Eyeshine

Eyeshine refers to a visible glow emitted by the eyes of many animals when they are illuminated by light, such as from a flashlight, vehicle headlights, or a camera flash. The glow occurs because light that enters the eye is reflected back out of the pupil by a reflective layer behind the retina, most commonly the tapetum lucidum. This anatomical feature boosts vision in low light by increasing the amount of light available to photoreceptors.

The presence and color of eyeshine vary among species. Colors can range from green and yellow to blue-green or red-tinted reflections, depending on the structure and pigment of the tapetum and surrounding tissues. Not all animals have a tapetum lucidum, and in those without it, the same strong eyeshine is not produced. The intensity of the glow depends on factors such as angle of illumination, distance, and the amount of reflective tissue.

Eyeshine is most commonly observed in nocturnal and crepuscular mammals, including cats, dogs, deer, and many other species. It can also occur in some other vertebrates with reflective retinal structures. In humans, a true tapetum lucidum is absent, so typical eyeshine is not seen; what is occasionally observed is light reflected from the retina or other ocular structures, which can be mistaken for eyeshine.

In field research and photography, eyeshine aids in nocturnal animal detection and identification, while in imaging it is important to distinguish it from the red-eye effect. See also tapetum lucidum and red-eye.