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Editors Selection IGR 16-3

Surgical treatment: Aqueous drainage devices

Comment by Nitin Anand on:

59586 Five-Year Treatment Outcomes in the Ahmed Baerveldt Comparison Study, Budenz DL; Barton K; Gedde SJ et al., Ophthalmology, 2015; 122: 308-316

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In-vivo testing of a novel adjustable glaucoma drainage device, Villamarin A, Stergiopulos N, Bigler S, Mermoud A, Moulin A, Roy S, Investigative Ophthalmology and Visual Science 2014;55:7520-7524 In an experimental study, Villamarin and colleagues implanted an adjustable glaucoma drainage device (AGDD) made of deformable silicone, in seven white New-Zealand rabbit eyes. The device body was implanted under a seven-by-seven mm limbal scleral flap, with the nozzle inserted into the anterior chamber and a distal outlet for drainage into the subconjunctival space. In the device body is an asymmetrically placed magnet and a peripheral deformable tube that can be progressively compressed by rotating the magnet. Thus, the angular position of the magnetic disk defines the length of the tube that is compressed. An external control unit (CU) can rotate the magnet without touching the device. The CU also has a compass that indicates the position of the magnet.

The implanted device was opened with the CU once a month for four months. IOP dropped in all eyes each time the implant was opened from a mean of 11.2 mmHg (range 7-17 mmHg) to 4.8 mmHg (4-7 mmHg). The IOP dropped by 8 mmHg even in the third to fourth month. Histopatholgy was reassuring, with a mild granulomatous reaction around the device in most eyes.

The study has significant translational implications. In eyes with a low propensity to fibrosis, it can be implanted like the Express shunt to allow for an anterior filtration bleb. IOP can be titrated keeping it in the high normal range in the early postoperative period. If adjuvant Mitomycin C is used, the ability to regulate flow may be of great advantage in the long-term. Late hypotony could possibly be reversed simply by completely closing the device.

The AGDD may be used in conjunction with various implants designed to direct flow posteriorly like the Baerveldt or Molteno implant. Regulating the early IOP is problematic with these implants. Surgeons use various permutations of intraluminal sutures, external suture ligatures and slits in the tube to regulate IOP. The AGDD may offer a solution. The device may be closed or partially open in the early postoperative period depending on the IOP. Early hypotony and IOP spikes, two persistent problems for tube surgeons, could possibly be eliminated. Another possible innovation may be to design an AGDD with a longer nozzle to enable more posterior implantation and drainage.

The short follow-up is a limitation of rabbit eye experimental studies. The article alludes to trials with the device on human eyes and these are eagerly awaited.

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