Argon Laser Trabeculoplasty
Myranda R. Partin
Steven R. Sarkisian Jr.
Argon laser trabeculoplasty (ALT) was introduced by Wise and Witter in 1979.2 Many attempts using different lasers were tried earlier but these lasers were either unstable or their parameters caused too many side effects. ALT dominated the market until the FDA approval of selective laser trabeculoplasty (SLT) for the treatment of open-angle glaucoma in 2002.3 Argon laser trabeculoplasty remained the standardof-care method of laser therapy to the trabecular meshwork (TM) for open-angle glaucoma until 2005.4 The Glaucoma Laser Trial performed over two decades ago had demonstrated equivalency between ALT and medical treatment as initial treatment modalities in patients with glaucoma. This was revolutionary for its time as there were very few hypotensive eye drops available and other glaucoma surgical alternatives were invasive.
ALT uses thermal energy to achieve an IOP decrease. The melanin absorbs the laser light energy and converts it into heat, which in turn creates thermal damage with subsequent coagulative necrosis.5 The amount of damage is not limited to the treatment area but extends beyond the trabecular cells that contain melanin.6 The surrounding tissue also obtains considerable damage. According to Hollo, following ALT, the uveoscleral meshwork is severely destroyed around the area of the laser spots, and the surrounding collagen fibers are heat damaged.7 A membrane is formed by migrating endothelial cells, which covers the meshwork between the laser spots and is responsible for the late pressure rise and treatment failure after ALT. This endothelial membrane and thermal damage were not seen after 532-nm SLT.7 According to the mechanical theory, ALT causes coagulative damage to the TM, which results in collagen shrinkage and subsequent scarring of the TM (Figure 11.1). This tightens the meshwork around the area of each burn and reopens the adjacent, untreated intertrabecular spaces.6 The cellular theory proposes that in response to coagulative necrosis induced by the laser there is a migration of macrophages, which phagocytose debris and thus clear the TM (Figure 11.1).2
 FIGURE 11-1 Electron microscopy showing TM modification seen by argon laser trabeculoplasty on the left and selective laser trabeculoplasty on the right. The argon laser trabeculoplasty laser burns and leaves a definite scar behind.8 (Reprinted with permission from Pham H, Mansberger S, Brandt JD. I. Argon laser trabeculoplasty. The gold standard: Argon laser trabeculoplasty versus selective laser trabeculoplasty. Surv Ophthalmol. 2008;53(6):641-646.) |
INDICATIONS
Key Indications
Primary open-angle glaucoma (POAG)
Ocular hypertension
Pigment dispersion syndrome (PDS) or pigmentary glaucoma
Pseudoexfoliation syndrome (PXE) or pseudoexfoliative glaucoma
Normal tension glaucoma (NTG) also known as low-tension glaucoma
Primary angle closure (PAC) or PAC glaucoma (PACG) after successful angle-closure treatment.
Gonioscopy should always be performed before initiating any laser trabeculoplasty to ensure an open angle and to document any angle abnormalities or previous surgical changes. POAG, pseudoexfoliative glaucoma, and pigmentary glaucoma respond best to ALT. In POAG and PXE, patient’s ALT success rate ranges from 80% to 97%.1,2,9 Pigmentary glaucoma patients still have great success at 44% to 80% at one year.10
A study done to evaluate the effectiveness of SLT versus ALT in PXE and pseudoexfoliative glaucoma showed an equivalent efficacy between the two lasers. Laser
trabeculoplasty has been thought to be of great success due to hyperpigmentation in the TM from the accumulation of proteinaceous material in PXE patients.
trabeculoplasty has been thought to be of great success due to hyperpigmentation in the TM from the accumulation of proteinaceous material in PXE patients.
Patients with NTG in one study showed a 4.9-mm Hg decrease in IOP at 12 months with a gradual tapering of the pressure-lowering effect over the course of a 21.6-month follow-up.11 As with all types of glaucoma, the pressure-lowering effect diminishes over time with ALT. There are not many other studies conducted studying ALT in NTG. However, one other study with SLT also concluded laser trabeculoplasty as a successful treatment option for NTG.12
As with SLT and most other glaucoma treatments, a lower preoperative IOP such as in low-tension glaucoma is likely thought to be a negative predictor of success. The treating clinician should factor that in when gauging expectations of IOP reduction following any laser trabeculoplasty, including ALT, in low-tension glaucoma.
