Integrating Trabecular Microbypass Procedures Into Clinical Practice
Advice on getting started.
The common goal of glaucoma treatment is to lower IOP to a level that is safe for the optic nerve of an individual patient. Surgical treatment is usually required when topical medication and/ or laser procedures are not tolerated and/or do not sufficiently reduce the IOP. Although trabeculectomy is still the gold standard in glaucoma surgery, microinvasive glaucoma surgery (MIGS) procedures may be effective and safer alternatives.
Two trabecular microbypass procedures are currently available in the United States, ab interno trabeculotomy (Trabectome; NeoMedix) and a trabecular microbypass stent (iStent Trabecular Micro-Bypass Stent; Glaukos). Both are performed under gonioscopic guidance and can be easily combined with cataract surgery. During the Trabectome procedure, the surgeon uses electrocautery to ablate the trabecular meshwork and inner wall of Schlemm canal. He or she may remove up to 90 or 120 circumferential degrees of tissue. The iStent creates a permanent communication between the anterior chamber and Schlemm canal, overcoming the primary site of increased outflow resistance.
Numerous studies1-5 have evaluated the safety and efficacy of the Trabectome and iStent. Most included a limited number of patients and a follow-up time of 1 year or less. The studies show that the procedures lead to an IOP reduction from baseline of between 18% and 31% when combined with cataract surgery to produce final postoperative IOPs in the midteens. With both MIGS procedures, hyphema and IOP spike have been reported. Fortunately, neither intervention creates a filtering bleb, so the well-known bleb-related complications of hypotony, dysesthesia, and infection are nonissues.
When trying to find appropriate patients for MIGS, it is important not to oversell the procedures. These surgeries are designed for a patient with mild to moderate open-angle glaucoma, and they may be offered at the same time as cataract surgery (iStent or Trabectome) or as a stand-alone procedure (Trabectome). If the patient needs an IOP in the low teens, then I would recommend trabeculectomy or glaucoma drainage device surgery.
Success with MIGS requires skill at intraoperative gonioscopy. As first cases, I would select patients who have at least a moderately pigmented angle to help highlight the anatomy of the angle. Prior to performing their first procedures, surgeons can “practice” on their routine cataract patients. After implanting the IOL, ophthalmologists can become familiar with the gentle pronation skills necessary for MIGS procedures by using a Sinskey hook or a similar instrument to approach the nasal angle under gonioscopic guidance.
Ideally, surgeons should select left eyes for their first iStent cases if they are right-handed or right eyes if they are left-handed, because the “forehand” approach to the angle is generally more comfortable than the “backhand” approach to the angle. If the ophthalmologist simply cannot master the backhand concept, it is perfectly fine to use a “left” iStent for both eyes (right-handed surgeon) or a “right” iStent for both eyes (left-handed surgeon).
The surgeon should also be prepared for blood reflux into the anterior chamber with the Trabectome or iStent once Schlemm canal is entered. The blood can obscure the view of the angle, but it is usually easily cleared with viscoelastic or irrigation/aspiration. Before surgery, it is important to discuss with the patient that, in some cases, the iStent cannot be placed successfully due to poor visualization.
MIGS can help patients with mild to moderate glaucoma achieve manageable IOPs while avoiding most, if not all, of the serious complications of established glaucoma surgical procedures. More of these trabecular microbypass procedures are in development. By maintaining conjunctival integrity, MIGS allows patients to postpone more invasive surgical intervention while limiting the burden of glaucoma medication, thus improving their quality of life.
Leon W. Herndon, MD, is a professor of ophthalmology at the Duke University Eye Center in Durham, North Carolina. He received an honorarium from Glaukos in the past. Dr. Herndon may be reached at (919) 684-6622; firstname.lastname@example.org.
- Minckler DS, Baerveldt G, Alfaro MR, Francis BA. Clinical results with the Trabectome for treatment of open-angle glaucoma. Ophthalmology. 2005;112(6):962-967.
- Minckler D, Mosaed S, Dustin L, et al. Trabectome (trabeculectomy-internal approach): additional experience and extended follow-up. Trans Am Ophthalmol Soc. 2008;106:149-159.
- Francis BA, Minckler D, Dustin L, et al. Combined cataract extraction and trabeculotomy by the internal approach for coexisting cataract and open-angle glaucoma: initial results. J Cataract Refract Surg. 2008;34(7):1096-1103.
- Samuelson TW, Katz LJ, Wells JM, et al. Randomized evaluation of the trabecular microbypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology. 2011;118(3):459-467.
- Arriola-Villalobos P, Martínez-de-la-Casa JM, Díaz-Valle D, et al. Combined iStent trabecular micro-bypass stent implantation and phacoemulsification for coexistent open-angle glaucoma and cataract: a long-term study. Br J Ophthalmol. 2012;96(5):645-649.