Five Fascinating Facts Behind the Phenomenon of Red Eyes

Our exploration begins with the scientific explanation for red eyes. In fact, it boils down to the reddish hues being a result of light reflecting off the blood vessels at the back of the eye. This happens when we take a picture with the flash on, the light enters the eye, reaches the back, and is reflected out again, resulting in glowing red eyes.

A fascinating detail to note is that within the flash's milliseconds-long duration, our pupils do not get sufficient time to constrict. Most mammals possess a layer of tissue, the tapetum lucidum, behind the retina that aids night vision by reflecting light back through the retina, increasing the light available to photoreceptors, but humans lack this feature.

The red-eye effect can be significantly pronounced in individuals who have a lighter eye color. The reason being, people with lighter eyes - blue, green, or hazel, have less pigmentation in multiple layers of the eye than those with brown eyes. With less pigmentation, the eye is less able to absorb flashbulb light, leading to a substantial red-eye effect.

Red Eyes: A Medical Sign

Moving on, it's worth noting that while red eyes in photographs are often harmless, having red eyes in person can signal a health issue. Allergies, dry air, sun exposure, dust, foreign bodies, infections, and cryings are common causes of red eye. More seriously, diseases like glaucoma or uveitis can also result in red eyes.

Glaucoma is the name for a group of eye conditions in which the optic nerve becomes damaged, often due to an associated increase in fluid pressure in the eye. In contrast, uveitis is the inflammation of the uvea, the pigmented layer that lies between the retina and the outer fibrous layer composed of the sclera and cornea.