is the clear window
to the eye. Light rays passing through the cornea
are refracted (or bent)
by the cornea and then are refracted again
as they pass through the crystalline lens
on their way to the back of the eye
The combined refractive capabilities of the cornea and the lens direct rays
of light to focus sharply on the retina to produce a distinct image. Individuals
who have an imprecise focusing mechanism, but who have a clear cornea and lens,
can wear either contact lenses
or glasses to direct an image
crisply on the retina.
However, when the transparency
of the cornea is compromised by disease or
trauma, light rays are no longer allowed to travel unimpeded through the eye and
a distortion in the visual image results. The cornea has in effect become a
which cannot be treated with medication and a new cornea must
be provided to restore vision. Some of the conditions that may require corneal
transplant surgery include: keratoconus
, corneal opacification or
decompensation as a result of trauma or disease, and corneal decompensation
as a result of previous intraocular surgery.
corneal transplant surgery (otherwise known as penetrating keratoplasty)
is indicated, the patient is registered with the Eye Bank. The Eye Bank
is responsible for coordinating the collection and distribution of donated
corneal tissue. The demand for corneas is so great that a patient may have to
wait approximately four to eight weeks before tissue is available. We prefer to
schedule the patient far enough in advance to achieve the highest priority for
corneal tissue on the day of surgery. The corneas are obtained from deceased
individuals who have either willed this tissue to the Eye Bank or have had their
next of kin request a donation. The donated cornea is processed by the Eye Bank
and placed in an enriched liquid medium that allows the tissue to remain viable
for approximately one week prior to surgery (although most patients receive
their cornea within 2 to 3 days from the time of death of the donor).
The donated corneal tissue is transferred to the patient as indicated below
and then sutured in place using 10-0 nylon (a gauge thinner than a
human hair). The post-operative appearance of corneal transplant surgery is shown below.
The suture is removed approximately one year after surgery. In some cases, new
sutureless transplant procedures called
may be employed to achieve a more rapid visual recovery.