The Ocular Hypertension Treatment Study is a multi-center clinical trial sponsored by the National Eye Institute, designed to determine the efficacy and safety of topically administered eye lowering medication

Inclusion Criteria:

• Qualifying IOP in at least one eye of each participant must be more than or equal 24 mmHg but less than or equal to 32 mm HG calculated from two separate consecutive determination taken at least 2 hours, but not greater than 12 weeks apart.
• Normal and reliable 30-2 Humphrey Visual Fields in both eyes.
• Normal Optic disc in both eyes on clinical examinations and stereoscopic photographs as determined by the Optic Disc Reading Center.

Exclusion Criteria:

• Visual acuity worse than 20/40 in either eye on qualifying exam.
• Previous intraocular surgery: laser trabeculoplasty, laser iridotomy, filtering surgery, combined cataract extraction/filtering procedures, penetrating keratoplasty and retinal detachment repair.