The purpose of this study is to investigate the safety and efficacy of up to three concentrations of DE-117 ophthalmic solution (Low Dose, Medium Dose, and High Dose) as monotherapy and as adjunctive therapy (DE-117 ophthalmic solution with 0.0015% tafluprost) in subjects with primary open-angle glaucoma or ocular hypertension.

This is a two stage study.

Stage One will explore the dose response of three concentrations of DE-117 as monotherapy compared with 0.0015% tafluprost and placebo. The safety and efficacy of DE-117 as adjunctive therapy (with 0.0015% tafluprost) compared with 0.0015% tafluprost and placebo will also be evaluated. In addition, the additive effect of adjunctive therapy of each concentration will be compared with the corresponding monotherapy concentration.

Stage Two will assess the safety and efficacy of the optimal DE-117 concentration as monotherapy compared with 0.0015% tafluprost. The safety and efficacy of the optimal DE-117 concentration as adjunctive therapy (with 0.0015% tafluprost) compared with DE-117 monotherapy and 0.0015% tafluprost will also be evaluated.

Inclusion Criteria:

1. Male or Female, 18 years of age or older
2. Current diagnosis of primary open-angle glaucoma or ocular hypertension in both eyes
3. Qualifying intraocular pressure (IOP) in at least one eye at Baseline

Exclusion Criteria:

1. Closed/barely open anterior chamber angle or a history of acute angle closure in either eye
2. Anticipate the need to initiate or modify medication (systemic or topical) that is known to affect intraocular pressure (IOP) during the study period
3. Females who are pregnant, nursing or planning a pregnancy
4. Presence of any abnormality or significant illness that could be expected to interfere with the study.