tapetum lucidum


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tapetum

 [tah-pe´tum] (L.)
1. a covering structure or layer of cells.
2. a stratum in the human brain composed of fibers from the body and splenium of the corpus callosum sweeping around the lateral ventricle.
tapetum lu´cidum the iridescent epithelium of the choroid of animals that gives their eyes the property of shining in the dark.

tapetum lucidum

A layer of tissue in the choroid of the eye between the vascular and capillary layers in some animals, but not in humans. This membrane reflects light shined into the animal's eyes. It produces a green reflection, readily seen in cats.
Synonym: tapetum choroideae
See also: tapetum

tapetum lucidum 

A reflecting pigment layer lying behind the visual receptors of the retina of certain mammals (e.g. cats, dogs), birds and fish, which gives a shining appearance to the eyes when illuminated in the dark. The tapetum is located either in the pigment epithelium or in the choroid and covers either the whole fundus or more often only the upper and back portion. The role of the tapetum lucidum is to increase the probability of visual stimulation of the photoreceptors by reflecting light back after having already traversed them once, thus aiding vision in dim illumination. In some species the tapetum consists of guanine crystals.
References in periodicals archive ?
Their sight is quite good, especially in dim light, thanks to a reflecting structure (tapetum lucidum) behind the retina, which is what makes their appearance so bloodcurdling.
This is due to the presence of a specialized reflecting layer behind the retina called the tapetum lucidum. It is an important structure in the eye of many nocturnal species, and is particularly well-developed in cats.
The relatively large size of her eyes, the dense population of rods in her retina, and the tapetum lucidum layer behind the retina are all adaptations aimed at maximizing night vision.
At one month the dog showed dull, greyish brown coloration of entire fundus, the optic nerve head was small and flat due to immature myelination with no signs of tapetum lucidum and no discernible difference between tapetal and nontapetal fundus.
Thanks to the tapetum lucidum, a cat's sensitivity to light is thought to be about six times greater than that of a human's.