Between 10% and 20% of cases of keratoconus will progress to a point where vision correction is no longer possible, thinning of the cornea becomes excessive, or scarring causes problems of its own, and a corneal transplantation or penetrating keratoplasty becomes required.
After either of the above patients will need some sort of correction to restore their vision. In early stages of keratoconus, glasses or soft contact lenses can suffice to correct for the mild astigmatism. As the condition progresses, these may no longer provide the person with a satisfactory degree of visual acuity, and most practitioners will move to manage the condition with rigid contact lenses, known as rigid, gas-permeable, (RGP) lenses. RGP lenses provide a good level of visual correction, but do not arrest progression of the condition. In a small number of people scarring of the cornea occurs therefore preferably Scleral lenses are prescribed for cases of advanced or very irregular keratoconus; these lenses cover a greater proportion of the surface of the eye and hence can offer improved stability.