Ultrastructural studies of the human round window membrane.

An ultrastructural study of 14 round window membranes of seven human ears 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 these layers participate in absorption and secretion of substances to and from the inner ear. A comparison of morphological features of round window membranes suggests that the average thickness of 70 microns does not change with advancing age. However, in the elderly, the connective tissue has a looser arrangement; there is an increase in ground substance; and elastic fibers thicken. Fibroblast nuclei become larger, rounder, and less uniform and have extensions. The ultrastructure of the "false round window membranes," with epithelial cells of the same type bounding both sides, suggests that these membranes consist of juxtaposed epithelial folds of the overlying promontory.