Dragon Anatomy Subjects - Theories of Dragon Eyes
By Dee Dreslough
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On Earth, there are three types of eyes that have evolved (that we know about...) There is one other type of eye structure found in dragons which are not found in other Earth species. Forwarding this fourth theory, the Opaline/Crystaline Eye Structure is the main purpose for this document.
The Simple Eye (Vertebrates and many Dragons):
The most common Earth eye seen in dragons is the simple eye. This is what humans, cats, dogs and other vertebrates use. It consists of a large fluid filled spheroid. The front end has a lens for focusing light at the back of the eye, which contains rods and or cones for receiving and interpreting signals of color, movement or intensity. To control the amount of light entering the eye, the simple eye uses an Iris, which can expand or contract to reflect more light in or out. This determines the 'color' of the eye -- in humans, it can be blue, brown, green, gold, grey or a wide variety of colors. In dragons, it can be an even greater variety, or change color depending on the breed of dragon. Many dragons have eyes that change color with mood. The iris protects a lens, which is used to focus the light into an image on the surface of the back of the eye (the retina).
This subject is well covered by many encyclopedias, so in the interest of space, I'll just give some good links for information:
The Compound Eye (Insects and some Dragons, as well as other alien species):
The third common Earth type eye is the compound eye. This eye is found in insects on Earth, in some dragons, and in some species referred to as dragons. This eye consists of hundreds of simple eyes (without lenses) or one faceted lens that sends information to the back of the eye in a pixelated form. They receive information about the world in a kind of mosaic pattern. This means that they're excellent at interpreting movement, but not terribly great at fine resolution unless the number of simple eyes making up the compound eye is in the thousands. For dragons and dragon-like species using this eye, they often do have simple eyes numbering in the thousands. These eyes also have good color reception -- often in the ultraviolet or infrared ranges as well as that of visible light. They reflect light, and may seem to glow, but they do not actually emit light.
Uniquely Draconic Eyes
The Opaline Eye (Found in dragons and some other related species):
Dragons are often drawn with large, cloudy GLOWING eyes without pupils. Now, this presents an interesting challenge to the Earth scientist to explain, because if an eye emits light, it technically can't see any light coming into the eye at that wavelength! Basically, it's like shining a flashlight in your own eye -- you blind yourself. However, the draconic Opaline eye emits light at certain wavelengths for a very important purpose; similar to a construct used in the Vertebrate eye found in many Earth species.
A nerve cell, like a rod or cone found in our eyes, is only triggered when the input it receives changes. Because of this, our own eyes are always wiggling imperceptably. If our eyes held perfectly still in our heads, when we were looking at a relatively still scene, it would just fade from view. We'd then be blind until something in the scene moved to retrigger our nerve cells to see it. To prevent this blinding, our eyes wiggle constantly to keep the input changing and the nerve cells firing.
The opaline eye structure lacks muscles to constantly jiggle the eye. It is always focused (not requiring a lens) because it receives light in a three dimensional plane. Different depths of the crystal core have different nerve receptors. Rather than focusing an image on a flat surface, like a human eye, the light penetrates to different depths in the transparent crystal core of the opaline eye. It's like seeing the world as a hologram. This allows the dragon to see color, form and movement more clearly than humans could even imagine.
The core of the eye is made up of long hexagonal or octagonal crystals, each coating a set of receptor nerves for color or changes in wavelenght of light. The crystals are fragile, and protected by the thick bone orbit of the dragon's scull, as well as a fluid layer and a clear scleral layer like the cornea of a human eye. The crystal structure and nerves are very sensitive, and wouldn't operate well if constantly moved by muscles. They don't require muscles to move the focus of the eye because of the way it receives light in 3D.
The clouded vitreous solution serves the same purpose as the Iris in a human eye; it helps block out too much light from striking the crystal receptors. The fluid dynamically responds to the amount of light striking the eye; in full sunlight, it is practially opaque, and in darkness, nearly transparent. It's a bit like those 'change color' sunglasses humans have.
So, instead of jiggling to keep retriggering the nerve cells in the eye, the eye has tiny light emitting cells that constantly flash to trigger the nerves when input from the outside doesn't trigger the nerves itself. The light is emitted at one color wavelength, making the cells around the light emitter sensitive to the wavelengths directly above and below the light emitter on the spectrum. For instance, if an eye flashes a tone of green, the cells around the emitter are then more receptive to blue and yellow.
Because of this, these eyes almost always change color with mood -- or, more accurately, with the proximity of the point of interest. Red colors are shorter wavelengths, and are used by this kind of eye to see immediate objects. A dragon's fury can make it literally 'short sighted', as this red light is best for use in close combat situations. It blocks out any distance views, and focuses completely on it's target.
Purple, with the longest wavelength, is good for taking in wide scenes. When a dragon is reflective or thinking deeply, this is the equivalent of kind of 'phasing out' or unfocusing your eyes to kind of take in the whole scene. Humans do this -- they focus on nothing, and see everything with a bit of a blur.
Wavelengths in between are best for regular viewing - blues, greens, yellows, oranges allow viewing of both close objects and objects far away within the crystaline matrix.
Different parts of the eye can flash with different colors at the same time to allow the dragon to take in various items. It's the same as us focusing on objects close to us, and then far away.
Because the crystaline structure is intensely light sensitive, dragons with this kind of eye can see in near total darkness. In fact, they can see in total darkness when their light emitters emit enough light to reflect off objects in the environment. This is like sonar in bats -- the dragon emits light to reflect off objects and be received by the crystal core in the same way a bat emits a sound to bounce off objects in the environment and be heard by the bat. But, because the light emitters aren't particularly strong, the dragon can only see close to itself in total darkness. Basically, it can't fly fast, but it can fly slowly (near hovering) or walk around and avoid striking objects close to it. It's like a human walking around with only a dim candle for light.
Simple Pigment Eye (not found in dragons):
The first common Earth eye is the pigment eye. This is an extremely primitive eye that essentially heats differently when struck by light, sending a signal down the nerve to the primitive brain of the animal that uses this kind of eye. Dragons, being highly evolved critters, don't use this kind of eye. This is used more by planaria, jellyfish and simpler creatures on Earth. I include it only in the interest of being complete.
and text (c) 1996-2008 Dee Dreslough unless otherwise noted.