A mix of environmental and physiologic factors give rise to myopia, some of them quite surprising, according to a new study of twins conducted in the UK.

Researchers analyzed a subset of the Twins Early Development Study, a longitudinal evaluation of 1,991 subjects recruited at birth between 1994 and 1996. Subjective refraction was obtained from the twins’ optometrists, with myopia defined as mean spherical equivalent ≤-0.75 diopters. Mean age of subjects was 16.3 years.

The team used a ‘life-course epidemiology’ approach, which considers the influence of gestational and early childhood factors on long-term development, to appropriately weight myopia risk factors during critical periods of eye growth. Adjusted odds ratios (ORs) for myopia were estimated t each life stage.

Factors significantly associated with myopia included level of maternal education (OR 1.33), fertility treatment (OR 0.63), summer birth (OR 1.93) and hours spent playing computer games (OR 1.03). In addition, the researchers noted associations with socioeconomic status, educational attainment, reading enjoyment and certain cognitive variable (particularly verbal cognition) at multiple points over the life course.

“A greater understanding of contemporaneous, early life factors associated with myopia risk is urgently required, particularly in younger-onset myopia,” the authors wrote in their study, “as this correlates with higher severity and increased complications in adult life.”