- Parkinson’s disease can affect the eyes, causing vision changes, dry eye, and reading difficulties.
- Researchers from Moorfields Eye Hospital and UCL Institute of Ophthalmology have found specific markers in the eye indicating the presence of Parkinson’s disease.
- Scientists say these markers can be found on average seven years before a person receives an official diagnosis.
More than 10 million people around the world have Parkinson’s disease — a neurological disease that affects a person’s ability to move.
Researchers are still unclear as to why a person may get Parkinson’s disease, but there are some indications that disturbances of the gut microbiome might play a role. And because early symptoms of Parkinson’s disease develop gradually, they can sometimes be hard to spot.
One area of the body that can show signs of Parkinson’s disease is the eyes. People with Parkinson’s disease may experience changes to their vision, dry eye, and/or difficulty reading or keeping their eyes fully open.
Now, researchers from Moorfields Eye Hospital and UCL Institute of Ophthalmology have found specific eye markers indicating Parkinson’s disease.
Scientists say these markers can be found on average seven years before a person receives an official diagnosis.
This study was recently published in the journal Neurology, the medical journal of the American Academy of Neurology.
Using OCT scans to spot Parkinson’s signs
For this study, Dr. Siegfried Wagner, Honorary Clinical Senior Research Fellow at the NIHR Biomedical Research Centre at Moorfields Eye Hospital and UCL Institute of Ophthalmology and lead author of this study, and his team used artificial intelligence to analyze data from two different datasets — the AlzEye dataset and the U.K. Biobank database.
Scientists used data from retinal eye scans taken by optical coherence tomography (OCT).
“OCT is a non-invasive imaging modality which can generate cross-sectional images of the retina,” Dr. Wagner explained. “In many ways, OCT is analogous to ultrasound, except rather than sound waves, it uses the backscattering of light to generate images imparting much greater resolution.”
Through an OCT scan, a doctor can see the layers of the retina and measure their thickness. This can help in the diagnosis of certain diseases, including age-related macular degeneration, glaucoma, diabetic retinopathy, and holes in the macula.
Looking for Parkinson’s markers
Upon analyzing data from the eye scans, the researchers found differences in two specific layers of the inner retina in people with Parkinson’s disease — the ganglion cell-inner plexiform layer and the inner nuclear layer.
“Thinning of the ganglion cell-inner plexiform layer has been seen in several neurological diseases, from multiple sclerosis to Alzheimer’s dementia, and it may reflect generalized loss of brain tissue. Abnormalities in the inner nuclear layer have only really been seen in cadaveric studies thus far,” Dr. Wagner said.
“It’s fascinating to find changes here as cells using dopamine are found between this layer and the ganglion cell-inner plexiform layer. We are speculating but it is possible that we are observing a primary dopamergic-related degeneration in patients with Parkinson’s disease,” he added.
The researchers found the reduced thickness of both these layers was associated with a higher risk of developing Parkinson’s disease.
Why the eyes?
According to Dr. Wagner, the researchers decided to look for markers of Parkinson’s disease in eye scans because the disease is characterized by the loss of cells using the neurotransmitter dopamine.
“The eye represents an accessible window into the brain and, importantly, also houses cells using the chemical dopamine,” he explained to Medical News Today.
“Previous work has shown that features of dopamine cell loss can be found in histological studies of retinal tissue in people with Parkinson’s disease; however, it has never been consistently observed in in-vivo imaging,” he said.
Dr. Wagner, however, also said it is important to highlight this is an early-stage research finding an association between differences in retinal morphology and the development of Parkinson’s disease.
“Translating this into individual risk stratification requires considerable further work,” he continued.
“We are investigating multimodal retinal imaging as well as high dimensional modeling approaches based on deep learning for (the) prediction of Parkinson’s disease. We’re also planning to investigate the utility of retinal imaging in prodromal Parkinson’s disease,” he said.
Could this lead to an early intervention for Parkinson’s?
After reviewing this study, Dr. Daniel Truong, a neurologist and medical director of The Parkinson’s and Movement Disorder Institute at MemorialCare Orange Coast Medical Center, told Medical News Today the idea that we can detect markers of Parkinson’s disease through eye scans up to seven years before clinical presentation is revolutionary.
“Together with other prodromal signs such as loss of the sense of smell, constipation, REM sleep behavior disorder, this early detection could open up new avenues for early interventions, allowing us to potentially alter the course of the disease or at least manage symptoms more effectively,” he continued.
“Interestingly, the method of detection is not invasive. OCT scans of the retina are quick, highly detailed, and noninvasive, providing valuable insights not just about eye health but broader health conditions, too,” he said.
However, Dr. Truong did state he had a few reservations about this study.
“First and foremost, while these findings are promising, it’s essential to understand how they will translate to real-world clinical settings,” he explained.
“The question would be the cost-effectiveness, accessibility, and the psychological aspect of prediction on healthy patients is also an issue. The study itself is not yet ready to predict if an individual will develop Parkinson’s definitively,” he said.
Getting regular eye exams is important
Medical News Today also spoke with Dr. Howard R. Krauss, a surgical neuro-ophthalmologist and director of Pacific Neuroscience Institute’s Eye, Ear & Skull Base Center at Providence Saint John’s Health Center in Santa Monica, California, who was not involved in the study. He also voiced concerns about the findings.
“Whenever a paper is published, the media picks it up as a breakthrough. The public picks it up as an indication that they can pick up their telephone, call their ophthalmologist, have an OCT done, and learn whether or not they’ll develop Parkinson’s disease, and that’s clearly not the case. An OCT will not tell you if you have, may have, or will have Parkinson’s disease,” he explained.
Dr. Krauss also said it’s important to note that other conditions can cause thinning of the ganglion cell layer and other retina layers that are not specific to Parkinson’s disease.
“Glaucoma, macular degeneration, retinal vascular disease, and a whole host of other things can cause thinning of the ganglion cell layer. In addition to, which was not touched on in this paper, even nearsightedness causes thinning of the ganglion cell layer, so it’s not a specific finding,” he pointed out.
Dr. Krauss said what’s more valuable is finding ophthalmic signs of Parkinson’s disease during a clinical examination.
“For example, patients with Parkinson’s disease have a higher incidence of dry eye, in part because they have a reduced blink rate,” he detailed.
“Patients with Parkinson’s disease have a higher incidence of difficulties with reading because even their eye movements are affected by Parkinson’s disease, and some will present with double vision. So careful clinical examination by an ophthalmologist or neuro-ophthalmologist can find early findings consistent with Parkinson’s disease,” he said.
“In my own practice, over the decades, I have not infrequently been the first practitioner to suggest to a patient that they may have Parkinson’s disease based on findings in their eye examination. So if nothing else, this [study] serves as a reminder that one should have [r]egular eye examinations because there is indeed a lot about the eye and about the examination findings of the eye that tell us about a variety of systemic diseases, including Parkinson’s disease.”
— Dr. Howard R. Krauss
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