Scanning electron microscopy of human ocular tissues: trabecular meshwork.

Scanning electron microscopic studies of the trabecular meshwork are presented and discussed which suggest that the trabecular endothelium is distinctly different from the corneal endothelium. The trabecular endothelial cells appear to be larger, with less prominent cell borders, and to have a thinner basement membrane than the corneal endothelial cells. The transition between the two types of endothelium takes place at the anterior border of a smooth zone (Zone S) which is located immediately anterior to Schwalbe's ring. The corneoscleral trabecular sheets are composed of trabecular endothelial cells which cover a central connective tissue framework. Holes or tunnels measuring 2 /i to 5 /i in diameter appear to pass through the trabecular sheets. In the tissues studied to date with the scanning electron microscope, the holes appear to be transcellular rather than intercellular. The inner wall of Schlemm's canal contains tiny dark indentations (or openings) measuring 0.25 fi to 0.75 n in diameter. The uveal meshwork is composed of a network of bands two to three layers thick, measuring 4 fi in diameter with nuclear thickenings to 10 n. The individual bands branch in a random manner and cover the inner surface of the trabecular sheets. Schwalbe's ring is apparently produced by their oblique and circumferential insertions into the limbal stroma at the posterior margin of Zone S.