Contributor: Gordon K. Klintworth
Keratoconus is usually bilateral, although onset may initially involve one eye. The onset occurs at the time of puberty, with progressive worsening. Initially symptoms include decreased visual acuity due to severe astigmatism. Slit lamp examination can reveal irregular linear or branching defects in Bowmanís layer at the conical apex and in long-standing cases, a Fleischer ring at the base of the cone. Features of keratoconus include iron deposits in the epithelium around the base of the cone (Fleischer ring), a thinning of the corneal stroma, small fractures in Bowman layer are and often striae in Descemet membrane, which sometimes ruptures. In long-standing cases an intraepithelial iron deposits in the corneal epithelium as a ring (Fleischer ring) near the base of the cone. It is apparent in 50% of corneas with keratoconus.
Bowman layer. Small fractures or dehiscences in Bowman layer are common and may result in opaque superficial corneal scars.
The corneal stroma becomes thinner than normal in keratoconus. As the apex of the cone protrudes (rarely >10 mm), the cornea becomes progressively thinner. Amyloid deposition can also cause corneal opacification. Striae commonly develop and Descemet membrane may rupture in severe cases. Complications include acute hydrops, and corneal opacification. When acute hydrops (edema) occurs, the cornea can regain its transparency. However, the defects in Descemetís membrane become scarred and may rupture.
Associations. Associated disorders include retinopathy of prematurity, ectopic lentis, congenital cataract [cataract - congenital], microcornea, blue sclera, and vernal catarrh. Keratoconus occurs in 0.5% to 15% of persons with Down syndrome. Keratoconus is rare in patients with retinitis pigmentosa, but examples of the coexistence of these two conditions has been documented several times. Whether the association is coincidental or not remains to be determined. A history of vernal conjunctivitis is often present in individuals with keratoconus. As with other forms of atopic dermatitis eye rubbing is common and may contribute to the corneal disorder. The mechanism behind the association is not clear, but excessive eye rubbing is common in atopic dermatitis and one hypothesis suggests that the eye rubbing may contribute to the keratoconus.
Noninflammatory thinning of the central corneal stroma takes place in keratoconus causing a cone-shaped cornea . Scarring and astigmatism associated with this disorder often prevents adequate refractive correction and decreases visual acuity. Frequently a brown stainable intraepithelial iron arc or ring surrounds the conical portion of the cornea (Fleischer ring). Numerous breaks in Bowman's layer associated with thinning of the central corneal stroma characterizes advanced cases. The endothelium in corneas with keratoconus is usually unremarkable, but endothelial cell loss may accompany ruptures of Descemet membrane ("corneal hydrops"). Rarely keratoconus recurs in the graft.
The keratoconus develops in teenagers; this may be complicated by acute corneal hydrops (edema - cornea) that heals with severe scarring. Non-inflammatory thinning of the central corneal stroma takes place in keratoconus causing a cone-shaped cornea . An associated scarring and astigmatism often prevents adequate refractive correction and decreases visual acuity. Frequently intraepithelial iron creates a brown Fleisher ring. in the cornea. Numerous breaks in Bowman's layer are associated with thinning of the central corneal stroma in advanced cases. The corneal endothelium is usually unremarkable in keratoconus, but a loss of corneal endothelial cells may accompany ruptures of Descemet membrane and corneal hydrops. Keratoconus very rarely recurs in the graft after penetrating keratoplasty.