Credit: MaxPixel.

Patients in the advanced stage of Parkinson’s disease experience severe and debilitating symptoms, such as rigidity and bradykinesia. There is currently no cure for this terrible disease, but the earlier it’s caught, the better it can be kept under control by medication before the problems with movement become irreversible. This is why the latest research out of South Korea is so exciting — it suggests that in the future a simple eye test could diagnose Parkinson’s.

The study involved 49 volunteers. On average, they were age 69, and they had been diagnosed with Parkinson’s disease 2 years prior but were still unmedicated. They were compared to 54 age-matched healthy individuals.

Researchers performed a complete eye exam on each participant, along with eye scans that emit light waves to image each layer of the retina. Additionally, 28 patients with Parkinson’s disease had dopamine transporter positron emission tomography (PET) imaging to measure the density of dopamine-producing cells in their brains.

Parkinson’s disease (PD) appears after dopamine-producing neurons die, causing symptoms such as tremor, slowness, stiffness, and balance problems. High levels of glutamate, another neurotransmitter, also appear in PD as the body tries to compensate for the lack of dopamine. The cause of Parkinson’s is largely unknown but scientists are currently investigating the role that genetics, environmental factors, and the natural process of aging have on cell death and PD.

The current study’s results suggest that PD not only kills dopamine-producing neurons but also thins the retina — specifically, the two inner layers out of the retina’s five layers.

“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 of the Seoul Metropolitan Government – Seoul National University Boramae Medical Center in South Korea.

In individuals with PD, the innermost layer of the retina had an average thickness of 35 micrometers while this measured 37 micrometers for participants without PD. The researchers say that thinner retinas correspond with loss of brain cells that produce dopamine. Perhaps most importantly, the measurements also correspond with the severity of the disease. For instance, people with the most thinning of the retina (30 micrometers) also showed the most severe PD symptoms while patients with the thickest retina layer (47 micrometers) had the least severe PD symptoms.

“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.”

The findings appeared in the journal Neurology.