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Editors Selection IGR 16-4

Surgical Treatment: Trabeculectomy vs. Goniotomy in advanced PACH

Comment by Anand Naik Bukke & Tanuj Dada on:

104517 Efficacy and safety of trabeculectomy versus peripheral iridectomy plus goniotomy in advanced primary angle-closure glaucoma: study protocol for a multicentre, non-inferiority, randomised controlled trial (the TVG study), Gao X; Lv A; Lin F et al., BMJ open, 2022; 12: e062441

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Xinbo Gao et al. report the study protocol for a multicenter, non-inferiority, randomized controlled trial with the aim of evaluating the efficacy and safety of trabeculectomy versus surgical peripheral iridectomy (SPI) plus goniosynechialysis (GSL) plus goniotomy (GT) in 88 patients with advanced primary angle closure glaucoma. The primary outcome is intraocular pressure (IOP) at 12 months postoperatively, while secondary outcomes include cumulative success rate of surgery, surgery-related complications and number of IOP-lowering medications.

It is important to understand that the major mechanisms leading to primary angle closure disease are pupillary block, an anteriorly placed/thick lens and plateau iris.¹ After laser iridotomy is done as the initial therapy to relieve pupillary block, the lens plays a pivotal role in disease progression.² The treatment put forth in the present study does not address lens based mechanisms/plateau iris and this is not the current standard of care. It is important to evaluate the anterior chamber depth (ACD), lens thickness and lens vault and in eyes with a very shallow ACD performing a trabeculectomy alone or performing GSL+GT would not be a good choice. Additionally performing three procedures (SPI +GSL+GT) makes it impossible to attribute the proposed IOP lowering to any specific procedure as each of the above has the potential to lower IOP.

The control group will undergo Trabeculectomy with Mitomycin C, however the dose mentioned in the study protocol has huge variability with concentrations ranging from 0.2 mg/ml to 0.5 mg/ml and duration ranging from one minute to five minutes which can significantly alter safety and efficacy outcomes within the group.³ A uniform dose and duration would have been ideal. Regarding the intervention group, a surgical iridectomy is performed after a conjunctival incision. We would have preferred a laser iridotomy prior to the surgical procedure as SPI makes the eye prone to additional complications.⁴

The location of the GT in the study is variable (nasal or infero-nasal) and the exact circumference to be operated is not fixed (mentioned up to 120 degrees) which can impact outcomes. Additionally, GT has to be performed with either a microhook or microblade which can have different outcomes as the hook makes an incisional goniotomy with intact TM leaflets while the blade cuts and removes TM leaflets.

Although this technique of GSL + GT has not been previously evaluated in phakic PACG, addition of GSL to lens extraction has not been found to be superior to lens extraction alone with recurrence of PAS on follow up.⁵ In the present study, deepening of the anterior chamber with viscoelastic and GSL would lead to temporary opening of the anterior chamber angle which would have a high tendency to close as the anterior chamber remains shallow without lens removal.

The protocol mentions that participants will be withdrawn from the study in case of severe adverse events occurring during the study and surgical failure. These must be included in the analysis to get a proper perspective of study outcomes.

The authors are to be commended for taking on this challenging study which also requires a high degree of surgical expertise. Operating on advanced PACG without performing a laser iridotomy and performing filtering surgery or GSL+GT without consideration of the lens in decision making and disease alleviation is likely to be the major limitation of the proposed study.

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