Tapetum lucidum

This cat's tapetum lucidum makes its eyes flash yellow in a photograph

The tapetum lucidum (Latin: "bright carpet") or tapetum is a reflecting layer behind the retina of the eye; it serves to reflect light back to the retina, increasing the quantity of light caught by the retina. This improves vision in low light conditions but can cause the perceived image to be blurry from the interference of the reflected light. It is found in many animals, particularly nocturnal animals with good night vision, such as cats. It is responsible for the feline equivalent of the red-eye effect, causing cats' eyes in flash photographs to appear to be glowing in one of a wide variety of colours including blue, green, and yellow.

Bottlenose Dolphins also have a tapetum lucidum. Humans do not.

The tapetum works roughly on the interference principles of thin-film optics, as seen in other reflective tissues such as butterfly wings (see Blue Morpho). However, different species have different types of structured tissue that lead to different mechanisms of reflective interference. Known tapetum structures include:

• Retinal tapetum in teleosts, crocodiles, marsupials and fruit bats
• Choroidal guanine tapetum in elasmobranchii
• Choroidal tapetum cellulosum in carnivores, rodents and cetacea
• Choroidal tapetum fibrosum in cows, sheep, goats and horses

External links

Comparative morphology of the tapetum lucidum (http://www.blackwell-synergy.com/links/doi/10.1111/j.1463-5224.2004.00318.x/full/) (needs subscription)

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