The sclera and the cornea form the rigid outer covering of the
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.