title: Intra- and intersession repeatability of a double-pass instrument.
abstract: OBJECTIVE
  To evaluate the intra- and intersession repeatability of the optical quality parameters provided by the Optical Quality Analysis System (OQAS), which is based on the double-pass technique.
  
  
  METHODS
  We performed optical quality measurements using the OQAS on 20 eyes of 10 healthy subjects who had best spectacle-corrected visual acuity of 20/20 or better. Measurements were performed by the same examiner in three different sessions that were separated by 10-min intervals. The subject's eye was realigned at the beginning of each session. During each session, three consecutive measurements were taken without realignment. The following optical quality parameters were analyzed: the modulation transfer function cutoff frequency (MTFcutoff), the Strehl ratio, the OQAS values (OV) at contrasts of 100%, 20%, and 9%, and the objective scatter index (OSI).
  
  
  RESULTS
  The mean coefficients of repeatability obtained for the first session were 4.51 (MTFcutoff), 0.049 (Strehl ratio), 0.15 (OV 100%), 0.21 (OV 20%), 0.28 (OV 9%), and 0.11 (OSI), which were similar to those found in the second and third sessions. The confidence limits in the Bland and Altman charts when the intrasession repeatability was assessed (in a comparison of the first and second measurements of the first session) ranged from -3.16 to 3.94 (MTFcutoff), -0.060 to 0.069 (Strehl ratio), -0.12 to 0.18 (OV 100%), -0.20 to 0.23 (OV 20%), -0.29 to 0.27 (OV 9%), and -0.12 to 0.13 (OSI). The same limits when the intersession repeatability was assessed (in a comparison of the first and second sessions) ranged from -5.30 to 5.49 (MTFcutoff), -0.054 to 0.050 (Strehl ratio), -0.17 to 0.17 (OV 100%), -0.22 to 0.19 (OV 20%), -0.26 to 0.29 (OV 9%), and -0.12 to 0.13 (OSI).
  
  
  CONCLUSIONS
  Our findings showed that OQAS is a clinical instrument with a good intra- and intersession repeatability and that the realignment of the eye does not introduce any additional variability in the measurements.
authors.affiliation: Centre for Sensors, Instruments and Systems Development (CD6), Universitat Politécnica de Catalunya (UPC), Terrassa, Barcelona, Spain. mvilasec@oo.upc.edu
authors.forename: Meritxell
authors.initials: M
authors.lastname: Vilaseca
authors.forename: Elvira
authors.initials: E
authors.lastname: Peris
authors.forename: Jaume
authors.initials: J
authors.lastname: Pujol
authors.forename: Rosa
authors.initials: R
authors.lastname: Borras
authors.forename: Montserrat
authors.initials: M
authors.lastname: Arjona
mesh_terms: D057128:Aberrometry / Q000379:methods / Q000592:standards; D003941:Diagnostic Techniques, Ophthalmological / Q000592:standards*; D006801:Humans; D019654:Lens Implantation, Intraocular; D017063:Outcome Assessment, Health Care / Q000379:methods* / Q000592:standards*; D011446:Prospective Studies; D054140:Refractive Surgical Procedures; D015203:Reproducibility of Results