A progressive degenerative disease that causes corneal thinning, Keratoconus results in the inability of the cornea to hold its normal shape. The cornea gradually changes from a smooth round shape to a protruding nipple or cone shape.
Keratoconus is thought to be hereditary. New research is leaning toward a correlation between allergy sufferers and eye rubbing. Allergy sufferers who frequently “knuckle-rub” their eyes are more susceptible to developing keratoconus. Early keratoconus is most easily diagnosed thru corneal topography, which is essentially a mapping of the corneal surface.
Later stages can be diagnosed during a slit lamp exam, where the conical shape is readily apparent. Keratoconus causes blurred vision and distortion, and in its early stages can be treated with glasses, custom soft contact lenses, or rigid gas permeable lenses.
As the disease progresses surgical intervention is required.
Current surgical options include INTACS and corneal transplants.
- INTACS are surgically implanted corneal inserts that are placed peripherally, outside the central optical zone, to reshape the cornea and correct the nearsightedness caused by keratoconus. INTACS are replaceable if vision changes, or removable if desired. The procedure has been FDA approved since august 2004.
- Corneal transplants (PKP and DALK) involve the removal of a damaged or diseased cornea and subsequent replacement with a donor cornea.
- PKP (Penetrating Keratoplasty) is the replacement of the entire cornea, all 5 layers, with a donor cornea.
- DALK – (Deep Anterior Lamellar Keratoplasty), involves the replacement of the epithelium, Bowman’s layer, and the stroma, leaving the patients own healthy Descemet’s membrane and inner endothelium intact. By retaining the inner two layers, the chance for graft rejection is eliminated. The downside to DALK is the difficulty of dissecting down to Descemet’s layer without puncturing it.
Future treatment options include corneal collagen cross-linking.
Corneal cross-linking – Involves treating the cornea with a combination of riboflavin drops (vitamin b-2), and ultraviolet-a light.
Corneal cross-linking strengthens the areas in the cornea that have been weakened thru progressive corneal thinning. It produces structural changes in the cornea via the production of strong chemical bonds between the collagen fibrils and their adjacent fibrils. The UV light induces this bond formation in the presence of riboflavin.
The subsequent stronger/stiffer cornea can then undergo laser vision correction or INTAC implantation. Treatment by corneal collagen cross-linking is widespread in Europe. As of yet, it is not fully approved by the FDA in the United States, but as of 2011 several registered clinical trials were underway.