Tapetum lucidum

The tapetum lucidum is a reflective layer located at the back of the eye in many animal species, which helps improve night vision. It reflects light so that it crosses the retina a second time, increasing the amount of light captured by photoreceptors and improving vision in low-light conditions.

Depending on their anatomical specificities, which vary between species, tapetum lucidum are classified into 4 categories:

• Retinal tapetum, part of the retinal pigmented epithelium (Crocodiles, marsupials, bats, etc.).

• Choroidal guainine tapetum, located behind the retina, reflecting light through palisade-like cells containing flattened hexagonal guanine crystals (Sharks, rays, etc.).

• Choroidal tapetum cellulosum, composed of layers of cells containing highly reflective crystals of varying composition and shape (Primates, carnivores, rodents, cetaceans...).

• Choroidal tapetum fibrosum, formed by an arrangement of reflective extracellular fibers. (Cattle, equines, sheep, goats...)

This tissue is the reason for the brilliant appearance of the eyes of certain domestic animals. Humans, like other diurnal animals, lack tapetum lucidum.