title: Wavefront analyzers induce instrument myopia.
abstract: OBJECTIVE
  To assess the accuracy of three wavefront analyzers versus a validated binocular open-view autorefractor in determining refractive error in non-cycloplegic eyes.
  
  
  METHODS
  Eighty eyes were examined using the SRW-5000 open-view infrared autorefractor and, in randomized sequence, three wavefront analyzers: 1) OPD-Scan (NIDEK, Gamagori, Japan), 2) WASCA (Zeiss/Meditec, Jena, Germany), and 3) Allegretto (WaveLight Laser Technologies AG, Erlangen, Germany). Subjects were healthy adults (19 men and 21 women; mean age: 20.8 +/- 2.5 years). Refractive errors ranged from +1.5 to -9.75 diopters (D) (mean: +1.83 +/- 2.74 D) with up to 1.75 D cylinder (mean: 0.58 +/- 0.53 D). Three readings were collected per instrument by one examiner without anticholinergic agents. Refraction values were decomposed into vector components for analysis, resulting in mean spherical equivalent refraction (M) and J0 and J45 being vectors of cylindrical power at 0 degrees and 45 degrees, respectively.
  
  
  RESULTS
  Positive correlation was observed between wavefront analyzers and the SRW-5000 for spherical equivalent refraction (OPD-Scan, r=0.959, P<.001; WASCA, r=0.981, P<.001; Allegretto, r=0.942, P<.001). Mean differences and limits of agreement showed more negative spherical equivalent refraction with wavefront analyzers (OPD-Scan, 0.406 +/- 0.768 D [range: 0.235 to 0.580 D] [P<.001]; WASCA, 0.511 +/- 0.550 D [range: 0.390 to 0.634 D] [P<.001]; and Allegretto, 0.434 +/- 0.904 D [range: 0.233 to 0.635 D] [P<.001]). A second analysis eliminating outliers showed the same trend but lower differences: OPD-Scan (n=75), 0.24 +/- 0.41 D (range: 0.15 to 0.34 D) (P<.001); WASCA (n=78), 0.46 +/- 0.47 D (range: 0.36 to 0.57 D) (P<.001); and Allegretto (n=77), 0.30 +/- 0.62 D (range: 0.16 to 0.44 D) (P<.001). No statistically significant differences were noted for J0 and J45.
  
  
  CONCLUSIONS
  Wavefront analyzer refraction resulted in 0.30 D more myopia compared to SRW-5000 refraction in eyes without cycloplegia. This is the result of the accommodation excess attributable to instrument myopia. For the relatively low degrees of astigmatism in this study (<2.0 D), good agreement was noted between wavefront analyzers and the SRW-5000.
authors.affiliation: School of Life and Health Sciences, Aston University, United Kingdom.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Cervino
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Hosking
authors.forename: Gurjeet K
authors.initials: GK
authors.lastname: Rai
authors.forename: Shezhad A
authors.initials: SA
authors.lastname: Naroo
authors.forename: Bernard
authors.initials: B
authors.lastname: Gilmartin
mesh_terms: D000328:Adult; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation*; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000175:diagnosis* / Q000503:physiopathology; D012029:Refraction, Ocular; D015203:Reproducibility of Results