The cornea is the outermost transparent layer of the eye present in the anterior portion of the eye. It covers the tiny aperture of the eye, i.e. pupil, the visible pigmented portion, iris and aqueous humour. The main function of the cornea is to refract the light entering the eyes. Cornea accounts for most of the focusing function and optical power of the eyes.
The human eye is triple-layered. The three layers are sclera, choroid and retina. The sclera is the outermost layer of dense connective tissue. The anterior portion of the sclera is known as the cornea. The main characteristics of the cornea are the following:
- It is the anterior portion of the eye, which covers the pupil, iris and the aqueous chamber. It is an extension of the sclera.
- It is composed of proteins and cells and devoid of blood vessels. Albumin is the most abundant protein present in the cornea.
- Aqueous humour and tears nourish this layer.
- The cornea is sensitive to touch, chemicals, heat, etc. It contains unmyelinated nerve endings. These nerve endings are responsible for the involuntary reflex of closing the eyelid on touch and preventing foreign particles from entering and damage to the eye.
- The human cornea is made up of five layers. They are following:
1. Corneal epithelium – Consist of multiple layers of non-keratinised stratified squamous epithelium cells, which are frequently regenerated from the basal layer.
2. Bowman’s layer – Mainly composed of collagen fibres and protects stroma.
3. Corneal stroma – It is a thick and transparent middle layer made up of collagen fibres and interconnected keratocytes.
4. Descemet’s membrane – It functions as a basement membrane for corneal endothelium.
5. Corneal endothelium – It is made up of mitochondria rich squamous or cuboidal cells. They get their nourishment from aqueous humour and do not regenerate like corneal epithelium. It maintains the fluid content and regulates the solute and fluid transport between different layers of cornea and aqueous humour.
The main function of the cornea is the refraction of light and focusing. Around 60 to 75% of the focusing ability of eyes is due to the cornea. The rest is due to the lens. The accommodation ability is due to the lens, which changes its shape to focus from distant to near objects.
The corneal epithelium allows tears to spread across the cornea and keep it moist. It helps in providing clear vision.
This was in brief about Cornea. Test your understanding with MCQs on Structure of Eye, only at BYJU’S.