The “red-eye effect” occurs when a camera captures light reflecting from the retina at the back of the subject’s eye when a flash is used at night and in dim lighting.
Light rays travel through the cornea and pupil of the eye to focus on the retina, a layer of light-detecting cells at the back of the eye. From here, the retina converts the light rays into electronic pulses that travel along the optic nerve to the brain to create visual images. In fact 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 the subjects 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. The 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) which gives the retina it’s normal red color.
There are several ways to reduce the “red-eye effect”.
1. Tell your subjects not to look directly at the camera which avoids the direct angle flash.
2. Make the room brighter. The darker the environment, the more dilated the subjects pupils become which increases the likelihood of red eye effect.
3. Turn on the anti-red-eye function on your camera. Most cameras and smart phones have this feature. This function emits shorts flashes of light in quick succession before the camera actually takes the picture, giving the subjects pupils time to constrict.
4. Make the flash and lens further apart if you have an external flash attachment.
If a family member or friend seems to always have just one eye that shows red or reflects the light, that could be a sign of an eye disorder and they should see their optometrist for a thorough eye exam.
Info from All About Vision, provided by Antone Optical