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Myopia is the most common eye trait worldwide and the prevalence is increasing. It is known to be highly heritable; total genetic variation explains up to 70–80% of variance. In an attempt to better understand the genetic architecture of myopia, with an ultimate view to better predict genetic risk and develop targeted treatments, several genome-wide association studies have been performed in the last 6 years. In this review we focus on what a genome-wide association study involves, what studies have been performed in relation to myopia to date, and what they ultimately tell us about myopia variance and functional pathways leading to pathogenesis. The current limitations of genome-wide association studies are reviewed and potential means to improve our understanding of the genetic factors for myopia are described. [ABSTRACT FROM PUBLISHER]

Purpose Monozygotic ( MZ) twin pairs discordant for disease allow careful examination of environmental factors whilst controlling for genetic variation. The purpose of this study was to examine differences in environmental risk factors in MZ twins discordant for myopia. Methods Sixty four MZ twin pairs discordant for refractive error were interviewed. Discordant twins were selected from 1326 MZ twin pairs from the Twins UK adult twin registry with non-cycloplegic autorefraction. Discordancy was defined as ≥2 Dioptres (D) difference in spherical equivalent (SphE) and discordant for class of refractive error. In a 35-item telephone questionnaire twins were separately asked (and scored) about the risk factors urban/rural residence, occupational status and highest educational level. They responded with more (1), less (−1) or the same (0) as their twin on time spent outside, playing outdoor sport, and on close work aged <16 and 16-25 years. The lower SphE twin's score was subtracted from the higher SphE twin's score, and mean values of the difference calculated for each variable. Results Sixty four twin pairs were included (mean age 56, range 30-79 years; mean difference in refraction 3.35 D, S.D. 1.55 D, median difference 2.78 D). Within discordant MZ twin pairs, the more myopic twin was associated with having a higher occupational status (mean score between 16 and 25 years −0.11; 95% CI −0.19 to −0.04; mean score aged >25 years −0.23, 95% CI −0.28 to −0.17), being resident in urban area (mean score −0.26; 95% CI −0.33 to −0.18) and performing more close work (mean score <16 years −0.11; 95% CI −0.18 to −0.05; mean score aged 16-25 years −0.17, 95% CI −0.24 to −0.10) than their twin. The twins who spent more time outdoors (mean score <16 years 0.09; 95% CI 0.03-0.15; mean score aged 16-25 years 0.28, 95% CI 0.15-0.41) or performed more outdoors sports (mean score <16 years 0.13; 95% CI 0.04-0.21; mean score aged 16-25 years 0.23, 95% CI 0.10-0.36) were less likely to be myopic than their twin. Conclusions This study has confirmed known environmental risk factors for myopia. These data will allow selection of discordant twins for epigenetic analysis to advance knowledge of mechanisms of refractive error development. [ABSTRACT FROM AUTHOR]

Purpose School-age myopia is becoming more common in Asia and North America; data from the United Kingdom has suggested a significant amount of myopia develops after the age of 17 years. Age of spectacle wear has been used as a proxy of myopia severity in a recent large genome-wide association study. The purpose of this study was to examine the age of onset of spectacle wear in a large British twin cohort, to examine the reliability and reproducibility of self-reported age of onset as a proxy measure of myopia severity, and to see if there is evidence in the UK of a rising prevalence of myopia. Methods Non-cycloplegic autorefraction was performed on over 6000 subjects from the Twins UK cohort, a large, well-characterized volunteer cohort of British, predominantly Caucasian female twins, between 1998 and 2010. Questionnaires asking age of first spectacle wear were conducted in 2003 and 2008. Myopia was defined as worse than or equal to −1.00 Dioptres, and adult onset myopia as occurring on or after the age of 17 years. Results Autorefractive data was available on 6097 participants at a mean age of 53 years. The mean S.E. was −0.36 D ( S.D. 2.67, range −25.13 to +9.38). 1705 subjects (28%) were myopic with a mean refractive error of −3.54 ( S.D. 2.51, range −25.13 to −1.00) and the median age of first glasses wear was 15 years (mean 18.4 years, S.D. 12.24, range 0-74). Of those who provided an age at which they first wore glasses in both questionnaire sources ( n = 628), there was median difference in response of 0 years ( S.D. 7.18, mean 0.7, maximum 53). A statistically significant cohort effect for increased myopia prevalence across a range of age groups between 1998-1999 and 2008-2010 was identified, with myopia prevalence increasing from 27% to 34% in those aged 50-54 and from 16% to 32% in those aged 55-59. Conclusions Almost half the myopes in this UK-based population wore glasses after the age of 17; further research into adult-onset myopia is required. Although self-reported age of glasses is reproducible and reflects severity, it only explains approximately 15% of the variance of spherical equivalent, so is a rough proxy of refractive error, but still may be useful in large-scale population studies without access to refraction. We have demonstrated a significant cohort effect for increased myopia prevalence in the UK population over a 10-year period. [ABSTRACT FROM AUTHOR]