Author Response, Regarding “Simultaneous Implantation of an Ahmed and Baerveldt Glaucoma Drainage Device for Uncontrolled Intraocular Pressure in Advanced Glaucoma”
On behalf of the authors of “Simultaneous implantation of an Ahmed and Baerveldt glaucoma drainage device for uncontrolled intraocular pressure in advanced glaucoma,” we thank Dr Gupta for the observations and questions regarding our report. Please find these questions addressed as follows.
As acknowledged in our manuscript, this study was retrospective and, therefore, subject to the typical limitations of retrospective investigation—most notably here, loss of follow-up data, particularly after 1 year. Another limitation of this retrospective study is the absence of a standardized follow-up schedule, as the postoperative follow-up schedule was determined by the surgeon. Data were included here for postoperative months 1 and 3 as these were dates nearly uniformly chosen for follow-up by the surgeons—assessment of the hypertensive phase of an Ahmed valve, typically defined as elevated intraocular pressure (IOP) within 3 months, can be evaluated from these time points.1
Although Dr Gupta notes the participation of 6 surgeons in this study as a weakness, this could be equally argued as a strength, demonstrating this technique is generalizable to multiple surgeons. Notably, all 6 surgeons in this study are experienced, glaucoma-fellowship–trained physicians who were proficient in implantation of glaucoma drainage devices (GDDs) over this study time period. We did not collect data regarding tube placement in the anterior chamber versus the pars plana versus the ciliary sulcus—tube position was determined by the surgeon pending the individual factors in each case. The GDD models used were primary the Ahmed FP7 and Baerveldt 350, although, again drainage device model was at the discretion of the individual surgeon. We did not examine the difference between the drainage device models for complications such as erosion, leak, or blebitis—notably, the incidence of these complications was so small that such analysis may not be appropriate.
In regards to hypotony, we would reference Figure 2 within the article, which illustrates a Kaplan-Meier survival curve with “failure” including the criteria of IOP not between 5 and 18 mm Hg (thus denoting hypotony with IOP<5 mm Hg as a failure). To provide more specific detail, rates of hypotony with hypotony defined as an IOP of ≤5 mm Hg: postoperative days 1 to 7 of 59 eyes (11.9%); posteroperative months 1 to 7 of 53 eyes (13.2%); and postoperative years 1 to 2 of 27 eyes (7.4%). As noted in Table 3, no patients developed hypotony maculopathy and 2 patients (3.4%) required tube ligation or removal for hypotony. Dr Gupta mentions preoperative IOP in this study (25.5±9.8 mm Hg) is lower than in some studies of single GDD implantation—it is notable that subjects in this study belong to a very specific advanced glaucoma population, requiring 3.4±1.4 medications and with 46% having prior glaucoma surgery. Therefore, comparisons between this population and those included in studies of single GDD implantation may be difficult.
To clarify, of the patients included who had prior glaucoma surgery, only 1 patient was status post-GDD—this GDD had been removed before this study. The other surgeries were primarily trabeculectomy.
We hope the above responses are useful in clarifying our experience with the technique of simultaneous implantation of Ahmed and Baerveldt GDDs.