Optometrists are at the forefront of diagnosing and treating patients with glaucoma. That responsibility is unlikely to change anytime soon, considering the stagnant number of ophthalmology residency graduates and the aging US population (see also The Numbers Don’t Lie).1
Glaucoma treatment typically begins with topical drops, progresses to laser therapy, and then moves to invasive surgery, but recent research and technological advances are changing the paradigm. For example, the Laser in Glaucoma and ocular Hypertension Trial (LIGHT) indicated that first-line selective laser trabeculoplasty is more cost-effective than topical drops and provides better clinical outcomes for patients with open-angle glaucoma and ocular hypertension.2 Combined with the advent of microinvasive glaucoma surgery (MIGS), the current trend is toward earlier surgical intervention.
MIGS procedures are generally safer than filtration surgery, and postoperative recovery is faster. The risk of serious complications, such as hypotony and choroidal hemorrhage, is significantly lower with MIGS than with filtration surgery.3,4
NeoMedix (acquired by MicroSurgical Technology) paved the way for MIGS procedures when the company introduced the Trabectome in 2004. Since then, several companies have released MIGS devices. The field is evolving rapidly, and it is important for optometrists to be aware of both current options and the development pipeline. A simple approach is to categorize MIGS procedures by their mechanism of action.
GONIOTOMY
Procedures in this category include the Trabectome, gonioscopy-assisted transluminal trabeculotomy, and the Kahook Dual Blade (New World Medical), which all lower IOP by excising tissue and thus increasing aqueous outflow from the trabecular meshwork and Schlemm canal. Goniotomy may be used to treat any stage of glaucoma, and it may also be performed on patients with peripheral anterior synechiae and pseudoexfoliative glaucoma. Contraindications include angle-recession, pigmentary, and neovascular glaucoma (NVG). Goniotomy may be performed alone or in combination with cataract surgery.
Two recent additions to this category are the Sion Surgical Instrument (Sight Sciences) and the Glaukos iAccess Trabecular Trephine (Glaukos). The Sion shares many features with the Trabectome, but one big difference is that the Sion lacks a blade. The goal of the design is to improve the safety of goniotomy by making the removal of trabecular meshwork tissue easier and the risk of complications lower. Surgeons can opt to use the Sion in combination with other procedures, such as cataract surgery. Long-term data on the device are not available.
The iAccess excises microscopic (220-μm) sections of the trabecular meshwork. The device may be used in a standalone procedure or in combination with cataract surgery, laser treatment, or another MIGS procedure.5 In a nonrandomized, observational case series, cataract surgery and placement of an iStent inject W were performed with and without iAccess on 92 and 63 eyes, respectively. Three months after surgery, IOP had decreased by 1.4 mm Hg and 3.8 mm Hg in the non-goniotomy and goniotomy groups, respectively. All eyes were being treated with one topical medication at baseline; 80% to 85% of eyes in both groups no longer required topical medications after surgery.6
TRABECULAR BYPASS
Several MIGS devices bypass the trabecular meshwork and increase aqueous outflow through Schlemm canal. These include the iStent family of devices (Glaukos) and the Hydrus Microstent (Alcon). This form of MIGS is indicated for early and moderate open-angle glaucoma only. Of the available devices, only the iStent infinite, which is in pre-clinical trials, may be implanted as a standalone procedure.
The newest device in this category is the iStent infinite. Three implants are placed to cover an area of 240,˚ with 97% of the Schlemm canal left intact. Trials of the standalone procedure included patients with uncontrolled glaucoma who had a history of either incisional or cyclodestructive surgery or were on maximum tolerated topical therapy.7 The primary endpoint was an IOP reduction of greater than 20%. In the prior surgery group, 73.4% of eyes achieved the target (average decrease of 5.5 mm Hg at 12 months). In the maximum therapy group, 90% of eyes achieved the target (average decrease of 8.1 mm Hg), and the use of topical drops was reduced by greater than 30% in more than half of the eyes.7
AB INTERNO CANALOPLASTY
Ab interno canaloplasty or ABiC is performed using the iTrack (Ellex). The procedure increases aqueous outflow through Schlemm canal via viscodilation. It may be performed in patients with any stage of glaucoma, open or narrow angles, peripheral anterior synechiae, angle recession, pigmentary dispersion syndrome, and inactive NVG.
COMBINED PROCEDURES
The Omni Surgical System (Sight Sciences) and Streamline Surgical System (New World Medical) combine two mechanisms of action: canaloplasty (ie, vasodilation of Schlemm canal) and goniotomy (ie, removal of trabecular meshwork tissue). Surgery may be performed as a standalone procedure or in combination with cataract surgery. The systems are indicated for any stage of glaucoma, but are not approved for use in patients with peripheral anterior synechiae, pseudoexfoliative glaucoma, angle recession, pigmentary dispersion syndrome, or NVG.
SUBCONJUNCTIVAL SURGERY
The Xen Gel Stent (Allergan/AbbVie) is indicated for multiple forms of glaucoma, including inactive NVG, and is often used when IOP is uncontrolled. The stent may be implanted as a standalone procedure or in combination with cataract surgery.
With an ab interno approach, a corneal incision is made so that the stent may be inserted through the sopranos trabecular meshwork. Some surgeons prefer to use an ab externo approach because it gives them more freedom in positioning and the application of mitomycin C. Both approaches have been found to reduce IOP similarly.8
The rate of complications, especially fibrosis and hypotony, is higher with this procedure—often classified as a MIGS plus procedure—than with other forms of MIGS. For example, almost one quarter (24.6% of eyes) experience hypotony during the primary Xen Gel trial.7 Close postoperative observation of patients is essential. If IOP rises, then bleb needling and injections of mitomycin C may be necessary.
a game-changer
The new wave of MIGS procedures is exciting not only because it offers more options to patients and surgeons, but because the improvements in safety and efficacy will better prevent visual field progression. ODs are in the driver’s seat to elevate our patients’ access to MIGS procedures. Continue to be an eye care champion for your aging patients and be aware of the rapidly changing MIGS world that will benefit them.
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