title: Scheimpflug camera measurement of anterior and posterior corneal curvature in eyes with previous radial keratotomy.
abstract: OBJECTIVE
  To compare the anterior and posterior corneal curvature in eyes with previous radial keratotomy (RK) to normal unoperated eyes.
  
  
  METHODS
  In this retrospective observational case series, 29 eyes from 29 consecutive patients were analyzed and compared to a control group of 71 unoperated eyes. Corneal imaging was obtained by a rotating Scheimpflug camera (Pentacam, Oculus Optikgeräte GmbH). Anterior and posterior corneal curvature radii were measured at the 3-mm zone.
  
  
  RESULTS
  The mean anterior and posterior corneal radii were 9.54 ± 0.89 and 8.54 ± 1.01 mm, respectively, both values being significantly higher than in the control group (7.81 ± 0.28 and 6.40 ± 0.24 mm, respectively, P<.0001). The mean anterior-to-posterior corneal curvature ratio was 1.12 ± 0.07, a value significantly lower than in the control group (1.22 ± 0.03, P<.0001). Mean corneal flattening was more evident in the posterior (33.44%) than in the anterior (22.15%) corneal curvature. The mean keratometric index, as calculated with the Gullstrand equation for thick lenses, was 1.3319 ± 0.0026, a value significantly higher than in the control group (1.3281 ± 0.0011, P<.0001). Linear regression detected a significant and directly proportional relationship between the number of radial incisions and flattening of both corneal surfaces (P<.0001).
  
  
  CONCLUSIONS
  After RK, both corneal surfaces flatten but do not deform in parallel as commonly accepted, as shown by the fact that the anterior-to-posterior corneal curvature ratio decreases. This finding invalidates the standard keratometric index and thus has relevant implications for intraocular lens power calculation in RK eyes.
authors.affiliation: SEKAL Rovigo Microsurgery, Rovigo, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Camellin
authors.forename: Giacomo
authors.initials: G
authors.lastname: Savini
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Hoffer
authors.forename: Michele
authors.initials: M
authors.lastname: Carbonelli
authors.forename: Piero
authors.initials: P
authors.lastname: Barboni
mesh_terms: D003315:Cornea / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007646:Keratotomy, Radial; D008297:Male; D008875:Middle Aged; D010781:Photography / Q000379:methods*; D012029:Refraction, Ocular / Q000502:physiology*; D012189:Retrospective Studies