COSOPT (Timolol/Dorzolamide Combination) Normal Tension Glaucoma Study (MK0507A-161)(COMPLETED)

Inclusion Criteria: * Patients who have not been treated with a glaucoma medication within 6 weeks prior to study participation after diagnosis with primary open-angle glaucoma * Patients with primary open-angle glaucoma based on gonioscopy * Patients with normal tension glaucoma diagnosed based on accompanying optic disc cupping and reappearance of visual field defect corresponding to retinal nerve fiber layer defect. * Subjects with \< 22 mm Hg of diurnal IOP measured using Goldmann applanation tonometer (every two hours between 9 a.m. and 5 p.m.) Exclusion Criteria: * Patients with another type of glaucoma but primary open-angle glaucoma * Patients treated with other glaucoma medications within 6 weeks prior to study participation * Patients with a history of chronic ocular inflammation or recurrent ocular inflammation * Patients using contact lenses * Patients who are allergic to timolol or dorzolamide * Patients with a history of any of the following COSOPT (timolol/dorzolamide combination) contraindications: * Reactive airway diseases * Sinus bradycardia, second or third degree atrioventricular block, overt cardiac failure, cardiogenic shock * Severe renal impairment * Patients with a history of significant ocular trauma or intraocular surgery within 6 months before participating the study, or intraocular laser surgery within 3 months before the participating the study * Patients with a history of a corneal disease * Patients who are using steroid or used the drug for more than 2 weeks within 12 months before participating the study * Pregnant women