Dear Editor

We read with great interest the article by Vysniauskiene et al.1 Their efforts in evaluating the intraocular pressure (IOP) changes of the contralateral eyes after trabeculectomy with mitomycin C (MMC) is appreciated. They concluded that a month after trabeculectomy, the mean IOP in contralateral eyes decreased. Of note, among the 24 fellow eyes in the study, 11 (45.8%) had topical ocular hypotensive therapy. Among the remaining 13 (54.2%) who had not, 12 of them had undergone trabeculectomy with MMC. We would be grateful if the authors may like to share with us their opinions as to whether the presumed “ophthalmotonic consensual reaction?may be modified in an unknown way by the topical medications or surgery, thereby affecting the interpretation of their results.

The decision by ophthalmologist to offer trabeculectomy is likely to be made at a point when the IOP is high on the variation curve. Therefore the decreased IOP in the fellow eye could be due to the “regression to the mean effect. The IOP of the fellow eye was measured 1 day before surgery, as well as 1 day and 1 month after surgery. As the study was conducted between 1995 and 2000, we would be interested to know the long term IOP changes after surgery. We suggest that this may help to lessen the effect of regression to the mean, as well as to see how long will the “ophthalmotonic consensual reaction? persist beyond 1 month.

As the IOP in glaucoma patients is unlikely to follow a normal Gaussian distribution, and it appeared that the data set was not yet tested for normality, the use of non-parametric counterparts such as Wilcoxon signed rank test is probably more appropriate.

We would like to commend the authors for conducting the study on this interesting topic. We wish that the issues raised will help broaden the discussion.

References

1 I Vysniauskiene, T Shaarawy, J Flammer, IO Haefliger. Intraocular pressure changes in the contralateral eye after trabeculectomy with mitomycin C.

2 Weekers L. Modification experimentales de l'ophtalmotonous. Reaction ophtalmotonique consenuelle. Arch Ophthalmol (Paris) 1924;41:641- 58.