Birth Order and Myopia. (December 2013)

• Record Type: Journal Article
• Authors: Guggenheim, Jeremy A.; McMahon, George; Northstone, Kate; Mandel, Yossi; Kaiserman, Igor; Stone, Richard A.; Lin, Xiaoyu; Saw, Seang Mei; Forward, Hannah; Mackey, David A.; Yazar, Seyhan; Young, Terri L.; Williams, Cathy
• Is Part Of: Ophthalmic epidemiology. Volume 20:Number 6(2013)
• Page Start: 375
• Page End: 384
• Publication Date: 2013-12
• Subjects: Blindness -- Prevention -- Periodicals; Eye -- Diseases -- Epidemiology -- Periodicals; Ophthalmology -- Periodicals; 614.5997
• DOI: 10.3109/09286586.2013.848457
• Languages: English
• ISSNs: 0928-6586

Abstract

<abstract> <title>Abstract</title> <p> <italic>Purpose</italic>: An association between birth order and reduced unaided vision (a surrogate for myopia) has been observed previously. We examined the association between birth order and myopia directly in four subject groups.</p> <p> <italic>Methods</italic>: Subject groups were participants in (1) the Avon Longitudinal Study of Parents and Children (ALSPAC; UK; age 15 years; <italic>N</italic> = 4401), (2) the Singapore Cohort Study of Risk Factors for Myopia (SCORM; Singapore; age 13 years; <italic>N</italic> = 1959), (3) the Raine Eye Health Study (REHS; Australia; age 20 years; <italic>N</italic> = 1344), and (4) Israeli Defense Force Pre-recruitment Candidates (IDFC; Israel; age 16–22 years; <italic>N</italic> = 888, 277). The main outcome was odds ratios (OR) for myopia in first-born versus non-first-born individuals after adjusting for potential risk factors.</p> <p> <italic>Results</italic>: The prevalence of myopia was numerically higher in first-born versus non-first-born individuals in all study groups, but the strength of evidence varied widely. Adjusted ORs (95% confidence intervals, CIs) were: ALSPAC, 1.31 (1.05–1.64); SCORM, 1.25 (0.89–1.77); REHS, 1.18 (0.90–1.55); and IDFC, 1.04 (1.03–1.06). In the large IDFC sample, the effect size was greater (a) for the first-born versus fourth- or higher-born comparison than for the first-born versus second/third-born comparison (<italic>p</italic> < 0.001) and (b) with increasing myopia severity (<italic>p</italic> < 0.001).</p> <p> <italic>Conclusions</italic>: Across all studies, the increased risk of myopia in first-born individuals was low (OR < 1.3). Indeed, only the studies with >4000 participants provided strong statistical support for the association. The available evidence suggested the relationship was independent of established risk factors such as time outdoors/reading, and thus may arise through a different causal mechanism.</p> </abstract>