LETTERS

Mitomycin-C in photorefractive keratectomy Evaluating intraoperative mitomycin-C (MMC) exposure for 60, 30, and 15 seconds after wavefrontguided myopic photorefractive keratectomy (PRK) in 28 eyes and using the fellow eye as control, Hofmeister et al.1 conclude that MMC may not be needed to prevent haze after modern PRK. They say, “There was no clinically significant difference in haze formation between MMC eyes and control eyes. . . .” We wonder whether the study had the power to draw such a conclusion. Even in earlier reports with older ablation profiles and no MMC, “clinically significant” haze was observed in only about 2% of eyes after myopic PRK,2 so testing only 28 patients carries a high risk of b error; ie, missing the actual efficacy of the treatment. Furthermore, the title of the paper indicates a study of high myopia, whereas mean preoperative spherical equivalent was 5.98 diopters (D) (range 4.4 to 8.0) and the abstract does not report the number of eyes studied. Haze can be a severe complication and its prevention is crucial. Our concern is that the article may corroborate the idea of omitting MMC in highly myopic PRK, thus affecting the safety of the treatment. As a last consideration, in “What Was Known,” the authors state that the “. . . use of MMC 0.02% (0.2 mg/mL) applied for 2 minutes . . . reduces the incidence of post-PRK haze,” but this is not the common practice nor what is indicated in the literature. As the authors correctly state in their discussion, apart from an early study evaluating a 2-minute exposure,3 MMC is usually applied for shorter times even in more haze-prone procedures such as hyperopic PRK,4 and the issue of reducing time exposure has been successfully addressed by Virash et al.,5 who found unchanged efficacy of MMC after a 12-second application. Antonio Leccisotti, MD, PhD Stefania V. Fields, AO Siena, Italy REFERENCES 1. Hofmeister EM, Bishop FM, Kaupp SE, Schallhorn SC. Randomized dose-response analysis of mitomycin-C to prevent haze after photorefractive keratectomy for high myopia. J Cataract Refract Surg 2013; 39:1358–1365 2. Hersh PS, Stulting RD, Steinert RF, Waring GO III, Thompson KP, O’Connell M, Doney K, Schein OD; the Summit PRK Study Group. Results of phase III excimer laser photorefractive keratectomy for myopia. Ophthalmology 1997; 104:1535–1553 3. Carones F, Vigo L, Scandola E, Vacchini L. Evaluation of the prophylactic use of mitomycin-C to inhibit haze formation after

508

Q 2014 ASCRS and ESCRS Published by Elsevier Inc.

photorefractive keratectomy. J Cataract Refract Surg 2002; 28:2088–2095 4. Leccisotti A. Mitomycin-C in hyperopic photorefractive keratectomy. J Cataract Refract Surg 2009; 35:682–687 5. Virasch VV, Majmudar PA, Epstein RJ, Vaidya NS, Dennis RF. Reduced application time for prophylactic mitomycin C in photorefractive keratectomy. Ophthalmology 2010; 117:885–889

Reply : We share the concern of Drs. Leccisotti and Fields that the casual reader might use the results of our article as a license to omit MMC when performing PRK. Severe corneal haze can be visually devastating and when our patients develop haze, it affects not only the quality of their vision, but also their ability to deploy with their military unit. Any patient with a high refractive error can develop haze after PRK, including patients with high myopia, high hyperopia, and high astigmatism.1–3 Our review of the literature showed an incidence of post-PRK haze as low as 10% and as high as 63% in high myopia with earlier excimer lasers.1,4,5 The sample size in our prospective study was small: 56 eyes of 28 patients. The sample size was powered to detect a 1-unit difference in haze score if only 18 eyes were studied. Based on the available literature, we were very surprised to discover that none of the placebo eyes in our study developed more than trace (1.0) haze at any point in the 12-month follow-up, as our expectation had been that many of these eyes would experience vision-threatening haze. Our interpretation of this finding is that current laser technology causes less thermal damage to the unablated corneal stroma than technologies used a decade ago, but another confounder was the 4-month tapered dose of topical fluorometholone, which helps to suppress fibroblast activity. Our standard practice prior to this study was to apply MMC 0.01% for 60 seconds following PRK only for ablations deeper than 55 mm: myopia, astigmatism, or hyperopia. However, not all cases of vision-threatening haze that we see at the Navy Refractive Surgery Center San Diego occur in patients with high refractive errors. Furthermore, compliance with a 4-month steroid taper is difficult in the face of unexpected deployments. The complete elimination of haze in the MMC group and the excellent safety profile of MMC with regard to endothelial cell counts have encouraged us to broaden our indications for low concentrations of MMC at short durations for a broad spectrum of refractive errors. Further study is needed to elucidate the true incidence of haze following PRK with modern excimer lasers and the best ways to prevent this harmful complication. dElizabeth M. Hofmeister, MD, Frank M. Bishop, MD, Sandor E. Kaupp, MS, Steve C. Schallhorn, MD

0886-3350/$ - see front matter http://dx.doi.org/10.1016/j.jcrs.2014.01.020

Mitomycin-C in photorefractive keratectomy.

Mitomycin-C in photorefractive keratectomy. - PDF Download Free
65KB Sizes 3 Downloads 3 Views