the superior rectus 7.7 mm. The insertions of the superior oblique and inferior oblique muscles are posterior to the equator (Fig. 1.8). The long tendon for the superior oblique muscle inserts superiorly and slightly laterally; the line of insertion is convex posteriorly and laterally. The inferior oblique muscle inserts posterolaterally. Because this muscle has no tendon, the muscular Þbers attach directly; the line of insertion is convex superiorly and laterally. The most posterior point lies 5 mm temporal to the optic nerve, external to the macula.

TenonÕs capsule, the fascial sheath of the eyeball, is closely connected to the outer portion of the sclera or episclera by delicate lamellae, particularly when it fuses with the muscle tendon insertions anteriorly and with the optic nerve

dural sheath posteriorly. TenonÕs capsule lies anteriorly between two vascular layers: the conjunctival plexus and the episcleral plexus, both of which nourish it.

1.3.1.1 Scleral Foramina

The sclera is an incomplete sphere that terminates anteriorly at the anterior scleral foramen surrounding the cornea and posteriorly at the posterior scleral foramen surrounding the optic nerve canal.

Anterior Scleral Foramen

The anterior scleral foramen has an elliptical appearance externally (horizontal diameter of 11.6 mm and vertical diameter of 10.6 mm) and a circular appearance internally (diameter of

Fig. 1.9 Diagrammatic representation of the corneoscleral junction in longitudinal section, illustrating the watch glass-like insertion of cornea into sclera, and the

relationships between sclera, peripheral cornea, conjunctiva, and TenonÕs capsule, the canal of Schlemm, and the trabecular meshwork and iris

11.6 mm); it is not a discontinuity in the outer coat of the eye but is an anatomical concept of the sclera without the cornea. The sclera meets and merges with the cornea at the anterior scleral foramen forming the corneoscleral junction, where the irregular scleral Þbers tend to bend with the regular corneal lamellae. The corneoscleral junction is an area measuring about 1.5Ð2 mm wide; the concave scleral side is formed by the external scleral sulcus in its outer surface and by the internal scleral sulcus in its inner surface (Fig. 1.9). The external layers of the internal scleral sulcus merge with the stroma of the cornea. The internal layers of the internal scleral sulcus contain the trabecular meshwork and the SchlemmÕs canal anteriorly and the scleral spur posteriorly; the trabecular meshwork merges with the DescemetÕs membrane. Because the scleral spur attaches to the meridional ciliary

muscle, tension on the scleral spur by the muscle opens the trabecular meshwork [3, 18].

The corneoscleral junction can be best distinguished in a gross specimen of an enucleated eye after refrigeration because the cornea thickens and opaciÞes, whereas scleral thickness is not modiÞed; however, it is indistinguishable in microscopic sections because of the similar structure of cornea and sclera.

Posterior Scleral Foramen

The sclera allows the passage of the optic nerve through the posterior scleral foramen. The site of this perforation is located 3 mm medial to the midline and 1 mm below the horizontal meridian. The outer two-thirds of the scleral Þbers continue backward, fusing with the dural and arachnoid sheaths of the optic nerve (Fig. 1.10). The inner third of the scleral Þbers crosses the posterior