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Literature review shows single application of low-dose MMC can prevent, treat haze after surface procedures
In more than 750 refractive surgery patients treated with MMC, there have been no serious complications associated with this anti-cancer agent, according to Dr. Schallhorn, director, cornea and refractive surgery, Naval Medical Center, San Diego, who presented a report during the Hot Topics Symposium.
After reviewing more than 28 papers from the literature, Dr. Schallhorn noted a trend toward lower and lower dosing, referring to duration and concentration. "Use of mitomycin (in refractive surgery) has gone from topically applied drops used for days or weeks down to low concentrations of mitomycin applied for just a few seconds," Dr. Schallhorn said. "That is certainly the trend in the literature, anecdotally and clinically."
In this non-comparative, non-randomized retrospective study, 35 eyes of 30 patients who had undergone PRK and developed significant haze (grade 3 or 4) and regression had significant improvement in haze and best spectacle-corrected visual acuity (BSCVA) after the 2-minute application. The majority of eyes (31) had significant improvement with a haze grade less than 1 and only two eyes still experienced haze that required re-treatment of scraping and MMC application. The follow-up was 12 months.
Prophylactic MMC use
MMC used prophylactically after PRK was reported to be safe and effective in eyes with high myopia, according to a prospective, double-masked, randomized clinical trial published last year (Ophthalmology 2005;112:208-218;discussion 219).
Researchers from the University of Padova, Padova, Italy, randomly assigned intraoperative MMC 0.02% application to one eye and fluorometholone (FML) to the other eye of 36 patients who underwent PRK for correction of > 7 D of myopia. At a mean follow-up of 18 months, there were no toxic effects.
"MMC yielded better outcomes in terms of better uncorrected visual acuity, faster recovery of contrast sensitivity, and quite a difference in corneal haze between the two eyes," Dr. Schallhorn noted.
At 12 months follow-up, 20% of the eyes treated with FML had developed corneal haze and none of those treated with MMC did, he said.
In a large retrospective report, researchers from the Yonsei Eye Center, Seoul, South Korea, used intraoperative application of MMC in varying doses of 30 seconds to 2 minutes depending on the ablation depth after PRK.
They found at 6 months postoperatively that 86% of the 1,011 eyes had achieved 20/20 or better UCVA and 98% had 20/40 UCVA or better. Three percent of eyes had haze, mostly grade 1.
Only two eyes (0.2%) had grade 3 haze in this patient population treated for moderate to high myopia. No eye lost 2 or more lines of BCVA (J Cataract Refract Surg 2005;31:2293-2298).
"In my clinical practice, the incidence of significant haze is much greater than 0.2% when treating high myopia without MMC," Dr. Schallhorn explained.
It was noted that two eyes (0.2%) experienced delayed epithelial closure requiring 10 days to heal.
This can occur without the use of MMC, he continued.
Although the results of therapeutic and prophylactic use of a single low-dose MMC application after surface ablation appears to be safe and effective, the researchers still do not understand the dose-response curve, he said.