ALT can be very effective after the opening of the angle from peripheral iridotomy in PACG patients. A study conducted with 19 Japanese patients, after peripheral iridotomy, had a 66% probability of success at the end of three years after ALT.13
CONTRAINDICATIONS
Key Contraindications
PAC or PACG
A relatively high preoperative IOP (>30 mm Hg) in conjunction with advanced optic nerve damage, in which cases a possible postoperative transient IOP elevation is thought to pose a significant risk for the patient’s vision
Glaucoma associated with uveitis, trauma, ischemia/neovascularization, juvenile open-angle glaucoma, or angle dysgenesis
A history of previous ALT failure in the same or fellow eye
Little or no trabecular pigmentation (negative predictor for success)
Aphakic or pseudophakic glaucoma (relative contraindication)
Young age (relative contraindication)
ALT will likely be unsuccessful if a majority of the angle is not seen. The exact amount of visible TM needed is unknown but speculated to be at least half.
Patients with previous or active uveitis are poor responders to laser trabeculoplasty due to inflammatory debris in the angle or angle structure modification. ALT could possibly cause further damage by reactivating inflammation or further damaging the angle.10,14
An IOP spike in a patient who has advanced glaucoma or an impending central visual field defect may be at too high of a risk to consider ALT. Without prophylactic hypotensive eye drops such as brimonidine or apraclonidine, about one third of patients have a rise in IOP over 5 mm Hg, and 12% to 50% will have spiked over 10 mm Hg 1 hour after treatment. Thankfully these prophylactic hypotensive eye drops can effectively prevent a rise in IOP in all but about 3% to 5% of cases.1,15
Repeating ALT is typically contraindicated if the patient has previously had 360° of treatment. Around 30% of cases can respond with an adequate drop in IOP.1,16
This drop in IOP can be short lived due to the rapid loss of effectivity in two thirds of those cases at one year.1,16 SLT can be utilized successfully over previous ALT burns or in eyes who had failed with ALT.17
This drop in IOP can be short lived due to the rapid loss of effectivity in two thirds of those cases at one year.1,16 SLT can be utilized successfully over previous ALT burns or in eyes who had failed with ALT.17
Patients with aphakia typically have a poor response to ALT; however, an IOP-lowering effect of around 6 mm Hg has been reported.1 However, if there is any vitreous in the anterior chamber, ALT has a high failure rate. It is still unknown the mechanism behind ALT failure along with glaucoma secondary to complicated cataract surgery.18
INFORMED CONSENT CONSIDERATIONS
Key Informed Consent Adverse Events Listed as Follows
IOP spike
Inflammation
Transient blurring of vision
Bleeding/hyphema
Lack of efficacy
Loss of efficacy over time
Informed consent is important not only for liability purposes but also to help the patient understand more about the procedure. A brief summary in laymen terms should include how the laser works on the pigmented region of the drain in their eye. The mechanism by which this occurs is twofold: mechanically pulling open the TM by creating small burn spots and cellular from their immune cells cleaning out the drain. The combination of these two mechanisms is likely what lowers the eye pressure, which is the only modality of treatment. Although laser trabeculoplasty is considered a minor procedure, it still needs to be taken seriously.
Key informed consent adverse events include but are not limited to an IOP spike, postoperative inflammation, discomfort during or after the procedure, transient blurring of vision, ineffectiveness of the procedure, bleeding, or corneal edema. It should be documented that the patient was counseled on alternative options, informed of risks of the procedure including that the procedure may not work, and future alternative methods of treatment could be required. Such alternatives include hypotensive eye drops, monitoring, or more invasive glaucoma surgery.
A note from the counseling physician should be included and phrased similar to, “I have counseled this patient as to the nature of the proposed procedure, the attendant risks involved, and the expected results.” The patient’s and doctor’s names should be printed and signed with the date as well as a witness signature.
PREOPERATIVE CARE
Key Preoperative Considerations
Pre-laser measurement of IOP
Gonioscopy assessing for openness of the angle, amount of pigment in the TM, indications and contraindications
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