Cutting Edge Glaucoma - Issue 2

MINIATURIZATION IN GLAUCOMA MONITORING AND TREATMENT: A REVIEW OF NEW TECHNOLOGIES THAT REQUIRE... • 53  direct outflow into the suprachoroidal space; and interventions that create an opening under the conjunctiva, a filtering operation ab interno. Since the trabecular meshwork is considered the main point of resistance to aqueous humor outflow, bypassing this structure and directing the flow from the anterior chamber into Schlemm’s canal seems to be a reasonable approach. It should be clear from planning such an intervention that the postoperative IOP cannot be lower than the episcleral venous pressure (EVP). The latter is not easy to evaluate but is reported in different studies to be in the range 7.6–9.1 mmHg [36]. The literature gives the impression that this approach probably has the greatest amount of published clinical experience. At the moment (and to the best of our current knowledge, given that newcom- ers appear quite rapidly in the field of MIGS), three stents for trabecular bypassing are available: iStent, iStent inject, and Hydrus. All three of them come with a specific injector system and have been implanted in a relatively large number of stand-alone procedures and as part of an extended cataract operation. iStent inject holds a special place among MIGSs, as it is the smallest of all the available microstents. It nevertheless seems to be able to lower IOP considerably. In a recent study, two iStent injects were implanted in each of 99 eyes. Preoperatively, the mean IOP was 22.1 ± 1.3mmHg (under topical antiglaucomatous medication) and 26.3 ± 3.5mmHg (after a washout phase). Twelve months after the implantation of the iStent inject, the IOP had dropped by 40.2% compared to the baseline pressure and was reduced to a mean 15.7 ± 3.7 mmHg. About a quarter of the study eyes required additional IOP reduction by topical medications. An IOP of 18 mmHg or lower with and without medication was achieved by 81% and 66% of the patients, respectively [44]. The Hydrus microstent is inserted through a clear corneal incision into Schlemm’s canal. After the implantation, it dilates Schlemm’s canal in the complete nasal quadrant. That mecha- nism causes the aqueous humor to bypass the trabecular meshwork. Pfeiffer et al . published a prospective, randomized, single-masked 2-year clinical study comparing the efficacy and safety of a combined procedure with the Hydrus microstent implanted during cataract surgery and cataract surgery alone. Mean baseline IOPs were 26.3 ± 4.4 mmHg in the Hydrus plus cataract surgery study arm and 26.6 ± 4.2 mmHg in the phacoemulsification (PE/IOL) study arm. At the 24-month follow-up visit, mean IOPs were 16.9 ± 3.3 mmHg in the Hydrus/PE/IOL study arm and 19.2 ± 4.7 mmHg in the PE/IOL study arm. Twenty-four months after implantation, four out of five patients with Hydrus/PE/IOL experienced a decrease in IOP of 20% or more. This was achieved in a mere 46% of patients treated with PE/IOL only [35]. A device that creates outflow via the suprachoroidal space is the iStent Supra. It is CE approved and currently in the process of undergoing FDA approval. A prospective randomized trial involv- ing more than 500 patients is currently under way across 36 sites. A recent publication reported on the effects of having one iStent Supra implanted in 80 patients together with two iStents. After 48 months, 97% and 98% of the eyes achieved IOP ≤ 15 and ≤ 18 mmHg, respectively, on one medication [27]. Another option for MIGS is the subconjunctival approach. Not unlike in trabeculectomy, the aqueous humor is provided with a new, nonphysiological outflow. The XEN gel stent is insert- ed through a small, self-sealing, clear corneal incision. The device is brought into place in the