PURPOSE: To describe the distribution of ocular biometry and refraction in Japanese adults. DESIGN: Cross-sectional analysis of a prospective cohort study. PARTICIPANTS: A total of 9,850 individuals participated in the first follow-up of the Nagahama Prospective Cohort for Comprehensive Human Bioscience (the Nagahama study) conducted between 2013 and 2016. Participants were aged between 34 and 80 years old. METHODS: All participants underwent axial length (AL, mm), anterior chamber depth (ACD, mm), corneal diameter (white to white, mm), and central corneal thickness (CCT, μm) measurement (IOL Master, Carl Zeiss Meditec, Dublin, CA, USA), and refraction (spherical equivalent: SE, diopter) and corneal curvature (CC, mm) measurement (ARK-530A, Nidek, Aichi, Japan). Distribution of these ocular biometric parameters and prevalence of myopia, high myopia, and extreme myopia are summarized. MAIN OUTCOME MEASURES: Distribution of ocular biometry and refraction. RESULTS: After standardization to the national population of 2015, estimates of mean AL and SE were 24.21 mm and -1.44 D, respectively. Estimates of mean CC, corneal diameter, CCT, and ACD were 7.69 mm, 12.01 mm, 543.96 μm, and 3.21 mm, respectively. After standardization of age and sex, the prevalence of myopia (SE ≤ -0.5D) and high myopia (SE ≤ -6.0D) were 49.97% and 7.89%, respectively. About 70% of the younger participants (age of 34 years to 59 years) showed myopia, while high myopia was observed in about 10%. While the number of individuals with myopia or high myopia was higher in the younger age-groups, the prevalence of more extreme phenotypes remains stable across all ages, especially in females. Participants with AL of more than 30 mm were observed only in older females (n = 5, 0.05%). CONCLUSIONS: We showed detailed distributions of various ocular biometry and refraction using a large general Japanese cohort. Prevalence of myopia and high myopia from 2013 to 2016 were higher than those in earlier studies, which would reflect recent environmental change. On the other hand, constant prevalence of extreme myopia across all ages suggests high genetic predisposition of the extreme phenotype.