title: Repeatability and agreement of two A-scan ultrasonic biometers and IOLMaster in non-orthokeratology subjects and post-orthokeratology children.
abstract: OBJECTIVE
  Our aim was to determine the repeatability of measurements of axial length (AL) and anterior chamber depth (ACD) made with two ultrasonic biometers and the IOLMaster in a group of non-orthokeratology (ortho-k) adult subjects and to investigate the agreement among instruments in children undergoing ortho-k therapy and in children wearing spectacles.
  
  
  METHODS
  To determine repeatability, AL and ACD were measured twice in 22 non-ortho-k young adults using two A-scan ultrasonic biometers (A-5500 and A-2500) and the IOLMaster. To determine agreement, AL and ACD were measured with the same instruments in 30 children undergoing ortho-k therapy and 30 spectacle-wearing children.
  
  
  RESULTS
  In the adult subjects, there were no significant differences in ACD and AL measurements obtained from the three instruments (repeated measures ANOVAs, p > 0.05). There was also no significant between-measurement difference for each instrument. The between-measurement agreement was better for the IOLMaster (95% limits of agreement (LA): -0.04 and +0.05 mm for both AL and ACD) than for the two A-scan ultrasonic biometers (95% LA: -0.12 and +0.11 mm for AL; -0.22 and +0.27 mm for ACD). Among the children, AL measurements with all three instruments were not significantly different from each other for both the children undergoing ortho-k therapy and those wearing spectacles (repeated measures ANOVAs, p > 0.05). The 95% LA of differences obtained from any two instruments were also comparable for both groups of subjects (within -0.20 mm and +0.20 mm). ACD measurements of the children were significantly different among the three instruments (repeated measures ANOVAs, p < 0.05). No significant differences in ACD measurements were found between A-5500 and A-2500 for both groups of children (paired t tests, p > 0.017).
  
  
  CONCLUSIONS
  The repeatability of AL and ACD measurements with the IOLMaster was very good, and was better than with the A-scan ultrasonic biometers. The agreements in AL measurements between A-scan ultrasonic biometers and IOLMaster were comparable in both the ortho-k and the spectacle-wearing subjects, and were comparable to the repeatability of the A-scan ultrasonic biometers. ACD measurements between A-scan ultrasonic biometry and the IOLMaster were not comparable. AL measurements with the IOLMaster can replace the measurements from the two A-scan ultrasonic biometers used, however, the reverse is not true. AL and ACD measurements with all three instruments were unaffected by the flattened cornea following ortho-k lens wear.
authors.affiliation: School of Optometry, The Hong Kong Polytechnic University, Hong Kong SAR, China. soben@polyu.edu.hk
authors.forename: Ben
authors.initials: B
authors.lastname: Chan
authors.forename: Pauline
authors.initials: P
authors.lastname: Cho
authors.forename: Sin Wan
authors.initials: SW
authors.lastname: Cheung
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D000867:Anterior Chamber / Q000000981:diagnostic imaging*; D002648:Child; D005139:Eyeglasses; D005260:Female; D006801:Humans; D008297:Male; D033401:Microscopy, Acoustic / Q000295:instrumentation*; D009216:Myopia / Q000000981:diagnostic imaging* / Q000628:therapy; D015588:Observer Variation