Sources of bias in studies of optic disc and retinal nerve fibre layer morphology

Interest in the morphology of the optic disc and nerve fibre layer in glaucoma has increased with the advent of new instruments able to make quantitative measurements of the optic disc and nerve fibre layer structure. Particular attention is given to the potential that these instruments may have to diagnose the condition(s) that we call glaucoma—that is, to classify individuals as “normal” or “glaucomatous”. The usual way in which we evaluate a test is to apply it to a “normal”, reference, population and to a population believed to have the disease on the basis of other “gold standard” tests, …