PRK with MMC yields negligible impact on endothelial cell density

Use of mitomycin C 0.02% did not significantly affect the corneal endothelium after PRK, according to a surgeon.

“The application of [MMC] 0.02% … had no adverse effect on endothelial cell density and the amount of refractive error of up to 8 D. Ablation depth had no significant correlation with endothelial cell density,” Farid Karimian, MD, told colleagues at the joint meeting of the American Academy of Ophthalmology and Middle East Africa Council of Ophthalmology in Chicago.

MMC has offered mixed results since it was introduced to prevent corneal haze, Dr. Karimian said.

“Mitomycin can potentially damage all of the main corneal cell layers: epithelium, stroma and endothelial cells. Possible contributing factors are its concentration, duration of exposure and type of ablation,” he said.

Dr. Karimian presented results of a study coauthored with Mohammad Reza Jafarinasab, MD.

Patients, methods

“The purpose of our study was to evaluate how mitomycin 0.02% can affect central corneal endothelial cell density or morphology,” Dr. Karimian said. “And does it have any relationship to the amount of correction?”

The study included 42 eyes of 21 patients with moderate myopia up to 8 D who underwent PRK with concomitant topical MMC. Average patient age was approximately 26 years.

PRK was performed at a maximum ablation depth of 122 µm; average ablation depth was 99 µm. The maximum duration of exposure to MMC was 40 seconds. The duration of MMC exposure was increased according to the degree of refractive error and resulting ablation depth, Dr. Karimian said.

“We have a special protocol for each [degree of refractive error] and increasing the duration of mitomycin C application,” he said. “If in a regular patient cornea is ablated more than 70 µm, MMC is applied for 10 seconds. But if you go to 100 µm, application time is increased up to 30 seconds.”

Irrigation with chilled balanced salt solution was performed at the conclusion of the procedure. All patients were fitted with therapeutic contact lenses.

“We use chilled [balanced salt solution] to reduce pain and reactions in the cornea,” Dr. Karimian said.

Dr. Karimian and colleagues performed specular microscopy preoperatively and 6 months postoperatively to evaluate endothelial cell density and morphology. Results were presented as standard deviations on the t-test with positive regression analysis.

Minimal impact on endothelium

Study results at 6 months after surgery showed that mean endothelial cell density diminished from 2,920 cells/mm² preoperatively to 2,802 cells/mm² postoperatively. The 4% reduction was statistically insignificant.

“This 4% reduction in endothelial cell density was comparable to a 4.1% variation that was observed in repeated measurements of endothelial cells in non-operated eyes,” Dr. Karimian said.

The slight reduction in endothelial cell density had no effect on spherical equivalent refractive error. No cases of postoperative haze or ocular surface disease were identified. Endothelial cell morphology was also unaffected. – by Matt Hasson

• Farid Karimian, MD, can be reached at Ophthalmic Research Center, No. 23, Amir Ebrahimi St., Boostan 9 St., Pasdaran Ave., Tehran 16666, Iran; 98-21-22587317; fax: 98-21-22825390; e-mail: karimianf@yahoo.com.
• Disclosure: No products or companies are mentioned that would require financial disclosure.