What problems can occur?
The principle problems affecting the cornea are loss of clarity, poor focus, infection and, rarely, perforation.
The cornea is kept clear by the layer of cells lining the back of the cornea constantly pumping water out of it. These cells may become damaged by injury, most commonly cataract surgery, or by disease, most commonly endothelial dystrophy. The cells which pump the water out of the cornea (endothelial cells) do not get repaired or replaced by the body. If the corneal endothelial cells are lost or damaged, the only way to restore normal function is with a corneal transplant.
Scarring following infection or injury can make the cornea cloudy and misshapen. Scarring can block and scatter the light entering the eye and make the focus poor. The eye will have blurred vision, light scatter will cause glare, making vision poor particularly when looking towards a low sun or car headlights. Some recovery of scarring will occur, but this is a slow process, taking up to two years to complete.
A peculiar condition, with a peculiar name - pterygium - can allow abnormal conjunctiva to grow across the cornea causing an abnormal appearance and also eventually loss of vision with scarring.
There are some conditions which cause the cornea to become weakened and mis-shapen. The commonest of these is keratoconus, where the cornea becomes slightly cone shaped, like the tip of a rugby ball. This shape change makes it impossible to fully correct vision with glasses.