Purpose: To compare the demarcation line depth after 2 different protocols of simultaneous laser in situ keratomileusis and collagen crosslinking (LASIK Xtra).
Methods: Twenty-three patients receiving bilateral LASIK Xtra were included in this comparative interventional study. The corneal stroma was soaked with 0.22% riboflavin for 90 seconds before flap repositioning. One eye was then randomized to receive either 18 mW/cm of ultraviolet A irradiation for 120 seconds or for 180 seconds, whereas the fellow eye received the other irradiation duration. The demarcation line on anterior-segment optical coherence tomography and grading of corneal haze on slit lamp were compared at postoperative month 1.
Results: The average age was 29.0 ± 8.2 years. There was no statistical difference in 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), 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 (P = 0.76).
Conclusions: The depth of the demarcation line was the same after receiving 18-mW/cm irradiation for either 2 or 3 minutes. The amount of early postoperative corneal haze was also similar. We postulate that there was lack of oxygen in the corneal tissue to fuel the photochemical reaction despite given additional time.