The relationship between intraocular pressure and glaucoma in a defined population. Data from the Egna-Neumarkt Glaucoma Study

PURPOSE: To provide data on the prevalence of ocular hypertension and glaucoma and on the diagnostic validity of tonometry. METHODS: In this cross-sectional, population-based study, 4,927 subjects over 40 years of age were examined. Each subject underwent a complete ocular examination as part of the Egna-Neumarkt Glaucoma Study. These examinations were carried out by trained, quality-controlled ophthalmologists, according to a predetermined standard protocol that included a medical interview, applanation tonometry, computerized perimetry, optic nerve head examination and other ocular measurements. The following data were recorded: mean IOP, prevalence of ocular hypertension, primary open-angle glaucoma and normal tension glaucoma. Sensitivity, specificity and the predictive value of the tonometric test, as well as the distribution of IOP in the different groups were also determined. RESULTS: The overall prevalence of ocular hypertension, hypertensive primary open-angle glaucoma and normal tension glaucoma corresponded to 2.1, 1.4 and 0.6%, respectively. Other types of glaucoma accounted for a further 0.9%. The sensitivity and specificity of the tonometric test in recognizing glaucoma (cut-off between 21 and 22 mm Hg) were, respectively, 80.1 and 97.8%. The predictive values of the positivity and negativity of the test were 52.1 and 99.4%, respectively. CONCLUSIONS: The prevalence of ocular hypertension and glaucoma was similar to that found in several recent epidemiological studies. Tonometry alone is obviously not sufficient to ascertain or to exclude the presence of glaucoma; its diagnostic validity however is high and should never be underestimated. An elevated IOP is the main risk factor for glaucoma, with the degree of risk increasing as the level of IOP increases.