Clinical manifestations of keratoconus include reduced visual acuity, increased astigmatism, thinning of the cornea and protrusion of the cornea, as observed in the shape of the corneal surface. Spectacles are utilized in the treatment of early keratoconus, whereas hard contact lenses or intracorneal support rings are used in more advanced forms of the disease. A corneal transplant operation is applied to a far-advanced keratoconus. Photohardening of the cornea may serve as a suitable preventive treatment.