title: Agreement in Measurement of Optic Cup-to-Disc Ratio with Stereo Biomicroscope Funduscopy and Digital Image Analysis: Results from the Nigeria National Blindness and Visual Impairment Survey.
abstract: To determine agreement in estimations of vertical cup-to-disc ratio (VCDR) between clinical stereo-biomicroscopic funduscopy and digital fundus image analysis.
  
  
  
  Systematic sampling of 1-in-7 from a sample of 13,591 participants aged ≥40 years gave a subsample who were examined in detail. VCDR was estimated clinically by 60 diopter aspheric lens biomicroscopic funduscopy (c-VCDR) and by digital fundus images (i-VCDR) graded at the Moorfields Eye Hospital Reading Centre. Spearman's correlation coefficient, paired t-test and the Bland-Altman method to assess limits of agreement (LOA) between the two methods were applied.
  
  
  
  Of 1759 participants in the subsample, 848 participants (48%) with normal frequency doubling technology (FDT) visual fields and data for i-VCDR and c-VCDR in both eyes (n = 1696 eyes) were included in the analysis. By absolute difference of VCDR values for each eye between the two methods, 1585 eyes (94%) differed by ≤0.2. Mean i-VCDR was 0.381 (standard deviation, SD 0.156), and mean c-VCDR 0.321 (SD 0.145). i-VCDRs were significantly larger by a mean difference of 0.061 (SD 0.121; 95% confidence interval, CI, 0.055-0.066; p < 0.001). The 95% LOA assessed by the Bland-Altman method were lower limit -0.182 (95% CI -0.192 to -0.172) and upper limit 0.303 (95% CI 0.293-0.313). The 95% LOA intervals narrowed with higher VCDR.
  
  
  
  Digital image analysis and clinical assessment are two distinct methods to measure VCDR; with larger i-VCDRs in this survey. Applying i-VCDR cut-off values to c-VCDR measurements in the Nigeria Blindness Survey might have underestimated glaucoma prevalence. It is recommended that all participants in glaucoma surveys have VCDR by digital image measurement.
authors.affiliation: a International Centre for Eye Health (ICEH), London School of Hygiene & Tropical Medicine (LSHTM) , London , UK.|b Department of Ophthalmology , College of Health Sciences, University of Abuja , Nigeria.
authors.forename: Fatima
authors.initials: F
authors.lastname: Kyari
authors.affiliation: a International Centre for Eye Health (ICEH), London School of Hygiene & Tropical Medicine (LSHTM) , London , UK.
authors.forename: Clare
authors.initials: C
authors.lastname: Gilbert
mesh_terms: D000328:Adult; D000368:Aged; D001766:Blindness / Q000175:diagnosis* / Q000209:etiology; D005260:Female; D005901:Glaucoma / Q000150:complications / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009549:Nigeria; D015588:Observer Variation; D009887:Ophthalmoscopy / Q000379:methods*; D009898:Optic Disk / Q000000981:diagnostic imaging*; D010781:Photography / Q000379:methods; D066167:Slit Lamp
keywords: Bland-Altman plot; Nigeria; glaucoma; limits of agreement; vertical cup-to-disc ratio (VCDR)