Abstract
Purpose::
To investigate early life biological and social influences (acting prenatally, perinatally or in childhood) on development of primary myopia, using a life course epidemiologiocal approach to elucidate pathways.
Methods::
Subjects comprised a random 23% sub-sample of the 1958 British birth cohort (all those born in one week in 1958), who have been followed up at intervals from birth as part of a broader study of health and disease. Based on autorefraction at 44 years, subjects were categorised by their spherical equivalent (SE): high myopia (-6 or more), mild or moderate myopia (-5.99 to -0.75) or emmetropia (-0.74 to +0.5). Myopia was also dichotomised as ‘early’ or ‘late’ onset, based on optical correction by 16. A priori, we investigated factors (below) known to influence childhood growth as well as postulated to influence refraction. Multinomial regression analysis was undertaken using a conceptual framework which explicitly accounts for the temporal sequence of factors being investigated, and allowing their primary and secondary roles to be distinguished.
Results::
Findings are based on 2130 subjects: 882 (41%) with emmetropia and 65 (3%) with high and 1183 (56%) with mild or moderate myopia. After adjustment we found myopia was significantly and independently associated with having a father in a non-manual social class (OR 1.2 [1.05, 1.45]), an older mother (1.02 [1.01, 1.04] per year of age) and having intra-uterine growth retardation (low birth weight for gestational age, 1.2 [1.04, 1.25]); specific associations varied by time of onset of myopia. High myopia was less likely in those whose mother continued to smoke during pregnancy (0.41 [0.19, 0.90]. Greater adult height was associated with being myopic but patterns of height and rate of growth during childhood differed for ‘early’ and ‘late’ onset of myopia. Higher maternal education, housing-based socio-economic measures and breast feeding were only associated univariately.
Conclusions::
The development of myopia is influenced by ‘distal’ social and biological early life factors that have an important impact on human growth and development in general. This may partly explain the recent increase in frequency and severity of myopia in some populations, and thus predict further changes in others. Research directed at these factors will be important in elucidating the interplay of genetic, environmental and social/behavioural determinants in refractive error.
Keywords: myopia • development