title: Evaluation of corneal hysteresis and corneal resistance factor after corneal cross-linking for keratoconus.
abstract: BACKGROUND
  To evaluate corneal hysteresis (CH) and corneal resistance factor (CRF) in keratoconic (KC) eyes before and after corneal collagen cross-linking (CXL). Furthermore, to determine potential correlations with a series of corneal and demographic factors.
  
  
  METHODS
  The study consisted of 50 KC eyes that underwent CXL. CH and CRF were measured by the ocular response analyzer (ORA). Correlations were attempted with uncorrected visual acuity (UVA), best spectacle-corrected visual acuity (BSCVA), central corneal thickness (CCT), mean keratometry (Km), astigmatism (Astig.), residual astigmatism, age, and gender. Fifty non-KC eyes served as controls.
  
  
  RESULTS
  CH and CRF (mean ± SD) for non-KC eyes were 10.1 ± 1.9 mmHg and 9.7 ± 2.4 mmHg respectively, while for KC eyes preoperatively they were 8.2 ± 1.4 mmHg (p = 0.007) and 7.4 ± 2.3 mmHg (p = 0.01) respectively. Non-significant differences were detected between preoperative and postoperative CH and CRF measurements in KC eyes (p = 0.518 and p = 0.479 respectively). Significant correlations were found between ORA parameters and BSCVA, CCT, Km, Astig. and residual astigmatism.
  
  
  CONCLUSIONS
  ORA parameters demonstrate significant differences between KC and non-KC eyes. Both CH and CRF present significant correlations with visual acuity and corneal parameters. CXL exerts a non-significant impact on ORA measurements.
authors.affiliation: Eye Institute of Thrace and Department of Ophthalmology, Democritus University of Thrace, Dragana, Alexandroupolis, Greece. mggkika@yahoo.gr
authors.forename: Maria
authors.initials: M
authors.lastname: Gkika
authors.forename: Georgios
authors.initials: G
authors.lastname: Labiris
authors.forename: Athanassios
authors.initials: A
authors.lastname: Giarmoukakis
authors.forename: Anna
authors.initials: A
authors.lastname: Koutsogianni
authors.forename: Vassilios
authors.initials: V
authors.lastname: Kozobolis
mesh_terms: D000293:Adolescent; D000328:Adult; D001251:Astigmatism / Q000503:physiopathology; D001696:Biomechanical Phenomena; D003094:Collagen / Q000378:metabolism*; D003315:Cornea / Q000503:physiopathology*; D003319:Corneal Stroma / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000378:metabolism*; D004548:Elasticity / Q000502:physiology*; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000378:metabolism / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000627:therapeutic use; D011446:Prospective Studies; D012256:Riboflavin / Q000627:therapeutic use; D014466:Ultraviolet Rays; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin