title: Corneal refractive power and symmetry changes following normalization of ectasias treated with partial topography-guided PTK combined with higher-fluence CXL (the Athens Protocol).
abstract: OBJECTIVE
  To investigate preoperative and postoperative anterior and posterior keratometry and simulated corneal astigmatism in keratoconic eyes treated with collagen cross-linking combined with anterior surface normalization by partial topography-guided excimer ablation (the Athens Protocol).
  
  
  METHODS
  Anterior and posterior corneal keratometry were measured by Scheimpflug imaging for 267 untreated keratoconic eyes. Following treatment, they were assessed 1 year postoperatively.
  
  
  RESULTS
  Before treatment, average anterior keratometric value was 47.06 ± 6.02 diopters (D) for flat and 51.24 ± 6.75 D for steep. The posterior keratometric values were -6.70 ± 0.99 D (flat) and -7.67 ± 1.15 D (steep). Anterior astigmatism was on average with-the-rule (-1.97 ± 6.21 D), whereas posterior astigmatism was against-the-rule (+0.53 ± 1.02 D). The posterior and anterior astigmatism were highly correlated (r(2) = 0.839). After treatment, anterior keratometric values were 43.97 ± 5.81 D (flat) and 46.55 ± 6.82 D (steep). Posterior keratometric values were -6.58 ± 1.05 D (flat) and -7.69 ± 1.22 D (steep). Anterior astigmatism was on average with-the-rule (-1.56 ± 3.80 D), whereas posterior astigmatism was against-the-rule (+0.45 ± 1.29 D). The statistically significant (P < .05) keratometric changes indicated anterior surface flattening -3.09 ± 2.67 D (flat) and -4.19 ± 2.96 D (steep). The posterior keratometric changes were not statistically significant (P > .05).
  
  
  CONCLUSIONS
  Before treatment, there was a strong correlation between posterior and anterior corneal astigmatism. After treatment, statistically significant anterior keratometric values flattened. The posterior surface keratometric values did not demonstrate statistically significant postoperative change: there was minimal posterior change, despite the significant anterior surface normalization.
authors.forename: Anastasios John
authors.initials: AJ
authors.lastname: Kanellopoulos
authors.forename: George
authors.initials: G
authors.lastname: Asimellis
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000503:physiopathology; D003094:Collagen / Q000378:metabolism; D003131:Combined Modality Therapy; D003315:Cornea / Q000503:physiopathology*; D003319:Corneal Stroma / Q000378:metabolism; D019781:Corneal Topography; D003432:Cross-Linking Reagents / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000378:metabolism / Q000503:physiopathology / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D018903:Photorefractive Keratectomy; D017319:Photosensitizing Agents / Q000627:therapeutic use; D012029:Refraction, Ocular / Q000502:physiology*; D012256:Riboflavin / Q000627:therapeutic use; D016896:Treatment Outcome; D014466:Ultraviolet Rays; D055815:Young Adult
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin