Ocular and systemic factors related to intraocular pressure in Japanese adults: the Tajimi study

As intraocular pressure (IOP) and age are consistent risk factors of glaucoma, it is of special interest to know the association between IOP and possibly relating factors including age in Japan where a high prevalence of normal-tension glaucoma has been reported. The aim of this report was to evaluate the distribution of and factors related to applanation IOP in a population-based study in Japan.

A randomly sampled group of 3021 residents (response rate 78.1%) of Tajimi City, aged 40 years or older, underwent screening examinations including measurements of IOP with Goldmann applanation tonometry and central corneal thickness.

Among right eyes without glaucoma, suspected glaucoma or other disorders which could affect correct IOP measurements, IOP averaged 14.6 (SD 2.7) and 14.5 (2.5) mm Hg in men and women, respectively, with no significant intergender difference (p = 0.342). Multiple regression analyses revealed that age was significantly negatively correlated with IOP (non-standardised beta (B) = -0.020/year, p = 0.0001). Higher body mass index (B = 0.14/BMI, p<0.0001), higher mean blood pressure (B = 0.022/mm Hg, p<0.0001), history of diabetes (p = 0.0019), thicker cornea (B = 0.014/microm, p<0.0001), higher myopia (B = 0.055/dioptres, p = 0.0043) and steeper corneal curvature (B = -0.72/mm, p = 0.0002) were also significantly correlated with higher IOP.

In an adult Japanese population, applanation IOP averaged 14.5 mm Hg and was negatively correlated with age after adjusting for other related factors. A positive correlation between IOP and myopia was found.