Why do we get Red eyes, blue eyes when we take pictures?

–Karthik Gurumurthy

“Red eye”occurs when a person looks directly at the camera when his or her picture is taken. If the flash is on the same axis as the visual axis of the camera, the reflection of the light off the blood vessels in the person’s retina will give an eerie, satanic “red eye” look. People with light colored eyes usually exhibit the worse red eye effect; those individuals with dark-colored eyes may have enough pigment in the back of their eyes to mask this so-called red reflex. Dogs, cats and almost all domestic animals have a special reflective layer in the back of the eye termed the tapetum, which enhances nocturnal vision. Light passes through the animal’s retina from outside of the eye and is then reflected back through the retina a second time from the reflective tapetal layer beneath the retina. This double simulation of the retina helps these species to see better than humans do in dim light situations. The color of this tapetal layer varies to some extent with an animal coat’s color.