Reevaluation of normal intraocular pressure (IOP) was attempted to investigate possible background factors that contribute to variations in IOP. It is well known that IOP increases with age among Western populations, while in the Japanese IOP has been confirmed to decrease with aging. Such paradoxical results can not be reasonably explained without considering systemic conditions rather than local factors peculiar to different races. Accumulated evidence indicates that IOP is positively correlated with blood pressure, obesity and other cardiac risk variables. Incorporation of these factors by stratifying the sample may provide the baseline IOP in those who are different in systemic conditions.