title: Influence of time separation on variability estimates of topographic measurements with confocal scanning laser tomography.
abstract: OBJECTIVE
  Confocal scanning laser tomography is a new technique with significant potential in the treatment of glaucoma. Before new techniques are widely implemented in clinical practice, factors that affect the variability of measurements should be identified. The purpose of this study was to determine the influence of various time separations between images on test-retest variability of topographic measurements.
  
  
  METHODS
  Our sample contained 10 healthy subjects whose mean age was 46.30 years (range 25-60 years). For each subject we obtained six sets of three images each with the Heidelberg Retina Tomograph. The images in set 1 were obtained in one sitting, in set 2 separated by 1 h each, in set 3 by 1 day each, in set 4 by 1 week each, in set 5 by 2 weeks each, and in set 6 by 4 weeks each.
  
  
  RESULTS
  The mean (+/-1 standard deviation) test-retest variability, estimated in terms of the 90% confidence interval, ranged from 55.63 (+/-24.37) mum in set 1 to 64.37 (+/-28.00) mum in set 4. The differences between the variability estimates were not statistically significantly different among the six sets of images.
  
  
  CONCLUSIONS
  Our results show that the short-term and long-term variability of topographic measurements with scanning laser tomography are not different. Since variability was not influenced by images obtained at different sittings, our study suggests that the alignment algorithms used by the Heidelberg Retina Tomograph are robust.
authors.affiliation: Departments of *Ophthalmology and dagger;Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: B C
authors.initials: BC
authors.lastname: Chauhan
authors.forename: C A
authors.initials: CA
authors.lastname: Macdonald