Laser Trabeculoplasty

Continuing Education Activity

Laser Trabeculoplasty is performed as an additional measure to lower the intraocular pressure in patients with Open-angle Glaucoma. It can also be performed in a closed-angle glaucoma patient with a patent iridotomy. This procedure is relatively safe and is gaining popularity. This activity outlines and highlights the role of the interprofessional team in evaluating and treating patients who undergo laser trabeculoplasty.

Objectives:

• Describe the treatment considerations for patients with glaucoma.
• Outline the presentation of a patient with glaucoma who would be a candidate for laser trabeculoplasty.
• Identify the common indications and contraindications for laser trabeculoplasty.
• Summarize the common complications of laser trabeculoplasty.

Introduction

Glaucoma is defined to be a progressive optic neuropathy that can lead to irreversible blindness. There are various known risk factors for glaucoma. However, intraocular pressure (IOP) appears to be the only known modifiable risk factor for control of onset and progression of optic neuropathy.[1] Besides the medical and surgical therapy for glaucoma, laser treatment has received considerable attention as an effective modality in recent times. Laser trabeculoplasty commonly practiced are argon laser trabeculoplasty ( ALT) and selective laser trabeculoplasty (SLT) to increase aqueous humor outflow and thus lower the intraocular pressure.[2]

Wise and Witter described the first protocol for argon laser trabeculoplasty in 1979. They demonstrated the safety and efficacy of ALT in a group of patients with open-angle glaucoma (OAG). The safety and long-term efficacy of ALT were studied in the Glaucoma Laser Trial (GLT). In the GLT, eyes receiving 360 degrees ALT were compared with medical monotherapy with a follow-up period of  2.5 to 5.5 years, concluding that trabeculoplasty was as efficacious as medical therapy in reducing intraocular pressure. However, ALT did not become primary therapy in patients with primary open-angle glaucoma (POAG) because of a reduction in efficacy over time, so it was used as an adjunctive therapy.

Laser trabeculoplasty gained popularity with the introduction of selective laser trabeculoplasty (SLT). SLT uses a Q-switched frequency-doubled Nd: YAG laser in the trabecular meshwork, which appears less destructive than ALT. However, it has been noticed that both ALT and SLT are equally efficacious in reducing intraocular pressure in open-angle glaucoma.

Anatomy and Physiology

Anatomy of Angle of the Anterior Chamber

Clinically the structures are visualized by gonioscopic examination. The structures forming the angle of the anterior chamber are as follows (posterior to anterior):

• Ciliary Body Band

  • It is formed by the anterior-most part of the ciliary body between its attachment to scleral spur and iris insertion.
  • It appears a grey or dark brown band
  • the gonioscopy. It is the most posterior landmark.
• Scleral Spur

  • This posterior part of the scleral sulcus is related to the ciliary body posteriorly and corneoscleral meshwork anteriorly.
  • It appears as a white band on gonioscopy.
• Trabecular Meshwork

  • It appears as a band anterior to the scleral spur. It has two parts clinically, anterior non pigmented and posterior pigmented. The posterior is the draining part hence, pigmented.
  • It is responsible for 90% of the aqueous humor outflow.
  • It has three components-

    • The uveal meshwork- the innermost portion which consists of cord-like endothelial cells, the intertrabecular spaces are relatively large, around 70 microns in diameter, offering little resistance to the passage of aqueous.
    • The corneoscleral meshwork- lies anterior to the uveal meshwork forms the thickest portion of the trabecular meshwork. The intertrabecular spaces are lesser, around 35 microns, offering greater resistance.
    • The juxtacanalicular meshwork- the outer part of the trabecular meshwork, lines the endothelium of the Schelmm's canal. The intertrabecular spaces are around 7 microns, offering maximum resistance to aqueous outflow.
• Schwalbe's Line

  • It appears as a fine ridge just in front of the trabecular meshwork, formed by the prominent end of the Descemet membrane of the cornea.
  • It marks the anterior limit of the structures forming the angle of the anterior chamber.[3]

Physiological Aspects of Outflow

The aqueous humor flows from the posterior chamber via the pupil in the anterior chamber. It exits the anterior chamber via the following routes:

• Trabecular meshwork - about 90% aqueous flows through this route.
• Uveoscleral pathway - about 10% aqueous flows via the uveoscleral pathway
• Iris - some aqueous also drains via the iris.

Indications

• Patients with OAG, uncontrolled by medical therapy - the IOP remains above the target IOP despite maximum medical therapy that can be tolerated[4]
• In patients with OAG with poor compliance to medical treatment, the IOP remains above the target IOP, and the glaucomatous optic atrophy worsens.
• Patients with OAG with poor tolerance to medical therapy
• Patients with pseudoexfoliation or pigmentary glaucomas
• Angle-closure glaucoma with a patent iridotomy
• When the glaucoma surgery needs to be deferred or delayed

Contraindications

• Inflammatory glaucoma - as post-laser inflammations will increase, leading to further IOP spikes.
• Advanced glaucoma
• Poor visualization of the TM due to synechiae- as the site of action is trabecular meshwork.

