Why look at the eye to understand Parkinson's?
Parkinson's disease comes from the gradual loss of brain cells that make dopamine, a chemical messenger. Tremor and stiffness often show up late, long after the damage has started. Brain scans that can show it are costly and hard to access.
The retina, at the back of the eye, grows from the same tissue as the brain. It also has dopamine cells. It can be imaged in cross section, layer by layer, with optical coherence tomography (OCT): a quick, no-contact scan that works a bit like an ultrasound, but with light.
How did researchers run the study?
The team used two large UK databases. The first, AlzEye, covers 154,830 patients aged 40 and older seen at Moorfields Eye Hospital in London. It was used to compare 700 people already living with Parkinson's with more than 105,000 people without it.
The second, UK Biobank, follows volunteers from an eye scan done between 2006 and 2010. Of 50,405 participants, 53 were later diagnosed with Parkinson's. Software automatically measured the thickness of three retinal layers on each OCT scan.
Two retinal layers were thinner
In people with Parkinson's, two layers were thinner, even after accounting for age, sex, ethnicity, diabetes, and high blood pressure: the ganglion cell layer (about 2.12 micrometers thinner) and the inner nuclear layer (about 0.99 micrometer thinner). The second layer is the hub of dopamine activity in the retina, and the authors describe this link as a new finding.
Among UK Biobank volunteers, a thinner retina in these same layers was linked to a higher chance of developing the disease. Diagnosis came 2,653 days, or about 7 years, after the eye scan on average. The link held even after removing people diagnosed within two years of their scan.
Key figures
- 154,830patients in the AlzEye database (London), including 700 with Parkinson's
- 50,405UK Biobank volunteers followed after an OCT eye scan
- 2,653 dayson average (about 7 years) between the eye scan and diagnosis, in 53 volunteers
- -2.12 µmthinner ganglion cell layer in people with Parkinson's
Living with Parkinson's: tracking your days with Mima
For now, this study does not change your care: no eye exam is used to screen for Parkinson's, and the retina is still a research topic.
If you live with Parkinson's or support someone who does, Mima helps you note how you feel day by day (tremor, sleep, fatigue) and turns it into a clear picture for your neurologist. You can also prepare a question like: "Should I share my eye exam results with my care team?"
What this could mean, down the road
The authors say these results point to a possible role for retinal imaging in identifying people at higher risk, alongside other signs. OCT is increasingly available, both in hospitals and in the community.
Today, an OCT scan is not used to screen for Parkinson's. If your eye doctor does one, it is to check the health of your eyes.
A link, not a test
The differences are tiny: about 2 thousandths of a millimeter for the most affected layer. The authors write that the practical value as an early marker for an individual is currently limited. The study also cannot say whether these changes help cause the disease or result from it.
Only 53 volunteers developed the disease, and diagnoses came from hospital records, not from an exam by a neurologist. UK Biobank volunteers were mostly White. Future studies will need to follow how the retina changes over time.
Frequently asked questions
Can an eye exam detect Parkinson's disease?
Not today. This study shows a link across large groups, but the differences are too small to work as a test for one person.
What is an OCT eye scan?
Optical coherence tomography (OCT) is a quick, no-contact scan that shows the retina in cross section, layer by layer. It is mainly used to monitor eye diseases.
How early do retinal changes show up before Parkinson's?
In UK Biobank, Parkinson's was diagnosed about 7 years on average after the eye scan where the retina was already slightly thinner.
Why is the retina linked to Parkinson's?
The retina grows from the same tissue as the brain and contains dopamine cells, and dopamine is what runs low in Parkinson's disease.
The original study
Wagner SK, Romero-Bascones D, Cortina-Borja M, et al. “Retinal Optical Coherence Tomography Features Associated With Incident and Prevalent Parkinson Disease” Neurology, August 21, 2023. DOI : 10.1212/WNL.0000000000207727
Read the full study in NeurologyThis article summarizes a scientific study and is not medical advice.