Inter-observer variability in a computer-assisted optic nerve head assessment system.

A computer-assisted optic nerve head analysis system was used to measure parameters of the optic nerve head from one eye from each of 15 subjects. The subjects comprised three groups of five, being glaucomatous, ocular hypertensive, and normal. The 15 images produced were analysed in a randomized masked fashion by ten observers of varying levels of experience to test the inter-observer variability of the measurements. An analysis of variance demonstrated significant differences in the measurements made by the different observers. Fisher's F-test showed that all the parameters assessing the pallor area of the optic nerve head had significantly lower inter-image variance (reported previously) compared with inter-observer variance (at the 5% level). Variability in taking measurements of the pallor area of the optic nerve head is mainly due to observer variations rather than the image variations.