This Is What Causes Red-Eye in Photos—and How You Can Stop It

Nothing sabotages the perfect shot more than a disconcerting pair of piercing red eyeballs.

camera-lensdenniro/ShutterstockIt happens all too often: you take a group photo with your friends, and while they look like they’re having a complete blast, you emerge looking like evil incarnate in the form of a red-eyed zombie.

The appearance of red eyes in pictures, otherwise deemed as the “red-eye effect,” may seem rather complex, but the science behind it is actually pretty simple. Basically, you can attribute this annoying aesthetic nuisance to the human eye.

Think of your eyeball as a high-quality camera with more advanced megapixels than any camera invented to this day. (Many optometrists reference the human eye as such due to their many similarities—here’s what else your eye doctor wants you to know about your eyes.) Just as light enters the lens of a camera, light enters the eye through the cornea and pupil to focus on the retina. In a camera, the computer in the camera will then take the grid of electrical charges and convert them into millions of tiny squares—or pixels. In the eye, however, the retina converts the light rays into electronic pulses that travel along the optic nerve to the brain and formulate a visual representation.

Ultimately, this red glare happens because the camera’s flash and the human’s flash coincide. The camera captures light reflecting from the back parts of your eye, specifically when the flash is used at night or in dim lighting. In dark environments, the pupil dilates and becomes larger to allow as much light in as possible. According to All About Vision, when the flash goes off, the pupils of your eyes don’t actually have enough time to constrict to reduce the amount of sudden light entering them. Consequently, a huge burst of light reaches the fundus (the interior surface of the eye) and bounces back, which is then captured on film.

As for the color, this light will appear red due to the rich blood supply of the choroid, a layer of connective tissue between the retina and sclera (the white part of the eye) that nourishes the retina and provides it oxygen.

The darker the environment a person is in when the image is captured, the wider their pupils are and the greater chance they have of falling victim to red eyes. Since children’s eyes will dilate at a different pace than adults, this also explains why kids tend to get this effect more easily than their parents.

That doesn’t mean you’re doomed to vampiric eyes whenever you’re out at night; there are ways to counteract the effect. While the obvious solution would be to stand in a better-lit setting when a photograph is being shot, another effective technique is to constrict the pupils just before the picture is taken. That’s the way those cameras with red-eye reduction settings work; they utilize a two-flash system in which an initial flash causes the pupil to constrict, and the second flash (that actually takes the picture) comes moments later. (Check out these 10 easy ways to look better in photos.)

You can also try to avoid looking directly at the flash when the photo is shot (fabricated candid photos anyone?) or moving the flash away from the lens if you have an SLR camera. These techniques will increase the angle at which the light enters the eye, thus decreasing the likelihood of it reflecting back to the lens.

Another clever (and straightforward) method? Don’t be drunk! All About Vision shares that people under the influence of alcohol have slower reaction times, which will also affect the response time of your eyes. Because the pupils don’t close fast enough, red-eye will happen far more often when you’re intoxicated. (If that’s easier said than done, here are 17 tips to help you cut back on alcohol).

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Hana Hong
Hana Hong is a journalist/storyteller who writes for Reader's Digest, InStyle, CollegeFashionista, Her Campus, and The Fashion Network, among other publications. She hails from the midwest, where she graduated from the University of Illinois with a BA in News-Editorial Journalism, but has a passion for the East Coast.