New Treatments for Keratoconus

The Medical Letter® On Drugs and Therapeutics
Published by The Medical Letter, Inc. • 145 Huguenot Street, New Rochelle, NY 10801 • A Nonprofit Publication
Volume 53 (Issue 1365) May 30, 2011

Keratoconus is a fairly common, progressive, noninflammatory, corneal-thinning disorder in which the cornea has a conical shape. Rigid gas permeable (RGP) contact lenses or corneal transplantation are effective treatments, but intracorneal ring segments and collagen cross-linking procedures offer some new alternatives in the management of the disease.

THE DISEASE

Keratoconus has a variable presentation, ranging from myopic astigmatism requiring only spectacle correction to significant corneal stromal thinning, corneal protrusion, and corneal scarring requiring corneal transplantation. It has an incidence of 1 in 2000 and usually appears in puberty and progresses through the 3rd or 4th decade. Some studies have suggested an association with autoimmune disorders, but most patients have isolated bilateral keratoconus.

STANDARD TREATMENT

Management of early keratoconus generally begins with spectacle correction, but most patients lose the ability to function effectively with only spectacle correction. Soft contact lenses may also temporarily provide functional visual acuity for patients with very mild keratoconus. With more advanced irregular astigmatism and corneal warping, soft lenses may fail to correct vision, and RGP contact lenses become necessary. RGP lenses can be difficult to fit, but they often provide excellent visual acuity for many years in patients who can tolerate them. Up to 20% of keratoconic eyes eventually require corneal transplantation.

NEW TREATMENT MODALITIES

Intracorneal Ring Segments

Originally designed to treat low (mild) myopia, intracorneal ring segments are also used for treatment of mild to moderate keratoconus.1 The semi-circular or crescent-shaped segments are surgically inserted into the corneal stroma to support the cone and flatten the central cornea.2 They may improve vision or contact lens tolerance and delay the need for corneal transplantation. Some patients do not tolerate the segments; they usually can be removed without incident and, if indicated, a corneal transplant can still be performed. Since this is a relatively new technique, its stability over time is uncertain.

Collagen Cross-Linking

The newest therapy for keratoconus is the induction of stromal collagen cross-linking by using ultraviolet (UVA) light and riboflavin.3 Corneal collagen cross-linking (CXL) is the first treatment for keratoconus that can slow or stabilize the disease; it may decrease astigmatism and improve corneal curvature. Using riboflavin as a photosensitizer, followed by UVA exposure, collagen fibers in the cornea develop chemical covalent bonds by photopolymerization. The chemical bonding ‘cross-links’ the cornea, increasing strength and stability within the corneal stroma. Corneal epithelium, which regenerates, acts as a barrier to riboflavin absorption and must be removed before treatment.

CONCLUSION

Keratoconus is a fairly common progressive corneal disorder that can severely affect vision. Contact lenses and corneal transplantation are still the standard of care. Implantation of intracorneal ring segments and UVA-induced collagen cross-linking may offer some additional options, but their place in the therapy of this disorder still remains to be established. ?

1. D Piñero and JL Alio. Intracorneal ring segments in ectatic cornea disease – a review. Clin Experiment Ophthalmol 2010; 38:154.

2. YS Rabinowitz. INTACS for keratoconus. Int Ophthalmol Clin 2010; 50:63.

3. Wollensak G. Crosslinking treatment of progressive keratoconus: new hope. Curr Opin Ophthalmol 2006;17:356.