Corneal shape guides astigmatism treatment after transplant surgery

San Francisco-"The choice of corneal procedure that the surgeon will perform to correct astigmatism after corneal transplantation depends on the corneal shape," said Sheraz Daya, MD, FACS, at the American Society of Cataract and Refractive Surgery annual meeting.

Astigmatic keratotomy

"This is a general rule of thumb; however, more effect can be achieved and sometimes no effect at all," he explained. "Performing it outside the graft will not work and should not be attempted."

This procedure can be performed at the slit lamp.

"The advantage of using the slit lamp is that the depth of the incision can be assessed using the slit beam," Dr. Daya said. "A 15° blade (Alcon Laboratories) can be used to accomplish the incision. The sharp end of the blade is kept away from the cornea. The procedure can be done in several phases, and can be titrated to increase the effect over time."

This procedure, he pointed out, can be very effective and is repeatable; however, stability is an issue, which is the reason he prefers to use other surgical options.

The disadvantages are that the cornea can be perforated, especially if the patient has been referred from a surgeon who did not achieve good graft-host apposition. Because of this he advised keeping a suture kit and operating microscope handy.

Wedge resection

Wedge resection is the surgical procedure of choice to correct very high levels of astigmatism.

Dr. Daya described a patient with 10 D of astigmatism after a corneal transplantation procedure. A residual cone in the host rim became increasingly ectatic, which caused lifting of the graft. In this case, Dr. Daya removed the area of disease, the host rim, causing the ectasia. The incision was sutured with 10-0 Mersilene sutures, which are inelastic, and in this case the aim was to overcorrect by 50%, he explained.

Dr. Daya described the wedge procedure. He first marks the area to be removed and uses the Orbscan (Bausch & Lomb) for guidance. An area slightly wider than the elevated area must be removed. A diamond knife is used to make the incision to the correct depth. A pair of Vannas scissors is used to remove the wedge. The cornea is then sutured back together.

In one of the first cases in which this procedure was performed, Dr. Daya reported using a combination of nylon and Mersilene sutures, which did not work well. He suggested using only Mersilene sutures and then removing the sutures after a minimum of 6 months.

In the previously mentioned patient who had 10 D of astigmatism, using this technique the patient had 5 D of astigmatism 1 day after wedge resection; after 2 months the astigmatism decreased further to 2.5 D.

Dr. Daya reported on a small series of patients in the Journal of Cataract and Refractive Surgery (Ilari L, Daya SM. Corneal wedge resection to treat progressive keratoconus in the host cornea after penetrating keratoplasty. J Cataract Refract Surg 2003;29:395-401), all of whom had received small grafts to treat keratoconus. The wedge resection had a good outcome in all patients, he pointed out.

Laser vision correction

Surface laser vision correction to treat astigmatism following penetrating keratoplasty may be a risky procedure. Some investigators have reported on keratectomy using mitomycin-C, but Dr. Daya reported no experience with it.