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One Miraculous Organ
By Frances Maguire Paist, Staff Writer
(Page 1 of 3)
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
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