Keratoconus is a noninflammatory, often bilateral, corneal dystrophy characterised by progressive cone-shaped bulging and thinning of the cornea. Incidence in the general population is estimated at 1/2000. However, with the development of new techniques for examination of the cornea, this appears to be an underestimate. The condition is usually diagnosed at 18-20 years of age. It manifests as a moderate to severe reduction in visual acuity, resulting from myopia and irregular astigmatism caused by the deformation and altered transparency of the cornea. The decrease in visual acuity is often accompanied by glare intolerance, photophobia and ocular irritation. Keratoconus is most likely a genetic condition and numerous studies are underway to identify the genes involved. In most cases, keratoconus occurs in isolation, without any associated pathology. However, more than 50% of patients present manifestations of an allergic reaction. Diagnosis is made by ophthalmologic examination revealing a progressive decrease in visual acuity that is often difficult to correct with eyeglasses, and evolving astigmatism. Cone-shaped deformation, opacity or striae may observed by slit-lamp examination of the cornea. In most cases, keratoconus is 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. A keratoconus prediction index (KPI) allows estimation of the probability that these anomalies of corneal topography are related to keratoconus. Management depends on the severity of the disease: visual acuity in patients with mild forms can be corrected using eyeglasses or contact lenses, whereas those with moderate disease require contact lenses. Patients with severe disease require a corneal transplant (or penetrating keratoplasty). Corneal transplant (required in around 10% of cases) is considered in patients for whom treatment with contact lenses fails, and in those with severe disease and corneal scarring. A second graft is sometimes required in case of reoccurrence after the corneal graft. Alternative correction techniques are currently being tested, including intracorneal ring segment (INTACS) implantation for reducing corneal distortion. Another potential approach involves increasing the rigidity of the cornea by exposure to UV irradiation. Refractive surgery is generally contraindicated in patients with keratoconus as anatomical and functional outcomes, as well as the degree of scarring, are unpredictable. Keratoconus is a progressive pathology that evolves until the patient reaches 30-40 years of age before stabilising. Vigorous eye rubbing may lead to more rapid progression of the disease. Acute keratoconus (hydrops), resulting from rupture of the Descemet membrane, may occur in rare cases and requires corneal transplantation.
Last update: November 2006