A new South Korean study finds that a thinning retina appears to correspond with a known sign of Parkinson’s disease — the loss of dopamine-producing brain cells.

Parkinson’s disease is a progressive nervous system disorder. Nerve cell damage in the brain leads to a drop in dopamine levels, which can lead to symptoms such as tremors, stiffness and a loss of balance.

“Our study is the first to show a link between the thinning of the retina and a known sign of the progression of the disease — the loss of brain cells that produce dopamine,” said study author Jee-Young Lee, M.D., Ph.D., of the Seoul Metropolitan Government – Seoul National University Boramae Medical Center in South Korea.

“We also found the thinner the retina, the greater the severity of disease. These discoveries may mean that neurologists may eventually be able to use a simple eye scan to detect Parkinson’s disease in its earliest stages, before problems with movement begin.”

The study involved 49 individuals (average age of 69) who had been diagnosed with Parkinson’s disease an average of two years earlier but had not yet started medication. They were compared to 54 age-matched people without the disease.

Researchers gave each participant a complete eye exam as well as high-resolution eye scans that use light waves to take pictures of each layer of the retina, the layer of light-sensitive nerve cells at the back of the eyeball. A total of 28 participants with Parkinson’s disease also had dopamine transporter positron emission tomography (PET) imaging to measure the density of dopamine-producing cells in the brain.

The results reveal that the Parkinson’s patients exhibited thinning of the retina, most notably within the two inner layers of the five layers of the retina. In those with the disease, the innermost layer of the retina in one section of the eye had an average thickness of 35 micrometers (μm) compared to an average thickness of 37 μm for those without the disease.

Importantly, this thinning of the retina corresponded with the loss of brain cells that produce dopamine. It also corresponded with the severity of disease. When disease disability is measured on a scale of one to five, the people with the most thinning of the retina, or thickness of less than 30 μm, had average scores of slightly over two, while those with the least thinning, or thickness of about 47 μm, had average scores of about 1.5.

“Larger studies are needed to confirm our findings and to determine just why retina thinning and the loss of dopamine-producing cells are linked,” said Lee. “If confirmed, retina scans may not only allow earlier treatment of Parkinson’s disease but more precise monitoring of treatments that could slow progression of the disease as well.”

There were a couple limitations to the study: The scans focused only on part of the retina, and the study was just a snapshot in time and did not follow participants over a long period.

The findings are published in the journal Neurology.

Source: American Academy of Neurology

Thinning of Retina May Signal Parkinson’s Disease