Color-changing mood eyes?

Do you know someone who swears their eyes change color depending on their mood? Do they claim that this change is as dramatic and obvious as if their eyes were a mood ring?  The idea that people might have color-changing mood-eyes is rather fascinating. But is this even possible?

In the human animal, the iris (the colored part of your eye) gets its color from eumelanin (a type of melanin that is a black pigment) which is produced by melanocytes (the cells that make melanin). Different colors arise due to the variations among eumelanin produced by melanocytes, and the density of melanocytes in the iris. One reason eye color might change due to an individuals mood is if melanocyte production is affected by emotion.

There is no scientific evidence to indicate that among the other chemical changes that occur in the body and in the brain during different mood states, melanocyte activity is also affected. (Let’s also not forget that melanocytes are all over the body, not just in the eyes. So, if mood states did affect melanocyte activity, it would probably not be relegated only to the irises).

But Ziztur, you might say, I swear I saw someone’s eyes change at some point! You did not see a change in the actual color of the iris. There are two reasons why the iris might appear to change color: color perception, and dilation and constriction of the iris itself.

The iris is what causes the pupil to dilate and constrict (get bigger and smaller), using tiny muscles. So, when the iris changes shape, it may also appear to change color, much in the same way that a balloon seems to get lighter when you inflate it. The iris is more complex than the pure color of a balloon though, as different parts of the iris contain malanocyte variations. The difference in color isn’t very perceptible in uniformly colored eyes like my gray ones, but is more noticeable in people with hazel eyes, as they have more of a variation in color. Emotion does have an affect on pupil dilation/constriction, as does exposure to light, seeing an item of interest, alcohol, etc. It’s a function of the brainstem. There are receptors in the iris associated with the autonomic nervous system, and that causes pupils to dilate when someone is angry, exited, afraid, or in a heightened autonomic state.

Blood flow may also play some role in perceived eye color change. Much like when increased blood flow due to capillary dilation to the face will make a person’s skin appear redder (especially in light-skinned people), the same thing may be happening to your eyes and irises.

Check out the color perception illusions here. You will not believe your eyes, as the differences in perceived color are incredible. Our perception of color is strongly affected by the colors surrounding it – check out this link: Seeing is Believing!

Researchers have also found no link between personality traits and eye color.(Lester 1987, Rim 1983)

There are certain instances in which permanent change to the iris color does occur. This may be due to injury, the increased production of melanin following birth, exposure to the sun, certain eye treatments for glaucoma, etc. There is no scientific backing for color-changing mood eyes, but plenty of scientific backing for perceptual illusions.

Don’t believe me? Good. don’t take what someone says on the internet at face value. Do a Google Scholar or Scirus search for peer-reviewed journal articles on the subject. I did for several hours and found absolutely nothing. If you find something, please send it to me! Conversely, if you can only get the abstract, then send me the article reference and I will see if I can get it (with my magical graduate school powers) E-mail me: Ziztur@ziztur.com

References:

Lester, D., 1987. Eye color, ectomorphy and autonomic nervous system
balance. Personality and individual differences 8, 767–768.
Rim, Y., 1983. Eye-colour, ethnic origin or family size? Personality and
individual differences 4, 101–102.
Wiki entry on eye color
Wiki entry on pupils

More optical illusions and visual curiosities!