Treating Corneal Abrasions
The cornea is truly the eye's window. It's the
transparent, domed "watch glass" that sits over the sclera (the
"white" of the eye). Through this clear porthole the iris and pupil
are easily visible; looking further still beyond them, we can see
all the way to the back of the eye - the vitreous, retina, and optic
nerve.
The wafer-thin cornea (amazingly, only about 1 millimeter thick) is
like a cake with five layers, each with its own special function. On
top are epithelial (outer lining) cells; this vital layer (also
called the epithelium) protects the rest of the cornea and provides
a smooth surface for tears.
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Next comes the cellophane-thin Bowman's
membrane; then the tough, transparent stroma, the bulk of
the cornea (the cake itself); then another layer of
cellophane, called Descemet's membrane. These middle three
layers act as scaffolding, providing structural support to
the cornea as it arches over the front of the eye. Last is
the single layer of endothelial (inner lining) cells (also
called the endothelium). Because this important layer
touches the aqueous of the eye's anterior chamber, it serves
as a sort of "bilge pump," keeping the cornea free of excess
moisture. When this pump malfunctions, the cornea can swell,
and this can distort or even damage vision.
The cornea normally does not contain any blood vessels.
However, it is rich in sensory nerve fibers: under the
epithelial layer alone are about seventy of them, which
helps explain why the cornea is so sensitive to pain. |
The epithelial cells act as a protective
blanket, like enamel on a tooth, insulating the nerve fibers
from the world. When that blanket is frayed - or, continuing the
tooth analogy, when the enamel is cracked or has a cavity -
those ultra sensitive nerves react painfully. Even a small loss
of epithelial cells can be excruciating, if it exposes these
nerve endings.
Corneal Abrasions
Because of the abundance of nerves throughout its layers, even a
slight injury or irritation to the cornea can result in a lot of
discomfort or pain. An abrasion - a scrape of the epithelium, or
outer surface - is the most common injury to the cornea. It can
happen so easily - when the eye gets too close to a baby's
fingernail, for instance, or the corner of an envelope, or a
tree branch. All of a sudden it feels as if there's a hot poker
in your eye.
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Other symptoms include redness, a feeling
like there's a piece of grit in your eye, and extra
sensitivity to bright lights. Because it's often difficult
to see the actual injury with the naked eye, eye doctors
rely on special fluorescent dyes, which target and highlight
areas of damage, to help us determine the extent of the
wound. Fortunately, despite the severe discomfort and
blurred vision that often accompany corneal abrasions, these
injuries usually heal fairly quickly, sometimes in a matter
of hours, sometimes within a few days - and don't leave any
lasting damage.
For treatment, basically, the cornea must heal itself, and
all we can do is provide the best conditions possible.
(Think of skin injured by a scrape or burn; it hurts until
your skin lays down new layers of cells, which insulate the
nerves beneath.) Thus, the main treatment for a corneal
abrasion is simply to patch the eye. |
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It's not quite as easy as it sounds - in other words, you shouldn't
try to do it yourself with an eye patch from the drugstore - because
to be effective, the eye patch must immobilize the eyelid and
prevent it from rubbing over the injured area.
The epithelial cells need time to multiply and coat the injury,
which means that the patch needs to be tight enough to keep the
eyelid still. It takes several eye patches - generally three - to
create enough bulk to secure the lid. (Eye doctors either stack
three patches over the eyelid or use two, with the one directly on
the eyelid folded in half.)
The eye pads are fixed over the eyelid with at least four pieces of
surgical tape, extending from the forehead to the cheek. Sometimes,
when eye patches can't be tolerated or when the abrasion doesn't
appear to be healing, eye doctors apply a special "bandage" contact
lens over the abrasion. Bandage contact lenses allow the patient to
avoid having to cope with the nuisance of wearing a large and bulky
eye patch and enables the abraded eye to see while it heals. |
