The outermost stratum of eye globe i.e. sclera is vascular or avascular.?
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The sclera, also known as the white of the eye, is the opaque (usually white, though certain animals, such as horses and lizards, can hold black sclera), fibrous, protective, outer layer of the eye containing collagen and elastic fiber.[1] It is derived from the neural crest.[2] In children, it is thinner and shows some of the underlying pigment, appearing slightly blue. In the elderly, however, fatty deposits on the sclera can make it appear slightly sickly.
The sclera forms the posterior five sixths of the connective tissue coat of the globe. It is continuous with the dura mater and the cornea, and maintains the shape of the planet, offering resistance to internal and external forces, and provides an attachment for the extraocular muscle insertions. The sclera is perforated by plenty of nerves and vessels passing through the posterior scleral foramen, the hole i.e. formed by the optic nerve. At the optic disk the outer two-thirds of the sclera continues with the dura mater (outer coat of the brain) via the dural sheath of the optic nerve. The inner third beside, on the other hand, along with some choroidal tissue forms a plate (lamina cribrosa) across the optic nerve next to perforations through which the optic fibers (fasciculi). The thickness of the sclera varies from 1mm at the posterior pole to 0.3 mm simply behind the rectus muscle insertions. The sclera's blood vessels are mainly on the surface, and together near the conjunctiva (which lies on top) This is a thin layer covering the sclera. Along with the vessel of the conjunctiva, those of the sclera renders the inflamed eye bright red. Source(s): anildudeanil(a)yahoo.com
Avascular..
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