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Editors Selection IGR 9-4

Surgical treatment: MMC

Comment by Paul Palmberg on:

13921 Trabeculectomy with mitomycin C in pseudophakic patients with open-angle glaucoma: outcomes and risk factors for failure, Fontana H; Nouri-Mahdavi K; Caprioli J, American Journal of Ophthalmology, 2006; 141: 652-659

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In a single surgeon series Fontana et al. (577) pressure control outcomes for a MMC trabeculectomy in pseudophakic eyes. MMC was applied for only one to three minutes, most often only one minute. The mean IOP was lowered from 19 to 10 mmHg at one and two years. The authors are to be congratulated for giving success rates by three different levels of pressure lowering/med reduction that correspond to appropriate target pressures for different stages of glaucoma. The one-year success rates of 87% for < 19 mmHg, 83% for < 16 mmHg and 76% for < 13 mmHg are good. However, at two years the success rates were down to 67%, 58% and 50%, and at three years (interpolating the lifetable) about 63%, 46% and 40%.

Are those 'acceptable long-term success rates'? Was the authors' acceptance of literature supporting that a one-minute application of MMC was as good as three to five minutes a wise choice? A careful reading of the citations in fact does not adequately support that notion. Megevand (Ophthalmology 1995; 102: 84-90) had only an average 12-month follow up in the two-minute application group. Manners (British Journal of Ophthalmology 2001; 85: 159-163) treated 25 patients for five minutes, 18 patients for two minutes and four patients for one minute. They switched from one exposure time to another during the study and thus would be expected to have very different average follow ups! No lifetable comparison is given. Finally, Kim (American Journal of Ophthalmology 1998; 126: 755-762) has a good sample size and randomized between two exposure times, but gives a three-year lifetable with an undefined failure criterion of not reaching 'a goal' and no information about how many patients were being followed at each year.

We have some evidence that a five-minute exposure may be significantly more effective over a long period of follow up in higher risk patients (Palmberg P, Ishida K, in: Coleman AL, Morrison JC (eds) Management of Cataracts and Glaucoma, 2005), in which the success rates for combined procedures were: by < 21 mmHg - 98% at one year, 95% at two years, 91% at five years and 86% at eight years, and by < 16 mmHg - 77% at one year, 70% at two years, 62% at five years and 54% at eight years, a much less steep fall-off over time. This matter remains uncertain, and is worthy of further controlled investigation.

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