Depression is often referred to as “the blues.” New research suggests it should actually be called "the grays."

To someone who is depressed, the world can seem flat or dull. This was long thought to be purely psychological. It turns out, though, that depression may affect how the eyes function—altering visual perception in a way that actually makes the world look gray, reports the November 2010 issue of the Harvard Mental Health Letter.

In an intriguing study, researchers placed electrodes near volunteers’ eyes as they viewed a series of checkerboard patterns with varying degrees of black-and-white contrast. The electrodes recorded electrical responses in the retina, the part of the eye that reacts to different wavelengths of light and then transmits electrical signals along the optic nerve. The brain then interprets these electrical signals as color, shape, and contrast.

Volunteers with major depression were much less able to detect differences in black-and-white contrasts on the checkerboards than those who weren't depressed. The most severely depressed volunteers also registered the lowest levels of activity in the retina.

Dr. Michael Miller, editor in chief of the Harvard Mental Health Letter, notes that this study suggests that impaired contrast perception may explain why the world seems gray when people are depressed. Future research is necessary to replicate the findings, and to determine what other factors may contribute.

Read the full-length article: "How depression may alter visual perception"