title: Increased corneal hysteresis after corneal collagen crosslinking: a study based on applanation resonance technology.
abstract: OBJECTIVE
  A reliable tool for quantification of the biomechanical status of the cornea in conjunction with corneal collagen crosslinking (CXL) treatment is needed.
  
  
  OBJECTIVE
  To quantify the biomechanical effects of CXL in vivo.
  
  
  METHODS
  A prospective, open, case-control study was conducted at the Department of Ophthalmology, Umeå University, Umeå, Sweden. Participants included 28 patients (29 eyes) aged 18 to 28 years with progressive keratoconus and corresponding age- and sex-matched healthy individuals serving as controls. All participants were monitored during a 6-month period between October 13, 2009, and November 5, 2012.
  
  
  METHODS
  Corneal hysteresis after CXL for keratoconus.
  
  
  RESULTS
  A difference in corneal hysteresis between the control group and the patients with keratoconus was found at baseline, both with an applanation resonance tonometer (ART) and an ocular response analyzer (ORA), at mean (SD) values of -1.09 (1.92) mm Hg (99% CI, -2.26 to 0.07; P = .01) and -2.67 (2.55) mm Hg (99% CI, -4.05 to -1.32; P < .001), respectively. Increased corneal hysteresis was demonstrated with an ART 1 and 6 months after CXL, at 1.2 (2.4) mm Hg (99% CI,-0.1 to 2.5; P = .02) and 1.1 (2.7) mm Hg (99% CI, -0.3 to 2.6; P = .04), respectively, but not with ORA. A decrease in corneal thickness was seen 1 and 6 months after treatment (-24 [26] µm, P < .001; and -11 [21] µm, P = .01, respectively), and a corneal flattening of -0.6 (0.7) diopters was seen at 6 months (P < .001). No significant change in intraocular pressure was identified in patients with keratoconus with any method, except for an increase at 1 month with Goldmann applanation tonometry (P = .005).
  
  
  CONCLUSIONS
  To our knowledge ART is the first in vivo method able to assess the increased corneal hysteresis after CXL treatment. Given the large-scale use of CXL in modern keratoconus treatment, a tool with this capacity has a great potential value. Refinement of the ART method of measuring and quantifying corneal biomechanical properties will be a subject of further studies.
authors.affiliation: PhD student, Department of Clinical Sciences, Ophthalmology, Umeå University, Umeå, Sweden.
authors.forename: Jeannette
authors.initials: J
authors.lastname: Beckman Rehnman
authors.affiliation: Department of Clinical Sciences, Ophthalmology, Umeå University, Umeå, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Behndig
authors.affiliation: Department of Radiation Sciences, Biomedical Engineering, Umeå University, Umeå, Sweden.
authors.forename: Per
authors.initials: P
authors.lastname: Hallberg
authors.affiliation: Department of Clinical Sciences, Ophthalmology, Umeå University, Umeå, Sweden.
authors.forename: Christina
authors.initials: C
authors.lastname: Lindén
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D003094:Collagen / Q000378:metabolism*; D003315:Cornea / Q000503:physiopathology*; D003319:Corneal Stroma / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000627:therapeutic use*; D004548:Elasticity / Q000502:physiology*; D005260:Female; D006801:Humans; D007429:Intraocular Pressure; D007640:Keratoconus / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D008297:Male; D017319:Photosensitizing Agents / Q000627:therapeutic use; D011446:Prospective Studies; D012256:Riboflavin / Q000627:therapeutic use; D014065:Tonometry, Ocular / Q000295:instrumentation*; D014466:Ultraviolet Rays; D055815:Young Adult
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin