Keratoconus is a slowly progressive thinning and bulging of the cornea, usually bilateral, beginning between ages 10 and 25. Its cause is unknown.
Risk factors include the following:
The distorted cone shape of the cornea causes major changes in the refractive characteristics of the cornea (irregular astigmatism) that cannot be fully corrected with glasses. Progressing keratoconus necessitates frequent change of eyeglasses. Contact lenses may provide better vision correction and should be tried when eyeglasses are not satisfactory. Corneal transplant surgery may be necessary if visual acuity with contact lenses is inadequate, contact lenses are not tolerated, or a visually significant corneal scar (caused by tearing of stromal fibers) is present.
Newer treatments improve visual results by increasing tolerance of contact lenses and thus saving selected patients from transplantation. These include implantation of corneal ring segments, which push up the shoulders of the cone and thereby reduce the relative magnitude of the cone, and corneal collagen cross-linking, an ultraviolet light treatment that stiffens the cornea and thereby prevents further corneal thinning and bulging.
(See also Introduction to Corneal Disorders.)