Dear Editor,
We would like to thank Pandey et al.,[1] for the interest and feedback on our article. We take this opportunity to reiterate that the primary purpose was to report on the lack of erosion with the needle technique in children, a technique that does not require donor material and cuts down operative time considerably.[2]
The only significant change in technique between the first and the later children was the more common use of viscolelastic in those operated more recently, but since there were very few children in whom its use was formally demonstrated we did not analyze that variable.
The success rate is indeed influenced by including or excluding children with short follow-up. Final survival of surgery lowers to 23.5% at 96 months. We are including a new Kaplan-Meier graph that is plotted with all eyes for comparison purposes [Fig. 1].
The endophthalmitis case had developmental glaucoma due to Axenfeld-Rieger, she had first a blebitis at the trabeculectomy site, it was diagnosed eight months after the Ahmed glaucoma valve (AGV) was implanted, it did not respond to topical fortified antibiotics and was eventually eviscerated.
Table 3 clearly shows 24 cases failing due to bleb fibrosis, all these were managed by removing the fibrosis, four of these had to have a second implant in the same eye to finally control intraocular pressure (IOP). We did not attribute a particular previous surgery to a failed event, but we did find that previous glaucoma surgeries increase the risk of valve failure.
You are correct in pointing out that a control group was not attempted, while controls and preferably a randomized design would have been ideal, the technique was already accepted practice in the clinic, and our more modest goal was to report the results as expected in day to day practice. A lot of the literature consists of such series and we tried to follow the guidelines to make such reports more acceptable.[3] All surgeons were taught first in several adult, simpler cases, before they had the chance of operating on a child.
Regarding success criteria we did use what is usually reported, namely an IOP below 21, but the scatterplot in figure 2 of the original article[2] (designed around the WGA recommendations for reporting surgical trials[3]) serves the purpose of presenting each eye with both the initial preoperative IOP and IOP at last control, so any person can use a different cutoff value to compare with previous and future similar studies. In fact, we included a line for using 15 mmHg as a success criterion and a diagonal line for using a 30% reduction, so if you combine these lines with counting failures due to different criteria (namely, counting triangles) you can get a global success rate with stricter criteria of 57%.
Figure 1.
Kaplan-Meier plot of survival including all 204 eyes, even those with less than 6 months of follow-up, from 167 children receiving an Ahmed valve between 1994 and 2002
References
- 1.Pandey N, Dwivedi V. Evaluation of Ahmed glaucoma valve implantation through a needle-generated scleral tunnel in Mexican children with glaucoma. Indian J Ophthalmol. 2011;59:523. doi: 10.4103/0301-4738.86334. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Albis-Donado O, Gil-Carrasco F, Romero-Quijada R, Thomas R. Evaluation of Ahmed glaucoma valve implantation through a needle-generated scleral tunnel in Mexican children with glaucoma. Indian J Ophthalmol. 2010;58:365–73. doi: 10.4103/0301-4738.67039. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Shaarawy T, Grehn F, Sherwood M, editors. The Netherlands: Kugler Publications; 2009. WGA guidelines on design and reporting of glaucoma surgical trials. [Google Scholar]