Understanding Early Glaucoma Surgeries

Classic glaucoma surgeries, such as aqueous drainage implantation, are often invasive and contingent on the failure of topical medications. Additionally, patient adherence to topical hypotensive medications is an ongoing battle due to a variety of factors that include cost, dry eye disease, patient dexterity limitations, and patient cognitive decline. Therefore, it makes sense for optometrists to both be aware of and understand the surgeries that can be performed earlier in the disease process anddecrease patient reliance on topical medications. These procedures include selective laser trabeculoplasty (SLT), procedural pharmaceuticals, and minimally invasive glaucoma surgeries (MIGS). 

This article helps lay the foundation for ODs to identify patients who may benefit from these procedures. 

SLT

SLT is the use of a low-energy, frequency-doubled Nd:YAG laser that specifically stimulates pigmented cells in the trabecular meshwork (TM) to improve aqueous humor outflow. Mild adverse events include transient blurred vision and photophobia.

In the first 3 months of treatment, each additional 1 mm Hg of IOP reduction is associated with an approximate 10% decrease in disease progression risk.¹ The Laser in Glaucoma and Ocular Hypertension Trial emphasized the efficacy and cost-effective nature of SLT as a first-line therapy.² As a result, optometrists should consider SLT at the time of glaucoma diagnosis, or shortly thereafter.² The newly FDA-approved Voyager (Alcon) direct SLT is a viable option for patients, as the procedure does not require a gonioprism during the 3-second treatment.

Of note: Optometrists in 15 states can now perform in-office laser procedures, including SLT. These states are Alaska, Arkansas, Colorado, Indiana, Kansas, Kentucky, Louisiana, Mississippi, Montana, Oklahoma, South Dakota, Virginia, West Virginia, Wisconsin, and Wyoming.

Procedural Pharmaceuticals
Drug-delivering implants are an excellent option for patients whose glaucoma responds to topical prostaglandin therapy and who may possess a barrier to adherence. Two are FDA-approved: the Durysta (AbbVie) (Figure 1) and the iDose TR  (Glaukos). Both implants are placed intracamerally, requiring a referral to an ophthalmologist. A caveat: The IOP-lowering effects of these implants are not permanent, dissipating at some point beyond 18 and 36 months, respectively.^3,4  Therefore, it is important for optometrists to counsel their patients regarding the transient nature of these two implants and to emphasize the importance of continued follow-up and care for their ongoing glaucoma management.

MIGS

MIGS are surgical interventions that are efficacious, involve minimal tissue disruption, and provide a swift recovery.⁵ Mild to moderate primary open-angle glaucoma patients who have any barrier to therapeutic compliance are ideal MIGS candidates. Adverse events, such as hyperemia and inflammation, are usually mild. 

The most commonly performed MIGS are angle-based and involve dilation of Schlemm canal, tissue excision, or TM stenting. 

The FDA-approved MIGS that dilate Schlemm canal are the iTrack Advance (Nova Eye Medical), the OMNI Surgical System (Sight Sciences), and the Streamline Surgical System (New World Medical). Each device consists of a handpiece and a microcatheter that expresses viscoelastic both at a device-specific rate and volume. 

The FDA-approved MIGS devices that work to excise TM tissue include the iAccess (Glaukos), the Kahook Dual Blade GLIDE (New World Medical), the OMNI Surgical System (Sight Sciences), the SION (Sight Sciences), the Tanito Microhook (Inami), and the Trabectome (MicroSurgical Technology).

Surgeons usually strip and remove 2 to 4 clock hours of TM, most often inferior nasally. However, this location can vary depending on the surgeon’s personal preference.

TM stenting involves placing a physical stent in the angle to facilitate aqueous outflow through Schlemm canal. The FDA-approved stents are the Hydrus Microstent (Alcon), the iStent Inject W (Glaukos), and the iStent Infinite (Glaukos). When the traditional outflow pathway of the TM is not a viable option, surgeons have the option to take advantage of other avenues for aqueous outflow.

The FDA-approved subconjunctival shunt is the XEN gel stent (AbbVie). It is a 6 mm x 45 μm hydrophilic gelatin stent that creates an outflow pathway to the subconjunctival space via a low-lying, compact bleb-positioned superior-temporally or superior-nasally (Figure 2).

A sudden rise in IOP in the months after implantation of the stent warrants an immediate referral back to the surgeon, as this could indicate fibrosis formation that can be addressed by needling.

The AlloFlo Uveo (Iantrek) is a 5 mm x 500 μm allogenic, microtrepined scleral allograft that creates a cleft to direct aqueous into the suprachoroidal space. The handpiece and carrier are the AlloSert Uveo (Iantrek). Following the voluntary market withdrawal of the Cypass microstent (Alcon) in 2018, this procedure fills the need for safe and efficacious access to the uveoroscleral outflow, making it a welcomed addition to the OD’s surgical armamentarium.

As glaucoma patients may also require cataract surgery, both MIGS and cataract removal can often be performed concurrently. The most commonly performed MIGS during cataract surgery involve TM stenting. 

Communicating with the surgeon regarding postoperative care, such as keeping an eye out for transient hyphema, is imperative to successful comanagement and outcomes.

Failure to refer patients to surgeons who offer the option of MIGS during cataract surgery can affect disease progression, resulting in a greater risk of visual field loss and the need for incisional glaucoma surgery.⁶

It is important to keep in mind that until the safety and efficacy of the off-label usage of multiple MIGS during cataract extraction can be demonstrated, most commercial payers have followed the lead of the Centers for Medicare and Medicaid Services, limiting reimbursement to a single MIGS procedure performed concurrently with cataract surgery.

A Call to action

By 2050, the number of people in the United States diagnosed with glaucoma is projected to rise to 6.3 million.⁷ This affirms the critical role ODs play in both identifying and managing glaucoma. By embracing the knowledge of interventions that can be employed earlier in the disease process, ODs can improve these patients’ quality of life and secure their place as valuable members of the health care team.