Eyeshine is a visible effect of the tapetum lucidum. When a light is shone into the eye of an animal having a tapetum lucidum, the pupill appears to glow. Eyeshine can be seen in many animals, in nature and inflash photographs. In low light, a hand-held flashlight is sufficient to produce eyeshine that is highly visible to humans (despite our inferiornight vision); this technique, spotlighting, is used by naturalists and hunters to search for animals at night. Eyeshine occurs in a wide variety of colors including white, blue, green, yellow, pink and red. However, because eyeshine is a form of iridescence, the color varies slightly with the angle at which it is seen and the color of the source light.
White eyeshine occurs in many fish, especially walleye; blue eyeshine occurs in many mammals such as horses; yellow eyeshine occurs in mammals such as cats, dogs, and raccoons; and red eyeshine occurs in rodents, opossums and birds. The human eye has no tapetum lucidum, hence no eyeshine.
The eye contains several photostable pigments that all absorb in the short wavelength region, and hence contribute somewhat to the red eye effect. The lens cuts off deep blue and violet light, below 430 nm (depending on age), macular pigment absorbs between 400 and 500 nm, but this pigment is located exclusively in the tiny fovea. Melanin, located in the retinal pigment epithelium (RPE) and the choroid, shows a gradually increasing absorption towards the short wavelengths. But blood is the main determinant of the red color, because it is completely transparent at long wavelengths and abruptly starts absorbing at 600 nm. The amount of red light emerging from the pupil depends on the amount of melanin in the layers behind the retina. This amount varies strongly between individuals. Light skinned people with blue eyes have relatively low melanin in the fundus and thus show a much stronger red-eye effect than dark skinned people with brown eyes. The same holds for animals. The color of the iris itself is of virtually no importance for the red-eye effect. This is obvious because the red-eye effect works best when photographing dark adapted subjects, hence with fully dilated pupils. Photographs taken with infra-red light through night vision devices always show very bright pupils because, in the dark, the pupils are fully dilated and the infra-red light is not absorbed by any ocular pigment.
White eyeshine occurs in many fish, especially walleye; blue eyeshine occurs in many mammals such as horses; yellow eyeshine occurs in mammals such as cats, dogs, and raccoons; and red eyeshine occurs in rodents, opossums and birds. The human eye has no tapetum lucidum, hence no eyeshine.
The eye contains several photostable pigments that all absorb in the short wavelength region, and hence contribute somewhat to the red eye effect. The lens cuts off deep blue and violet light, below 430 nm (depending on age), macular pigment absorbs between 400 and 500 nm, but this pigment is located exclusively in the tiny fovea. Melanin, located in the retinal pigment epithelium (RPE) and the choroid, shows a gradually increasing absorption towards the short wavelengths. But blood is the main determinant of the red color, because it is completely transparent at long wavelengths and abruptly starts absorbing at 600 nm. The amount of red light emerging from the pupil depends on the amount of melanin in the layers behind the retina. This amount varies strongly between individuals. Light skinned people with blue eyes have relatively low melanin in the fundus and thus show a much stronger red-eye effect than dark skinned people with brown eyes. The same holds for animals. The color of the iris itself is of virtually no importance for the red-eye effect. This is obvious because the red-eye effect works best when photographing dark adapted subjects, hence with fully dilated pupils. Photographs taken with infra-red light through night vision devices always show very bright pupils because, in the dark, the pupils are fully dilated and the infra-red light is not absorbed by any ocular pigment.
Do Bigfoot's Eyes Shine?
In primates the prosimians (primitive primates such as the lemur and aye-aye) exhibit such a feature as the tapetum lucidum. While the great apes do not. Likewise many other animal species in far ranging groups show this characteristic, to most it will be most familiar in a household pet like the cat.
It can be fairly safe to say that if Bigfoot exists it is a form of primate (this includes the possibility of a relic humanoid), and to acquire this tapetum would make it an even more amazing discovery indeed. The ultimate answer though as to what kind of vision these creatures may have cannot be described as of yet. A specimen would be needed, and to identify the vision capabilities it would have to be a relatively new specimen with the eyes intact, as the information needed cannot be preserved in a skull, only on the living tissue.
In primates the prosimians (primitive primates such as the lemur and aye-aye) exhibit such a feature as the tapetum lucidum. While the great apes do not. Likewise many other animal species in far ranging groups show this characteristic, to most it will be most familiar in a household pet like the cat.
It can be fairly safe to say that if Bigfoot exists it is a form of primate (this includes the possibility of a relic humanoid), and to acquire this tapetum would make it an even more amazing discovery indeed. The ultimate answer though as to what kind of vision these creatures may have cannot be described as of yet. A specimen would be needed, and to identify the vision capabilities it would have to be a relatively new specimen with the eyes intact, as the information needed cannot be preserved in a skull, only on the living tissue.
