Sir,

We read with interest the article by Das et al1 on their experience on the use of Ahmed valve in the treatment of refractory glaucoma among Indian eyes. The encapsulation rate shown in this paper are indeed very different from our paper published using a similar glaucoma implants in Asian eyes.2

It was mentioned in the article that no ‘hypertensive phase’ was observed and the authors attributed this to the continuous egression of aqueous through the dissected scleral flap. Such scleral flap is expected to be quite thin and certainly will not be as deep as what one would expect in nonpenetrating trabeculectomy as the authors made no attempt to create such depth at the time of dissection. If that was the case, egression of fluid through the scleral flap is not likely. If the egression of fluid is from the anterior chamber entry wound, the presence of the scleral flap would make no difference.

Furthermore, if there is still drainage through the scleral flap 4 weeks after the operation, it would be hard to determine whether the control of the IOP is due to the slceral flap draining or the Ahmed valve. If there is no encapsulated bleb, what would be the causes of failure?