Commentary on: Nonpenetrating deep sclerectomy in advanced open-angle glaucoma

This retrospective review is probably one of the very few Indian studies available on the safety and efficacy of nonpenetrating deep sclerectomy (NPDS) with Mitomycin-C (MMC) in advanced glaucoma. This is because only very few centers in South India are performing NPDS. I congratulate the authors for their analyses. The follow-up period was limited to 1 year. They had an intraocular pressure (IOP) reduction of 52.1% from baseline and a decrease in the number of anti-glaucoma medications (AGMs) by 45% at the end of the first year. 55.6% required additional bleb needling for IOP control. They concluded that NPDS with MMC with or without phacoemulsification was a safe surgery for management of advanced glaucoma. Maheshwari et al.[1] also had a similar IOP reduction in advanced glaucoma, but only 35% patients needed an additional procedure for control of IOP. However, as compared to advanced glaucoma, NPDS in childhood glaucoma has shown a higher success rate with respect to reduction in IOP and complications as compared to trabeculectomy.[2,3] Al-Obeidan et al.[2] showed that the probability to survive was 74.6% after the 12th month with the mean IOP decreasing to 11.5 ± 3.0 mmHg compared to 31.9 mmHg preoperatively. Yet, a Brazilian study found that NPDS effectiveness did not differ among different glaucoma stages.[4] Studies have shown that advanced glaucoma requires IOP in the range of 8–12 mm Hg or lower to prevent the progression of the disease, more so in patients with normal tension glaucoma.[5,6] Since these values approach the clinical definition of hypotony, a thin line exists between the very low IOP needed to achieve control of glaucoma and the devastating complication of hypotony. To walk this tightrope, surgeries such as NPDS provide a barrier in the form of the Trabeculo-Descemet’s membrane, which keeps the anterior chamber (AC) deep with lesser inflammation, which in the long run decreases the chances of cataract formation. Although IOP reduction targets for clinical studies can be achieved using the standard definitions of complete and qualified success, the need for a very low target IOP should be incorporated in studies where advanced glaucoma is considered. Most of our surgeries did not achieve this goal. The present results are also more in tune with targets for mild-to-moderate glaucoma where the advent of minimally invasive glaucoma surgery (MIGS) has completely revolutionized the scene. Studies with the XEN stent combined with phacoemulsification were as effective and safe as phaco with NPDS at 9 months; however, NPDS alone may be more effective than the XEN gel stent in reducing IOP in patients with OAG, with longer surgical success.[7,8] The former had a 25.6% mean drop in IOP in the NPDS group as compared to the 18.9% drop in the Xen group. Suture gonioscopy-assisted transluminal trabeculotomy (GATT), a form of MIGS, has also provided similar efficacy and a better safety profile as compared to trabeculectomy.[9] Both NPDS and Ex-PRESS produce an IOP-lowering effect of approximately 25%. Success rates are similar after both procedures, and both seem to lead to a stabilization of visual loss.[10] Studies have also indicated that the 3-year success rate for IOP control for trabeculectomy with MMC was 68–79%[4,5] NPDS has a steeper learning curve as compared to the so-called gold standard trabeculectomy. The peeling of the juxtacanalicular trabecular meshwork with the capsulorrhexis forceps is an important step in this surgery. The creation of the deep flap is a challenge, and for that, the superficial flap must be thin, which itself is a challenge. Furthermore, the accidental perforation of the Trabeculo-Descemet’s membrane may require conversion to trabeculectomy, thereby abandoning NPDS. Since a bleb is formed in NPDS too, all the complications associated with it and its management will be present as in a trabeculectomy. Therefore, controversy exists regarding the safety and efficacy of this procedure as compared to trabeculectomy, more so in the patients with advanced glaucoma. The long-term safety profile of NPDS must be taken into consideration. The concern for transconjunctival oozing is high.[11] Finally, the efficacy and safety of a surgical procedure for glaucoma can also be indirectly determined by its acceptance by the glaucoma surgeons. More than 25 years down the line, acceptance of NPDS appears to be on the decline, especially for cases of advanced glaucoma, the increasing numbers of which are becoming more and more apparent.[12]