title: Scheimpflug analysis of corneal power changes after myopic excimer laser surgery.
abstract: OBJECTIVE
  To assess the ability of corneal power measurements by a rotating Scheimpflug camera to measure the refractive change induced by myopic excimer laser surgery.
  
  
  METHODS
  G.B. Bietti Foundation-IRCCS, Rome, Italy.
  
  
  METHODS
  Evaluation of diagnostic test.
  
  
  METHODS
  The following corneal power measurements by the Pentacam Scheimpflug camera were analyzed: average keratometry (K), true net power (calculated by Gaussian optics formula), and total corneal refractive power (TCRP) at 2.0 mm, 3.0 mm, and 4.0 mm, calculated by ray tracing on a ring and as the average of the zone inside the ring. The difference between the preoperative and postoperative values was compared with the subjective surgically induced refractive change (SIRC) and with the difference between the preoperative and the postoperative anterior corneal power measured by Placido corneal topography (Keratron).
  
  
  RESULTS
  In 36 consecutive eyes, the average K significantly underestimated the SIRC as determined by subjective refraction (-4.47 diopters [D] ± 1.81 [SD]) and corneal topography (-4.38 ± 1.81 D). The 3.0 mm and 4.0 mm ring total corneal refractive power significantly overestimated the SIRC. The remaining values did not show statistically significant differences with respect to the SIRC. The 3.0 mm zone TCRP and the 2.0 mm ring TCRP provided the lowest median difference compared with the SIRC (-0.07 D and -0.17 D, respectively) and the closest agreement.
  
  
  CONCLUSIONS
  The corneal power values provided by the Scheimpflug camera accurately reflected the SIRC after myopic excimer laser surgery. The best options seem to be the 3.0 mm zone TCRP and the 2.0 mm ring TCRP.
authors: G.B. Bietti Foundation-IRCCS, Rome, Italy. giacomo.savini@alice.it
authors: Giacomo
authors: G
authors: Savini
authors: Kenneth J
authors: KJ
authors: Hoffer
authors: Michele
authors: M
authors: Carbonelli
authors: Piero
authors: P
authors: Barboni
mesh_terms: D000328:Adult; D000368:Aged; D001251:Astigmatism / Q000503:physiopathology / Q000601:surgery; D003315:Cornea / Q000503:physiopathology*; D019781:Corneal Topography; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D010781:Photography / Q000295:instrumentation / Q000379:methods*; D018903:Photorefractive Keratectomy; D011184:Postoperative Period; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult