As is the case with so many other maladies, the sooner that Parkinson's disease is definitively diagnosed, the better. With that in mind, scientists from the University of Southern California in Los Angeles now believe that it may be possible to detect the disease earlier than ever, via analysis of the patient's tears.

Led by Dr. Mark Lew, the researchers chose to study tears due to the fact that they contain proteins which are produced by the tear gland in response to nerve signals. Because Parkinson's affects nerve function outside of the brain, it was hypothesized that any changes in nerve function would thus result in changes to protein levels in the tears.

In order to test their theory, the scientists analyzed tear samples of 55 people with Parkinson's, along with samples from 27 people without the disease, but who were the same age and gender as the test subjects.

What they found was that the base version of a protein known as alpha-synuclein was lower in the Parkinson's patients' tears, while another version of the protein – oligomeric alpha-synuclein – was higher in that same group. Oligomeric alpha-synuclein is alpha-synuclein that has formed aggregates, which are implicated in nerve damage associated with Parkinson's disease.

Plans now call for research to be conducted on a larger test group, to see if the protein-level changes can be detected before other symptoms even begin to appear.

"Knowing that something as simple as tears could help neurologists differentiate between people who have Parkinson's disease and those who don't in a noninvasive manner is exciting," says Lew. "And because the Parkinson's disease process can begin years or decades before symptoms appear, a biological marker like this could be useful in diagnosing, or even treating, the disease earlier."