Introduction
Laser trabeculoplasty is a new technique to lower intraocular pressure in individuals with open-angle glaucoma. Argon laser trabeculoplasty was first done in 1979 by Wise and Witter to treat uncontrolled glaucoma. The efficiency of this new technique was studied in a clinical trial called the glaucoma laser trial (GLT). During this trial, the eyes received 360 degrees of laser therapy.
Laser trabeculoplasty can be performed on an individual with closed-angle glaucoma. This is a safe procedure. Despite being an effective technique, it did not replace the primary therapy medications in such individuals. The use of laser trabeculoplasty was limited to as an adjunct to failed medical therapy or surgery. Laser trabeculoplasty gained attention with the introduction of selective laser trabeculoplasty (SLT).
What Are the Different Types of Laser Trabeculoplasty?
There are two types of laser trabeculoplasty, argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT). These are used to increase the outflow of the aqueous matter through the trabecular meshwork, thus lowering the intraocular pressure (IOP) in conditions like glaucoma and ocular hypertension.
What Is Glaucoma?
Glaucoma is a group of eye diseases that can lead to vision loss and irreversible blindness. The optic nerve at the back of the eyes gets damaged. There are several risk factors leading to glaucoma. Intraocular pressure is one of the factors controlling the onset and progression of the condition. The symptoms begin gradually, which is not usually noticed by the individual. Only a detailed, comprehensive eye examination can help one detect the condition. Apart from medical and surgical therapy, laser treatment has also gained popularity as an effective technique in the treatment of glaucoma. Laser trabeculation works by increasing the outflow of aqueous humor leading to a reduction in intraocular pressure.
When Is Laser Trabeculoplasty Indicated?
Laser trabeculoplasty is indicated in the following conditions:
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In individuals with medically uncontrolled open-angle glaucoma. The intra-ocular pressure in such individuals remains elevated despite medical therapy.
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In individuals with open-angle glaucoma who are not responding well to medical treatment, the intraocular pressure remains above the target intraocular pressure, deteriorating the optic atrophy.
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In open-angle glaucoma patients because they are intolerant to medical therapy.
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When there is a need to delay the glaucoma surgery.
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Individuals with pseudoexfoliation or pigmentary glaucoma.
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In individuals with angle-closure glaucoma with iridotomy.
What Are the Contraindications of Laser Trabeculoplasty?
Laser trabeculation is contraindicated in the following conditions:
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In individuals with advanced glaucoma.
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In individuals with inflammatory glaucomas, increased inflammation after laser therapy leads to increased intraocular pressure.
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Conditions where there is improper visualization of the trabecular meshwork due to synechiae (adhesion).
What Happens Before the Procedure?
Before carrying out laser trabeculoplasty, a detailed medical and ocular history is taken. The preoperative examination includes a gonioscopic evaluation - a painless examination to assess whether the drainage angle is open or closed. This is done with the help of a slit lamp with a Zeiss, Posner, or Sussman lens or with a single or triple mirror Goldmann lens. The trabecular meshwork is also checked for visibility without indentation since it is treated by laser trabeculoplasty. If the approach through the iris is steep, but the trabecular meshwork is seen by rotating the eye towards the mirror, it suggests a good angle for the treatment. One should look for the presence or absence of synechiae (adhesion), as it can threaten the procedure. The degree of pigmentation of the trabecular meshwork is evaluated as it may affect the energy level selected for laser trabeculoplasty.
Intraocular pressure-reducing medications such as Apraclonidine or Brimonidine are administered. They help reduce the spike in intraocular pressure immediately after the procedure. Topical anesthetic drugs are used just before the procedure to numb the eye.
The individual is aware of the risks, benefits, and other procedures. Informed consent is obtained from the patient before the procedure.
What Happens During the Procedure?
Before starting laser trabeculoplasty, an alpha-adrenergic agonist is administered to the eye to reduce the risk of a spike in intraocular pressure. A topical anesthetic agent is used just before the procedure to numb the eye. In argon laser trabeculation, the laser is set at a spot for 0.1-second, with a varying power of 300 to 1000 mW.
The procedure's desired result is the blanching of the trabecular meshwork or the production of a small bubble. In the case of a large bubble, the energy is aimed downward. The laser light is adjusted through the goniolens at the junction of the trabecular meshwork, where the anterior non-pigmented and posterior pigmented edges meet. If the laser light is focused on the extreme posterior part, it may increase inflammation, intraocular pressure, peripheral anterior synechiae, and pigment dispersion.
A 360-degree treatment is usually associated with an increase in intraocular pressure. An additional 180 degrees of the treatment can be done later on.
In SLT, the frequency of the laser is doubled. The laser light is focused over the trabecular meshwork. The precise focus of the laser is optional, as it is in ALT or SLT. The laser light is not in sharp focus when the trabecular meshwork is aimed at it. The outcome is the formation of tiny bubbles near the trabecular meshwork. In one session, 180 or 360 degrees are used in the treatment. The laser spots can be placed continuously or in different areas.
What Are the Complications of Laser Trabeculation?
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Increase in Intraocular Pressure - This is one of the most common complications of laser trabeculoplasty. The frequency of a rise in intraocular pressure is reduced a little with the use of alpha-adrenergic agonists before the procedure.
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Corneal Edema - Fluid accumulation in the cornea occurs due to the reactivation of the herpes simplex virus.
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Hyphema - The collection of blood in the anterior chamber of the eye.
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The formation of peripheral anterior synechiae.
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The formation of low-grade iritis.
Conclusion
Laser trabeculoplasty uses laser beams to treat open-angle glaucoma. The procedure targets the trabecular meshwork and alters the pores in the meshwork, thus increasing the outflow of the aqueous humor and reducing the intra-ocular pressure. However, the procedure is only sometimes effective and lasts a few years. Regular follow-up is required after the procedure, and one may still need surgery for complete treatment.
