According the AAO website, keratoconus is an uncommon condition in which the normally round, dome-like cornea (the clear front window of the eye) becomes thin and develops a cone-like bulge. Keratoconus literally means “cone-shaped cornea.” Keratoconus is a non-inflammatory eye condition in which the normally round dome-shaped cornea progressively thins causing a cone-like bulge to develop. This results in significant visual impairment.
Because the cornea is irregular and cone shaped, eyeglasses do not appropriately correct the vision in patients with keratoconus. This is a result of the glasses not conforming to the shape of the eye. It should be no surprise that patients with keratoconus see best with rigid contact lenses since these lenses provide a clear surface in front of the cornea allowing the light rays to be projected clearly to the retina. Therefore; the vast majority of patients are treated with rigid contact lenses. There are however some excellent new surgical options for patients with keratoconus who cannot tolerate these lenses. Many patients are initially unaware they have keratoconus and see their eye doctor because of increasing spectacle blur or progressive changes in their prescription.
The actual incidence of keratoconus is not known. It is not a common eye disease, but it is by no means rare. It has been estimated to occur in 1 out of every 2,000 persons in the general population. Keratoconus is generally first diagnosed in young people at puberty or in their late teen years.