Tapetum lucidum

The tapetum lucidum /təˈpiːtəm/ (Latin: "bright tapestry; coverlet", plural tapeta lucida) is a layer of tissue in the eye of many vertebrates. Lying immediately behind the retina, it reflects visible light back through the retina, increasing the light available to the photoreceptors, though blurring the initial image of the light on focus. The tapetum lucidum contributes to the superior night vision of some animals. Many of these animals are nocturnal, especially carnivores that hunt their prey at night, while others are deep sea animals.

Similar adaptations occur in some species of spiders, although these are not the result of a tapetum lucidum. Most primates, including humans, lack a tapetum lucidum, and compensate for this by perceptive recognition methods.

Eyeshine is a visible effect of the tapetum lucidum. When light shines into the eye of an animal having a tapetum lucidum, the pupil appears to glow. Eyeshine can be seen in many animals, in nature and in flash photographs. In low light, a hand-held flashlight is sufficient to produce eyeshine that is highly visible to humans (despite our inferior night vision); this technique, spotlighting, is used by naturalists and hunters to search for animals at night. Eyeshine occurs in a wide variety of colors including white, blue, green, yellow, pink and red. However, since eyeshine is a type of iridescence, the color varies with the angle at which it is seen and the minerals which make up the reflective tapetum-lucidum crystals.

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