title: Comparison of the Central and Peripheral Corneal Stromal Demarcation Line Depth in Conventional Versus Accelerated Collagen Cross-Linking.
abstract: OBJECTIVE
  To compare the stromal demarcation line depth at the corneal center and its periphery in conventional versus accelerated collagen cross-linking (CXL).
  
  
  METHODS
  Patients with keratoconus who received either conventional 30-minute CXL with 3.0 mW/cm² irradiation intensity (group 1) or accelerated 10-minute CXL with 9.0 mW/cm² irradiation intensity (group 2) were included. The stromal demarcation line at the corneal center and 3-mm periphery measured at the first postoperative month using anterior segment optical coherence tomography were compared.
  
  
  RESULTS
  Thirty-three patients were included (18 in group 1, 15 in group 2) in this study. The mean demarcation line depth at center was 295 ± 62 μm in group 1 and 203 ± 45 μm in group 2 (P < 0.001). The mean depths at 3-mm periphery (nasal, temporal, superior, and inferior) in group 1 were 260 ± 64 μm, 269 ± 44 μm, 232 ± 46 μm, and 242 ± 66 μm, respectively. The corresponding measurements in group 2 were 204 ± 62 μm, 201 ± 55 μm, 196 ± 68 μm, and 189 ± 53 μm. Apart from the superior peripheral cornea (P = 0.064), the demarcation line depth measured at other peripheral regions was deeper in group 1 compared to that of group 2 (P < 0.015). The peripheral demarcation line depth was significantly shallower than observed in the central line depth for group 1 (P = 0.001), but not for group 2 (P = 0.177).
  
  
  CONCLUSIONS
  The stromal demarcation line depth was shallower after accelerated CXL compared to that of conventional CXL at the corneal center and its periphery. The volume of cross-linked stroma appears to be larger after conventional CXL compared to its accelerated counterparts.
authors.affiliation: *Department of Ophthalmology, LKS Faculty of Medicine, the University of Hong Kong, Hong Kong; †Department of Ophthalmology, Hong Kong Eye Hospital, Hong Kong; ‡Department of Ophthalmology and Visual Sciences, the Chinese University of Hong Kong, Hong Kong; and §Department of Ophthalmology, Hong Kong Sanatorium and Hospital, Hong Kong.
authors.forename: Alex L K
authors.initials: AL
authors.lastname: Ng
authors.forename: Tommy C Y
authors.initials: TC
authors.lastname: Chan
authors.forename: Jimmy S M
authors.initials: JS
authors.lastname: Lai
authors.forename: Arthur C K
authors.initials: AC
authors.lastname: Cheng
mesh_terms: D000328:Adult; D003094:Collagen / Q000378:metabolism*; D003319:Corneal Stroma / Q000378:metabolism / Q000473:pathology*; D019781:Corneal Topography; D003432:Cross-Linking Reagents; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology*; D008297:Male; D017319:Photosensitizing Agents / Q000627:therapeutic use*; D012029:Refraction, Ocular / Q000502:physiology; D012256:Riboflavin / Q000627:therapeutic use; D041623:Tomography, Optical Coherence; D014466:Ultraviolet Rays; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin