Over the last few years, many researchers have been working to find ways to identify Alzheimer's disease in its earliest stages, before major symptoms develop. Research has begun to suggest that certain signs of deterioration in the retina could mirror early neurodegeneration, and new research presented at the recent Annual Meeting of the American Academy of Ophthalmology has solidified the growing body of evidence that Alzheimer's disease can be diagnosed in seconds using a non-invasive eye scan.

This field of research has been greatly accelerated due to the development of a new type of non-invasive imaging technology called optical coherence tomography angiography (OCTA). This new technology allows clinicians to rapidly generate high-resolution images showing the volumetric blood flow inside an eye.

A team at Duke University has been utilizing OCTA technology to investigate changes in the retina that are associated with Alzheimer's disease. The research compared the optical data gathered from Alzheimer's patients to both healthy subjects, and those with mild cognitive impairment.

The early results presented recently revealed several clear biomarkers in subjects with Alzheimer's, including a thinning of a layer of the retina and a decrease in small retinal blood vessels at the back of the eye. Importantly, these changes were not seen in patients with straightforward mild cognitive impairment, suggesting this may be a good way to differentiate between the early stages of Alzheimer's and simple age-related cognitive degeneration.

A second study presented at the AAO Annual Meeting, from researchers at the Sheba Medical Center in Israel, examined the eyes of subjects with a family history of Alzheimer's but who had not yet begun to display any symptoms of the disease. This research revealed a noticeable thinning of the inner layer of the retina could be identified in subjects with a genetic history of Alzheimer's. Subsequent brain scans found that the retinal thinning correlated with a reduction in the size of the hippocampus. The researchers hypothesize that this retinal thinning may be an effective biomarker signaling the onset of Alzheimer's long before major clinical symptoms appear.

"This project meets a huge unmet need," says Sharon Fekrat, lead author of the Duke University study. "It's not possible for current techniques like a brain scan or lumbar puncture (spinal tap) to screen the number of patients with this disease. Almost everyone has a family member or extended family affected by Alzheimer's. We need to detect the disease earlier and introduce treatments earlier."

This new research affirms several studies suggesting signs of early neurodegeneration can be seen in the eye. A study from South Korea earlier this year revealed a potential connection between a thinning of the retina and the onset of Parkinson's disease, while a fascinating 2017 study from Cedars-Sinai Medical Center discovered that the same toxic proteins thought to be responsible for the progression of Alzheimer's disease could be detected on the retina.

All of this research still offers no indication that any macular degeneration is actually caused by neurodegeneration, or vice versa, however if these early-stage biomarkers can be effectively confirmed with enough data to offer consistent diagnoses, then we would have an invaluable tool to help battle a variety of brain diseases.

The new research was presented at AAO 2018, the 122nd Annual Meeting of the American Academy of Ophthalmology.