How an eye test could detect Alzheimer's

What if Alzheimer's could be diagnosed through a routine visit to the opticians? Researchers may have brought us a step closer to such a feat, after developing an optical imaging system that can detect a hallmark of the disease.

In a proof-of-concept study, researchers reveal how a noninvasive, high-resolution imaging technique was able to detect beta-amyloid plaques in the retinas of patients with Alzheimer's disease.

Study co-author Maya Koronyo-Hamaoui, Ph.D., of the Maxine Dunitz Neurosurgical Institute at Cedars-Sinai in Los Angeles, CA, and colleagues recently reported their findings in the journal JCI Insight.

Alzheimer's disease is the most common form of dementia, accounting for around 60 to 80 percentof cases. The condition is characterized by problems with memory and thinking, as well as changes in mood and behavior, and these problems become more severe over time.

It is estimated that around 5.5 million people in the United States are living with Alzheimer's. Every 66 seconds, one more person in the U.S. is diagnosed with the disease.

While research into the precise causes of Alzheimer's is ongoing, scientists know that the condition involves the degeneration and death of brain cells. The buildup of a protein called beta-amyloid isconsidered a key culprit in the process.

Beta-amyloid and Alzheimer's

Beta-amyloid is a sticky fragment of the amyloid precursor protein, which resides in the fatty tissue surrounding brain cells, or neurons.

In Alzheimer's disease, these beta-amyloid fragments clump together, forming "plaques" in the brain that disrupt neuronal communication and trigger immune cell activity. This leads to inflammationand brain cell death.

As such, beta-amyloid plaques are considered a hallmark of Alzheimer's. At present, healthcare professionals use positron emission tomography or cerebral fluid analysis to detect the presence of beta-amyloid and make an Alzheimer's diagnosis.

However, Dr. Koronyo-Hamaoui and colleagues note that such techniques are not only invasive, but their availability is limited and their costs are high, making population-wide screening challenging.

Recent studies have shown that beta-amyloid can be detected in the retina, which is the light-sensitive tissue that lines the back of the eye and sends signals to the brain.

For their study, Dr. Koronyo-Hamaoui and team tested the efficacy of a novel retinal imaging technique for identifying beta-amyloid deposits and diagnosing Alzheimer's disease.

Detecting beta-amyloid in the retina

The new technique involves autofluorescent imaging of the retina using a specially designed ophthalmic camera and state-of-the-art image processing software. The researchers tested the imaging method on 16 Alzheimer's disease patients and age-matched controls.

The team reports that the retinal imaging technique identified a 4.7-times greater abundance of beta-amyloid plaques in the retinas of patients with Alzheimer's disease, compared with the retinas of the controls.

The researchers also tested the imaging method on the retinas of 23 deceased patients who had Alzheimer's disease, alongside the retinas of 14 age-matched deceased individuals who did not have the disease.

Again, this revealed a higher abundance of beta-amyloid plaques in the retinas of Alzheimer's patients than in those of the controls.

What is more, in both living and deceased patients with Alzheimer's disease, the researchers found that neuronal loss in the retinas as a result of beta-amyloid plaques correlated with neuronal loss in the patients' brains.

Taken together, Dr. Koronyo-Hamaoui and colleagues believe that their findings indicate that retinal imaging may be a feasible, low-cost screening technique for the detection of Alzheimer's disease.

"The geometric distribution and increased burden of retinal amyloid pathology in AD [Alzheimer's disease], together with the feasibility to noninvasively detect discrete retinal amyloid deposits in living patients, may lead to a practical approach for large-scale AD diagnosis and monitoring."

The team plans to test their technology in further clinical trials, with the aim of eventually bringing retinal imaging to the forefront of Alzheimer's diagnosis.