Refractive errors after penetrating keratectomy improve with advanced surface ablation, mitomycin C

Key Points

Hong Kong-Advanced surface ablation with an excimer laser and application of topical mitomycin C (MMC) 0.2% results in increased vision when used to treat refractive errors after penetrating keratoplasty, according to Michael Lawless, FRACO, who spoke at the World Ophthalmology Congress.

"The decision-making process in refractive surgery after corneal transplantation is different from that in normal patients," said Dr. Lawless, medical director, Vision Eye Institute, Chatswood, New South Wales, Australia.

The main points to consider are the endothelial cell quality and medium-term viability of the graft, the host disease (which is keratoconus in most cases) and possible progression of refractive error associated with the disease, the graft host scar, corneal irregularity, the refractive error and stability, a correlation between refractive and keratometric astigmatism, and the presence or absence of cataract.

The mean preoperative sphere was –1.41 D, the mean cylinder –4.93 D, the mean spherical equivalent (SE) –4.22 D, and the average K value 46.42.

Postoperatively, Dr. Lawless said all parameters improved significantly (p < 0.05) at 1 and 3 months, at which time point there was 100% follow-up of patients. The SE was close to plano with a wide standard deviation.

"There was a trend toward improvement in the best spectacle-corrected visual acuity; there was still some irregular astigmatism present," he said. "However, 10.3% of eyes lost two or more lines of best-corrected visual acuity [BCVA] at 1 month. At 3 months, 5.8% lost two or more lines of BCVA. The overall trend was toward improvement in BCVA."

The maximum astigmatism that could be corrected was 6 D, but some patients had up to 10 or 12 D, according to Dr. Lawless. He also said that 25% of eyes achieved BCVA of 20/20 at 3 months compared with only 10% of eyes that achieved that vision preoperatively.

"This trend in improved BCVA tended to increase with time. In certain patients, we found that this improvement continued at 6 and at 12 months postoperatively," Dr. Lawless said.

Comparison with LASIK

He and his colleagues compared their results with those of a study they published in the British Journal of Ophthalmology (1999;83:1013-1018), in which LASIK was performed after corneal transplantation. Twenty-six eyes with very similar demographic data to those of the study conducted by Dr. Lawless were included in the study; the procedures were performed by the same three surgeons.

Three months after LASIK, he said, the cylinder was –3.7 D, and the SE was 1.95 D. These patients did well with LASIK after corneal transplantation at 1 and 3 months postoperatively. A slight trend pointed toward improvement in the BCVA, but 15.9% lost two or more lines of BCVA 1 month after treatment; at 3 months after treatment, 14.3% lost two or more lines compared with the lower percentages that lost two or more lines with the surface ablation and MMC procedure, according to Dr. Lawless.

A comparison of the results of the LASIK procedure after corneal transplantation indicated that the patients who underwent the surface excimer laser with MMC procedure fared significantly better than patients treated with LASIK in SE and in the magnitude of the refractive astigmatism, he said. No significant difference existed between the two procedures in the mean BCVA or the corneal topography astigmatism.

"Advanced surface ablation with MMC applied for up to 60 seconds is an effective treatment for patients who are ametropic following corneal transplantation," Dr. Lawless concluded. "In our hands, the procedure is safer and more accurate than LASIK. The results continue to improve after 3 months postoperatively."