The thinning of retina -- the lining of nerve cells in the back of the eye -- could be linked to Parkinson's disease, a finding that can boost diagnoses to detect the disease in its earliest stages, researchers have found.According to the study, the thinning of the retina is linked to the loss of brain cells that produce dopamine, a substance that helps control movement -- a hallmark of the Parkinson's disease that impairs motor ability."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 Jee-Young Lee, from the Seoul National University 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," Lee added.The study, published in the journal Neurology, involved 49 people with an average age of 69 years who were diagnosed with Parkinson's disease two years earlier but who had not yet started medication. They were compared to 54 people without the disease who were matched for age.The team evaluated each participant with a complete eye exam, high-resolution eye scans as well as PET scan and found retina thinning, most notably in the two inner layers of the five layers of the retina, in those with Parkinson's disease.In addition, the thinning of the retina corresponded with the loss of brain cells that produce dopamine and the severity of the disease.If confirmed in larger studies, "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", Lee said.