Epidemiological aids to clinical decision making in primary open angle glaucoma.

We have described the epidemiological analysis of one aspect of the King's College Hospital computerized data base; namely initial intraocular pressure as an indicator of visual field loss. The methods involved the use of the four-fold table to determine sensitivity and specificity at different pressure levels. From these results (1) the changes in the pre and post test probability of field loss are calculated and (2) a 'sensitivity/specificity trade off curve' or 'decision curve' is constructed. In this way the optimal 'cut-off level' or 'operating point' for a population of specific type and composition can be determined. The factors concerned in decision making are always complex but such an approach allows a rational and quantifiable alternative to reliance on clinical impression and intuition. The results have significance in relation to decisions on the management of patients and on population screening programmes for glaucoma.