Intraocular pressure in an ophthalmologically normal Japanese population

Purpose: To investigate the distribution of intraocular pressure (IOP) measured by Goldmann applanation tonometry (GAT) and factors correlating with IOP, with special attention to age, in a large sample of ophthalmologically normal Japanese subjects. Methods: A total of 7313 subjects (2847 male, 4466 female) were selected as a normal Japanese sample. The following exclusion criteria applied: abnormal results suggestive of any eye diseases in slit-lamp examination, fundus photography or visual field testing using frequency-doubling technology; corrected visual acuity < 0.7, and contact lens wear within 1 week of study examinations. All subjects were sourced from the Eye Disease Screening Service in Tajimi City, which carried out a screening programme between September 2000 and October 2001. All data, including subject age, gender, body mass index (BMI), systolic blood pressure (BP), laterality, refraction, corneal radius and IOP measured with GAT were collected from subject records. Central corneal thickness (CCT) was measured by SP-2000P specular microscopy. Levels of IOP and correlating factors were statistically analysed. Results: Average IOP was 14.1 +/- 2.3 mmHg (mean +/- standard deviation; n = 7313 x 2). Mean IOP levels in male and female subjects were 14.1 +/- 2.3 mmHg and 14.1 +/- 2.2 mmHg, respectively. There was no difference in IOP between male and female subjects. Multiple regression analysis indicated that IOP had negative correlations with age, corneal radius and refraction (p < 0.0001), and positive correlations with CCT, systolic BP and BMI (p < 0.0001). Conclusions: In a large-scale population of ophthalmologically normal Japanese subjects, IOP measured by GAT was significantly and negatively correlated with age. It was also negatively correlated with corneal radius and refraction, and positively with CCT, systolic BP and BMI.