title: A novel instrument for logging nearwork distance.
abstract: OBJECTIVE
  To validate a novel ultrasonic sensor for logging reading distances. In addition, this device was used to compare the habitual reading distances between low and high myopes.
  
  
  METHODS
  First, the stability and sensitivity of the ultrasonic device were determined by repeated measures using artificial targets. Then, thirty Hong Kong Chinese (20-30 years) were recruited, of whom fifteen were considered to be high myopes (mean ± S.D. = -8.7 ± 0.5 D) and 15 to be low to non-myopes (mean ± S.D. = -2.0 ± 0.2 D). Each subject read a newspaper with their habitual visual aid continuously for 10 min in two sessions at their preferred working distance(s). The reading distances were recorded continuously using a novel nearwork analyzer. The modal working distance was considered as the 'habitual' reading distance. In addition, habitual reading distance was reported orally by each subject.
  
  
  RESULTS
  The nearwork analyzer gave accurate and repeatable measurements over a range of distances and angles. Using this instrument, high myopes were found to have a significantly shorter reading distance than low myopes or non-myopes (mean ± S.D. = 35.9 ± 9.8 cm vs 50.9 ± 24.8 cm; two-sample t-test, p = 0.04, df = 18). The reading distances reported orally by the subjects were not correlated with those recorded by the nearwork analyzer.
  
  
  CONCLUSIONS
  The nearwork analyzer was found to be an effective tool for measuring nearwork reading distance in a small group of emmetropic and myopic adults over a 10 min interval. Differences between the reading distance between high myopes and low/non-myopes was detected by the device. Further study is needed to determine if a closer working distance is a cause or effect of myopia development.
authors.affiliation: Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
authors.forename: Tsz-wing
authors.initials: TW
authors.lastname: Leung
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Flitcroft
authors.forename: Josh
authors.initials: J
authors.lastname: Wallman
authors.forename: Tat Hing
authors.initials: TH
authors.lastname: Lee
authors.forename: Yongping
authors.initials: Y
authors.lastname: Zheng
authors.forename: Carly Siu-yin
authors.initials: CS
authors.lastname: Lam
authors.forename: Chea-su
authors.initials: CS
authors.lastname: Kee
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000453:epidemiology* / Q000209:etiology; D009907:Optometry / Q000295:instrumentation*; D011932:Reading; D015203:Reproducibility of Results; D055815:Young Adult