Changing what we think about lasers

Laser treatment

Argon Laser Trabeculoplasty (ALT) was the first glaucoma laser treatment that was designed to address this issue. The efficacy and safety of the ALT were assessed in the 1990's in the Glaucoma Laser Trial (GLT). This study randomized OAG patients to initial treatment with ALT versus topical medication, and found that eyes treated initially with ALT had lower IOP and better visual field and optic disc appearance than their fellow eyes treated initially with topical medication. The authors concluded that initial treatment with ALT was at least as efficacious as initial treatment with topical medication.³ However, this study was conducted before newer prostaglandin analogues became available, and may not be applicable to the current practices. Moreover, a concern has been raised regarding possible thermal trabecular meshwork (TM) damage adjacent to each ALT application, which may have implication on disease progression and response to further medical therapy.

SLT is often used as a second line treatment after inadequate response to topical medications and before proceeding to glaucoma surgery, however, there is accumulating evidence that SLT may be useful also as a first line treatment option.

Accumulating evidence

A prospective study conducted by Melamed et al. followed patients with OAG or ocular hypertension treated by SLT as an initial treatment. They found a mean IOP decrease of 30% from baseline with only 7% of patients who required adding topical medications to control their IOP after 18 months.⁹

McIlraith et al. prospectively assigned patients to either SLT or latanoprost as an initial treatment, according to patient's choice. Both treatments were equally effective, with reduction of about 31% in both groups after one year.¹⁰ A randomized prospective study conducted in the UK by Nagar et al. compared 90degree, 180degree and 360degree SLT with latanoprost for ocular hypertension (OHT) and OAG. This study did not find statistically significant differences between patients treated with 360-degree SLT compared with latanoprost. In this study, more than 80% of patients had IOP reduction of >20% after being treated with 360degree SLT.¹¹

These findings are supported by the SLT/Med study¹² - a recent prospective randomized study performed by Katz et al. that aimed to compare outcomes of SLT with drug therapy as an initial therapy. This study included 18 study site centres, and the coordinating centre was Wills Eye Institute in Philadelphia, Pennsylvania, USA.

Sixty nine patients (127 eyes) with OAG or OHT were randomly assigned to either 360-degree SLT or prostaglandin analogue. If target IOP range was not attained with SLT, additional SLT was the next step (repeat 180-degree SLT followed by another 180degree SLT), or in the medical arm additional medications were added. Data collection terminated with 54 patients reaching 9 to 12-months follow-up. In this study, there was a comparable reduction in IOP between the 2 groups with 26.4% mean IOP reduction in the SLT arm and 27.8% mean IOP reduction in the medical arm at the last follow-up visit. By last follow-up, 11% of eyes received additional SLT and 27% required additional medication. One of the strengths of this study is randomizing patients rather than eyes (unlike the GLT study), and thereby eliminating the concern of possible crossover effect of glaucoma medications.