By the time the symptoms of Alzheimer's disease appear, the disease itself has been lurking in the brain for decades and the damage has been done.

A non-invasive eye scan being studied by Cedars-Sinai neuroscience researchers could help identify people at high risk for Alzheimer's disease years before they experience symptoms, according to a new study published today in the Journal of Clinical Investigation Insight.

The hope is that eventually the scan will be used as a screening device to detect the disease early enough to intervene and change its course, says Dr. Keith L. Black, chair of the Department of Neurosurgery.

"The eye is our new window to the brain," Dr. Black says. "This study is important because it reconfirmed the results from our first eye scan study in 2010, that the earliest accumulation of plaques can be detected noninvasively in the brain up to 20 to 30 years before Alzheimer's disease becomes symptomatic."

More than 5 million Americans have Alzheimer's disease. That number will triple by 2050, according to the Alzheimer's Association.

The eye scan, conducted using an imaging device developed especially for this study, allows physicians to see the crucial warning sign of the condition: a sticky buildup called amyloid plaque which accumulates on the outside of nerve cells. The study found a correlation between the amount of these plaques found in the retina–the layer of tissue on the back of our eyes—with the amount of plaque detected using positron emission tomography (PET) scans. PET scans are diagnostic tests used to see how well organs and tissues are working by injecting radioactive dye that can then be picked up the scanner.

Read: When Should I Be Concerned About Memory Loss?

Looking at the retina has a few advantages. The scan could be easily repeated, allowing doctors to trace the progression of the disease over time. It's also a direct, non-invasive, and inexpensive method for looking at these plaques in the brain.

The study also helped pinpoint where in the retina the plaques tend to appear—so now the researchers know exactly where to look to find the signs of Alzheimer's disease.

Patients who get the scan first drink a solution that contains curcumin—a component of the spice turmeric. The substance causes the plaques in the brain to "light up" and be found by the scan.

Dr. Black's mother was diagnosed with Alzheimer's disease and died of it 10 years later. This inspired him to study the disease, and look for ways to catch the disease early.

WATCH: Dr. Black and his team talk about using retinal scans to detect Alzheimer's and how to prevent the disease in this video.

Disclosure: The optical imaging technology was developed by Keith L. Black, MD, chair and professor of the Department of Neurosurgery at Cedars-Sinai. Cedars-Sinai licensed the technology to NeuoroVision Imaging LLC, a company in which Black is chairman, founder, and equity holder. Maya Koronyo-Hamaoui and Yosef Koronyo are founding members of Neuro Vision Imaging. Cedars-Sinai has an equity interest in the company.