Mitomycin C administered during PRK is safe and effective method to prevent corneal haze and did not cause severe complications over the long term in a recent study that included 59 patients (115 eyes) who were followed for a mean of 65 months postoperatively.
The mean preoperative spherical equivalent was about –8.0 D. The epithelium was removed using an application of 20% alcohol solution for 30 seconds. All procedures were performed using an excimer laser. MMC 0.02% was applied to the eye for from 30 seconds to 2 minutes followed by irrigation with balanced saline solution. Postoperative care consisted of a steroid and nonpreserved nonsteroidal anti-inflammatory drug, Dr. Lee explained.
"The visual acuity results indicated that 76% of eyes were within 0.5 D of the intended correction, and 84% were within 1 D of the intended correction," Dr. Lee said. "The refractions remained stable throughout the follow-up visits."
Complications included mild corneal haze in six eyes. No complications that developed were related to the use of MMC.
At 1 year after PRK, Dr. Lee used confocal microscopy to compare eyes of the patients who underwent PRK with intraoperative MMC with those of patients in two other groups, i.e., normal volunteers and those who underwent PRK only.
"There was no difference in the endothelial cell count in any of the three groups," he said. "There was a significant decrease in the keratocyte population in the superficial corneal stromal layer both in the PRK only group and in the PRK with MMC group. There was no significant difference in all stromal layers between the PRK only group and the PRK with MMC group."
The patients who underwent PRK with MMC were followed for up to 5 years. At the 1-year examination, Dr. Lee observed decreases in the keratocyte density of 2.3%, 9.8%, and 16% in the posterior, middle, and anterior stroma, respectively. At 5 years, however, they further decreased to 18%, 29%, and 37% in the posterior, middle, anterior stroma, respectively, he said. These decreases were similar to those seen with PRK-only and LASIK that were reported previously in the literature.1
The rate of decrease in keratocytes was –4.5% per year in PRK with MMC, –3.3% per year in PRK alone, and –4.2% per year in the LASIK group.
Up to 1 year postoperatively, the endothelial cell count was similar, and the keratocyte count decreased significantly only in the anterior stromal layer. At 5 years postop, however, Dr. Lee found a significant decrease in all the corneal stromal layers.
"This decrease was similar to that seen in cases that underwent PRK alone or LASIK," he said. "I was unable to find any evidence that MMC carries a more severe risk of decreasing the keratocyte count. After 5 years, no severe complications developed, and using MMC during PRK seems safe."
1. Erie JC, Patel SV, McLaren JW, Hodge DO, Bourne WM. Corneal keratocyte deficits after photorefractive keratectomy and laser in situ keratomileusis. Am J Ophthalmol. 2006;141:799-809.