Ocular status determines details of keratoplasty

Detroit-Basic keratoplasty techniques vary depending on the ocular status, said Jayne S. Weiss, MD, a professor of ophthalmology and pathology and the director of refractive surgery, Kresge Eye Institute, Detroit. Preoperative medications, patient positioning, trephines, wound construction, and suturing techniques must be considered to reach the ultimate goal of the best possible postoperative vision for patients, she said.

"These drugs can be administered 1 hour before the procedure," Dr. Weiss said, noting that some ophthalmologists begin administering these drugs 3 to 4 days before surgery. Outside of the United States, she said, some ophthalmologists have used chloramphenicol.

"If a cataract is to be removed, then the pupils are dilated, and if the eye is phakic, then the pupil is constricted. However, beyond that, there are personal preferences." she said.

Some ophthalmologists use mydriatic agents for vitrectomy, some use nothing, some use miotic agents in the presence of a posterior chamber IOL, and others use nothing in such cases, she said.

In patients with phakic eyes who are undergoing a corneal transplant procedure, other factors come into play in addition to constriction of the pupil. One factor, Dr. Weiss said, is the problem encountered with positive pressure.

"This is one of the only surgeries currently performed that is an open-sky procedure," she said. "Ocular hypotensive agents have been used for phakic corneal transplantations in the presence of keratoconus, a history of multiple grafts, and in pediatric patients and other patients at high risk for positive pressure." Many ophthalmologists use mannitol in this situation, she said.

Because this surgery is an open-sky procedure, patient positioning must be considered, Dr. Weiss said. "Surgeon preferences regarding positioning range from a reverse Trendelenburg to keeping the chin and forehead at the same level with the iris parallel to the floor or rotating the head 20° opposite the eye undergoing surgery," she said.

In addition to these important factors, she said, other considerations must be addressed during keratoplasty, given that the goal of the surgery is to improve vision. "Other factors include the presence of a cataract, IOL subluxation, iris prolapse, or membranes. These have to be treated at the same time the corneal transplant is performed," Dr. Weiss said. "In addition, the reasons that the cornea failed also must be addressed. If there is vitreous prolapse with vitreous touching the corneal endothelium, this must be treated while the eye is open to prevent recurrence."

Postoperative astigmatism

Minimizing the amount of postoperative astigmatism is another important factor; postoperative astigmatism can result in poor vision despite a successful transplant and a clear compact graft.

A variety of trephines are available for use during keratoplasty procedures. Dr. Weiss described how to size the host trephine, size the donor trephine, and center the trephination on the patient.

"One thing that all surgeons agree on is that the area of pathology must be removed," she said. "Coming in close contact with the limbus must be avoided because of the potential for ingrowth of blood vessels and the higher risk of postoperative rejection of the graft."

In a case with poor corneal endothelium such as in Fuchs' dystrophy, a sufficient amount of donor endothelium should be provided when preoperative corneal edema exists, Dr. Weiss said.