Effects of argon laser trabeculoplasty in the Early Manifest Glaucoma Trial.

PURPOSE To analyze reduction of intraocular pressure (IOP) by argon laser trabeculoplasty (ALT) in the Early Manifest Glaucoma Trial and factors influencing the effect of such treatment. DESIGN Cohort study based on 127 patients from the treatment group of the Early Manifest Glaucoma Trial, a randomized clinical trial. METHODS Patients randomized to the treatment arm of the Early Manifest Glaucoma Trial received a standard treatment protocol (topical betaxolol hydrochloride followed by 360-degree ALT) and then were followed up prospectively at 3-month intervals for up to 8 years. One eye per patient was included in the analyses. We investigated the relationship between IOP before ALT and subsequent IOP reduction and other factors that might have influenced the effect of ALT, including stage of the disease, trabecular pigmentation, presence of exfoliation syndrome, and treating surgeon. RESULTS The mean ± standard deviation IOP before ALT and after betaxolol treatment was 18.1 ± 3.9 mm Hg, and the mean ± standard deviation short-term IOP reduction 3 months after ALT was 2.8 ± 3.9 mm Hg (12.6 ± 20.5%). The IOP before ALT strongly affected IOP reduction (P < .001); each 3-mm Hg higher IOP before ALT value was associated with an additional mean IOP reduction of approximately 2 mm Hg. The treating surgeons also had a significant impact on IOP reduction (P = 0.001), with mean values ranging from 5.8 to -1.3 mm Hg. CONCLUSIONS In this cohort, which included many patients with low IOP levels, IOP before ALT markedly influenced the IOP reduction induced by ALT, seen as a much larger decrease in eyes with higher IOP before ALT. The treating surgeon also had a significant impact on ALT outcome.