Surgical and Laser management of glaucoma

• Summary
• Laser Treatment
• Trabeculectomy
• Non penetrating glaucoma surgery
• Deep sclerotomy
• Viscocanalostomy
• Canaloplasty
• Trabectomey
• Glaucoma drainage devices
• Complications include
• Summary of indications
• Author(s)

Summary

In this article we discuss the non medical management of glaucoma - the various laser and surgical treatments.

Laser Treatment

Laser trabeculoplasty

This involves delivery of laser to the trabecular meshwork to enhance aqueous outflow and consequently lower IOP. There are three types, selective laser trabeculoplasty, argon laser trabeculoplasty, and micropulse laser trabeculoplasty. Laser trabeculoplasty is used in a range of open angle glaucomas, particularly after failure of medical therapy, however particularly SLT with it’s good safety profile is increasingly being used as a primary therapy.

In Selective laser trabeculoplasty, a 532 mm frequency doubled, 1 switched Nd:YAG laser is used to target the melanin pigment in the trabecular meshwork. The energy delivered to the trabecular meshwork is much lower than with argon laser, with mild complications (transient inflammation, peripheral anterior synechiae formation and mild IOP elevation).

In Argon laser trabeculoplasty, the principle is the same as SLT however laser burns are targeted to the trabecular meshwork which receives thermal damage, (therefore repeat treatment is not usually performed unlike SLT). Complications are as for SLT, however can be more severe, including cystoid macular oedema.

Micropulse laser trabeculoplasty (MLT) is a newer technique which uses very short pulses of laser to deliver thermal energy. It is far less damaging, using a much smaller area targeted than SLT.

Laser iridotomy

This is mainly used in the case of primary angle closure glaucoma, but may also be useful in secondary angle closure with pupillary block. A hole is created in the iris, thereby allowing aqueous humour to train directly from the posterior to the anterior chamber, hence relieving pupillary block. In general, Nd:YAG laser achieves better results than argon with less damage to the cornea, lens and retina.

Diode laser cycloablation

Diode laser cycloablation lowers IOP by destroying part of the ciliary epithelium, and consequently reducing aqueous secretion (link our other article here about how aqueous is produced). Cycloalation can also be done via diathermy, surgical excision, cryotherapy and ultrasound in addition to laser like discussed here. In the past, it was mainly used in end stage secondary glaucoma with little visual potential, mainly for pain management. However, over recent years it is used in eyes with good vision, especially those with poor prognosis of penetrating drainage surgery.

Diode lasers have the best absorbed wavelength by the ciliary epithelium compared to other wavelengths, as the melanin in the ciliary epithelium, with more targeted destruction and less inflammation.

Laser iridoplasty

Laser iridoplasty widens the anterior chamber angle by contraction of the peripheral iris away from the angle recess - which can break an episode of acute angle closure. The most common indication is electively in cases of plateau iris syndrome. Complications tend to be mild, but heavy treatment can be associated with a IOP spike. Altered accommodation is another side effect.

Trabeculectomy

Trabeculectomy is a type of glaucoma filtration surgery where a hole is created from under a scleral flap to allow aqueous outflow from the anterior chamber to the sub-Tenon space. In the sub conjunctival space, the aqueous collects and results in elevation of the conjunctiva, also known as a filtering bleb. From this bleb, aqueous can also enter into the tear film, be absorbed by conjunctival tissue, flow into lymphatics or drain into aqueous veins.

Indications include failure of conservative therapy, avoidance of excessive polypharmacy, and cases progressive deterioration despite adequate IOP control. In some advances cases, superior outcome may be achieved from early surgery as a primary therapy, particularly in younger patients.

Antimetabolites are often used during trabeculectomy in order to prevent ‘bleb failure’ as a result of natural scarring during wound healing. Usually, 5-fluorouracil (5-FU) or mitomycin C (MMC) are used. They are often applied to the site by soaking a small sponge and placing it onto the sclera before the hole is created. It can also be injected pre-op into the subconjunctival space.

Complications of trabeculectomy:

• Shallow anterior chamber
• Failure of filtration
• Late bleb leakage
• Bleb associated bacterial infection and endophthalmitis

Non penetrating glaucoma surgery

Deep sclerotomy

This is the most widely known non penetrating surgery - where decemet window is created to allow aqueous to diffuse from the AC —> subconjunctival space, resulting in a shallow filtration bleb.

Viscocanalostomy

Here, Schlemm’s canal is dilated using injection of sodium hyaluronate. This disrupts the inner and outer walls and disogrnizes the juxta-canalicular zone, increasing conventional aqueous outflow and uveoscleral outflow. The superficial scleral flap is sutured watertight, avoiding external subconjunctival filtration and allowing draiange through the ostia of Schlemm’s canal + suprachoroidal space.

Canaloplasty

This is a variant of viscocanalostomy, instead using a microcatheter to perform a 360 degree (entire circumference) cannulation of Schlemm’s canal

Trabectomey

This is an electrosurgical device that is used ab interno (meaning, approached from the inside of the eye) through gonioscopy. Through this, a strip of the trabecular meshwork and the inner wall of the Schlemm Canal is removed.

The main indication is POAG. IOP reduction achieved is less than by trabeculectomy, so topical medication is often still needed.

Glaucoma drainage devices

Glaucoma drainage devices create a communication between the anterior chamber and the sub Tenon space via a tube attached to a posteriorly explanted episcleral reservoir. In other words - they divert aqueous humour from the anterior chamber to the external reservoir where a fibrous capsule forms 4-6 weeks after surgery. Reduction of IOP is due to passive, pressure dependent flow of aqueous.

Glaucoma drainage devices are available in a range of sizes, materials and designs. Examples include Molteno, Baerveldt, and Ahmed.

GDD may be indicated in eyes with severe conjunctival scarring, uncontrolled glaucoma despite previous trabeculectomy, secondary glaucoma where routine trabeculetcomy is less likely to be successful (e.g. neovascular glaucoma and traumatic glaucoma), and as a last resort in congenital glaucoma.

Complications include

• Excessive drainage resulting in hypotony and a shallow anterior chamber
• Malposition
• Tube erosion
• Corneal decompensation
• Double vision
• Early drainage failure
• Late drainage failure

Mini shunts

Examples include the ex-press mini shunt and the iStent.

The ex-press mini shunt is a titanium stent inserted under a scleral flap during a modified trabeculectomy, and a needle is used to enter the anterior chamber instead of reating a punch sclerostomy. The rate of complications such as hypotony appears to be lower than with standard trabeculectomy, with fewer postoperative interventions. The iStent is a tiny hooked titanium tube inserted into the Schlemm canal via the trabecular meshwork, and shows promise for reducing IOP in mild-moderate glaucoma. Implantation is relatively simple than conventional glaucoma surgery.

Summary of indications

Author(s)

Dr Sara Memon

Sara is the Co-Founder of Ophtnotes. She is a doctor who graduated from UCL Medical School in London. She won the Allen Goldsmith Prize in Ophthalmology. Sara is also the co-founder of PAMSA: an organisation linking doctors and medical students of Pakistani origin. She’s especially passionate about teaching and education, having presented a workshop she designed herself at the 2019 Annual GMC Conference.