The sclera and the cornea form the rigid outer covering of the eye.
All six ocular muscles insert into the sclera.
The sclera is fibrous, whitish opaque, and consists of nearlyacellular connective tissue with a higher water content than the cornea. The sclera is thickest (1 mm) anteriorly at the limbus of the cornea where it joins the corneal stroma and at its posterior pole. It is thinnest (0.3 mm) at the equator and beneath the insertions of the rectus muscles. The site where the fibers of the optic nerve enter the sclera is known as the lamina cribrosa. In the angle of the anterior chamber, the sclera forms the trabecular network and the canal of Schlemm. The aqueous humor drains from there into the intrascleral and episcleral venous plexus through about 20 canaliculi.
Vortex veins and the short anterior and posterior cili-ary arteries penetrate the sclera. The ciliary nerves course through the sclera from posterior to anterior.