Ultrastructure of the Optic Nerve Head

Astrocyte cell bodies and processes form a continuous limiting membrane of varying thickness over the optic disk surface. The surface contour is irregular in places. Basement membrane separates glia from vitreous. The layer of glia is continuous with the internal limiting membrane of the retina, which is similar but has a thicker basement membrane and is formed by foot plates of Müller cells (a kind of astrocyte) instead of spider-cell astrocytes. As throughout the central nervous system (CNS), the endothelium of the central retinal vessels is nonfenestrated and held together by tight junctions. The artery has a media of smooth muscle, but the media of the vein is discontinuous. The central retinal artery loses its internal elastic membrane as it enters the eye, where tissue pressure is higher. The vascular adventitia is enclosed by astroglia.