Calculating the predictive power of the Henson field screener in a population at risk of glaucomatous field loss.

Suprathreshold field screeners are in common use for the detection of glaucomatous field loss. The predictive power of a positive result (PP+) depends on the sensitivity and specificity of the screener in the population in which it is to be used. Using data from 755 normal individuals (1510 eyes), we calculated the PP+ of the Henson CFS2000 screening programme for a population aged 50 and over. 4.3% of normal eyes failed the screening programme. Ignoring one or two misses on the screening programme immediately adjacent to the disc reduced this figure to 1.3% and significantly improved the PP+ of the programme. Calculations of the PP+ at increasing glaucoma prevalence levels indicates this to be particularly relevant at low levels such as those encountered when screening middle aged and elderly populations. Optometrists should perform routine field analysis when screening for glaucoma provided they adhere to strict protocols.