Ocular biometry, refraction and time spent outdoors during daylight in Irish schoolchildren

BACKGROUND: Previous studies have investigated the relationship between ocular biometry and spherical equivalent refraction in children. This is the first such study in Ireland. The effect of time spent outdoors was also investigated. METHODS: Examination included cycloplegic autorefraction and non-contact ocular biometric measures of axial length, corneal radius and anterior chamber depth from 1,626 children in two age groups: six to seven years and 12 to 13 years, from 37 schools. Parents/guardians completed a participant questionnaire detailing time spent outdoors during daylight in summer and winter. RESULTS: Ocular biometric data were correlated with spherical equivalent refraction (axial length: r = -0.64, corneal radius: r = 0.07, anterior chamber depth: r = -0.33, axial length/corneal radius ratio: r = -0.79, all p < 0.0001). Participants aged 12-13 years had a longer axial length (6-7 years 22.53 mm, 12-13 years 23.50 mm), deeper anterior chamber (6-7 years 3.40 mm, 12-13 years 3.61 mm), longer corneal radius (6-7 years 7.81 mm, 12-13 years 7.87 mm) and a higher axial length/corneal radius ratio (6-7 years 2.89, 12-13 years 2.99), all p < 0.0001. Controlling for age: axial length was longer in boys (boys 23.32 mm, girls 22.77 mm), and non-White participants (non-White 23.21 mm, White 23.04 mm); corneal radius was longer in boys (boys 7.92 mm, girls 7.75 mm); anterior chamber was deeper in boys (boys 3.62 mm, girls 3.55 mm, p < 0.0001), and axial length/corneal radius ratios were higher in non-White participants (non-White 2.98, White 2.94, p < 0.0001). Controlling for age and ethnicity, more time outdoors in summer was associated with a less myopic refraction, shorter axial length, and lower axial length/corneal radius ratio. Non-White participants reported spending significantly less time outdoors than White participants (p < 0.0001). CONCLUSION: Refractive error variance in schoolchildren in Ireland was best explained by variation in the axial length/corneal radius ratio with higher values associated with a more myopic refraction. Time spent outdoors during daylight in summer was associated with shorter axial lengths and a less myopic spherical equivalent refraction in White participants. Strategies to promote daylight exposure in wintertime is a study recommendation.