Lynda Charters; Reviewed by Paul Healey, PhD, MMed, MBBS(Hons), FRANZCO

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Intraocular drainage surgery (IDS) may be relevant for patients with angle closure because the conventional outflow pathway can be blocked physically, first by the iris and then by secondary damage caused by the iris, inflammation and ischaemia in the trabecular meshwork (TM).

When considering the surgical approaches in these patients, removing the physical obstruction and enhancing the TM outflow by reducing the resistance with surgery to the TM may be the best options before considering enhancing or creating a nonconventional path of outflow, according to Dr Paul Healey. Dr Healey is clinical associate professor, based at the Centre for Vision Research, Westmead Institute for Medical Research; the Save Sight Institute, University of Sydney; and Westmead Hospital Eye Clinic and Sydney Eye Hospital, Sydney, Australia.

In theory, TM or Schlemm’s canal surgery for angle closure involves the same methods as established surgeries performed in open angles – remove, cut or dilate the TM or Schlemm’s canal.

Surgeons have several device options from which to choose, such as the Trabectome (NeoMedix), Kahook Dual Blade (New World Medical), Omni Glaucoma Treatment System (Sight Sciences) and iTrack (Nova Eye Medical) devices.

Trabecular microbypass stents include the Hydrus (Ivantis) or the iStent or iStent Inject (Glaukos Corporation). Dr Healey said any angle surgery is difficult in patients with angle closure because of the proximity of the iris to the TM.

“We know that the iris can cause further obstruction of the TM that can be hydrostatic or inflammatory. Therefore, in angle procedures that are inflammatory, we should consider what the risk of synechial closure in response to that inflammation might be,” Dr Healey said. If opting to use a stent in the TM to establish drainage in angle closure patients, surgeons must ensure that the stent outlets clear the iris, not just intraoperatively but also postoperatively, he emphasised.

There are few published evaluations of internal drainage surgeries in angle closure. So far, the only available data were obtained from iStent implantations combined with cataract surgeries, he said. To further complicate the issues associated with intraocular drainage surgeries in angle closure, no minimally invasive glaucoma surgery (MIGS) procedures or devices have been approved for this use. “The data we are discussing are purely experimental,” Dr Healey said.

Dr Healey recounted a study by Chansangpetch et al that evaluated the efficacy of cataract surgery with trabecular microbypass stent implantation in patients with angle-closure glaucoma.

 These patients had either open-angle glaucoma or angle-closure glaucoma treated with iridotomy but the IOP remained elevated. The patients underwent either cataract extraction alone or accompanied by iStent implantation.

The highest success rate was achieved in patients with angle closure who underwent phacoemulsification and iStent implantation; patients with angle closure treated with cataract extraction also did well. The patients in both angle closure groups saw a substantial decrease in the number of required medications postoperatively.

Another study reported a case series of iStent implantations and phacoemulsification in primary angle-closure glaucoma.

 The authors reported good decreases in IOP resulting from the combined procedure, but they also found that 27% of eyes had occlusion of the iStent by iris.

However, Dr Healey said the IOP was increased in only 2.7% of eyes. “While this may suggest some residual stent function, probably removal of the lens was the primary mechanism of preventing postoperative IOP increases in angle closure,” he said.

The risk factor for occlusion of the stent in this study was a deeper anterior chamber. “This actually makes sense because a patient with angle closure with a deeper central anterior chamber is more likely to have a nonpupil block/nonlens vault aetiology and therefore less likely to have an angle that is more open after lens removal,” he said.

Dr Healey handles these cases by first opening the closed angle, but he said iridotomy alone is usually inadequate. Lens extraction and sometimes goniosynechialysis are necessary to obtain close proximity to the TM.

He emphasised the importance of performing a procedure that is as minimally inflammatory as possible. “Think carefully about this when choosing the procedure,” he said. Finally, surgeons also must control the iris and the IOP during the postoperative period.

IDS in angle closure remains experimental. Investigators are collecting data regarding its efficacy as well as adverse effects.

Dr Healey said early case series often consist of two groups: those thought to have a higher probability of anatomic and physiologic success, and those for whom the choice of this procedure offered a lower risk of an adverse reaction compared with alternatives. “Evaluating outcomes from these and other studies will inform us of the value of these technologies in the management of angle closure and whether this is a procedure that is worth doing in the future,” Dr Healey explained.

Paul Healey, PhD, MMED, MBBS(HONS), Franzco
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Dr Healey is a consultant and adviser to Glaukos Corporation and receives lecture fees from the company. He is a consultant and adviser to Ivantis.

Chansangpetch S, Lau K, Perez CI, et al. Efficacy of cataract surgery with trabecular microbypass stent implantation in combined-mechanism angle closure glaucoma patients. Am J Ophthalmol. 2018;195:191-198.

Hernstadt DJ, Cheng J, Htoon HM, et al. Case series of combined iStent implantation and phacoemulsification in eyes with primary angle closure disease: one-year outcomes. Adv Ther. 2019;36:976-986.

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Intraocular drainage surgery in angle closure remains experimental and investigators are collecting data regarding its efficacy as well as adverse effects.

Author | Lynda Charters; Reviewed by Paul Healey, PhD, MMed, MBBS(Hons), FRANZCO

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