Late effects of local anesthetics on tympanic membrane structure.

With the rat tympanic membrane used as a model, various topical anesthetics in current clinical use (phenol, Bonain's liquid, and Xylocaine spray) were tested. Structural changes were observed for up to five months from the time of anesthetic application. The most protracted changes affect the lamina propria, which exhibits a pronounced thickening. The extent of the changes, however, differs according to the agent used; for example, phenol applied to discrete areas exhibited the least widespread changes. In the tympanic portion of the lamina propria, the connective tissue was loosely packed with less regularly arranged collagen fibers, while a tightly packed fiber bundle existed on the meatal side. It is inferred that the submucosal connective tissue layer is the portion of the connective tissue layer where the remodeling and reconstruction of the fibrous layer occur.