A corneal dystrophy occurs when any layer or tissue within the cornea begins to weaken and break down, or when the cornea builds up a cloudy material that impairs vision. While there are many kinds of corneal dystrophies, it is a relatively rare disease and less than 1% of all cases of blindness or partial-sightedness can be traced back to it. Though there are dozens of specific corneal dystrophies, most share many common elements in that they: Progress slowly Are hereditary Affect both eyes evenly Are not typically caused by outside factors (diet, exercise, climate, or pre-existing medical conditions)