The cornea is the most anterior, transparent section of the outer coat of the eye. The point at which the cornea, bulbar conjunctiva and sclera meet is called the limbus.

The cornea consists of four distinct layers:

1. The stratified epithelium, which is attached to its own basement membrane

2. The stroma, which makes up 90% of corneal thickness. It is made from keratocytes, uniform parallel collagen fibrils (which form lamellae) and ground substance.

3. Descemet’s membrane, which is the basement membrane of the endothelium. It consists of a single layer of cells and does not stain with fluorescein. Therefore in corneal ulceration where all stroma is lost, it can appear as a dark structure in the centre.

4. The endothelium. Similarly to Descemet’s membrane it is only one cell thick and acts to move ions from the stroma to the aqueous. Water follows, ensuring the stroma stays hydrated (and therefore helps to maintain its transparency)

Signs of damage or disease of the cornea include pigmentation, vascularisation (the normal cornea does not contain blood vessels, however after insult both deep and superficial vessels may grow to promote healing) and oedema (leading to lack of translucency).