Gordon MO, Gao F, Huecker JB, et al. - Researchers conducted this post hoc secondary analysis of two randomized clinical trials to ascertain if long-term intraocular pressure (IOP) variability data improve a prediction model for the development of primary open-angle glaucoma (POAG) in people with untreated ocular hypertension. Data were included from 709 of 819 candidates in the observation group of the Ocular Hypertension Treatment Study (OHTS) followed up from February 28, 1994, to June 1, 2002, and 397 of 500 candidates in the placebo group of the European Glaucoma Prevention Study (EGPS) followed up from January 1, 1997, to September 30, 2003. The addition of IOP SD, maximum, range, or coefficient of variation to a model that included mean follow-up IOP and baseline factors did not increase predictive accuracy significantly. Evidence from OHTS and EGPS indicates that long-term variability does not add substantial explanatory power to the prediction model as to which individuals will develop POAG with untreated ocular hypertension.