Minimally Invasive Glaucoma Surgery: An Overview

Educational Objectives

The goal of this program is to improve surgical management of glaucoma. After hearing and assimilating this program, the clinician will be better able to:

1. Evaluate various approaches for minimally invasive glaucoma surgery (MIGS) procedures.
2. Select patients who are most likely to benefit from MIGS.

Summary

Evolution of glaucoma management: medications for glaucoma have evolved over the years (eg, oral carbonic anhydrase inhibitors [CAI], β-blockers, α-adrenergic agonists, topical CAI, prostaglandins, Rho kinase inhibitors); advances in formulations (eg, gel, implant) improved ease of administration; preservative-free medications help with adherence and patient satisfaction; combination of drugs (eg, dorzolamide-timolol [Cosopt], brimonidine-timolol [Combigan]) reduce drop burden and preservative exposure; despite having novel targets and formulations, glaucoma medications are not effective in all cases; filtration surgeries (FS) are temporarily effective, and additional surgeries may be necessary

Disadvantages of topical eye drops: adherence may be poor; surface toxicities affect quality of life; β-blockers and α-adrenergic agonists have systemic side effects; long-term costs of refills are high; self-administration may be difficult in older patients

Filtration surgery: involves creating a channel that vents fluid from the anterior chamber to the subconjunctival space; complications of FS (eg, trabeculectomy, tube shunts) include hypotony and prolonged recovery time (often >1 mo); bleeding and infection are rare; FS eventually fail (eg, 3-10 yr)

Minimally invasive glaucoma surgery (MIGS): offers improved safety and recovery time (≈1 wk) compared with FS; MIGS does not lower intraocular pressure (IOP) as much as FS; novel designs and materials (eg, nitinol, titanium, gelatin) are used; MIGS lowers IOP over the years and helps reduce the drop burden; however, MIGS is not appropriate for patients at the greatest risk for vision loss from glaucoma; Chen et al (2019) opined that increased efficacy of glaucoma procedures generally occurs at the cost of a higher risk for surgical complications; MIGS is not an absolute replacement for FS but offers moderate IOP reduction and drop independence

MIGS Approaches

Enhancing outflow through Schlemm’s canal

Stent placement: bypasses the resistance created by the trabecular meshwork (TM); allow aqueous humor to flow freely from the anterior chamber to Schlemm canal and down through aqueous veins; Schlemm canal microstent (SCM; eg, Hydrus) — spans 90 degrees; scaffold opens Schlemm canal and allows fluid to percolate through easily; the HORIZON trial (Ahmed et al [2022]) randomized patients to SCM and cataract surgery (CS) or CS alone; at 5 yr, a larger proportion of patients in the SCM group were maintained on no drops or 1 drop (lower drop burden) and had a lower IOP compared with patients in the CS alone group; trabecular bypass stent (TBS; eg, iStent) — titanium rivet is used to bypass the resistance of the TM; in the COMPARE trial (Ahmed et al [2020]), SCM was better at reducing IOP and medication use compared with TBS

Destruction of TM: include gonioscopy-assisted transluminal trabeculotomy, first-generation dual-blade goniotomy (Kahook dual blade [KDB]), second-generation dual-blade goniotomy (KDB GLIDE), canaloplasty-trabeculotomy (OMNI Surgical System), 360-degree catheterization and pressurized viscodilation (iTrack microcatheter system), and bent ab interno needle goniotomy; TM is removed or ripped open; effective for reducing IOP; used frequently as an alternative to SCM or TBS; hydrogel may be injected to dilate Schlemm canal using canaloplasty-trabeculotomy to lower IOP

Subconjunctival shunts: may be referred to as minimally invasive bleb surgery; gelatin stent (XEN gel stent) is a small gelatin tube that is placed in the anterior chamber with the other end in the subconjunctival space; designed to prevent hypotony; potentially reduces complications and allows for quicker recovery; less effective than trabeculectomy

Suprachoroidal shunts: the suprachoroidal microstent (eg, CyPass) was withdrawn from the market for persistent corneal endothelial cell loss

Using MIGS in clinical practice: used more frequently than FS; prospective comparative trials are needed; discuss MIGS with patients who are candidates for CS and on topical eye drops; the speaker is comfortable with MIGS in patients with moderate or severe glaucoma, although adequate IOP reduction may not be achieved; appropriate use of MIGS may expand in future

Readings

Ahmed IIK, De Francesco T, Rhee D, et al. Long-term outcomes from the HORIZON randomized trial for a Schlemm’s canal microstent in combination cataract and glaucoma surgery. Ophthalmology. 2022;129(7):742-751. doi:10.1016/j.ophtha.2022.02.021; Ahmed IIK, Fea A, Au L, et al. A prospective randomized trial comparing Hydrus and iStent microinvasive glaucoma surgery implants for standalone treatment of open-angle glaucoma: the COMPARE study. Ophthalmology. 2020;127(1):52-61. doi:10.1016/j.ophtha.2019.04.034; Chen J, Gedde SJ. New developments in tube shunt surgery. Curr Opin Ophthalmol. 2019;30(2):125-131. doi:10.1097/ICU.0000000000000549; Gedde SJ, Vinod K, Wright MM, et al. Primary open-angle glaucoma preferred practice pattern®. Ophthalmology. 2021;128(1):P71-P150. doi:10.1016/j.ophtha.2020.10.022.

Disclosures

For this program, members of the faculty and planning committee reported nothing relevant to disclose.

Acknowledgements

Dr. Pitha was recorded at Wilmer Eye Institute Presents: 17th Annual Evidence Based Care Optometry Conference, held on March 3, 2024, in Baltimore, MD, and presented by Johns Hopkins University School of Medicine. For more information about upcoming CME activities from this presenter, please visit https://hopkinscme.cloud-cme.com/course/courseoverview?P=0&EID=51931. Audio Digest thanks the speakers and presenters for their cooperation in the production of this program.

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0.50 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0.50 CE contact hours.

Lecture ID:

OP621201

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.