The eyes of cats and other animals that are active after dark are equipped with a special reflective layer of cells-the tapetum lucidum-which lies behind the retina. This layer reflects light rays that are not caught by the eye's photosensitive cells and thus have no immediate effect on the retina. As a result, the light is not immediately lost, but has a second chance to stimulate the eye's photosensitive cells, thereby considerably increasing the overall amount of light received. This is why cats can see so well in the dark. The tapertum luciduam is also the reason why cat's eyes sometimes seem to glow so eerily at night. The glow is a result of light rays passing back through the retina after being reflected in the light-sensitive cells sot hat it leaves the eyes and can be seen by an observer.
Rathnavath Ravinaik
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