Keratoconus is an eye condition in which there is progressive thinning of the cornea resulting in a conical appearance of the cornea that impairs the patients’ vision. The onset is around puberty with slow progression until the third or fourth decades of life, when it usually arrests, although the ectasia can become stationary at any time (Kanski).
Kanski, Jack J. 2007. Clinical ophthalmology: a systematic approach. Edinburgh: Butterworth-Heinemann/Elsevier.