What Causes Red Eye

No rocket science, just a simple explanation...

You may have noticed that red eye only appears in pictures taken using a flash. The reason for this is simply that the flash causes red eye.

Humans have a curved plate covering the back of their eyeballs called the retina. This is the part of the eye that actually detects the presence of light. When the flash on a camera fires, the bright, white light emitted by the bulb travels into the eye, and bounces off the retina back into the camera lens.

If that was the entire story though, we would call it 'white eye'. While the light is inside our eye, it travels through many tiny blood vessels that are present to keep the eye alive. This is how the light gets its red color.

Of course, it takes a very powerful light to travel through these blood vessels, and return with enough intensity to be visible. If you shine a torch in someone's eye, it does not appear red for example. It is only the powerful flash bulb that makes this effect so visible.

Below the situation is illustrated. The red line shows a ray of light from the camera flash, travelling into the eye and bouncing off a section of the retina at the back of the eye. It comes out at an angle almost identical to the one at which it entered, but will now be colored red because of the blood vessels it has travelled through.

Once you know that this is why red eye occurs however, it becomes a lot easier to think of ways to combat it. Find out how to avoid red eye right here.

Kind Regards

Robert Redwood Robert Redwood - Bio
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