WHAT IS THE CORNEA?
The cornea is the clear part of the eye that covers the
pupil. Just like a clear window, the cornea is critical in maintaining a sharp
focus on objects. The inside layer of cornea, the endothelium, has a finite
number of cells that maintain clarity and do not regenerate. The epithelium, the
outside layer of the cornea, has cells that re-generate every 5-7 days - just
like your skin.
WHAT DAMAGES A NORMAL CORNEA?
Conditions that cloud the cornea or disrupt the smooth
surface will greatly impact how clearly a person sees. Infections, injuries, and
some ocular diseases can cause scarring that make the cornea more opaque. Common
causes include Fuchs' dystrophy and keratoconus. Fuchs' dystrophy is an
accelerated aging of the endothelium. The finite number of cells age and die at
a rapid rate causing corneal swelling. Keratoconus is a thinning and cone-like
formation of the cornea that causes irregularities in the way the cornea
focuses. Corneal decompensation can occur after cataract surgery although this
is a rare problem. These corneal diseases can often be treated with medications
or contact lenses, but if these measures fail to improve the vision, a cornea
transplant may be needed.
HOW SUCCESSFUL IS CORNEAL TRANSPLANTATION?
Approximately 40,000 corneas are transplanted yearly in
the United States. Success defined as clarity and acceptance by the body's
immune system is about 90%. Visual improvement may be limited by other eye
disease. Nevertheless, the vast majority of patients regain useful vision after
corneal transplantation. Because the cornea usually has no blood vessels in it,
it is considered an immune privileged tissue. This is in contrast to kidneys and
lungs which have a higher graft rejection rate, and require strong systemic
immune suppression. Usually only eyedrop steroids are needed to prevent
rejection.
HOW ARE DONOR CORNEAS OBTAINED? IS THERE A
LONG WAITING LIST?
Donor corneas are harvested from people after consent is
obtained within 12 hours after death. The tissue is closely inspected by
eye-bank
personnel under a powerful microscope. Blood from the donor is tested for any
communicable diseases such as hepatitis and AIDS. The cornea is offered only if
all blood tests are negative. The corneal tissue is kept in cold storage and
must be used within six days from death. Matching blood type is not necessary
for corneal transplantation.
The eye-banks can usually find tissue for patients if the surgery is scheduled one to two months in advance due to a predictable number of donors per week. Emergency tissue is readily found in rare cases when it is needed. We are very lucky in this country to have a steady supply of concerned citizens donating their eyes after death.
WHAT IS THE SURGERY AND RECOVERY LIKE?
Surgery is performed at the outpatient facility, and
typically takes about 60 to 90 minutes. At pre-op the eye and the lids are
anesthetized locally. Patients are sedated but are breathing on their own, and
often sleep through the surgery. Due to anesthesia, the surgery is painless.
Following surgery, the eye is patched overnight. The following day, the patch is
removed, and the eye is examined. Eye drops are started and continued for months
but in decreasing doses. Some scratchiness and soreness is normal the first few
weeks, and no heavy lifting or bending over past the waist is allowed while
healing begins. Visual rehabilitation takes quite a long time with this surgery
and comes in small incremental steps. Final vision is often not achieved for
nine to twelve months from the time of surgery. Sometimes temporary glasses can
be used at six months. Patients can often return to work one to two weeks after
surgery.