The purpose of this study is to evaluate the safety, efficacy, and dose response of brimonidine tartrate ophthalmic solution as compared to placebo in the prevention of allergen-induced conjunctival redness using a conjunctival allergen challenge (CAC) model.

It is hypothesized that low-dose brimonidine tartrate ophthalmic solution will be more effective than vehicle in the prevention of conjunctival redness induced by conjunctival allergen challenge when instilled prior to the allergen challenge.

Inclusion Criteria:

• Be at least 18 years of age;
• If female, cannot be not pregnant or nursing
• Have a positive skin test reaction to cat hair, cat dander, grasses, ragweed, dog dander, cockroach, dust mite, and/or trees within the past 24 months;
• Have a calculated best corrected visual acuity of 0.6 logMAR or better in each eye as measured using an ETDRS chart;

Exclusion Criteria:

• Have known contraindications or sensitivities to the use of any of the study medications(s) or their components;
• Have any ocular condition that, in the opinion of the investigator, could affect the subject's safety;
• Have a presence of active ocular infection;
• Use specified disallowed medications during the study or appropriate pre-study washout period;
• Have any significant illness;
• Have planned surgery (ocular or systemic) during the trial period or within 30 days after;
• Have used an investigational drug or device within 30 days of the study or be concurrently enrolled in another investigational drug or device study within 30 days of the study;
• Be a female who is currently pregnant or nursing.