Cornea Transplantation Surgery

The damaged cornea is removed and the corneal graft is stitched in place. The corneal graft is a transplant from a brain dead donor maintained on life support.

Corneal Transplant Surgery

The cornea 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 retina).

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 “dirty window” 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 (bullous keratopathy) as a result of previous intraocular surgery.

When 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, a new sutureless transplant procedure called DSEK may be employed to achieve a more rapid visual recovery.

Meticulous attention to detail is required for successful corneal transplant surgery. This starts with defining the geometric center of the cornea. Using instrumentation similar to that shown below, it is possible to accurately mark the center of the cornea. Once this is accomplished, the Hanna Trephine System can be used.

The Hanna Trephine System is designed to remove a circular disc of diseased cornea, with a specified diameter, from the patient. The diameter is determined by the size of the patient's cornea. Trephining the patient's cornea is facilitated with the use of a continuous, automated suctioning unit which aids in generating a uniform circular incision. In addition, the suction unit is used to trepine the donor tissue as well. Both components of the Hanna Trephine System (patient and donor trephination) use a special, finely finished circular blade. The sighting mechanism for trephining the patient's cornea allows a "bulls-eye" of the center marking on the cornea. After the donor has been transferred to the patient and secured with a continuous running 10-0 monofilament nylon suture, a critical adjustment of this suture is undertaken. Without consideration of suture tension and the control of astigmatism, the patient may achieve a clear graft but no functional vision. A qualitative keratometer which projects either a ring of light or a ring of dots is utilized to assist in achieving a spherical cornea. If the ring of light, when projected on the cornea, is spherical, the corneal transplant is spherical. However, if the projection of the ring of light is oval, the suture must be adjusted until the projected light is spherical. Although every effort is made to achieve sphericality at the time of surgery, differential healing of the corneal tissue may induce some astigmatism. However, it is possible to adjust the suture in the office using the same equipment. The suture may be adjusted several times if necessary to achieve excellent functional acuity.However, after the suture is removed, astigmatism may return because the stabilizing tension of the running suture has been released. Another technology can then be utilized to return the cornea to a more spherical surface.

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