Despite the fact that Parkinson’s is currently the second most common neurodegenerative disease worldwide, scientists are still very much at square one in terms of detecting and treating the condition. However, researchers believe they may now be able to diagnose the disease simply by looking at the cells in a patient’s retina.

Though this new technique has so far only been trialed in rats, the authors of a study that appeared this week in the journal Acta Neuropathologica Communications believe that their results could represent a major milestone in the battle against Parkinson’s.

The disease occurs as the dopamine neurons in a brain region called the substantia nigra undergo apoptosis, or cell death. However, sufferers normally don’t become aware until they begin to experience symptoms, which typically appear once around 70 percent of these neurons have died, and there is currently no way of detecting the disease prior to this advanced stage.

Researchers induced Parkinson’s in mice by injecting them on a daily basis with a neurotoxin called rotenone, which induces apoptosis by causing the mitochondria in brain cells to malfunction. Because the retina is an extension of the central nervous system, the study authors decided to investigate how neurons in the eye called retinal ganglion cells (RGCs) were affected by this experiment.

^{Parkinson's disease is caused by apoptosis of dopamine neurons in the substantia nigra. ktsdesign/Shutterstock}

They discovered that, after around 20 days of injections, they were able to see signs of Parkinson’s in the retina, as large numbers of RGCs began to undergo apoptosis. However, neurons in the substantia nigra did not become affected until around 60 days into the trial. As such, the researchers suggest that elevated levels of RGC apoptosis could provide an early indication of Parkinson’s disease, and may help to diagnose the condition long before symptoms appear.

As with all illnesses, early diagnosis is essential for treatment, so the team decided to investigate whether or not Parkinson’s could be halted in rats with high levels of RGC apoptosis. To do this, they injected the rodents with a substance called rosiglitazone, which promotes the formation and function of mitochondria and reduces inflammation.

This resulted in lower levels of apoptosis in the retina following at 20 days, as well as reduced apoptosis in the substantia nigra after 60 days. In other words, early treatment with rosiglitazone was able to stave off Parkinson’s disease.

Study co-author Francesca Cordeiro told the BBC that this research represents a "potentially revolutionary breakthrough in the early diagnosis and treatment of one of the world's most debilitating diseases.”