CORNEAL TRANSPLANTATION

Corneal transplantation (keratoplasty) is indicated for a number of serious corneal conditions, eg, scarring, edema, thinning, and distortion. The term penetrating keratoplasty denotes full-thickness corneal replacement; lamellar keratoplasty denotes a par- tial-thickness procedure.

Younger donors are preferred for penetrating keratoplasties; there is a direct relationship between age and the health and number of the endothelial cells. Because of the rapid endothelial cell death rate, the eyes should be enucleated soon after death and refrigerated immediately. Whole eyes should be used within 48 hours, preferably within 24 hours. Modern storage media allow for longer storage. Corneoscleral caps stored in nutrient media may be used up to 6 days after donor death, and preservation in tissue culture media allows storage for as long as 6 weeks.

For lamellar keratoplasty, corneas can be frozen, dehydrated, or refrigerated for several weeks; the endothelial cells are not important in this partial-thickness procedure.

Technique

The recipient eye is prepared by a partial-thickness cutting of a circle of diseased cornea with a suction trephine (cookie cutter action) and full-thickness removal with scissors or partial-thickness removal with dissection.

The donor eye is prepared in two ways. For penetrating keratoplasty, the corneoscleral cap is placed endothelium up on a suction Teflon block; the trephine (Figure 6-15) is pressed down into the cornea, and a full-thickness button is punched out. In lamellar keratoplasty, a partial-thickness trephine incision is made in the cornea of a whole globe and the lamellar button is dissected free. Certain refinements in technique, such as free hand grafts, may be necessary.

Refined sutures (Figure 6-16) and instruments and sophisticated operating microscopes and illuminating systems have significantly improved the prognosis in all patients requiring corneal transplants. There is no significant value to blood type matching in corneal transplant surgery.

Corneal graft rejection continues to be a major management problem (see Chapter 16), as does the difficulty in controlling postgraft astigmatism.

10.1036/1535-8860.ch6

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