What causes red-eye effect in photographs? -Read

It all concerns the camera flash reflecting off the eye at a specific wavelength

Hyderabad: In a world, where selfie-clicking and posting them online is the happiest pass time, imagine a scenario when your best friend posts a picture of yours in which your eyes are blood-shot red and you have the crazy zombie look.

So, what makes eyes look red in photographs? The answer is simple; it all concerns the camera flash reflecting off the eye at a specific wavelength.

The eyes enable us to see the world around and that’s why it is one of the five senses to perceive the world.  Light comes into the eye through the cornea. The retina then perceives the light and its images are sent to the brain via the optic nerve. The pupil controls the amount of light that gets to the retina. If it’s a sunny day, the pupil constricts and allows a small amount of light in. During night-time, the pupil dilates and becomes quite large to allow as much light as possible. Sitting between the retina and the sclera (the white part of the eye) lays a layer of connective tissue called the Choroid, an extremely vascular area containing many blood vessels.

When the light from a camera flash goes off, the pupils do not have time to constrict, so a large amount of light is reflected off of the Fundusmelanine (the eye’s interior surface). Due to the large amount of blood in the Choroid, the light picked up by the camera lens appears red. The closer the flash is to the camera lens, the greater the chance the lens sees the reflected light. The darker the environment a person is in, and thus the wider their pupils are, the greater the chance of having blood-shot eyes.

Other factors for the red-eye effect are the amount of melanin behind the retina and the person’s age. The red-eye effect is stronger in light-skinned people with blue eyes than in dark-skinned people with brown eyes. Children also tend to get a red-eye effect more as a child’s pupil will dilate faster than adults in low-light situations.