Keratoconus is a bilateral non-inflammatory corneal ectasia, the exact cause of which remains unknown.  It is estimated to occur in 1 out of every 2000 persons among the general population.  The onset of keratoconus is between the ages of 8 and 45-years, and it is usually diagnosed at 18-20 years of age.  Early symptoms include uncorrectable blurring of vision and visual distortion, resulting from myopia and irregular astigmatism caused by the deformation and altered transparency of the cornea. 

Diagnosis is based on ophthalmologic examination revealing a progressive decrease in visual acuity that is often difficult to correct with eyeglasses, in addition to evolving astigmatism.  Keratoconus may be confirmed by analysis of corneal topography by videokeratography and Orbscan, which allow visualisation of the variable degrees of bulging distortion of the anterior face of the cornea with a high level of precision.  Contact lenses may correct vision satisfactorily in patients with mild forms of the disease, but up to 20% of the patients require a corneal transplant (or penetrating keratoplasty).

Keratoconus has been found in a large number of systemic conditions, such as connective tissue disorders, Down syndrome, and other chromosomal disorders.  Less than 10% of keratoconus cases have a hereditary component and about 8% of patients have affected relatives.  Several mutations seem to be responsible.  For instance, mutations in the VSX1 homeobox gene (20p11.2) have been found in patients with keratoconus 1 (KTCN1), which is inherited in an autosomal dominant fashion.