Sydney, Jan 27: A simple eye test can help diagnose inherited mental health conditions such as bipolar disorder or manic depression, according to new evidence.

Monash University neuroscientist Steven Miller led a national team of researchers to test the binocular rivalry rates of 348 sets of twins -- 128 of whom were identical.

The test measured the twins' binocular rivalry -- the 'switching' of their visual perception from one image to the next, when two dissimilar images were simultaneously presented, one to each eye.

Miller's study of twins showed that switching rates were very similar between each set of identical twins, yet were substantially less so for non-identical twins, suggesting a genetic contribution to an individual's switching rate.

"By studying such a large group of identical and non-identical twins we can determine the likelihood of genetics being responsible for certain biological traits," Miller said.

Miller said testing of binocular rivalry was important because it could be an indication of a person's mental health, based on his previous study of switching rates in patients with bipolar disorder.

"A person without bipolar disorder will make the switch between images every one to two seconds. However, a person with bipolar disorder takes three to four seconds, and up to 10 seconds, to switch between the images," Miller said.

"These results highlight the link between our genetic make-up and the manifestation of certain medical illnesses like bipolar disorder.”

The next stage of the research would test the reliability of using the switch rate to assist in the diagnosis of bipolar disorder or a predisposition to bipolar disorder, said a university release.

"There is a lot of work ahead to find biological markers that could be used to screen for a person's susceptibility to a particular inherited condition, paving the way for more accurate clinical diagnoses and more effective genetic studies," Miller said.

The findings were published in the Proceedings of the National Academy of Sciences. --IANS