Keratoconus refers to the abnormal cornea curvature. Abnormal changes gradually make the cornea become thin and bulge outward. This makes the cornea become a cone shape, and thus cause the abnormal cornea curvature.
Because of the abnormal cornea curvature, the cornea's refractive ability is affected. This often leads to blurred or distorted vision. The common examples are myopia, hyperopia and astigmatism. In other circumstances, this can also cause corneal tissue swelling or scarring.
Keratoconus normally occurs during puberty. The major cause is genetic. Other causes may include: eye diseases (e.g. retinopathy, retinitis pigmentosa, conjunctivitis, etc.), eye injuries, or other disease complications.