Eye Shine, Why and How
By Craig Heinselman, 1999
Another interesting article on 'eye-shine' in spelunkers and feral children
can be read by clicking on this link:
Before an understanding of the cause and reason for the "eye shine" condition, an overview of the function and anatomy of the eye is needed. For the sake of simplicity, the discussion at hand will deal with mammalian eye make up, as although other animal groups do have a similar anatomy there are some differences. Even in mammals there are slight differences in the eye makeup, many on a chemical or cellular level. Chief among these differences is the ability to see color and the ability to see in low light. To understand the differences it is important to understand how the human eye works and from that a derivative can be made to other mammalian species.
The eye itself is composed of various components. The wall of the eye is made up of three different areas, the sclera, the cornea and the canals of Schlemm. Each has a different purpose. The sclera is the white membrane that keeps the eye its shape, it in turn is connected to a series of muscles that allow for the movement of the eye. These muscles being the medial rectus, inferior rectus, lateral rectus, inferior oblique, superior oblique and superior rectus. The cornea is the component at the front of the eye that is usually colorless and transparent, and it is through this that light waves pass. The canals of Schlemm offer a series of small sinuses to drain fluid from behind the cornea.
The middle layer of the eye is made up as well of various components, known as the uvea when spoken of as a group. Within this collective are the components of the uvea, the choroid, ciliary body and the iris. The ciliary body is made up of a muscle that aids in the function of the lens of the eye. The choroid acts as a blood supplier to other areas of the eye as well as preventing the reflection of light inside the eye with the help of pigmented granules. The iris in turn is attached to the ciliary body and contains the pupil. The pupil is but an opening in the eye itself that allows for light to enter the eye, and this light is controlled by the musculature of the iris. The iris is also the portion of the eye that is colored. This coloration is what gives us blue eyes, grey eyes and every other shade imaginable due to pigmentation. The deciding factor of eye coloration then relies on the individuals genetic makeup, this affects the two layers of the iris that create the coloration. The rear layer contains a blue pigment, while the front layer contains either no pigmentation of black pigmentation, called melanin. Depending on the level of melanin the eye color varies. If no melanin is present then the eyes are blue. If no pigmentation appears in either layer, than an albino condition of pink is present.
The innermost area of the eye is made of the retina. It is made of very specialized cells called receptor cells. These receptor cells come in two different forms, rods and cones. The fibers of these receptor cells form further back in the eye as the optic nerve that is crucial to the brains recognition of an image. The receptor cells each serve a specialized purpose in the area of sight. Rods are cylindrical in nature. Within the rod is a portion that contains a photosensitive chemical known as rhodopsin that aids in the filtering of low level lights. The cones are more conical in shape and are crucial for color recognition and intense light filtration. There are currently three forms of cones known, each unique due to a specialized photochemical pigment, these being erythrolabe, chlorolabe and cyanolabe. When light passes through the components of the eye, these rod and cone photoreceptors are stimulated and the information is relayed to the brain to form the image seen.
Now, to understand how the eye recognizes light and hence images, and to lead to why "eye shine" occurs, the physics of vision need to be looked at. Light is foremost a form of energy, radiant energy, As light travels from one source to another in can be refracted, that is bent. The refraction bends the light at a different angle. This refraction is important in the ability to see, as the curvature of the eye is such that a refraction of the light allows the light to be aimed into the retina, although some light will be lost in the process. In doing so the image seen is inverted and compacted, similar to what occurs when a picture is reflected in a mirror. These properties of light refraction apply both in bright light, like daytime, as well as dark light, like nighttime, as well as intermediate lighting such as the conditions at dawn and dusk.
In the typical eye, that has no added component than stated prior, an image and image recognition is lessened as light levels drop. Try walking into a room with no lights on from a room with all the lights on. For a short time everything will be dark and out of focus. This is called nigh-blindness and is caused by the eye not getting enough light. However, in a short spell (though in some people it does not due to vitamin deficiencies) limited image recognition will return, a process called dark adaptation. Within the photoreceptor called the rod, the chemical rhodopsin is the cause of dark adaptation. In bright light this chemical is damaged, but when the light is lowered the chemical reforms. Vitamin A allows for this to occur, and if this vitamin is diminished the return of vision in the dark is slower. The opposite occurs when going from a dark room to a lit one.
Now, in a species that lives a nocturnal existence or partial nocturnal existence the ability to recognize images as prey, predator and safety is essential. To allow for more light, certain species have adapted another component in the eye, it is located on the retina and is called the tapetum lucidum. This tapetum essentially allows for a doubling of the light. With the aid of a white mirror like substance called guanine, light passing through the retina is bounced back, allowing for two passes of the light. This bounce back of the tapetum lucidum is what appears as the "eye shine" in these animal species.
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. Even humans, who do not have this tapetum, do possess a limited "eye shine" that can be seen in red eye images in some photographs.
Now the question of whether or not such a creature as Bigfoot, if it does in fact exist, could see in color comes up at times as well. The problem here is that color recognition comes down to chemical properties in the eye as well as the presence of the photoreceptor cones. Additionally all mammals that posses color vision have a small indent on the retina called the fovea in which these cones are organized.
As was mentioned previously the cones are made of three distinctively different types of pigments, erythrolabe, chlorolabe and cyanolabe. Each it has been thought correlates to a color blue, green or red. These pigments react through chemical functions and create the color vision people see. The lack or inhibition of one or more of these pigmentation cones causes the various forms of color blindness. The strength of the light also plays a part in the color recognition, for example a light wavelength of 5000 to 5500 angstroms generates a green color, while one of 6750 to 7000 creates the red color. Factored in as well are the elements of hue, brightness and saturation that enhance or diminish the intensity of color depending on the viewing conditions and distances.
The color vision ability can be drawn to one thing, if a fovea is present than the likelihood of color vision to some extent is also present. This is not a hard and fast rule, but a good guide. For example the great apes posses a fovea, and in al likelihood have a form of color vision, while the douroucouli (Aotus trivirgatus) or the night monkey from South America does not have a fovea (or any cones for that matter) and so cannot posses color vision.
That is the crucial point. Color vision is much more specialized for a daytime existence, for at night the ability to see color is minimized due to insufficient light. To adapt to the insufficient light some species have the tapetum lucidum to allow for enhancement of the light. Despite this adaptation, many of these species also adapt enhanced hearing and smell as well as varied vision (like enlarged eyes and varied positions of the eyes on the head).
As for a connection to Hominology subjects, at this time, no steadfast attribute can be applied. 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. However, the possibility of color vision is more likely to occur. If humans and great apes possess color vision, to some extent, but do not posses a tapetum lucidum, and it is extracted that Bigfoot is a type of primate akin to a great ape or human, then the correlation to these primates can be loosely made.
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.
Copyright 1999 Craig Heinselman, Cryptozoologist
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