Red eyes in photos

The appearance of red eyes in pictures, known as the "red-eye effect," occurs when a camera captures light reflecting from the retina at the back of your subject's eye when a flash is used at night and in dim lighting.

The eye works very similar to the way a camera does. Light enters the clear covering of the eye, like the glass of a camera lens, and the pupil controls the amount of light that travels through the eye, like a camera aperture. The retina captures the incoming light and sends a record of it to the brain, like camera film.

When a camera flash goes off, the pupils of your subject's eyes don't have time to constrict to reduce the amount of light entering their eyes. Therefore, a large burst of light reaches their retinas, reflects back, and is captured on film. Eyes look red in photos due to the rich blood supply of the choroid, a layer of connective tissue at the back of the eye that nourishes the retina and gives it its normal red color.

So as the photographer, tell your subjects to look slightly away from the lens, so their eyes won't catch the flash at a direct angle. This will reduce the likelihood of red eyes in pictures. Or just make the room brighter!