http://theboard.byu.edu/questions/41891/
I know Marguerite St. Just was anxious to avoid having someone call her out on her answer so she quoted Claudio. But Claudio's answer didn't make any sense to me.
I couldn't understand how the iris was supposed to have anything to do with it. Contrary to what Claudio says the light does not go through the iris. The iris is a muscle which controls the amount of light going through the pupil.It passes through the blood rich choroid and hits the retina. The retina reflects it back out through choroid and then through the iris. As such, the light from the flash, which the camera records as a picture, has now gone through a "red filter" twice, making it appear red. The camera records this, and boom! The devil eyes.
As to why this happens to you more than to your dark-eyed kin...that has to do with melanin. In humans, melanin is most notably located in the hair, skin, and eyes. It's melanin that is "the primary determinant of human skin color," as well as eye color. The more of it you have, the darker your eyes/skin are, because you absorb more light. Thus, brown irises, which have a greater amount of melanin, have a greater chance of absorbing the light that is being reflected off the retina through the choroid. Those irises lacking melanin (i.e., light-colored eyes) have no chance to absorb the reflected light, and thus the red eye effect is more prominent with them.
So, if light does not go through the iris, is it true that blue-eyed people tend to show more red eye? Turns out that that is generally true. This article explains it:
http://www.allaboutvision.com/resources ... -photo.htmAre Red Eyes in Pictures Caused by Eye Color?
No. The iris — colored portion of your eye — has little effect on how likely you are to have red eyes in photos.
It is actually the amount of melanin, located in the retinal pigment epithelium and the choroid of your eye, that controls how much of the light is reflected back out, and not the iris.
Melanin absorbs light, so the more melanin you have, the less red light you will reflect back at the camera. Fair-skinned and blue-eyed people tend to have less melanin and typically have red eyes in photos more often than those with dark skin and brown eyes.
see also http://en.wikipedia.org/wiki/Red-eye_effect
So, it may be a minor technicality, but I learned something.