title: Repeatability and reproducibility of optic disc measurement with the Zeiss 4-mirror contact lens.
abstract: BACKGROUND
  A simple clinical quantitative method of optic disc diameter measurement using a 4-mirror gonioscope contact lens has been described recently.
  
  
  METHODS
  Intraobserver and interobserver variations are assessed on 77 eyes of 41 patients. Of these eyes, 63 had refractive errors within 3 diopters of emmetropia. The disc was measured by projecting a slit beam of known height onto the disc.
  
  
  RESULTS
  Intraobserver variation: the coefficient of variation was 3.04% for observer 1 (experienced) and 4.76% for observer 2 (novice). The mean of the three measurements by the two observers was not significantly different (P=0.2318). For observer 1, the mean variance of the eyes with higher refractive errors did not differ significantly from the eyes with lower refractive errors. Interobserver variation: the coefficient of variation was 4.52%. The measurements for the novice were slightly larger the smallest discs and slightly smaller for the largest discs (regression analysis P=0.0209).
  
  
  CONCLUSIONS
  Repeatability and reproducibility for this method are comparable with other methods of measurement. Until experienced with the technique, the authors recommend that the mean of three readings is used.
authors.affiliation: Department of Ophthalmology, University Hospital, Nottingham, NG7 2UH, UK.
authors.forename: A F
authors.initials: AF
authors.lastname: Spencer
authors.forename: S A
authors.initials: SA
authors.lastname: Vernon
mesh_terms: D005901:Glaucoma / Q000473:pathology*; D006068:Gonioscopy / Q000295:instrumentation; D006801:Humans; D007909:Lenses; D015588:Observer Variation; D009798:Ocular Hypertension / Q000473:pathology*; D009898:Optic Disk / Q000473:pathology*; D012030:Refractive Errors / Q000150:complications; D015203:Reproducibility of Results