A new field in glaucoma surgery

Sustained IOP reduction

Numerous studies have shown that implantation of an iStent results in a sustained reduction in intraocular pressure (IOP) that corresponds to a significant reduction in medication.² In a terminal washout study comparing cataract surgery alone to cataract surgery with an iStent, the stent group achieved an approximate 3 mmHg greater reduction in pressure than the group that received cataract surgery alone.³ In addition, the iStent group sustained their target pressures with one less medication than the cataractonly group.

I have implanted multiple iStents in phakic and pseudophakic patients, and find that one iStent generally translates to a reduction of one type of medication. When implanting two or three stents, I have seen an approximate 40% drop in pressure, resulting in IOP around 14 mmHg. This corresponds with the prospective, randomized dose response study assessing the IOP lowering effects of one, two or three trabecular micro-bypass stents in 94 subjects, 30 of whom presented at six months.⁶ Mean baseline IOP after medication washout was 24.9 mmHg in both the one- and twostent groups, and 24.5 mmHg in the threestent group. Mean IOPs at month six were 16.1 mmHg, 13.7 mmHg and 13.6 mmHg respectively. Patients were uncontrolled on two medications when they entered the study, and were controlled on one medication postoperatively.

Importantly, all studies show an overall favourable safety profile with both single and multiple stent implantation. In the dose response study, at day one a one-stent subject had transient hypotony and a threestent subject had a small hyphaema; both events resolved by one week. In the aforementioned study evaluating implantation of two trabecular micro-bypass stents, a small hyphaema in one subject at postoperative week one resolved by one month, and no other complications or adverse events were reported.⁵