New drainage devices reducing intraocular pressure

Growing range of drainage devices providing new options in the treatment 
of glaucoma

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A number of new drainage devices are now available which can provide significant reductions in intraocular pressure (IOP) with much less trauma to the eye than conventional filtration procedures, said Ingeborg Stalmans MD, PhD, Katholieke Universiteit Leuven, Belgium, at the XXXIII Congress of the ESCRS in Barcelona, Spain. The new devices are designed to provide a channel for the outflow of aqueous to the subconjunctival space, Schlemm’s canal or the suprachoroidal space. The surgery involved includes ab interno techniques that can be performed in conjunction with cataract surgery and ab externo techniques that are meant to be simpler and safer than trabeculectomy, Dr Stalmans said. SUBCONJUNCTIVAL DRAINAGE The Ex-PRESS shunt is an ab externo device that directs aqueous from the anterior chamber into a subconjunctival bleb. The stainless steel device consists of a 27-gauge shaft with an outer diameter of 0.4mm and a 50-micron or 200-micron axial lumen. The shunt’s implantation procedure is similar to a trabeculectomy and involves the creation of a scleral flap, but does not involve an iridectomy or removal of scleral tissue. Several studies conducted over the past 10 years suggest that it is as effective as trabeculectomy and is less traumatic to the eye, Dr Stalmans said. For example, in a prospective randomised study, the IOP reductions were statistically similar from three months onward in patients who underwent trabeculectomy and those who underwent implantation of the Ex-PRESS shunt (p=0.594). However, in the Ex-PRESS group, there was significantly less early hypotony (four per cent vs 32 per cent; p<0.001), and choroidal effusion (eight per cent vs 38 per cent; p<0.001). (Maris et al. J Glaucoma. 2007; 16:14-19) More recent comparative studies have shown similar results regarding IOP as well as showing quicker visual recovery (Beltran-Agullo, Journal of Glaucoma 2015;24: 181-186) and less endothelial cell loss (Casini et al, Am J Ophthalmol 2015:1185-1190) with the Ex-PRESS implant than with trabeculectomy. The XEN Gel Stent (AqueSys/Allergan) implant is another subconjunctival filtration device. However, it creates a filtration pathway from inside the eye. It is composed of a soft pliable collagen-derived gelatine material. It is inserted using a 27-gauge needle and (optionally) visualising the meshwork with a gonio mirror. The results in 216 open-angle glaucoma patients from the still ongoing APEX study showed that, 12 months following implantation of the XEN device, mean IOP was reduced from 21.4mmHg on a mean of 2.6 medications, to 13.8mmHg on a mean of 0.6 medications. Results were similar between patients who underwent phaco in combination with XEN implantation versus XEN implantation alone. SCHLEMM'S CANAL There are also now a range of ab interno devices that are designed to direct aqueous out through Schlemm’s canal. They include iStent® (Glaukos) and the Hydrus™ (Ivantis). Studies show that when combined with cataract surgery they generally reduce IOP just slightly more than cataract surgery alone, but also reduce the need for medications, Dr Stalmans noted. “These implants may not be the best choice for advanced glaucoma patients. But, if you have a patient with mild glaucoma in which a higher target pressure is sufficient, then you might consider using them,” she added. The iStent is a trabecular bypass device composed of non-ferromagnetic titanium. The L-shaped device has a 1.0mm-long shaft, which fits into Schlemm’s canal, and a snorkel with a 120-micron lumen, which extends into the anterior chamber. In an independent randomised controlled study, the mean IOP at 15 months was just 0.9mmHg lower in eyes that underwent cataract surgery and implantation of a single iStent than it was in eyes that underwent cataract surgery alone (14.8mmHg vs 15.7mmHg). However, patients with the iStent required significantly fewer medications (0.4 vs 1.3; p=0.007). (Fea et al, J Cataract Refract Surg 2010; 36:407-412) The Hydrus micro-stent is an intracanalicular scaffold which is eight times longer than the iStent. Results with the device so far suggest that, like the iStent implants, combining it with cataract surgery does not reduce IOP much more than cataract surgery alone, although it does reduce the need for medications. SUPRACHOROIDAL CHANNEL There are now also a number of new implants designed to direct the outflow of aqueous into the suprachoroidal space. They include implants designed for implantation using an ab externo approach, such as the Gold Shunt (SOLX), the STARflo™ (iSTAR) and the Aquashunt™ (OPKO), or for implantation with an ab interno approach, such as the CyPass® (Transcend Medical) and the iStent Supra® (Glaukos). The ab externo devices are invasive and limit further surgical options. The ab interno devices are still under investigation and their longer-term efficacy remains to be determined, Dr Stalmans said. Ingeborg Stalmans: ingeborg.stalmans@mac.com