PURPOSE: To retrospectively compare the safety and efficacy of lower dose mitomycin C (MMC) (0.002%) to that of the standard dose (0.02%) in eyes treated with photorefractive keratectomy (PRK) for myopia. METHODS: The clinical efficacy of 95 eyes receiving myopic PRK with a standard concentration of MMC (0.02%) is sequentially compared to 126 eyes receiving low dose MMC (0.002%). The topical exposure times for MMC varied between 30 seconds and 2 minutes in both groups, and direct contralateral eye comparison of these two exposure times was analyzed in a prospective subset of 39 patients from among the low dose group. Patients were examined preoperatively and postoperatively at 1, 3, 6-9, and 9-12 months. Haze, visual acuity, and efficacy ratio outcomes were analyzed RESULTS: The preoperative findings were overall statistically similar, except for higher spherical equivalent refractive error (P=.007) and best spectacle-corrected visual acuity (P=.007) in the standard MMC group. Postoperatively, haze levels ranged from 0 to 4+. With multivariable analysis, significantly less haze was noted among the standard dose MMC eyes for high myopia and higher ablation depth at all postoperative time points. In contrast, the haze levels were statistically similar for moderate myopia and lower ablation depths at the latter postoperative time points. The subset of contralateral eyes randomly receiving low dose MMC (0.002%) at either 30 seconds or 2 minutes exposure showed no significant difference in haze between these exposure times. CONCLUSIONS: The standard concentration of topical MMC (0.02%) is more effective than low dose MMC (0.002%) in preventing postoperative haze following surface ablation for myopia ≥-6.00 D and deeper ablation depth ≥75 μm. However, for moderate myopia and shallow depth, low dosing appears to be equally effective. The duration of MMC exposure appears to be less important than its concentration.
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