Schwalbe line's cells: a new cell type in the trabecular meshwork of Macaca mulatta

In the eye of Macaca mulatta, at the anterior end of the trabecular meshwork, just beneath the ridge known as Schwalbe line in gonioscopy, cells are present that contain secretory inclusions. These cells have been termed Schwalbe line's cells. They form a discontinuous cord, oriented circumferentially at the corneal periphery, deep to the endothelial lining of the anterior chamber. They are characterized by a prominent Golgi apparatus and by two types of secretory granules: round bodies, up to 0.6 micron in diameter and containing moderately dense material, and larger inclusions, up to 1 micron in diameter and consisting of stacks of osmiophilic lamellae. Membrane whorls and fragments are also commonly found in the spaces between the cells and possibly arise from exocytosis of the lamellar bodies. Schwalbe line's cells have been observed in young as well as in old animals. They are joined to one another by gap junctions and puncta adhaerentia. Because their cytoplasmic inclusions bear a striking morphological resemblance to the multilamellar bodies or cytosomes of the type II alveolar epithelial cells of the lung, the hypothesis is advanced that Schwalbe line's cells produce a phospholipid material that is released in the aqueous humor and thus facilitates its movement through the tissues of the sclerocorneal angle.