scleral foramen in a sieve-like manner forming the lamina cribrosa [19]. The lamina is slightly concave facing inward. The openings, lined by bundles of scleral Þbers covered by glial tissue, are short canals that provide a passage for the axons of the optic nerve. Myelination of the axons stops at the lamina cribrosa before entering the inner retina. One of the openings in the lamina is larger than the rest and permits the passage of the central retinal artery and vein. Because the lamina cribrosa is a relatively weak area, it is bowed posteriorly in glaucomatous eyes, forming a cupped disk.

1.3.1.2 Layers of the Sclera

The sclera may be divided into three layers: the episclera, the scleral stroma, and the lamina fusca.

Episclera

The episclera forms the superÞcial aspect of the sclera and merges with the underlying scleral stroma. The episclera consists of loosely arranged bundles of collagen, intermingled with Þbroblasts, occasional melanocytes, proteoglycans, and glycoproteins. Collagen bundles are thinner, Þbroblasts are plumper, and ground substance is more plentiful than in the sclera. The episclera has a rich blood supply anteriorly, where it lies closely connected with the subconjunctival tissue, rectus muscle insertions, and TenonÕs capsule. These vessels are mainly derived from the anterior ciliary arteries and, although usually inconspicuous, may be prominent when the tissue is inßamed. The posterior ciliary arteries serve as the source of the equatorial and posterior