Corneal Transplant
A transplant refers to living tissue moved from
one area to another. "Graft" is another word that
is frequently used that means, "transplant".
During a corneal transplant the central part of
an abnormal cornea is removed and replaced with
healthy corneal tissue from a donor. Donor corneas
are obtained from the undamaged eye of someone
who has died.
The Cornea
The cornea is the crystal clear dome-shaped front part of the eye
through which the colored iris and black pupil are seen. It is about
one-half inch in diameter, the size of a dime. The cornea is the
most important optical element in the eye. It is curved to help
focus rays of light onto the retina, and it provides over 2/3 of the
total focusing power of the eye. The cornea has five layers, each
with its own function. To focus well, the cornea must have a
smooth clear surface. The eyelids and tears act as windshield
wipers, lubricating and cleaning debris with each blink. The cornea must be kept moist.
Why Does the Cornea Fail?
The layers of the cornea provide different functions.
The outside layer of the cornea, the epithelium,
is protective, like very thin, fine skin. The cornea
is extremely sensitive. It has the highest concentration
of pain fibers in any part of the body. The pain
fibers are just below the epithelium. Thus, the
smallest particle of dirt can feel like a cinder and a
small scratch of the surface epithelium can be very
painful. Lack of oxygen from a poorly fitting or
overused contact lens can also cause corneal
swelling and severe pain. Fortunately, this outer
layer heals rapidly from most minor injuries. Most
injuries that involve only the outer layer will heal
without scarring.
The innermost layer of the cornea is called the
endothelium, it's one cell layer in thickness and
its function is to keep the cornea clear by
continuously pumping water out of the cornea.
The endothelial cells with which you are born
with are the only cells you have throughout your
lifetime. Any cells that are damaged cannot be
replaced. As we age, the number of endothelial
cells decreases. If the number of endothelial cells
decreases too much, the cornea begins to swell
with fluid and become hazy. In the early stages
of swelling,
medication can
be helpful, but
when the
cornea
becomes
increasingly
swollen, a
corneal transplant
is the
only solution.
This swelling is
called corneal
edema.
Corneal edema
acts like water
droplets behind your watch crystal that fog the
view of your watch dial.
In children, the most common cornea
problems are due to congenital abnormalities or
trauma with distortion and scarring of the cornea.
Trauma and scarring from infected ulcers of the
cornea are among the leading reasons for cornea
transplants among young adults. Hereditary
degeneration may become symptomatic in young
adulthood with a gradual decrease and distortion
of vision over time eventually leading to a cornea
transplant.
 
Who Can Be a Donor?
Anyone with healthy eyes can donate corneas.
A uniform donor card is available at automobile
registries or by calling the New England Eye Bank
(617-523-3937). Being an organ donor is a gift that lives on. There is no need to "tissue match" the
donor and recipient in corneal transplants. A family
will sometimes refuse permission for their loved
one to donate corneas because they are under the
incorrect impression the body will be disfigured,
but this is not so. Only the cornea is needed.
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