GLAUCOMA STENTS

Micro-invasive glaucoma surgery (MIGS) involving ab interno implantation of a trabecular micro-bypass stent (iStent, Glaukos Corp.) during cataract surgery is a safe and effective means of controlling intraocular pressure (IOP) over the long term in primary open-angle glaucoma (POAG) patients, according to a study presented at the XXX Congress of the ESCRS.

“Our data shows sustained long-term reduced IOP and medication use following iStent implantation and cataract surgery. In this series, implantation of a single iStent with cataract surgery resulted in long-term IOP control four years after surgery with a reduced medication burden. It is significantly more effective than cataract surgery alone while maintaining a safety profile that is similar to cataract surgery alone,†said Antonio Maria Fea MD, PhD.

Dr Fea described the iStent as an FDA-approved heparincoated titanium tube that is 1.0mm in length with a microscopic opening of just 120 microns in diameter. The device is inserted ab interno through a small temporal clear corneal incision, bypassing the trabecular meshwork and placed in Schlemm's canal without disrupting the scleral surface. It improves outflow by allowing aqueous humour to drain directly from the anterior chamber into Schlemm’s canal bypassing the obstructed trabecular meshwork.

A number of recent studies in the scientific literature with up to two years' follow-up suggest that the device is effective at controlling IOP over this time period and is well tolerated by the ocular structures, said Dr Fea. “There is accumulating evidence from recent studies that this device combined with cataract surgery is able to significantly reduce the intraocular pressure in patients with early to moderate open-angle glaucoma. A recent study by our Spanish colleagues Arriola-Villalobos et al. shows nice control of the IOP in 19 patients with a mean follow-up of 53 months. No anti-glaucoma medications were used at the end of follow-up in 42 per cent of patients,†he said.

Turning to his own clinical experience with the iStent, Dr Fea said that in 2010 his group published the outcomes of a prospective double-masked randomised clinical trial of patients with phacoemulsification alone or phacoemulsification with iStent implantation. Primary outcomes were IOP and reduction in medication use over 15 months and IOP after a one-month washout of ocular hypotensive agents at 16 months postoperatively.

The study included 36 eyes with cataract and mild to moderate OAG, IOP greater than 18 mmHg on one ocular hypertensive medication or any IOP reading if the patient was on more than one ocular hypertensive medication. Exclusion criteria were a glaucoma diagnosis other than POAG, peripheral anterior synechiae, cloudy corneas likely to inhibit gonioscopic view of the angle, previous ocular surgery, history of trauma or ocular surface disease, preproliferative or proliferative diabetic retinopathy, and age-related macular degeneration with macular scar or large macular atrophy that would inhibit potential visual acuity.

“The main results of the study showed that implantation of the micro-bypass stent combined with cataract extraction resulted in significantly lower IOP and a significant reduction in the use of ocular hypotensive medications 15 months postoperatively compared with cataract surgery alone. The mean decrease in the combined surgery group was 3.2 mmHg compared with 1.6 mmHg in the control group. At the final follow-up at 15 months, 67 per cent of patients in the combined treatment group were medication-free compared with 24 per cent in the control group,†Dr Fea said.

To try to determine the long-term effect of the iStent on IOP, Dr Fea decided to recall his patients for a follow-up visit. Of the 12 eyes originally enrolled in the combined iStent and phacoemulsification group, one patient was lost to followup and one refused the wash-out procedure. Of the original control group of 24 eyes, five patients had subsequently died, four were lost to follow-up, and one was unable to attend.

Looking at the mean medicated IOP over time, Dr Fea said the lower IOP in the treatment group carried through to month 55 of the follow-up, with a mean of 15.9 mmHg for combined group compared to 17.0 mmHg for control. A slight difference was also found in the mean use of ocular hypotensive medications, with sustained lower medication use in the treatment group, although this was not statistically significant. However, after washout of ocular hypotensive medications the IOP at month 56 decreased 0.3 mmHg in the treatment group versus an increase of 3.6 mmHg in the control group, said Dr Fea.

In terms of safety, both groups recorded excellent longterm best-corrected visual acuity, with no secondary surgeries or adverse events in the treatment group, and one case of macular drusen in the control group, he said. Summing up, Dr Fea said that most patients sustained long-term reduced IOP and medication use following iStent implantation and cataract surgery. “The IOP-lowering effect of phacoemulsification alone is not as consistent and as predictable as ophthalmologists would like, which is why the iStent will probably become a commonly used adjunctive device for many patients with mild to moderate glaucoma,†he concluded.