Collagen Crosslinking for Keratoconus

In this issue of JOVR, Derakhshan and co-authors 1 describe the results of crosslinking for patients with early keratoconus. Collagen crosslinking is a recently described technique of corneal tissue strengthening using riboflavin as a photosensitizer and ultraviolet A (UVA) radiation to promote the formation of intra-and interfibrillar covalent bonds by photosensitized oxidation. 2 To date, it is the only published intervention that may retard the progression of keratoconus. Collagen crosslinking has also been sequentially combined with other treatment modalities, namely intrastromal ring segments and photorefractive keratectomy, for treatment of keratoconus. 3 Other possible indications include keratectasia following laser in situ keratomileusis (LASIK) 4 , infectious keratitis and bullous keratopathy 5. In vitro studies on human and porcine corneas have shown a significant increase in corneal rigidity after crosslinking as indicated by an increase in Young's modulus. 6 This stiffening effect was found to be depth-dependent, i.e. anterior corneal layers were stiffer corresponding to maximum crosslinking effect. The first in vivo controlled clinical study was performed by Wollensak et al 7 and included 23 eyes with moderate or advanced progressive keratoconus. This study showed that crosslinking was effective in halting the progression of keratoconus over a period of 4 years. The authors reported mean reduction of 2.01 D in maximum keratometry and 1.14 D in spherical equivalent. These initial results were later supported by other studies showing varying degrees of improvement in visual acuity and reduction in keratometry with a progressive trend in improvement depending on the duration of follow-up. Collagen crosslinking has also been found to be relatively safe. Wollensak et al 7 reported no change in corneal and lens transparency, endothelial cell density, and intraocular pressure. Epithelial regeneration was completed normally within 4 days, and restoration of corneal sensitivity and repopulation of the corneal stroma occurred by 6 months. 10 Few complications have been described including corneal scarring and stromal haze which require a variable duration for resolution 11 , and infectious keratitis including bacterial 12 , acanthamoeba 13 and herpetic 14 infections. Derakhshan et al 1 have published their observational study on the effect of crosslinking as primary treatment for patients with early keratoconus. Their study enrolled 22 patients and treated 31 eyes with mean follow-up of 6 months. Their results show significant improvement in uncorrected and best spectacle corrected visual acuity, and reduction in spherical equivalent and keratometric readings. These changes however, were less marked than previously …