Equipment

Laser System

• Argon green laser light is used in ALT
• Q-switched Nd: YAG laser is used in SLT

Lenses used - A contact lens with a mirror to visualize the anterior chamber angle (gonioprism) is used in laser trabeculoplasty. The lens should have an anti-reflective coating on its front surface.

• Goldmann type three-mirror lens can be used. It has one mirror inclined at an angle of 59 degrees.
• Thorpe four-mirror gonioscopy lens, all the mirrors are inclined at 62 degrees. It has the advantage of simultaneous viewing of all the quadrants of the angle of the anterior chamber.
• Ritch trabeculoplasty lens- two mirrors are inclined at 59 degrees for viewing the inferior quadrants and two at 64 degrees to view the superior angles. It has a 17 diopter planoconvex lens which provides a magnification of 1.4, thus reducing a laser spot size.
• Latina lens- this lens is designed explicitly for SLT. It has a single mirror at a 63-degree angle. It has a magnification of 1.

Personnel

The team performing a laser trabeculoplasty may include:

• Attending and resident surgeons
• Nursing staff
• Operative room technicians

Preparation

History

A thorough medical and ocular history should be taken.

Examination

The preoperative examination must include:

• Gonioscopic examination of the angle of the anterior chamber- visibility of trabecular meshwork without indentation is noted as this is the target structure for trabeculoplasty. If the iris approach is steep, but the trabecular meshwork is visible by asking the patient to look towards the mirror, this implies there is sufficient angle area available for treatment. Any synechiae should be ruled out because it will obstruct access to the trabecular meshwork, hence a contraindication to the procedure. The degree of pigmentation of the trabecular meshwork should be noted because it will influence the initial energy level chosen for the procedure.[5][6]
• Intraocular pressure measurement- to record a baseline IOP before the procedure.
• Central corneal thickness
• Optic nerve evaluation using slit-lamp biomicroscopy for glaucomatous damage
• Visual field charting

Medications

1.  IOP lowering agents- either apraclonidine or brimonidine, both being alpha-adrenergic agonists. It decreases the chance of an IOP spike in the immediate post-op period.[7]
2. Topical anesthetic agents –immediately before the procedure to anesthetize the eye.

Informed consent should be obtained before the procedure. The patient should understand all of the risks, benefits, and alternatives to the procedure. It is essential to manage the expectations and address any questions about the procedure patient might have. Also, the possibility of failure of the procedure should be explained.

Technique or Treatment

Mechanism Of Action  

Several theories have been proposed the mechanism as follows

1. Cellular - suggests that the reduction in IOP occurs due to the cellular activity stimulated by the laser; there is increased recruitment of macrophages in the trabecular meshwork, which aids in the remodeling of the extracellular matrix, thus allowing for increased aqueous outflow.
2. Cytokine production- there is increased expression and secretion of IL-1 beta and TNF alpha in the first 8 hours after treatment; these mediate increased trabecular stromelysin expression, which leads to remodeling of the juxtacanalicular extracellular matrix of the trabecular meshwork. This improves the normal outflow facility, thereby decreasing IOP.
3. The increased conductivity of Schlemm's canal- SLT leads to a 3-fold increase in Schlemm's canal cells conductivity, thus increasing the transendothelial fluid flow across Schlemm's canal cells.
4. ALT- causes coagulative necrosis of the trabecular meshwork.
5. SLT- causes cracking of intracytoplasmic pigment granules and disruption of the endothelial cells of the trabecular meshwork

 Technique

Table

  Argon Laser Trabeculoplasty

Complications

1. IOP rise - the most common complication in patients undergoing laser trabeculoplasty. The frequency of IOP spikes can be reduced by two-thirds using prophylactic alpha-adrenergic agonists about 30-60 minutes before the procedure.[9] A severe and frequent IOP rise occurs with:

   • The use of higher energy levels,
   • 360-degree angle treatments,
   • Posterior placement of laser beam,
   • Heavy pigmentation of the angle, and
   • A low aqueous outflow facility. These IOP spikes are usually transient, occur in the first hour, and resolve with medical treatment. However, in cases with sustained IOP rise, surgical management is needed.[10]
2. Low-grade iritis
3. Formation of PAS
4. Corneal edema- occurs due to HSV reactivation. The inflammatory cascade following laser therapy reactivates the virus. 
5. Hyphema

Clinical Significance

The effect of either type of laser trabeculoplasty decreases gradually over time. A prospective study that randomized patients to 180° of SLT versus ALT, did not find any statistically significant difference in IOP lowering between the two types of laser trabeculoplasty. The effect of trabeculoplasty on the diurnal curve shows that both ALT and SLT decrease diurnal IOP fluctuation. In different subgroups of patients of POAG, both ALT and SLT have been found efficacious compared to medical treatment. In pseudoexfoliation glaucoma, SLT is equally efficacious in pseudophakic eyes compared to phakic ones, whereas ALT is generally performed in phakic eyes.

