Purpose: The Orinda Longitudinal Study of Myopia is a 12-year project examining predictive factors for the onset of myopia, the underlying etiologies of myopia, and normal eye growth in school children.
Methods: This paper reports on all measurements made of the ocular components (cycloplegic refractive error, corneal curvature, crystalline lens power, and axial ocular dimensions), parental history of myopia, and near work activity in children participating in the Orinda Longitudinal Study of Myopia between 1989 and 1993. An analysis of the interaction between parental history of myopia and children's near work is conducted on the cross-sectional study data from 1993.
Results: The cross-sectional and longitudinal data show a gradual decrease in refractive error from low hyperopia toward emmetropia, no shift in corneal curvature, a gradual decrease in crystalline lens power, thinning of the crystalline lens, and elongation of the eye between the ages of 6 and 14 years. Parental history is more contributory to a statistical model predicting myopia than is near work, but near work is a significant factor as well. We can find no evidence of statistical interaction between parental history and near work in explaining the presence or absence of myopia.
Conclusions: The emmetropization process is evident in the gradual decrease in refractive error toward emmetropia, the axial elongation of the eye, and the compensating decrease in crystalline lens power. Both nature and nurture play a role in the etiology of myopia, although the predominant role appears to belong to a positive parental history of myopia. This role does not appear to be through an interaction between parental myopia status and children's near work activity.