Prevalence and predictors of refractive error in a genetically isolated population: the Norfolk Island Eye Study

Background: We aimed to determine the prevalence and associations of refractive error on Norfolk Island. Design: Population-based study on Norfolk Island, South Pacific. Participants: All permanent residents on Norfolk Island aged >= 15 years were invited to participate. Methods: Patients underwent non-cycloplegic auto-refraction, slit-lamp biomicroscope examination and biometry assessment. Only phakic eyes were analysed. Main Outcome Measures: Prevalence and multivariate associations of refractive error and myopia. Results: There were 677 people (645 right phakic eyes, 648 left phakic eyes) aged >= 15 years were included in this study. Mean age of participants was 51.1 (standard deviation 15.7; range 15-81). Three hundred and seventy-six people (55.5%) were female. Adjusted to the 2006 Norfolk Island population, prevalence estimates of refractive error were as follows: myopia (mean spherical equivalent >=-1.0 D) 10.1%, hypermetropia (mean spherical equivalent >= 1.0 D) 36.6%, and astigmatism 17.7%. Significant independent predictors of myopia in the multivariate model were lower age (P < 0.001), longer axial length (P < 0.001), shallower anterior chamber depth (P = 0.031) and increased corneal curvature (P < 0.001). Significant independent predictors of refractive error were increasing age (P < 0.001), male gender (P = 0.009), Pitcairn ancestry (P = 0.041), cataract (P < 0.001), longer axial length (P < 0.001) and decreased corneal curvature (P < 0.001). Conclusions: The prevalence of myopia on Norfolk Island is lower than on mainland Australia, and the Norfolk Island population demonstrates ethnic differences in the prevalence estimates. Given the significant associations between refractive error and several ocular biometry characteristics, Norfolk Island may be a useful population in which to find the genetic basis of refractive error.