What causes red eyes when you take a picture of someone?
There is a reflection of the flash off of the back of the retina - the blood
vessels in the retina make the red light seem predominant.
To prevent this, fancy new cameras have an anti-red-eye feature. The flash
strobes at low power for a second before the picture is actually taken. The light
causes the subject's pupils to constrict, so that when the picture is taken you don't
see much of this reflection.
Click here to return to the Biology Archives
Update: June 2012