title: Initial surface temperature of PMMA plates used for daily laser calibration affects the predictability of corneal refractive surgery.
abstract: OBJECTIVE
  To investigate the relevance of initial temperature of the polymethylmethacrylate (PMMA) plates used as a target for photoablation during calibration of excimer lasers performed in daily clinical routine.
  
  
  METHODS
  An experimental argon fluoride excimer laser with a repetition rate of 1050 Hz, a radiant exposure of 500 mJ/cm², and single pulse energy of 2.1 mJ was used for photoablation of PMMA plates. The initial plate temperature varied from 10.1°C to 75.7°C. The initial temperature was measured with an infrared camera and the central ablation depth of a myopic ablation of -9.00 diopters (D) with an optical zone of 6.5 mm was measured by means of a surface profiling system.
  
  
  RESULTS
  The ablation depth increased linearly from 73.9 to 96.3 μm within a temperature increase from 10.1°C to 75.7°C (increase rate of 0.3192 μm/K). The linear correlation was found to be significant (P<.05) with a coefficient of determination of R²=0.95. Based on these results and assuming a standard room temperature of 20°C, optimal plate temperature was calculated to be 15°C to 25°C to maintain an ablation within 0.25 D.
  
  
  CONCLUSIONS
  The temperature of PMMA plates for clinical laser calibration should be controlled ideally within a range of approximately ±5°C, to avoid visually significant refractive error due to calibration error. Further experimental investigations are required to determine the influence of different initial corneal temperatures on the refractive outcome.
authors.affiliation: IROC Science to Innovation AG, Zurich. jeremy.wernli@irocscience.com
authors.forename: Jeremy
authors.initials: J
authors.lastname: Wernli
authors.forename: Silvia
authors.initials: S
authors.lastname: Schumacher
authors.forename: Christian
authors.initials: C
authors.lastname: Wuellner
authors.forename: Christof
authors.initials: C
authors.lastname: Donitzky
authors.forename: Michael
authors.initials: M
authors.lastname: Mrochen
mesh_terms: D002138:Calibration; D048988:Corneal Surgery, Laser / Q000295:instrumentation* / Q000592:standards*; D004780:Environment, Controlled; D006801:Humans; D054018:Lasers, Excimer / Q000592:standards*; D019904:Polymethyl Methacrylate; D013499:Surface Properties; D013696:Temperature
chemical_list: D019904:Polymethyl Methacrylate