The sclera is the external layer of the wall of the eyeball. It is made up of dense connective tissue. It differentiates into the cornea in the anterior part of the eye. It is mostly made up of collagen and elastic fibres. The sclera is also called the ‘white of the eye’. The other layers present beneath sclera are choroid and retina.
The main function of the sclera is to protect the eyes and maintain the shape of the eyeball. It also helps in controlling the movement of the eye.
The sclera is the supportive external membrane of the eye. It continues with the stromal cornea in the front. The main characteristics of the sclera layer are the following:
- It is the outermost layer of the eye. The anterior part differentiates into the cornea.
- The junction between the white sclera and transparent cornea is known as the limbus.
- It is made up of dense connective tissue.
- The conjunctiva membrane covers the sclera.
- The part of the sclera, which is under conjunctiva is known as the episclera. It is made up of loose connective tissue. It is densely vascular and provided with unmyelinated nerve fibres. It also contains fibroblast and melanocytes.
- Beneath episclera is the sclera proper, which is made up of dense connective tissue and gives the characteristic white colour to it.
- The innermost layer of the sclera is known as the lamina fusca and it is made up of elastic fibres. It is rich in melanocytes.
- The sclera is nourished by the vascular choroid layer and blood vessels in the episclera region.
- During embryonic development, the sclera is derived from the neural crest.
The sclera is a protective layer. It helps in maintaining the shape of the eyeball. Due to sclera, one can assess the movement of other’s eyes and know where they are looking. It is a mode of nonverbal communication. Extraocular muscles are attached to it, which control the movement of the eye.
Any change in the colour of the sclera has clinical significance. The yellowing of sclera is an indication of liver impairment and jaundice. The blue tint in the sclera in case of osteogenesis imperfecta is due to underlying blue veins of the choroid, which become visible on thinning of the sclera.
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