The Human Cornea

This is the outer ‘skin’ of the eye. Our eyes are exposed to the surrounding environment with dust, wind and microparticles causing damage. The epithelium is constantly reproduced by specialist stem cells, repairing any damage. Without this, you would very quickly lose vision. Epithelial cells are like waves continually moving across the surface from the peripheries to the middle.

This layer helps attach the constantly moving epithelial cells to the underlying structure. Any abnormality in this layer causes the epithelium to become loose, resulting in pain and blurred vision.

The stroma is the thickest layer. It is slowly reproduced over several years. Any damage to this layer causes vision blurring, which may slowly improve but is likely to be long-standing.

This layer is akin to Bowman’s. It helps attach the underlying endothelial cells to the stroma.

The endothelium is very important for maintaining the water balance and clarity of the cornea. Formed as a series of tightly packed cells, the endothelial cells behave similarly to a dam wall, preventing the fluid that fills the eye from escaping and waterlogging the cornea. These cells pump, continuously removing excess liquid from the cornea. Their action is similar to bilge pumps found on boats, which constantly pump water out of the hull, keeping it afloat. We are typically born with around 4000 cells per square millimetre. This number gradually decreases with age, so by age 40, we have about 3000 cells per square millimetre and only 2000 per square millimetre by the age of 80.