title: Reduced cross-linking demarcation line depth at the peripheral cornea after corneal collagen cross-linking.
abstract: OBJECTIVE
  To compare the corneal collagen cross-linking (CXL) demarcation line depth between the central and peripheral cornea after cross-linking using anterior segment optical coherence tomography.
  
  
  METHODS
  Retrospective interventional case series of 38 eyes with keratoconus or postoperative LASIK ectasia treated with riboflavin ultraviolet A CXL (UV-X, IROC). CXL demarcation line depth, corneal thickness, and the ratio of the CXL demarcation line depth to the corneal thickness were measured using anterior segment optical coherence tomography at the central cornea and at 2 and 4 mm from the corneal center in four regions: temporal, nasal, superior, and inferior. The CXL demarcation line depths at the center and periphery were compared using the Friedman test.
  
  
  RESULTS
  The CXL demarcation line was deepest in the central cornea (302 μm; range: 180 to 397 μm) and was reduced progressively toward the peripheral cornea, at nasal 2 mm (289.5 μm; range: 125 to 370 μm), at nasal 4 mm (206.5 μm; range: 100 to 307 μm), at temporal 2 mm (278.5 μm; range: 128 to 375 μm), and at temporal 4 mm (194 μm; range: 80 to 325 μm) (P<.001). The penetration proportion was greatest at the central cornea (64.8%; range: 44% to 80%) and was decreased toward the periphery, at nasal 2 mm (53.8%; range: 30% to 74%), at nasal 4 mm (33.8%; range: 19% to 53%), at temporal 2 mm (54.1%; range: 29% to 77%), and at temporal 4 mm (34.1%; range: 15% to 54%) (P⩽.001).
  
  
  CONCLUSIONS
  Both the CXL demarcation line depth and its proportion over the corneal thickness were greater at the central cornea than the peripheral cornea.
authors: Department of Opthalmology, Hong Kong Sanatorium and Hopsital, Hong Kong PR China.
authors: Jason C S
authors: JC
authors: Yam
authors: Arthur C K
authors: AC
authors: Cheng
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D003094:Collagen / Q000378:metabolism*; D003319:Corneal Stroma / Q000378:metabolism / Q000473:pathology; D003432:Cross-Linking Reagents / Q000627:therapeutic use*; D004108:Dilatation, Pathologic / Q000188:drug therapy; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis / Q000188:drug therapy* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000627:therapeutic use; D012189:Retrospective Studies; D012256:Riboflavin / Q000627:therapeutic use; D041623:Tomography, Optical Coherence; D014466:Ultraviolet Rays; D055815:Young Adult
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin