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Editors Selection IGR 11-2

Surgical Treatment: MMC versus MMC & amniotic membrane

Comment by Keith Barton on:

21678 Amniotic membrane transplantation in trabeculectomy with mitomycin C for refractory glaucoma, Sheha H; Kheirkhah A; Taha H, Journal of Glaucoma, 2008; 17: 303-307

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Sheha et al. (1254) report a prospective interventional study of 37 eyes with refractory glaucoma and a high risk of trabeculectomy failure. These eyes were randomised to receive either mitomycin C (MMC) (0.2mg/ml for two minutes and a single layer of amniotic membrane (AM) under a 4x3mm trabeculectomy flap or MMC alone. The authors report a somewhat staggering difference in success at one year (IOP control < 22 mmHg without medications) (12/15 or 80% in MMC+AM group, and 6/15 or 40% in the MMC-only group). The case mix in this study appears to have been similar in the two study groups. What is surprising is the high level of success in the MMC plus AM group in a study including patients that would have had a low chance of trabeculectomy success with MMC. The success rate, in terms of IOP control in the control (MMC only) group is around the level that would be expected for eyes with this level of risk for failure. While the authors speculate that the fibrosis-inhibitory properties of AM result in the higher success rate, it was the surgical technique that intrigued me. Rather than placing the AM solely under the scleral flap, they put a very impressive 10 x 15 mm sheet of AM on the scleral surface, thereby covering an area that encompassed, not only the area under the flap (the flap was flipped over the top of the AM), but a very wide area of the scleral surface surrounding the flap.

High risk eyes undergoing trabeculectomy with MMC (0.2 mg/ml for two minutes) and a single layer of amniotic membrane have a higher one-year success than those receiving just MMC alone

The principle site of healing in a trabeculectomy is usually the subconjunctival space, either on the flap surface (episcleral fibrosis) or peripheral to the bleb (ring of steel). Sub-scleral healing usually only becomes an issue when there is a large scleral flap and small sclerostomy, resulting in a large surface area of contact. When MMC is placed under the flap, it is likely that the Tenon's fibroblasts are also exposed, as it is difficult to limit MMC exposure to one area only, and a general reduction in healing results. The same is not true for AM.

However, using the technique presented in this paper, with a very wide application of AM, it seems that any anti-fibroblastic influence of AM would affect a wide area of the sub-conjunctival space, thereby explaining the better results. Although the authors alluded to this point, it was not emphasised in the article.

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