Your cornea is the outermost layer of your eye. It is clear and shaped like a dome. The cornea helps to shield the rest of the eye from germs, dust, and other harmful matter. It also helps your eye to focus. If you wear contact lenses, they float on top of your corneas.
Problems with the cornea include
Refractive errors
Allergies
Infections
Injuries
Dystrophies - conditions in which parts of the cornea lose clarity due to a buildup of cloudy material
Treatments of corneal disorders include medicines, corneal transplantation, and corneal laser surgery.
NIH: National Eye Institute