Eye Test Reveals Hidden Parkinson’s Before Symptoms

A simple eye exam could detect Parkinson’s disease years before the first tremors appear, potentially revolutionizing treatment timelines for millions of patients worldwide.

Researchers at Université Laval have discovered that the retina – the light-sensitive tissue at the back of the eye – responds differently to light stimuli in people with early-stage Parkinson’s compared to healthy individuals, even before classical motor symptoms develop.

“By the time a person consults a doctor because of motor problems such as tremors, the disease has been present for several years and the affected neurons are already engaged in an irreversible degenerative process,” explains study leader Martin Lévesque, professor at Université Laval’s Faculty of Medicine and researcher at CERVO Brain Research Centre.

The groundbreaking research, published in the May issue of Neurobiology of Disease, found distinct electrical patterns in the retinas of both newly diagnosed patients and mouse models of the disease. This “retinal signature” could serve as a biomarker for early detection.

Using electroretinography – a non-invasive technique that measures the electrical response of the retina to flashes of light – the team tested 20 people diagnosed with Parkinson’s within the past five years and 20 healthy age-matched controls.

“We placed an electrode on each participant’s lower eyelid and recorded their retinal response to a series of flashes of different intensity, frequency and color,” Lévesque noted. “The results we obtained for people with Parkinson’s had a distinct signature from those in the control group.”

Most intriguingly, the research revealed significant sex-specific differences in retinal responses. Female participants with Parkinson’s showed more pronounced changes in certain retinal measurements than their male counterparts, potentially offering new insights into how the disease manifests differently between sexes.

The team observed that bipolar cells – neurons that transmit signals from photoreceptors to ganglion cells within the retina – showed reduced activity in both humans and mice with early Parkinson’s. In the mouse models, they even detected abnormal accumulation of alpha-synuclein, the protein associated with Parkinson’s disease, in the retina before it appeared in the brain.

“The retina is a direct extension of the central nervous system and, consequently, offers a non-invasive way of exploring the brain,” explains Lévesque. This connection makes the eye a potential “window” into brain health.

Victoria Soto Linan, the study’s lead author and doctoral student at Université Laval, suggests that retinal screening could become a routine part of healthcare for people over 50. “By detecting the disease early, we could offer interventions that prevent the degeneration of the neurons involved in Parkinson’s,” she says.

Beyond early detection, the researchers believe their technique could provide a way to monitor disease progression and treatment effectiveness. As neurologists increasingly seek biomarkers that can track Parkinson’s before symptoms begin, this accessible screening method holds particular promise.

Currently, Parkinson’s affects over 10 million people globally, with most diagnoses occurring after substantial neurodegeneration has already taken place. The disease’s early stages can begin 10-15 years before classical symptoms emerge, making early detection tools like this potentially transformative for treatment outcomes.

The findings add to growing evidence that the eyes may offer crucial insights into neurological disorders, with similar approaches being explored for Alzheimer’s, multiple sclerosis, and other conditions. As our population ages, such non-invasive screening tools could become increasingly valuable for maintaining brain health through early intervention.