Viewpoint
The use of GDDs has minimized some of the complications more commonly seen with trabeculectomy. The AGV is widely used; because of the set internal resistance, it is not necessary to modify the implant at the time of surgery to prevent postoperative hypotony. However, the valve that obviates the need to modify the tube allows early percolation of aqueous, which may lead to the hypertensive phase. This phase usually occurs 1-6 weeks after surgery and can last as long as 6 months. Given that steroids are potent anti-inflammatory agents, it is plausible that they could help treat the hypertensive phase and improve IOP control after AGV implantation.
The TA group had a lower mean peak IOP overall, although this did not reach statistical significance. The frequency of the hypertensive phase was also lower in the TA group.
A limitation of this study is that follow-up was only up to 6 months, which is reported as the duration of the hypertensive phase. Long-term effects are unknown. In addition, only a single injection was given, but the half-life of TA in the subtenon space is not known to be that long. Therefore, longer-term studies with multiple injections may provide better and more statistically significant outcomes.
Perhaps an alternate study using subtenon TA at varied times and frequencies after the implantation might yield different results and complication rates. Given the current data, the investigators determined that because the findings do not support the use of subtenon TA at AGV implantation and the risk for complications increases, longer follow-up in this particular study was not needed.
This conclusion was probably a reflection of the two serious complications (early tube erosion and endophthalmitis) in the TA group. Both of these occurred in inferotemporal implants, which are known to have a higher rate of complications. Early tube erosion and endophthalmitis after a tube implant are still relatively rare, but serious, complications.
Therefore, TA may initially reduce the rate of the hypertensive phase, but the long-term outcomes are not statistically significant. The complication rate increases to a level that makes the risks outweigh the potential benefits. Therefore, at this time, intraoperative TA injections are not advocated. Further studies could still demonstrate a role for TA, but its use intraoperatively is not supported to date.
Abstract
Final Thought
A significant improvement in the success of Ahmed valves could be made by decreasing the hypertensive phase. The above studies demonstrate that reduction of inflammation may prove beneficial, but the approaches on how it can be accomplished are still under consideration. Thus far, preventing the conjunctiva from being exposed to inflammatory mediators seems more promising than trying to inhibit an inflammatory response with steroids, which may not be as useful.