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Protein Oxidation Levels After Different Corneal Collagen Cross-Linking Methods

Purpose: To evaluate advanced oxidation protein products (AOPP) levels, superoxide dismutase (SOD) enzyme activity, and total sulfhydryl (TSH) levels in rabbit corneas after different corneal collagen cross-linking (CXL) methods. Methods: Eighteen eyes of 9 adult New Zealand rabbits were divided into 3 groups of 6 eyes. The standard CXL group was continuously exposed to UV-A at a power setting of 3 mW/cm2 for 30 minutes. The accelerated CXL (A-CXL) group was continuously exposed to UV-A at a power setting of 30 mW/cm2 for 3 minutes. The pulse light–accelerated CXL (PLA-CXL) group received UV-A at a power setting of 30 mW/cm2 for 6 minutes of pulsed exposure (1 second on, 1 second off). Corneas were obtained after 1 hour of UV-A exposure, and 360-degree keratotomy was performed. SOD enzyme activity, AOPP, and TSH levels were measured in the corneal tissues. Results: Compared with the standard CXL and A-CXL groups (133.2 ± 8.5 and 140.2 ± 6.2 &mgr;mol/mg, respectively), AOPP levels were found to be significantly increased in the PLA-CXL group (230.7 ± 30.2 &mgr;mol/mg) (P = 0.005 and 0.009, respectively). SOD enzyme activities and TSH levels did not differ between the groups (P = 0.167 and 0.187, respectively). Conclusions: CXL creates covalent bonds between collagen fibers because of reactive oxygen species. This means that more oxygen concentration during the CXL method will produce more reactive oxygen species and, thereby, AOPP. This means that in which CXL method occurs in more oxygen concentration that will produce more reactive oxygen species and thereby AOPP. This study demonstrated that PLA-CXL results in more AOPP formation than did standard CXL and A-CXL.