The phenomenon of 'eye-shine' is seen in a variety of animal species, and is generally thought to be related to the presence of an intraocular reflecting structure, the tapetum lucidum. The tapetum lucidum is a biologic reflector system that is a common feature in the eyes of vertebrates. It normally functions to provide the light-sensitive retinal cells with a second opportunity for photon-photoreceptor stimulation, thereby enhancing visual sensitivity at low light levels. The tapetum lucidum is presented here according to a classification based on the location, as well as the composition, of this reflective layer. Finally, the physical and chemical properties, as well as the origins of the different tapeta lucida, are discussed and compared.
The anatomic and biochemical aspects of the tapetum lucidum in various vertebrates are examined. Morphologic observations were made from paraffin and plastic embedded specimens. Specimens were treated with traditional stains and observed by light and transmission electron microscopy.
Some species (primates, squirrels, birds, red kangaroo and pig) do not have this structure and they usually are diurnal animals. In vertebrates, the tapetum lucidum exhibits diverse structure, organization and composition. Therefore, the retinal tapetum (teleosts, crocodilians, marsupials, fruit bat), the choroidal guanine tapetum (elasmobranchs), the choroidal tapetum cellulosum (carnivores, rodents, cetacea), and the choroidal tapetum fibrosum (cow, sheep, goat, horse) are described.
The tapetum lucidum represents a remarkable example of neural cell and tissue specialization as an adaptation to a dim light environment and, despite these differences, all tapetal variants act to increase retinal sensitivity by reflecting light back through the photoreceptor layer. These variations regarding both its location and structure, as well as the choice of reflective material, may represent selective visual adaptations associated with their feeding behavior, in response to the use of specific wavelengths and amount of reflectance required.
Eyes that glow in the pitch-black night make for many a scary tale. But why do some animals' eyes glow at night?
"A lot of the animals we see, especially the ones that go out at night, have a special, reflective surface right behind their retinas," says Dr. Cynthia Powell, a veterinary ophthalmologist at Colorado State University. That light-reflecting surface, called the tapetum lucidum, helps animals see better in the dark. So perhaps what we are seeing with Sasquatch eye shine is a larger reflection due to the animals larger skull and occipital region which allows for a larger light reflection.
Eye shine is seen quite at night, what have you seen? Anything peculiar? Let us know in the comments below or email us. We'd love to hear from you.
By Chuck Geveshausen
Founder, Sasquatch Syndicate Inc.