Laser trabeculoplasty is a cost-effective procedure that can be performed as an adjunct to medical therapy or to control IOP when the surgical treatment is delayed. It is gaining popularity as a primary mode of treatment in several open-angle glaucoma patients.[11][12]

Enhancing Healthcare Team Outcomes

Glaucoma leads to irreversible damage to the optic nerve, thus vision, which can adversely impact a person's life personally and socially. Hence, an interprofessional approach should be adopted to identify, treat and delay the progression of glaucoma. The clinician should carefully examine to uncover early signs of glaucoma. If found, appropriate steps should be adopted. A physician in the periphery should refer the patient to a higher center for management.

Patient counseling plays an important role. A combined effort by the treating doctor, nurses, and pharmacist should explain the necessity of seeking early treatment. The importance of medication compliance should also be presented. Family members of a patient diagnosed with glaucoma should be encouraged to get themselves screened. Patients undergoing laser procedures should understand the importance of the procedure and any potential complications. Any misconception regarding the laser procedure should be clarified, and the patient should receive an explanation regarding the safety and efficacy of the procedure.

An interprofessional approach is key to addressing the global burden of glaucoma. There should be cooperation among each level to prevent the attack by glaucoma. [Level 5]

Review Questions

• Access free multiple choice questions on this topic.
• Comment on this article.

References

1.

Meier-Gibbons F, Töteberg-Harms M. [Structure/function/treatment in glaucoma: progress over the last 10 years]. Ophthalmologe. 2021 Dec;118(12):1216-1221. [PubMed: 34609610]

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Kagemann L, Wollstein G, Ishikawa H, Sigal IA, Folio LS, Xu J, Gong H, Schuman JS. 3D visualization of aqueous humor outflow structures in-situ in humans. Exp Eye Res. 2011 Sep;93(3):308-15. [PMC free article: PMC3196779] [PubMed: 21514296]

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Lee JH, Na JH, Chung HJ, Choi JY, Kim MJ. Selective Laser Trabeculoplasty for Medically Uncontrolled Pseudoexfoliation Glaucoma in Korean Patients. Korean J Ophthalmol. 2021 Dec;35(6):476-483. [PMC free article: PMC8666261] [PubMed: 34634862]

5.

Correia Barão R, Cutolo C, Tanito M, Hommer A, Faschinger C, Abegão Pinto L, Traverso C. Agreement Analysis on Angle Characteristics With Automated Gonioscopy. J Glaucoma. 2021 Dec 01;30(12):1039-1046. [PubMed: 34559700]

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Brusini P. Global Glaucoma Staging System (GGSS): A New Method to Simultaneously Assess the Severity of Both Functional and Structural Damage in Glaucoma. J Clin Med. 2021 Sep 26;10(19) [PMC free article: PMC8509816] [PubMed: 34640431]

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Yan J, Xiong X, Shen J, Huang T. The use of fixed dose drug combinations for glaucoma in clinical settings: a retrospective, observational, single-centre study. Int Ophthalmol. 2022 Mar;42(3):945-950. [PubMed: 34635957]

8.

Wang H, Cheng JW, Wei RL, Cai JP, Li Y, Ma XY. Meta-analysis of selective laser trabeculoplasty with argon laser trabeculoplasty in the treatment of open-angle glaucoma. Can J Ophthalmol. 2013 Jun;48(3):186-92. [PubMed: 23769780]

9.

Zhang L, Weizer JS, Musch DC. Perioperative medications for preventing temporarily increased intraocular pressure after laser trabeculoplasty. Cochrane Database Syst Rev. 2017 Feb 23;2(2):CD010746. [PMC free article: PMC5477062] [PubMed: 28231380]

10.

Thrane VR, Thrane AS, Bergo C, Halvorsen H, Krohn J. Effect of Apraclonidine and Diclofenac on Early Changes in Intraocular Pressure After Selective Laser Trabeculoplasty. J Glaucoma. 2020 Apr;29(4):280-286. [PubMed: 32053556]

11.

Lowry EA, Greninger DA, Porco TC, Naseri A, Stamper RL, Han Y. A Comparison of Resident-performed Argon and Selective Laser Trabeculoplasty in Patients With Open-angle Glaucoma. J Glaucoma. 2016 Mar;25(3):e157-61. [PubMed: 25651207]

12.

Bovell AM, Damji KF, Hodge WG, Rock WJ, Buhrmann RR, Pan YI. Long term effects on the lowering of intraocular pressure: selective laser or argon laser trabeculoplasty? Can J Ophthalmol. 2011 Oct;46(5):408-13. [PubMed: 21995983]

Disclosure: Ekta Shaw declares no relevant financial relationships with ineligible companies.

Disclosure: Priyadarshi Gupta declares no relevant financial relationships with ineligible companies.