Attempts to control IOP through medical therapy tend to be first-line treatment although patient compliance and ocular surface integrity remain a concern
Interest in Schlemm's canal has grown in recent years as glaucoma surgeons continue to look for techniques that will provide sustainable intraocular pressure (IOP) reduction with safe outcomes.
Large prospective studies have told us the risk of glaucomatous progression is substantially reduced with lowered IOP. In a study published in the Archives of Ophthalmology in 2003, each mmHg reduction in IOP was associated with about a 10% decrease in the risk of progression.1 This study also confirmed that the lower the IOP at follow-up, the lower the risk of progression.
Attempts to control IOP through medical therapy tend to be first-line treatment although patient compliance and ocular surface integrity remain a concern.2
In the last few years, several methods to reduce the trabecular resistance to outflow (such as trabeculotomy, trabecular aspiration and surgical implants) have been introduced. The major advantage of all these methods is the use of microincisions and the sparing of the conjunctiva; however, these surgical therapies have a high rate of complications. In an attempt to reduce the high complications rate and lack of sustained efficacy of available surgical therapies, Glaukos Corporation developed the iStent; recent studies have shown the efficacy of the iStent in improving trabecular outflow in implanted eyes.9
What is the iStent?
Results from a European trial of the iStent in patients undergoing combined glaucoma and cataract surgeries showed the iStent provided a mean IOP reduction of 4.4 mmHg along with a reduction of 1.2 medications. These reductions were maintained on the study cohort through the 12-month follow-up.10,11,12
Glaukos is currently enrolling patients in a Phase III, randomized, comparative, controlled, parallel-assignment FDA trial, and is also conducting Phase IV trials in Europe in phakic and pseudophakic eyes.
How to implant the iStent
Some technical abilities are necessary for the stent implantation procedure to be successful. The surgical protocol necessitates that the surgeon be familiar with gonioscopy and the angle appearance, and must correctly visualize the angle structures before attempting the implantation. An accurate knowledge of the angle anatomy greatly facilitates implantation; when the stent is implanted in the correct position, no resistance is felt as it enters the trabecular meshwork and Schlemm's canal. I found it helpful to analyze carefully with a slit lamp the trabecular meshwork of all the patients I have implanted.
I have implanted the iStent primarily in conjunction with cataract surgery using a temporal approach. The stent is implanted in the nasal quadrant and preserves the conjunctiva of the superior quadrants for eventual future surgical options.
Because the procedure also uses the patient's pressure-dependent, steady-state physiological outflow system, the potential for hypotony is virtually non-existent.
I have personally implanted the iStent in conjunction with cataract surgery in 10 patients with a preoperative IOP higher than 18 mmHg if the patient is on one medication or with any IOP if on more than one medication.