I appreciate Dr Oğuz bringing our attention to the issue of ciliary body intoxication as a possible complication of subconjunctival mitomycin C (MMC). However, I believe that there are much more realistic concerns about ocular surface toxicity of MMC than the possibility of damage to the ciliary body. A wide range of serious side effects, including scleral melt and necrosis, cataract formation, corneal endothelial cell damage, and glaucoma, have been reported after topical administration of MMC, and these could be avoided using preoperative subconjunctival injection of minimal doses of MMC. However, the evidence regarding possible MMC toxicity to the ciliary body is inconclusive and controversial.

Obviously, there may be several contributing factors to the possibility of ciliary body intoxication with MMC, among them, method of application, site of application, depth of application, exposure time, irrigation after application, and dose and concentration are widely investigated.

As cited by Dr Ogğuz, I am also interested in the work of Levy and associates on ciliary body toxicity of MMC; however, I believe the work is not especially relevant to our study. In their study, Levy and associates investigated the effect of subconjunctival injection of 0.08 mg MMC in rats. This is clearly in contrast to our method: our MMC dose (0.02 mg) was much lower, and human sclera is obviously thicker than that of rats and rabbits. In addition, studies that are more recent did not confirm uniformly the results of Levy and associates.

Most recently, Cetinkaya and associates, in an ultrastructural study, reported that subconjunctival injection of MMC 0.2 mg/mL is nontoxic to the ciliary body and concluded that MMC at this concentration seems to be safe for subconjunctival injection. Another study showed that even with low-dose application of MMC, the concentration in the inner side of sclera increases rapidly beyond the limits of the therapeutic range and suggested that the only means of reducing the ciliary body concentrations is to reduce the dose of application. Indeed, 62% of MMC is delivered to the sclera in the first minute and the time is of least importance in the diffusion amount afterward. This may be relevant to subconjunctival injection, because there is no considerable further MMC diffusion after 5 minutes in this study.

Georgopoulos and associates investigated the effect of irrigation on MMC concentration within scleral and subscleral fluid and concluded that low-dose application of MMC without irrigation may be a more rational approach to reduce its intraocular toxicity.

I thank Dr Oğuz for his comments on the necessity of intraocular pressure measurement as part of our study; however, considering the current available evidence, I believe that the problem of possible MMC toxicity in the ciliary body at a low dose is not a serious one and that the benefits of subconjunctival MMC injection before pterygium surgery outweigh the theoretical risks. However, further study with a larger sample size and longer follow-up is necessary to investigate the safety as well as efficacy of either method.

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Jan 17, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Reply

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