Keratoconus is an eye disease which affects the cornea - the front transparent tissue of the eye. Keratoconus is an eye disorder, which happens when the cornea progressively deforms, gets thinner and eventually changes to an irregular conical shape.
The result of this process is irregular corneal astigmatism, which is hard /sometimes impossible/ to correct with glasses or contact lenses. Usually the changes of the cornea are asymmetrical and affect both eyes. Less than 1% of all cases affect only one of the eyes.