Depression may be seen in the eyes

If depression has a color, it might be gray - at least in the eyes of the depressed.

This is because a study published in the July issue of Biological Psychiatry found that depressed people seem to have more difficulty distinguishing contrast differences than other people.

Using a pattern electroretinogram, an electrocardiogram for the eyes, researchers compared the visual electrical activity of 40 healthy people with 40 people who had received diagnoses of major depressive disorder. Twenty of the depressed people were on medication and 20 were not; regardless of medication, all the depressed participants suffered from symptoms of major depression.

At the beginning of each test, researchers had subjects stare at a bland checkerboard image on a computer screen.

"It's almost a gray-on-gray checkerboard," said contributing author Ludger Tebartz van Elst, a psychiatry and psychotherapy professor at the University of Freiburg in Germany.

The checkerboard flickered 12 times per second at this muted setting. Then researchers steadily increased the image's contrast, morphing the dull checkerboard into a crisp black-and-white image. At each contrast setting, researchers recorded the electrical activity of the participants' retinas.

They found that increasing contrast correlated with increasing electrical activity in the retinas of the healthy people. The retinas of those with depression reacted far less to the changing image.

"The more depressed, the more severe the depression, the lower the contrast gain," Tebartz van Elst said. As indicated by the electrical activity of the cells of the eye, depressed participants had more trouble noticing the change from low contrast to high contrast.

"We were lucky to find such an accessible, measurable indicator," he said. "It's like a thermometer of the ... sickness in the center of the brain at the level of the eye."

Currently, mental health professionals don't have an objective test to determine if people are depressed, said Tebartz van Elst. To diagnose depression, he usually relies on what patients tell him and what he observes when patients describe their symptoms.

Although more research is needed, Tebartz van Elst and his colleagues have opened the possibility that there might be an "objective measure for the subjective state of depression."

"If this is the case," he said, "this might have consequences not only for research but also for clinical diagnostic procedures."