Veterinary Gross Anatomy-II

SCLERA

• The sclera is a dense white fibrous membrane forming about four fifths of the fibrous tunic of the eyeball.
• Thickest in the vicinity of the posterior pole, it thins at the equator and increases in thickness toward the junction with the cornea.
• It is often pigmented. When non-pigmented it shows a bluish tinge.
• Its external surface gives insertion to ocular muscles and is covered in front by the bulbar conjunctiva.
• The internal surface is attached to the chorioid coat by pigmented connective tissue -the lamina fusca.
• The anterior border is oval, the long axis being transverse and is continuous with the cornea.
• The sclera here appears to form a bevel in which the cornea is fixed. Near the corneoscleral junction, there is a circular venous plexus, the plexus venosus sclerae (sinus venosus sclerae or canal of Schlemm).
• The canal will be described later under the iris angle.
• The optic nerve pierces the posterior part of the sclera a little below and lateral to the posterior pole (in the postero-ventrolateral quadrant).
• It composed of interlacing bundles of white fibres and few elastic fibres.

Blood supply

•  Ciliary arteries.

Nerve supply

• Ciliary nerves.

Vascular tunic

• It lies internal to the fibrous tunic and comprises the chorioid, ciliary body and iris.