21st February 2024

Layers Of the Eyeball – Fibrous Layer

The Sclera

The fibrous layer is the outermost layer and consists of the sclera and cornea, which are continuous with one another. The sclera is the white part of the eyeball, and it is primarily composed of collagen fibres. It is important for the protection of the eyeball, to maintain the shape of the eye and to allow attachment of the extraocular muscles to facilitate eye movement.

The sclera has three main layers: the episclera, scleral stroma and lamina fusca. The episclera is a thin connective tissue that covers the scleral surface and contains blood vessels. It provides vasculature for the conjunctiva. Scleral stroma forms the bulk of the sclera. It is composed of collagen fibres, fibroblasts, and proteoglycans. Its unique arrangement of collagen fibres contributes to the sclera’s strength while maintaining transparency.

The Cornea

The cornea is a transparent, dome-shaped structure at the front of the eye. It is responsible for approximately two-thirds of the eye’s refractive power to allow light to focus on the retina. To maintain clarity and transparency, the cornea lacks blood vessels and receives oxygen and nutrients from tear fluid and aqueous humour. 

The cornea has five distinct layers: 

• Corneal Epithelium – The outermost layer acts as a protective barrier and provides a smooth surface for the tear film.
• Bowman’s Layer – Located beneath the epithelium, it consists of collagen fibres and offers structural support. 
• Corneal Stroma  – makes up most of the corneal thickness; it consists of a network of collagen fibres arranged for transparency.
• Descemet’s Membrane – Found beneath the stroma, it provides a basement membrane for the corneal endothelium.
• Corneal Endothelium – The innermost layer helps maintain corneal transparency by regulating fluid balance