The eyeball itself is the result of three layers of specified tissue, which rounds off at about a 1 inch diameter sphere in the adult human body. The orbit of the skull houses about 4/5 of the human eye, while the rest gently protrudes out into the facial tissue.


The fibrous tunic outer layer is segregated into two divisions, the opaque sclera and the transparent cornea. The opaque sclera requires about 5/6 of this layer, leaving the remaining 1/6 for the transparent cornea.

The sclera is partly discernable, as it is recognized as the white portion of the eye. It’s main responsibility is to provide adequate protection to the layers underneath while simultaneously retaining the shape of the eye.

Elastic, collagenous fibers create the tissue composite of this harder outer layer. The extrinsic ocular muscles find this layer suitable for attachment.


Image: Eyeball

While this layer is innervated for pain receptors, it is uniquely avascular, meaning it is devoid of blood flow. The rear portion of the eyeball provides an exit point, through the sclera, for the optic nerve.


Rays of light enter the cornea, which is created to be convex in order to refract (or bend the rays of light) in a converging pattern to create the images which we call sight. The snugly packed dense connective tissue creates a transparent “lens” which is also devoid of vascular need.

There are few cells that are seemingly randomly placed throughout the cornea, but in actuality are presented in unusual but regular patterns. The sclera and the cornea are a continuation of each other, seamlessly meeting along the edge of the cornea’s circumference.

Additionally, the cornea creates a continuation with the bulbar conjunctiva of the sclera, right along the top layer of the cornea which is created by thin, non-keratinized stratified squamous epithelial cells. This layer is known as the anterior corneal epithelium.
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