Table 2

Sensitivity and specificity estimates for the criterion of an IOP ⩾21 mm Hg and the associated positive likelihood ratios (that is, sensitivity/1 − specificity) and PPV* (%) for glaucoma, given an IOP ⩾21 mm Hg. The PPV estimates have assumed a prevalence of undetected glaucoma of 1% and no additional patient risk factors (that is, pretest probability of glaucoma of 1%)

 IOP criterion ⩾21 mm HgSensitivity (95% CIs)Specificity (95% CIs)Likelihood ratio (+ve)Positive predictive value (%)
Daubs and Crick5 52% (48–56 )49% (43–55 )1.01.0
Tielsch et al 6 51% (44–58)84% (83–85)3.23.1
Harper and Reeves7 51% (39–63)97% (94–100)17.014.7
  • PPV = (prevalence × sensitivity)/((prevalence × sensitivity) + (1 − prevalence × 1 − specificity)).

  • 95% CIs are not given for these PPV estimates, since, for the purposes of this comparison, we have used Bayes's theorem and the sensitivity/specificity at an IOP cut off criterion ⩾21 mm Hg (assuming the same glaucoma prevalence rate in each case), rather than working back from the frequency of study cases.