpressed in the brains of those with Alzheimer’s disease, the most common form of dementia.
When Alzheimer’s is suspected, the diagnosis is usually confirmed with tests to evaluate behaviour and thinking abilities, often followed by a brain scan if available, however the only definitive diagnosis is examination of brain tissue after death.
According to a poster presented at the Association for Research in Vision and Ophthalmology meeting in Florida in the US in May, thioflavin S staining in the ex vivo retina, detected by polarimetry, showed an 84.2 per cent sensitivity and 72.2 per cent specificity in detecting Alzheimer’s disease
Laura Emptage, a research assistant in the Campbell Labs at the University of Waterloo in Canada, and colleagues explained that amyloid β is typically detected post-mortem.
“Its presence in the retina presents an opportunity for a non-invasive diagnosis. We took tissue from human patients, both with Alzheimer’s disease and without Alzheimer’s,” Ms. Emptage told Ocular Surgery News.
“We dissected out the retinas and initially looked at them with fluorescence to see if we could detect amyloid within the tissue. We found that it is present and it expresses within the retina in patients with Alzheimer’s disease. And we wanted to find a way to detect it that was less invasive.
PET scans, which are typically used to detect amyloid β in the brain, require the use of fluorophore injections. “We started looking at polarisation properties, thinking this would be a lot less invasive method,” she said.
The researchers used thioflavin S to stain ex vivo retinas from 19 patients with Alzheimer’s disease and 18 patients without, excluding those with a diagnosis of glaucoma. The retinas were examined for amyloid β deposits using fluorescence in both transmission and confocal scanning microscopy. Some of them were also examined for polarisation properties using a polarimeter on a fluorescence microscope.
Thioflavin S staining was found to have an 84.2 per cent sensitivity and 72.2 per cent specificity in detecting Alzheimer’s disease, the researchers stated in the poster.
“We found that crossed circular polarisation was very sensitive and specific to amyloid in the retina,” she said, adding the technique did produce some false negatives.”
Study authors believe the research could one day lead to a screening procedure. “If we could use the retina as a simple way to detect Alzheimer’s disease, it would greatly impact the quality of life for those people… With early detection… people could make decisions while they’re still cognitively functioning about their future care.”