Comparison of the demarcation line on ASOCT after simultaneous LASIK and different protocols of accelerated collagen cross-linking: a bilateral eye randomised study

Abstract

PURPOSE: To compare the early corneal morphological changes of two different protocols of simultaneous laser in-situ keratomileusis (LASIK) and accelerated collagen crosslinking (LASIK Xtra) in the treatment of myopia. SETTING: Hong Kong Laser Eye Center, Hong Kong SAR METHODS: 23 patients receiving bilateral LASIK Xtra were included. After femtosecond LASIK, while the LASIK flap was still lifted, the corneal stroma was soaked with 0.22% riboflavin solution for 90 seconds. After the flap was re-positioned, one eye was randomized to receive either 18 mW/cm2 of UVA irradiation for 120 seconds (total energy 2.16 J/cm2) or for 180 seconds (total energy 3.24 J/cm2), while the fellow eye received the other treatment protocol. The demarcation line was measured with an anterior-segment OCT (Optovue Inc, Fremont, USA) at postoperative 1 month. The grading of corneal haze on slit lamp was also compared. RESULTS: The average age was 29.0 ± 8.2. There was no statistical difference in the preoperative spherical equivalent refraction (p>0.05). At postoperative 1 month, a well-defined demarcation line was visible in 74% and 70% in the 2-and 3-minute groups respectively. The demarcation line depth was 282 ± 51 µm and 284 ± 43 µm respectively (p = 1.00), and the ratio of the demarcation line depth to the postoperative central corneal thickness was 0.69 ± 0.13 and 0.72 ± 0.10 (p = 0.61). There was no difference in the percentage of eyes with grade 1 or 2 corneal haze either (p=0.76). CONCLUSIONS: The depth of the demarcation line was the same with either 2.16 or 3.24 J/cm2 LASIK Xtra protocols. The amount of early postoperative corneal haze was also similar. This suggested that the early morphological change or the amount of tissue cross-linked was similar using the two different protocols. Since the UVA irradiation was given after repositioning of the LASIK flap, the intact corneal epithelium could have acted as a barrier limiting the penetration of the UVA despite a 50% difference in the irradiation duration.