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Positioning important when implanting trabecular micro-bypass stent
A surgeon explains why he pays special attention to the position of the patient and the placement of the device.
Open-angle glaucoma currently affects 2.2 million people in the United States, and that number is expected to increase to 3.36 million by 2020. It can be treated with medications, laser or filtration surgeries, but most cases of mild to moderate glaucoma have been without a surgical option with an appropriate risk profile. Fortunately, technologies are arising to meet the demand. The new category of microinvasive glaucoma surgery groups together a variety of novel surgical options for the treatment of glaucoma that have significantly lower risk profiles than traditional glaucoma surgeries. These devices are changing the glaucoma treatment paradigm and offering patients new options.
Jason Bacharach
The iStent trabecular micro-bypass stent (Glaukos) is one such MIGS device that gives comprehensive ophthalmologists and glaucoma specialists a low-risk surgical option for treating their patients with comorbid cataracts and mild to moderate glaucoma. The iStent is delivered ab interno through the same clear corneal incision used for cataract surgery and is implanted in Schlemm’s canal, creating a pathway for aqueous humor to drain from the anterior chamber.
The keys to successful implantation of the iStent are good visualization of the angle and being comfortable working in the angle using intraoperative gonioscopy. As surgeons re-master the technique, new options in goniolenses have been introduced into the marketplace to facilitate implantation and suit individual surgeon preference. All ophthalmologists have training and office experience using gonioscopy; thus, mastering intraoperative gonioscopy requires only a short and accessible learning curve. It is helpful to be able to identify typical landmarks such as Schwalbe’s line, the scleral spur, the trabecular meshwork and Schlemm’s canal.
Surgical procedure
My initial technique was to follow my normal operating procedures for cataract surgery. When the cataract surgical component is complete, I hyper-inflate the chamber with viscoelastic and occasionally instill a miotic into the anterior chamber to move the iris out of the angle so that I can visualize the deeper structures easier. Recently, if I have found the angle to be wide open during preoperative assessment, I will place the iStent before performing the cataract surgery. This modification ensures a clear view before any intraocular phacoemulsification energy, which could potentially cause some corneal haze. This modification has also reduced the per-case cost because I can complete the entire case with one tube of viscoelastic.
Positioning the patient is key to good visualization. If I have already performed cataract surgery, I turn the scope 30° toward the surgeon and move the head of the patient 30° away from the surgeon’s position, which may require you to adjust the tape on the head of the patient. Finally, I increase the magnification from a typical 8 to 10 times magnification to 10 to 12 times magnification for implantation of the device.
I then insert the applicator into the eye through the phaco incision, maintaining my finger on the trigger of the applicator so that I do not have to search for it when I need it. With one hand on the gonioprism lens with which I have already focused, I make a transpupillary approach at a 15° angle toward the trabecular meshwork. Searching for areas of pigmentation, I then touch the angle with the device because that allows me to confirm my position. I then engage Schlemm’s canal in an area of pigmentation with the device. Pigmented areas tend to be where collector channels are located, which may ultimately result in better efficacy. Once engaged, I slide the device into position so that the retention features on the stent are in Schlemm’s canal.
It is important to make sure the stent is seated properly. The snorkel portion of the iStent should be in the anterior chamber, and the retention features should be visible through the trabecular meshwork. The view through the inner wall will be cloudy but visible. Once comfortable with the placement, I press the trigger to release the device from the applicator. I use the back of the applicator to tap the heel of the stent to ensure that it is seated appropriately and then carefully remove the applicator from the eye. After this, I closely examine the ostium to be sure that it is open in the anterior chamber and that the stent is in the appropriate position. A small trickle of blood is a good sign because it demonstrates that the device is in Schlemm’s canal. This blood can be removed with a small injection of additional viscoelastic. I then remove the viscoelastic, creating a self-sealing wound, and follow a typical cataract post-surgical regimen in terms of postoperative therapy.
In a prospective, randomized, multicenter study, 72% of patients who received the iStent were able to sustain target pressures of 21 mm Hg or less while eliminating all glaucoma medications, as compared with 50% of patients who received cataract surgery alone. Two-year data from this same U.S. investigational device exemption trial have been published and demonstrated a sustained beneficial treatment effect that was statistically significant in the group that received the iStent.
The iStent procedure does not alter the risk profile of cataract surgery alone. Patients follow the same postoperative regimen, maintain quick visual recovery and have no long-term risk of infection as they would with a bleb. The safety profile and efficacy make it an exciting option to offer to my patients.
References:
Craven ER, et al. J Cataract Refract Surg. 2012;doi:10.1016/j.jcrs.2012.03.025.
Samuelson TW, et al. Ophthalmology. 2011;doi:10.1016/j.ophtha.2010.07.007.
For more information:
Jason Bacharach, MD, can be reached at North Bay Eye Associates, 104 Lynch Creek Way, Suite 15, Petaluma, CA 94954; 707-762-6622; email: jb@northbayeye.com.
Disclosure: Bacharach is an investigator for and consultant to Glaukos.