The purpose of this study is to evaluate the clinical efficacy and safety of Tobradex ST compared to AzaSite in the treatment of moderate to severe chronic blepharitis.

Inclusion Criteria:

• Have diagnosis of moderate to severe chronic blepharitis defined by a minimum score of at least "1" for one of the lid signs, one of the conjunctival signs, and one of the symptoms in at least one eye
• Have a minimum global score (the total signs and symptoms score) of 5 in the same eye qualifying.

Exclusion Criteria:

• Have known sensitivity or poor tolerance to the test article (tobramycin, dexamethasone, azithromycin) or its components or any therapy associated with the trial
• Have a history of ocular surgical intervention within six (6) weeks prior to Visit 1 or during the study
• Have any ocular infections (bacterial, viral or fungal) - active ocular inflammation (i.e. follicular conjunctivitis, iritis) or preauricular lymphadenopathy, other than blepharitis
• Have worn contact lenses in the 72 hours prior to visit 1 and for the duration of the study
• Are currently taking any medication known to cause ocular drying that has not been on a stable dose for at least 30 days
• Have used any topical ocular or systemic antibiotics within 7 days of enrollment. Stable (greater than 1 month prior to enrollment) use of topical antibiotics on the face (except around the eyes) for dermatologic conditions is allowed. Dose must continue unchanged for duration of study
• Have used any topical ocular - aerosolized/nebulized - or systemic corticosteroid agents within 14 days of enrollment. Stable (greater than 1 month prior to enrollment) use of inhaled (using mouthpiece) and nasal corticosteroids and topical dermal steroids (except around the eyelids) are allowed. Dose must continue unchanged for the duration of the study.