The round window membrane under normal and pathological conditions.

Current research and an overall review of round window membrane studies is presented and the concepts that have evolved from these studies are described. Ultrastructural studies of the round window membrane of rodents, felines, and primates disclosed three basic layers: an outer epithelium lining the middle ear, a middle core of connective tissue, and an inner epithelium bordering the inner ear. Morphological evidence suggests that the membrane participates in: (a) the release of mechanical energy supplied by the ossicular chain to the labyrinthine fluids; (b) an alternative route for sound energy to enter the cochlea; (c) secretion into and absorption from perilymph; and (d) the defense system of the middle and inner ears. Permeability of the round window is considered an accident and not a function of the membrane. The complications of permeability (potential ototoxicity) and its potential usefulness (drug delivery) are discussed.