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Editors Selection IGR 19-4
Surgical Treatment: Tocopherol and surgery outcome
Comment by Luca Rossetti on:
24188 Dietary tocopherol supplementation after trabeculectomy and phacotrabeculectomy: double-blind randomized placebo-controlled trial, Goldblum D; Meyenberg A; Mojon D et al., Ophthalmologica, 2009; 223: 228-232
Goldblum et al. (1344) report the results of a clinical trial testing the effect of dietary tocopherol supplementation on outcome of trabeculectomy or phacotrabeculectomy. The study is well designed and there is a control group treated with placebo. The trial's results clearly indicate that outcome of both trabeculectomy and phacotrabeculectomy is not different after tocopherol supplementation or placebo. Evidence about the antiproliferative and antifibrotic effect of alpha-tocopherol is weak; a paper from the same group showed that, among vitamin-E forms, only alpha-tocotrienol and not alpha-tocopherol had an antiproliferative effect on human fibroblasts in vitro at non toxic concentrations. It is true that this trial was a pilot study; however, there are some methodologic issues that, whether adopted, would have made the study results perhaps more conclusive. First, sample-size calculation was not mentioned and, in the presence of negative findings, the authors did not discuss the statistical power of their conclusions. Perhaps after considering the size of the study, the authors would have agreed to conduct a multicenter trial, which is preferable because it is less subjected to the 'surgeon/site' effect. One of the risks of running an undersized trial is the easy possibility of comparing two unbalanced groups: important prognostic variables like PEX, stage of the disease and IOP levels did not seem to be, in fact, similarly distributed in tocopherol and placebo groups. The are some other factors limiting the conclusiveness of this trial's findings: trabeculectomies and phacotrabeculectomies were studied together and this fact adds an important source of variability, in particular if the sample is small. In addition, the complication rates in both groups seem quite high (11/39, 28%) and this might have introduced a further problem in finding an effect of alpha-tocopherol, if this existed. Finally, a trial testing an effect of a dietary supplementation even though only for two months, should check for vitamin E in the blood; this would be interesting to know given the negative findings of this study.
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