Fibrous tunic of eyeball

Fibrous tunic of the eyeball is the outermost layer of the eye, serving as a protective envelope. It consists of two main parts: the sclera, which is opaque and constitutes the majority of the fibrous tunic, and the cornea, which is transparent and allows light to enter the eye. This layer plays a crucial role in maintaining the shape of the eyeball and providing attachment points for the extraocular muscles that control eye movements.

Structure

The fibrous tunic is divided into two distinct regions: the sclera and the cornea, each with unique properties and functions.

Sclera

The sclera is the white part of the eye, composed of dense, fibrous connective tissue. It covers approximately 5/6 of the eyeball's surface and provides mechanical support and protection. The sclera also serves as an attachment point for the extraocular muscles. Its dense structure helps maintain the shape of the eyeball and offers resistance against internal and external forces.

Cornea

The cornea is the transparent front part of the fibrous tunic, covering about 1/6 of the eyeball. It is a highly organized structure with no blood vessels, which helps maintain its transparency. The cornea refracts light entering the eye, contributing significantly to the eye's focusing power. It consists of five layers: the epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium.

Function

The primary function of the fibrous tunic is to protect the inner components of the eye while maintaining its shape. The sclera protects the eye from mechanical injury, while the cornea allows light to enter and plays a key role in vision by refracting light.

Clinical Significance

Alterations in the structure or function of the fibrous tunic can lead to various eye conditions. For example, keratoconus is a disorder in which the cornea becomes thinner and cone-shaped, leading to visual impairment. Scleritis is an inflammation of the sclera that can be associated with systemic autoimmune diseases and can cause severe pain and vision loss if not treated.

See Also

• Eye anatomy
• Visual system
• Refractive error
• Ophthalmology