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One Miraculous Organ
By Frances Maguire Paist, Staff Writer

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Perhaps the well-known song expresses it best. “Let’s start at the very beginning, a very good place to start. When you read, you begin with A-B-C, when you sing you begin with Do-Re-Mi.” And when you attempt to understand something as entirely complex and profoundly miraculous as the eye and our generation’s miracle of low vision assistive technology, the place to start is with the organ itself, that body part that lets us see, read, watch, observe, witness, perceive, distinguish, notice, glimpse, view, examine, and behold. Let this article be your encyclopedia of anatomy, a reference point for sight. With it as a foundation, become better prepared to delve into the exciting world of low vision assistive technology and the diseases that it helps to conquer.

A transparent “front window,” the cornea is the thick, nearly circular structure covering the eye and providing nearly 2/3 of its ability to focus. Normally clear and with a shiny surface, the cornea has no blood vessels. Quite sensitive, there are more nerve endings in the cornea than anywhere else in the body. One half millimeter thick in an adult, it has five layers: the epithelium, Bowman’s Membrane, the stroma, Descemet’s Membrane and the endothelium:

The epithelium is a layer of cells covering the surface of the cornea. It’s nearly five to six cell layers thick and quickly regenerates when an injury occurs. If a wound penetrates too deeply into the cornea, an opaque scar is sometimes left that can result in a loss of clarity and luster.

Bowman’s Membrane lies just beneath the epithelium. Tough and difficult to penetrate, it protects the cornea.

The stroma is the thickest layer of the cornea and is comprised of tiny collagen fibers running parallel to each other. This special formation of collagen fibers gives the cornea its clarity.

Descemet’s Membrane lies between the stroma and the endothelium and serves as a protective barrier against infection and disease.

The endothelium is just one cell layer thick. It pumps water from the cornea, keeping it clear. If it is damaged or diseased, its cells will not regenerate.
The conjunctiva is a thin, transparent surface covering the outer surface of the eye. It begins at the outer edge of the cornea, covers the visible part of the eye and lines the inside of the eyelids. Nourished by tiny blood vessels invisible to the naked eye, it secretes oils and mucous that moisten and lubricate the eye.

The sclera is the white of the eye and is a tough, opaque surface serving as the eye’s protective outer coat. At the back of the eye, the optic nerve is attached to the sclera. In children, the sclera is thinner and more translucent and tends to take on a bluish cast, but by adulthood, it takes on more of a yellowish cast.

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