A Clinical Trial of Phacoemulsification Versus Phacoemulsification & the iStent Implantation in POAG Patients

A Randomized, Double-Masked Clinical Trial of Phacoemulsification Compared With Phacoemulsification and Micro-Bypass Stent Implantation in Patients With POAG

This was a prospective, double-masked, 15-month clinical trial comparing efficacy of phacoemulsification alone to combined phacoemulsification and implantation of the iStent® trabecular micro-bypass stent in patients with primary open-angle glaucoma.

This was a prospective, randomized open-label study of 36 patients with POAG scheduled to undergo phacoemulsification with intraocular lens implantation ("cataract surgery"). Patients were randomized 2:1 to receive either cataract surgery alone (control group) or cataract surgery and iStent implantation (combined surgery group).

Implantation of the study stent occurred after cataract extraction and IOL insertion using the same small, temporal, clear-corneal incision (approximately 3 mm) used to perform phacoemulsification and IOL placement. The study stent was guided into Schlemm's canal using ab-interno gonioscopy (using a Swan-Jacobs gonioscope). (Figure 1) If no complications occurred during phacoemulsification, acetylcholine was injected in the anterior chamber after the IOL implantation to constrict the pupil. The anterior chamber was then filled with a viscoelastic agent to reform the anterior chamber and provide more clearance in the angle.

The anterior chamber was traversed with the applicator (the implant was on the tip of applicator) and the trabecular meshwork located. The leading edge of the device was gently slid through the trabecular meshwork and into Schlemm's canal at the nasal position (3 to 4 o'clock for the right eye; 9 to 8 o'clock for the left eye) with the tip of the implant directed inferiorly. If difficulty was encountered with the insertion at the primary location, we tried inserting about 0.5 clock hour inferiorly; and continued to move inferiorly as needed for subsequent attempts. Next, the device was released by pushing the button on the applicator, position of the stent was verified and the applicator was withdrawn.

The patients were instructed to discontinue all glaucoma medications after surgery. Standard post cataract extraction antibiotic and anti-inflammatory drug regimen was prescribed. Target pressure for each patient was determined prior to study entry. Following the assigned procedure, any patient with an IOP (as measured between 8 and 10 AM) that was greater than 2 mm Hg over their target was instructed to return twice in the following three days for re-measurement of their IOP. If the patient's IOP was > 2 mm Hg over their target pressure, ocular hypotensive agents were added. The medications were added in a pre-set schedule, with beta-blockers first, angiotensin-converting enzyme (ACE) inhibitors second, and prostaglandins third. If, however, on the third consecutive visit the patient's IOP was within 2 mm Hg of target, patient re-entered the normal visit schedule. Investigators were masked to treatment assignment both when measuring IOP and when determining when or if to add medications.

Inclusion Criteria:

• a previous diagnosis of POAG
• an IOP of > 18 mm Hg at three separate visits if on one medication, or subjects on at least two medications with uncontrolled IOP on three separate visits.
• all patients were deemed likely to follow surgeon instructions and were able to give informed consent.

Exclusion Criteria:

• any glaucoma diagnosis other than POAG
• the presence of peripheral anterior synechiae (PAS)
• a cloudy cornea likely to inhibit gonioscopic view of the angle
• any previous ocular surgery
• history of trauma or ocular surface disease
• the presence of peripheral anterior synechiae (PAS)
• a cloudy cornea likely to inhibit gonioscopic view of the angle