(Anatomy of the Eye)
It is vitally important to how well we see.
It begins with the most obvious feature, the iris (the pigmented, or coloured, portion of the eye). The more pigmentation, the darker the colour. The less the pigment, the bluer the eyes will be.
In the center of this pigmentation is a “black hole”, called the pupil. This is the opening through which light travels into the eye. The pupil controls the amount of light that enters. It becomes smaller in bright light and larger in dim light. A normal eye will contract and dilate when light is taken away or shone directly into the eye. This is a standard test medical personnel will make to determine normal brain function.
What is not readily seen is a sparkling-clear, dome-shaped membrane that covers the front of the eye. This is the cornea. Clear vision is just as dependent on a clear cornea as it is on a clear lens. When a foreign body hits the eye, it seems to land on the cornea, whose rich supply of pain fibers makes you feel as if sandy particles were trapped under the eyelids.
The white portion of the eye is called the sclera. This surrounds the cornea and extends completely around the eye, giving it strength and substance.
A thin membrane called the conjunctiva, covers the white of the eye and lines the inside of the lids. This portion has tiny blood vessels that, with mild infection (conjunctivitis), allergy, or pollution, can become enlarged, causing the eye to look bloodshot.
Working together, the cornea, pupil, and the lens focus light onto the back of the eye, called the retina. This is comprised of a thin, membrane that lines the inside of the back of the eye.
The eye is about the size of a ping-pong ball and is an extension of the brain. It only gathers information for processing. Although most people think that the eyes do the “seeing”, eyes do not see. It is the brain that does.
The retina, which can be compared to the film in a camera, “takes” the picture and the brain “develops” it. The retina sends the picture to the brain by way of a thick nerve called the optic nerve in the back of the eye.
To view an illustration, the eye has an inner layer (retina) and an outer layer (sclera). The middle layer is called the choroid or uvea, which is the darkly pigmented portion, rich in blood vessels, and resembles the skin of a grape (the name uvea means “grapes”). The uvea forms the iris in the front of the eye and the choroid in the back of the eye. Most of the blood circulation that nourishes the eye travels in the choroid.
Two other parts of the eye form the fluid portion. The space between the iris and the cornea is called the anterior chamber. It is filled with aqueous solution which resembles spinal fluid. New aqueous fluid is constantly being formed to replace aqueous that filters out of the eye.
A blockage of this fluid results in an elevated pressure of the eye resulting in glaucoma. Most of the inside cavity of the eye is filled with the vitreous, a jellylike material that gives the eye substance and volume. Annoying black spots or “floaters” could be protein particles that float in the vitreous.
