Why does red eye happen

It is extremely irritating, and fascinating at the same time to see a photograph with a person having bloody red eyes. Red-eye effect is a nemesis of all photographers, whether professionals or hobbyists. Most frequently, red eye appears in photographs clicked at night time or in dim light. The image of a cat or fox with diamond like shining eyes comes to mind upon seeing the red eye effect in a photograph. Nocturnal animals like these have a compound called guanine in the epithelium (or the retina) of the eye. In plain language, this makes the retina behave like a mirror. It reflects all the incident light. Scientifically, this is known as the tapetum lucidum layer. This is precisely why we see the eyes of these creatures glitter and glaze like a diamond when a torch is flashed at them in the night.

The case of red eye in humans is chemically different, but logically same. Prodigious reflection of camera flash light is the reason behind the observation of the red-eye effect in photographs taken in dim light. Though there is no tapetum lucidum layer, but the flash of a camera is so bright that it makes the retina reflect a good part of the light. The red shade of the reflection is a very interesting observation, and it occurs because of the reflection of the shade of the blood vessels in the eye!

Thankfully, the red-eye monster effect has lived enough already. Leading camera manufacturers make it a point to include red-eye reduction techniques in their products. The camera issues a primary flash just moments before the image is clicked. This is in order to make the pupil contract. The second flash is the ne that actually accompanies the picture click. One could always click images in well lit conditions, but that does not solve the problem of red-eye in night time images. Instead, one could always try to place the flash intelligently, so that the reflections from the retina do not attack the camera lens face first. Letting the camera flash glance off from obstacles to illuminate the target would also serve the purpose of red eye reduction.