title: Comparison of the Demarcation Line on ASOCT After Simultaneous LASIK and Different Protocols of Accelerated Collagen Crosslinking: A Bilateral Eye Randomized Study.
abstract: OBJECTIVE
  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.
authors: *Department of Ophthalmology, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China; †Hong Kong Laser Eye Center, Hong Kong SAR, China; ‡Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Kowloon, Hong Kong SAR, China; and §Department of Ophthalmology, Hong Kong Eye Hospital, Kowloon, Hong Kong SAR, China.
authors: Alex L K
authors: AL
authors: Ng
authors: Peter S K
authors: PS
authors: Kwok
authors: Ricky T K
authors: RT
authors: Wu
authors: Vishal
authors: V
authors: Jhanji
authors: Victor C P
authors: VC
authors: Woo
authors: Tommy C Y
authors: TC
authors: Chan
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000601:surgery*; D003094:Collagen / Q000378:metabolism* / Q000627:therapeutic use; D003318:Corneal Opacity; D003319:Corneal Stroma / Q000473:pathology*; D003432:Cross-Linking Reagents / Q000627:therapeutic use; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000601:surgery*; D017319:Photosensitizing Agents / Q000627:therapeutic use; D012256:Riboflavin / Q000627:therapeutic use; D041623:Tomography, Optical Coherence; D014466:Ultraviolet Rays; D014792:Visual Acuity; D055815:Young Adult
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin