Fluorescence shows promise for detecting amyloid β in retinas of Alzheimer's patients

ORLANDO, Fla. — Thioflavin S staining in the ex vivo retina, detected by polarimetry, showed an 84.2% sensitivity and 72.2% specificity in detecting Alzheimer’s disease, according to a poster presented here at the Association for Research in Vision and Ophthalmology meeting.

Laura Emptage, a research assistant in the Campbell Labs at the University of Waterloo, and colleagues explained in their poster that because amyloid β is overexpressed in the brains of those with Alzheimer’s disease — and typically detected post-mortem — it is an accepted marker of the disease.

“Its presence in the retina presents an opportunity for a noninvasive diagnosis,” they said in the poster.

“We took tissue from human patients, both with Alzheimer’s disease and without Alzheimer’s,” Emptage told Ocular Surgery News in an interview. “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.”

Emptage explained that PET scans, which are typically used to detect amyloid β in the brain, require the use of fluorophore injections.

“We started looking at polarization properties, thinking this would be a lot less invasive method,” she told OSN.
The researchers used thioflavin S to stain ex vivo retinas from 19 patients with Alzheimer’s disease and 18 patients without, they explained in the poster. Those with a diagnosis of glaucoma were excluded. The retinas were examined for amyloid β deposits using fluorescence in both transmission and confocal scanning microscopy. Some of them were also examined for polarization properties using a polarimeter on a fluorescence microscope.

Thioflavin S staining was found to have an 84.2% sensitivity and 72.2% specificity in detecting Alzheimer’s disease, the researchers stated in the poster.

“We found that crossed circular polarization was very sensitive and specific to amyloid in the retina,” Emptage said in the interview.

However, it produced some false negatives, the poster said.

Co-author Melanie Campbell, PhD, FOSA, PPhys, a professor at the University of Waterloo, said they saw a wide range of deposit density and numbers in different retinas.

“So that gives us the hope that there would be some way to stage the disease by the number or density of deposits,” she told OSN.

The instrument the researchers used is not commercially available but could be adapted, Campbell said.
“It’s a fairly easy retrofit to the instrument,” she said. “We’re looking at the design of the instrument to measure in vivo patients, so that it could be used as a screening procedure, like you do in diabetics.”

“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,” Emptage said. “Then people could make decisions while they’re still cognitively functioning about their future care.”

Disclosures: Campbell has a patent through the University of Waterloo. None of the other authors has a financial disclosure.