Statistical analysis of intraocular pressure was conducted on approximately 200,000 healthy subjects who were examined at the Aichi Prefectural Center of Health Care in Nagoya, Japan, during the last decade. The IOP was estimated with either Schl øtz or noncontact tonometers, which consistently showed a decreasing tendency of IOP with age in both sexes. Multivariate analysis on systemic values disclosed that obesity, systolic BP, and age were the most influential factors of IOP. Stratification of the sample by systolic BP, obesity index, and age indicated that young, obese, and hypertensive subjects had the highest IOP, while old, lean, and hypotensive subjects showed the lowest IOP. It was confirmed that the IOP is physiologically maintained by a counterbalance between the IOP-lowering effect of age and the IOP-raising effects of obesity and systolic hypertension, which are largely age dependent.