Accelerated corneal crosslinking concurrent with LASIK
November 1, 2012
Combination thearpy may provide option for reducing keratectasia
Ectatic changes can arise as early as 1 week after LASIK, or they can be delayed, occuring several years after the initial procedure.4,5 In many cases, penetrating keratoplasty is eventually performed to manage this complication. The incidence of keratectasia after LASIK has been estimated to be 0.04% to 0.6%.6,7 However, accurate clinical studies of incidence are not available.8,9 Although a number of clinical risk factors have been reported, the mechanisms of post-LASIK keratectasia remain unclear.10
Studies of the histologic changes in post-LASIK keratectasia demonstrate variable degrees of corneal thinning in the stromal bed and the flap.11 Although disruption of Bowman layer, which is typically observed in keratoconus has not been shown in most cases of postLASIK keratectasia, other pathologic findings, such as macrostriae in the stromal bed, thinning of the stromal collagen lamellae, minimal scarring at the flapstromal bed interface, lack of inflammation, and the presence of an iron ring around the area of steepening have been reported.12,13 Keratectasia after LASIK shares similar topographic and clinical characteristics with keratoconus, a noninflammatory disease characterized by thinning of the corneal stroma, defects in the Bowman layer, and protrusion of the central cornea.14,15
Collagen crosslinking (CXL) has emerged as a promising technique to slow or stop the progression of post-LASIK ectasia.18,19 The technique of corneal crosslinking involves photopolymerization of stromal fibres by the combined action of a photosensitizing substance (riboflavin) and UV light. Photopolymerization increases the rigidity of the corneal collagen and its resistance to deformation.
The most commonly used procedure for corneal crosslinking was described by Wollensak et al.20 The UVA illumination associated with this method uses a 3 mW/cm2 irradience, 370 nm source illuminating the riboflavin treated eye for 30 minutes, a cumulative dose of 5.4 J/cm2 .
The combination of LASIK and accelerated CXL may provide a method to reduce the risk of postoperative keratectasia in a population in which at risk patients are difficult to discern. In this small sample pilot group, we assessed the applicability of the technique of accelerated CXL procedures when performed in conjunction with LASIK at the time of operation.