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Keratoconus is a deterioration of the structure of the cornea with gradual bulging from the normal round shape to a cone shape.

The cause is unknown. Keratoconus is more common in contact lens wearers and people with nearsighted eyes. Some researchers believe that allergy may play a role.

This condition causes decreased visual acuity. The earliest symptom is subtle blurring of vision that cannot be corrected with glasses. (Vision can generally be corrected to 20/20 with gas-permeable contact lenses.)

Keratoconus is frequently discovered during adolescence. It can usually be diagnosed with slit-lamp examination of the cornea. Early cases may require a test called corneal topography, which creates a map of the curvature of the cornea.

When keratoconus is advanced, the cornea may be thinner in areas. This can be measured with a painless test called pachymetry.

Contact lenses are the primary treatment and are satisfactory treatment for most patients with keratoconus. Severe cases may require corneal transplantation.

Newer technologies may use high frequency radio energy. This energy shrinks the edges of the cornea, which pulls the central area back to a more normal shape. It can help delay or avoid the need for a corneal transplantation.

In most cases vision can be corrected with gas-permeable contact lenses. Where corneal transplantation is needed, results are usually good after a long recovery period.

Patients with keratoconus should not have laser vision correction. Corneal topography is usually done before laser vision correction to rule out people with this condition.

Young persons whose vision cannot be corrected to 20/20 with glasses should be evaluated by an eye doctor experienced with keratoconus.

There are no preventive measures. Some specialists believe that patients with keratoconus should have aggressive treatment of ocular allergy and should be instructed not to rub their eyes.

Kymionis GD, Siganos CS, Tsiklis NS, et al. Long-term follow-up of Intacs in keratoconus. Am J Ophthalmol. Feb 2007;143(2):236-244.

Fay A. Diseases of the visual system. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 449

Updated by: Paul B. Griggs, MD, Department of Ophthalmology, Virginia Mason Medical Center, Seattle, WA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.