The potential association between diabetes and primary open angle glaucoma (POAG) has been studied by many groups, with most studies supporting a weak association between the two diseases. The present population based study by Ellis et al, published in this issue of theBJO (p 1218), has determined anincidence for newly diagnosed glaucoma and ocular hypertension among diabetics and non-diabetics. The authors make the distinction that previous studies assessed prevalence rather than incidence when determining an association. However, with diseases that have a low incidence, such as POAG, determination of prevalence may be preferable, in …