Update on Techniques for Microinvasive Glaucoma Surgery

Educational Objectives

The goal of this program is to use of techniques for microinvasive glaucoma surgery. After hearing and assimilating this program, the clinician will be better able to:

1. Differentiate among microinvasive techniques for treatment of glaucoma.

2. Recognize why early studies did not find greater efficacy of minimally invasive devices for treatment of glaucoma compared with standard surgical approaches.

Summary

Microinvasive glaucoma surgery (MIGS): ab interno approach and minimal surgical trauma promote rapid recovery and enhanced safety; aqueous humor shunted into subconjunctival route (as in trabeculectomy and tube shunt surgery), Schlemm canal, or suprachoroidal (uveoscleral) outflow pathway

Rationale for MIGS: conventional management of glaucoma (topical medication or laser trabeculoplasty) adequate in majority of patients; MIGS may allow patients who need surgical treatment to avoid conventional procedures; candidates for MIGS include patients taking medication for glaucoma who undergo cataract surgery, those for whom administering medication challenging, and those who do not achieve targeted intraocular pressure (IOP) with medication; safety, ease of use, and predictability of MIGS increasing

Barriers: learning new techniques challenging, but worthwhile; conventional medical and surgical therapies focus on lowering IOP and preventing progression of disease; MIGS allows clinician to emphasize quality of life

Techniques: Schlemm canal — conventional outflow pathway appropriate in patients with modest goals for reduction of IOP and medication; subconjunctival pathway — reserved for patients with more advanced disease or need for greater reductions in IOP or medication; postoperative treatment typically more extensive

Surgery in Schlemm canal: good visualization most difficult aspect of procedure and necessary for safety; patient’s head should be turned 30° to 40° away from surgeon; operating microscope, 30° to 40° toward surgeon; surgeon must learn to work with hands farther from body than usual; during gonioscopy, clinician should avoid striae in cornea by using light touch with nondominant hand holding gonio prism; stem on Swan Jacob lens should be grasped without applying downward pressure; to prevent creation of striae, clinician should create incision carefully and work within incision; bubbles or heme should be aspirated from view or managed with cannula or viscoelastic

Efficacy of MIGS: early studies found only modestly greater efficacy for MIGS approaches; trials probably affected by learning curve; surgeon must identify optimal location for implant and place it in chosen spot; placing multiple stents might improve efficacy (evidence limited); use viscoelastic to improve visualization; 8-mm stent (Hydrus) covers ≈3 clock hours of canal and might facilitate outflow better than 2 multidirectional stents (iStent)

Gonioscopy-assisted transluminal trabeculotomy (GATT): draws on traditional approach for juvenile glaucoma; after small goniotomy incision made, illuminated microcatheter or blunted 5-0 polypropylene (Prolene) suture fed into canal; catheter threaded through 360° of canal; hyphema common in early postoperative period but usually resolves in first postoperative week; viscoelastic or balanced salt solution must be used to maintain appropriate IOP and prevent excessive reflux of heme from clouding view; GATT useful for steroid-induced glaucoma (pathology at level of trabecular meshwork [TM])

OMNI glaucoma treatment system: single-handed device incises into Schlemm canal and feeds catheter through; when device retracted, viscoelastic injected into canal to dilate and distend it, distal outflow system, and collector channels; device reextended for goniotomy

Efficacy: similar for majority of methods in Schlemm canal

Subconjunctival surgery using 6-mm gel microstent (XEN); 45-µm lumen creates resistance to outflow; protection against hypotony important advance compared with conventional surgery (lowest IOP 6-7 mm Hg); microstent made of cross-linked collagen hydrates and expands to fill needle tract during delivery; delivered through 27-G needle; placed as superficially as possible (placing stent superficial to Tenon fascia likely to minimize fibrosis); speaker uses mitomycin C, superior injection, and goniolens with mirror to view angle and TM; injector should be removed carefully to avoid dislodging stent; bleb more posterior and diffuse than in conventional operations

Early challenges when learning MIGS: include optimizing view, minimizing striae and excess pressure on eye, visualizing angle, and ensuring adequate depth of chamber and lack of tilt; trypan blue may be used to stain TM; cohesive viscoelastic used to push blood out of field

New devices: ab externo, subconjunctival, minimally invasive drainage device (PreserFlo) — microshunt longer and composed of bioinert SIBS (poly[styrene-block-isobutylene-block-styrene]); microporous silicone device that allows aqueous to slowly percolate from anterior chamber into subchoroidal space (MINIject) — under development for choroidal outflow; does not allow excessive tissue integration and ingrowth; microshunt that delivers aqueous to ocular surface (Beacon) — corrects dry eye and glaucoma; designed to prevent formation of biofilm

Readings

Baker-Schena L: MIGS: Expanding options for glaucoma treatment. EyeNet Magazine. February 2-19. Available at: https://www.aao.org/eyenet/article/expanding-options-for-glaucoma-treatment. Accessed March 27, 2020; Do AT et al: Subconjunctival microinvasive glaucoma surgeries: an update on the Xen gel stent and the PreserFlo MicroShunt. Curr Opin Ophthalmol 2020;31(2):132–138; King AJ et al: Subconjunctival draining minimally-invasive glaucoma devices for medically uncontrolled glaucoma. Cochrane Database Syst Rev 2018;12(12):CD012742; Pinchuk L et al: The use of poly(styrene-block-isobutylene-block-styrene) as a microshunt to treat glaucoma. Regen Biomater 2016;3(2):137–142; Shah M: Micro-invasive glaucoma surgery — an interventional glaucoma revolution. Eye Vis (Lond) 2019;6:29. Published 2019 Sep 29.

Disclosures

For this program, the following has been disclosed: Dr. Shah is a consultant for Allergan, Carl Zeiss Meditec, Glaukos Corporation, and Katena Products. The planning committee reported nothing to disclose. In his lecture, Dr. Shah presents information related to the off-label or investigational use of a therapy, product, or device.

Acknowledgements

Dr. Shah was recorded at the 18th Annual Downeast Ophthalmology Symposium, presented by the Maine Society of Eye Physicians and Surgeons and held September 20-22, 2019, in Bar Harbor, ME. For information on upcoming CME activities presented by the Maine Society of Eye Physicians and Surgeons, please visit maineeyemds.com. The Audio Digest Foundation thanks the speakers and the Maine Society of Eye Physicians and Surgeons 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 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 CE contact hours.

Lecture ID:

OP581102

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.

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