Design and statistical considerations: Ocular hypertension treatment study: Design issues

Objectives This report relates the design and conduct con-siderations in the planning of a large, multicenter clinical trial on the treatment of ocular hypertension. This trial will begin patient enrollment in January 1994. Methods The Ocular Hypertension Treatment Study (OHTS) is designed to evaluate the safety and efficacy of topical ocular hypotensive medication in the prevention or delay of glaucomatous visual field loss and/or optic disc cupping in ocular hypertensive individuals at moderate risk. The OHTS Planning Committee agreed that the appropriate study hypothesis was a treatment hypothesis for patients with ocular hypertension who were at moderate risk for developing open-angle glaucoma. The selection of a treatment hypothesis narrowed the possible study interventions to topical medication and excluded laser or surgery because medical treatment reflects current practice for the proposed study group. Study entry criteria were selected to represent ocular hypertensive individuals at moderate risk, defined as mean intraocular pressure in at least one eye ≥ 24 mm Hg on two visits, with normal Humphrey visual fields and optic discs. The trial will randomize patients to a treatment group or a close observation/no-treatment group in equal proportions. Glaucomatous visual field damage will be determined by visual field loss using Humphrey program 30-2 and progressive optic disc damage as determined by a reading center. The study sample size will be approximately 1,500 patients. Conclusion The goal of this study is to provide a definitive and simple answer to the long-standing question of whether topical ocular hypotensive treatment protects ocular hypertensive individuals at moderate risk from developing glaucomatous damage.