Uses

The tapetum lucidum enables an animal with it to see in dimmer light than the animal would otherwise be able to. This is of use to the animal, but it is of use also to humans. Human uses include scanning for reflected eyeshine to detect and identify the species of animals in the dark, and deploying trained search dogs and search horses at night. Historically, its function was regarded as simply to increase the light intensity of an image on the retina.^[10]

Using eyeshine to identify animals in the dark employs not only its color but also several other features. The color corresponds approximately to the type of tapetum lucidum, with some variation between species. Other features include the distance between pupils relative to their size; the height above ground; the manner of blinking (if any); and the movement of the eyeshine (bobbing, weaving, hopping, leaping, climbing, flying).

Manufactured retroreflectors modeled after a tapetum lucidum are described in numerous patents and today have many uses. The earliest patent, first used in"Catseye" brand raised pavement markers, was inspired by the tapetum lucidum of a cat's eye. A more recent use of retroreflectors, helping to provide secure communications between two stations in line of sight, is modeled after the combination of tapetum lucidum and bioluminescent "flashlight" in flashlight fish of the families Anomalopidae and Stomiidae (see Retroreflector). Some of these fish have been shown^[11] to use eyeshine both to detect and to communicate with other flashlight fish.

Pathology

In dogs, certain drugs are known to disturb the precise organization of the crystals of the tapetum lucidum, thus compromise the dog's ability to see in low light. These drugs include ethambutol, macrolide antibiotics, dithizone, antimalarial compounds, some receptor H(sub)2-antagonists, and cardiovascular agents. The disturbance "is attributed to the chelating action which removes zinc from the tapetal cells."^[12]

Gallery

Cat with both red and white eyeshine,heterochromia.

Cat with red eyeshine.

Cat with eyeshine.

Flashlight fish(Photostomia, Stomiidae).