Eyeball - Sclera

 Sclera:

• It is opaque
• It forms the posterior 5/6th of the eyeball
• It is composed of dense fibrous tissue which is firm.
• It maintains the shape of the eyeball.
• It is thickest behind, near the entrance of the optic nerve.
• It is thinnest about 6mm behind the sclero-corneal junction, where recti muscles are inserted.
• It is weakest at the entrance of the optic nerve. Here the sclera shows numerous perforations for the passage of fibres of optic nerve

Because of its sieve - like appearance, this region is called as lamina cribriosa.

• The outer surface of the sclera is white and smooth.
• It is covered by Tenon’s capsule.
• Its anterior part is covered by the conjunctiva, through which it can be seen as the white of the eye.
• The inner surface is brown and is grooved for ciliary nerves and vessels.
• It is separated from the choroid by perichoroidal space, 
• which contains a delicate cellular tissue, termed as suprachoroidal lamina or lamina fascia of the sclera.

The sclera is continuous anteriorly with the cornea at the sclera corneal junction or limbus.

The deep part of the limbus contains a circular canal, known as the sinus venosus sclerae or the canal of Schlemm.

The aqueous humour drains into the anterior scleral or ciliary veins through this sinus

• The sclera is fused posteriorly with the dural sheath of the optic nerve.
• It provides insertion to extrinsic muscles of the eyeball. 
• The recti in front of the equator and the oblique muscles behind the equator.
• The sclera is almost avascular.
• The loose connective tissue between the conjunctiva and sclera called as episclera is vascular

The sclera is pierced by number of structures.

1. Optic nerve pierces it a little inferomedial to the posterior pole of the eyeball

2. The ciliary nerves and arteries pierce it around the entrance of the optic nerve.

3. The anterior ciliary arteries derived from the muscular arteries to the recti, pierce near the limbus

4. Four venue vorticosae or the choroid veins pass out through the sclera just behind the equator. The sclera is fused posteriorly with the dural sheath of the optic nerve.

• It provides insertion to extrinsic muscles of the eyeball. 
• The recti in front of the equator and the oblique muscles behind the equator.
• The sclera is almost avascular.
• The loose connective tissue between the conjunctiva and sclera called as episclera is vascular

Watch lectures on YouTube:

Eyeball - Outer Tunic Of Eyeball - Sclera |Cornea |Sceleo-Corneal Junction |Limbus |Canal Of Schlemm