A corneal dystrophy is when any layer or tissue within the cornea begins to weaken and break down, or when the cornea builds up a cloudy material, impairing vision. While there are many kinds of corneal dystrophies, it is a relatively rare brand of disease, and less than one percent of all cases of blindness or partial-sightedness can be traced to a corneal dystrophy. Though there are dozens of specific corneal dystrophies, most share many common elements, such as being hereditary, progressing slowly, affecting both eyes evenly, and not typically being caused by outside factors such as diet, exercise, climate conditions or pre-existing medical factors.