New eye test may detect Alzheimer’s disease years before symptoms emerge, study suggests

A new study published in the Journal of Alzheimer’s Disease presents an innovative method that may detect signs of Alzheimer’s disease before symptoms appear—using a simple, noninvasive eye test. The technique, called dynamic light scattering spectroscopy, measures microscopic protein movement in the retina and could offer a faster, cheaper, and more accessible way to screen for the disease in its earliest stages.

Alzheimer’s disease is the most common form of dementia, a progressive neurological condition that gradually impairs memory, reasoning, and other cognitive abilities. It typically develops over many years, and by the time symptoms are obvious enough for a diagnosis, irreversible damage has often already occurred in the brain. That delay has made early detection a top priority in Alzheimer’s research, with hopes that identifying the disease sooner could allow for earlier interventions and better outcomes.

“The current ‘gold standard’ diagnostic method for Alzheimer’s disease is a PET scan. These are expensive, invasive, and uncomfortable for the patient, only to produce a qualitative reading that is accurate around 70% of the time in identifying the disease at a stage well beyond the point of any remedial action,” explained study author Jeffrey N. Weiss, the founder of Micron Ophthalmic.

“It was clear to me that something had to change. In my work as a physician and electrical engineer, I had employed dynamic light scattering spectroscopy and knew that it could be useful in providing a rapid, cost-effective, noninvasive, and quantitative measurement. Most impressively, we’ve seen that the technology is capable of diagnosing Alzheimer’s disease at least two years earlier than any current method, opening the window for preventative care.”

Dynamic light scattering measures how proteins naturally move in the body—a type of motion known as Brownian movement. Since molecular changes often occur before physical damage or visible symptoms appear, Weiss believed dynamic light scattering spectroscopy could detect the earliest signals of Alzheimer’s disease. Because the retina develops from the same tissue as the brain during fetal development, it offers a unique and accessible window into neurological health.

To test this theory, Weiss developed a dynamic light scattering spectroscopy device that works in tandem with a standard ophthalmic fundus camera. During the procedure, a patient’s pupil is dilated using common eye drops. The patient then stares at a dim red light while the system collects data for just five seconds. Embedded software captures and analyzes the patterns of protein motion in the retina, producing an autocorrelation curve—a mathematical representation of molecular activity.

The study involved several groups of participants. First, Weiss tested the reproducibility of the dynamic light scattering measurements by examining 17 healthy individuals with no history of neurological or eye disorders. The results were consistent across multiple variables, including sex, time of day, and whether the left or right eye was used. Importantly, the measurements were not affected by the participants’ age, suggesting that the test can reliably be used in older populations who are most at risk for Alzheimer’s.

Next, Weiss tested 15 individuals with mild cognitive impairment but no diagnosis of Alzheimer’s disease. Of these, four participants showed a distinctive pattern in their results indicating slower protein motion. These individuals went on to receive a formal Alzheimer’s diagnosis six to twelve months later, supporting the idea that dynamic light scattering spectroscopy might detect the disease well before clinical symptoms develop.

The study also included 17 individuals who had already been diagnosed with probable Alzheimer’s disease. Eleven of these participants had previously tested positive for amyloid buildup using PET scans. In all 11 cases, dynamic light scattering spectroscopy testing correctly identified the Alzheimer’s pattern. Of the remaining six, five were correctly classified as negative based on both PET and DLS results. One participant, who had a negative PET scan, showed a borderline DLS reading that may suggest very early changes missed by current imaging techniques.

The key feature observed in the dynamic light scattering measurements was a flattening of the initial portion of the autocorrelation curve in patients with Alzheimer’s. This flattening reflects a slowing in the movement of retinal proteins, a signal that likely corresponds to early dysfunction in the retinal nerve fiber layer—an area known to be affected in Alzheimer’s.

Traditional eye imaging techniques, such as optical coherence tomography, can also detect changes in this layer, but typically only after significant damage has occurred. In contrast, dynamic light scattering spectroscopy captures molecular-level changes that precede visible structural damage.

A major advantage of dynamic light scattering spectroscopy over other diagnostic tools is its accessibility. The test is quick, noninvasive, and inexpensive—costing only a few cents to perform and requiring no disposable components. It could be used in community clinics, nursing homes, and low-resource settings where PET scans or spinal taps are impractical. Additionally, the technology avoids common confounding variables that affect optical coherence tomography, such as glaucoma, age-related macular degeneration, or diabetic retinopathy.

“The retina is an outgrowth of the brain—it is important to acknowledge its growing relevance as an active observation site for biomarkers related to Alzheimer’s disease,” Weiss told PsyPost. “The test itself addresses many of the major issues in Alzheimer’s diagnostics: the complexity of testing in vulnerable populations, the cost-effectiveness of those tests, the elimination of ambiguity or subjectivity in the results, and most importantly, the stage at which we are able to identify the disease. In this regard, I hope that these findings suggest that there is hope in tackling what has previously felt impossible—treating the disease before there are symptoms.”

Despite these promising results, the study has limitations. The sample sizes were small, and the research was conducted in a single setting. Although the test demonstrated strong predictive potential, larger studies across more diverse populations are needed to confirm its accuracy and reliability. Further work is also needed to determine whether eye diseases that affect the retina could interfere with dynamic light scattering measurements, even if the eye appears healthy during routine examination.

“The next milestone for this device is to build a sufficient body of evidence that our findings become irrefutable,” Weiss said. “For this, we need to place the machines in a variety of Alzheimer’s sites and assess the results that are generated. After this, the obvious next step is to engage with the FDA process, with the objective being to approve the device for wider use.

“We have a host of options from there, but one that looks particularly enticing in terms of creating a generational impact through this invention is to use it as an accompaniment for Alzheimer’s drug trials. It can collect far more data, at far shorter intervals, for a far lower cost than any other technology currently employed for this purpose.”

The study, “Dynamic light scattering of the eye in the diagnosis of Alzheimer’s disease,” was published on November 25, 2024.