Corneal eye diseases Corneal eye diseases The cornea is the clear outermost layer of the eye. It is shaped like a dome and it is made up of 5 layers (or do we count dua’s layer?). Along with the lens, it helps the eye to focus. The most common corneal eye disease is dry eye which is believed to affect over 1/3 of Australian adults, and of this ½ are over 50. There is no cure, only treatment.