The Glaucoma Laser Trial (GLT): 6. Treatment group differences in visual field changes

PURPOSE: To determine the differences in visual fields during 42 months (3 1/2 years) of follow-up between eyes treated with argon laser trabeculoplasty first and eyes treated with topical medication first in patients with newly diagnosed primary open-angle glaucoma. METHODS: Visual field examinations were obtained at enrollment, three and six months, and at six-month intervals thereafter during follow-up of 271 patients enrolled in the Glaucoma Laser Trial. Numeric analyses of the examination results, including global indices and patterns of localized changes, as well as masked subjective clinical impression, were used to compare the two treatment groups. RESULTS: The mean threshold for eyes treated with laser trabeculoplasty first was 0.3 dB better than that for eyes treated with topical medication first averaged over follow-up (95% confidence interval, [- 0.1, 0.7]; P = .17). More eyes treated with topical medication first (82 [31%] of 261 eyes) than eyes treated with laser trabeculoplasty first (61 [23%] of 261 eyes) had confirmed localized deterioration at least once during follow-up (P = .02). Improvement was nearly twice as common as deterioration on masked subjective impression in both groups through 30 months (2 1/2 years). Eyes treated with laser trabeculoplasty first were judged to have slightly more improvement and slightly less deterioration than eyes treated with topical medication first. CONCLUSION: During follow-up, measures of visual field status for eyes treated with laser trabeculoplasty first were slightly better than those for eyes treated with topical medication first. Statistical significance was attained for only some of the differences, and the clinical implications of such small differences are not known.