The relationship between age and intraocular pressure in a Japanese population: The influence of central corneal thickness

Purpose. Previous cross-sectional Japanese studies have shown that intraocular pressure (IOP) decreases with age. However, central corneal thickness (CCT) variation should also be considered when examining the relationship between age and IOP, since tonometry has an inherent measurement error due to CCT variations. This study investigates the influence of CCT variation on the age-IOP relationship in a Japanese population. Methods. The right eyes of 1317 subjects from 40 to 80 years old selected from a general population using a random sampling method were assessed in cross-section. The IOP was measured with a non-contact tonometer, and CCT was measured with a specular microscope. The relationships between age, IOP, and CCT were assessed using correlation analyses, while the relationship between age and IOP controlled for CCT, blood pressure, and body mass index was investigated using multivariate regression analyses. Results. The mean (+/-SD) IOP value was 13.6 (+/-2.6) mmHg in men and 13.3 (+/-2.6) mmHg in women. The IOP correlated inversely with age in men (r = -0.14, p < 0.001), but showed only a marginal inverse correlation in women (r = -0.07, p = 0.066). The mean (±SD) CCT value was 518.3 (±33.2) μm in men and 511.1 (±33.0) μm in women. Only in men was an inverse correlation seen between CCT and age (r = -0.10, p = 0.009), but both genders had positive correlations between CCT and IOP (man: r = 0.44, p < 0.001; woman: r = 0.48, p < 0.001). In multivariate analyses, CCT was shown to have an effect on IOP measurement, however, it was shown that IOP still decreases with age in both sexes even when adjusted for CCT (p = 0.001). Conclusions. The IOP decreases with age in the Japanese, and CCT variation has practically no effect on the unique age-IOP relationship.