Subepithelial Versus Subcapsular Injections of Drugs

Abstract

Subconjunctival injections of drugs commonly are used in ophthalmic therapeutics; however, little attention has been paid to the depth of injection. It apparently has been assumed that the subepithelial connective tissues of the bulbar conjunctiva are too thin to present an appreciable barrier to the passage of drugs. Recently, Schlegel and Swan have studied the ocular penetration of procaine by quantitative analysis of the tissues of the rabbit eye.¹ They found that the forward extension of Tenon's capsule represents a considerable barrier to the penetration of this anesthetic into the iris, aqueous, and cornea after injections just under the conjunctival epithelium. They designated this as a "subepithelial" injection. Furthermore, Schlegel and Swan found that after subepithelial injections the drug solution was carried away from this area via the conjunctival vessels. The addition of epinephrine for vasocontriction or cutting off the circulation significantly enhanced the penetration of procaine from the subepithelial tissues into the