Principles of therapeutics.

Topical administration of drugs is the treatment of choice for diseases of the anterior segment. Drug levels attained by this means are usually of short duration, however, necessitating frequent therapy or continuous perfusion if prolonged drug levels are required. A drug-delivery device (collagen shield or contact lens) or subconjunctival injections can be used to augment topical therapy if frequent treatment is not possible. Subconjunctival injections are recommended for drugs that have low solubility and, hence, low corneal penetration. Retrobulbar injections are seldom indicated, except for regional anesthesia. Systemic administration is useful for anti-inflammatory therapy but it may be difficult to establish therapeutic levels of antibiotic agents in the eye because of the blood-ocular barrier. In severe cases, intraocular injection may be required.