Heritability of Peripheral Refraction in Chinese Children and Adolescents: The Guangzhou Twin Eye Study

Abstract

PURPOSE.To estimate the heritability of peripheral refraction in Chinese children and adolescents. METHODS. The authors examined 72 monozygotic (MZ) twins and 48 dizygotic (DZ) twins aged 8 to 20 years from a population-based twin registry. Temporal and nasal peripheral refraction, each 40°from the visual axis, and axial refraction were measured using an autorefractor. Relative peripheral refractive error (RPRE) was defined as the peripheral refraction minus the axial refraction. Heritability was assessed by structural equation modeling after adjustment for age and sex. 1 Longitudinal and crosssectional epidemiologic studies have suggested that the prevalence of myopia exceeds 70% among teenagers living in urban areas in East Asia.2-4 In recent population-based studies among adult Chinese living in urban and rural settings, myopic retinopathy has been the second-leading cause of blindness after cataract. 5,6 Despite intensive research in recent decades, the etiology of myopia remains elusive. Although on-axis refraction (central refractive error) is the major determinant of central visual acuity, there is increasing evidence suggesting that peripheral defocus also plays an important role in the development of myopia, 7-12 although one study has reported contradictory results. 13 In keeping with this notion, previous studies have shown that subjects with relative hyperopic peripheral refraction are more likely to have a prolate posterior eye shape. 14 -16 By contrast, those with relative myopic peripheral refraction are more likely to have an oblate posterior eye shape. 14 -16 Interestingly, there appears to be ethnic variation in the distribution of peripheral refraction, with East Asians having a greater degree of relative peripheral hyperopia (more prolate ocular shape) than do persons of European descent with similar central refractive power. [17][18][19] It remains unclear whether this ethnic difference is attributable to inherited genetic susceptibilities or socioenvironmental differences. It is therefore important to understand whether peripheral refraction is genetically determined. Such information may shed light on the mechanisms underlying the development of myopia.Twin studies offer a unique opportunity to estimate the relative contribution of genetic and environmental effects to the development of complex traits and diseases. 20 In classic twin studies, it is assumed that monozygotic (MZ) twins share 100% of their genes, whereas dizygotic (DZ) twins share, on average, 50%. The heritability of a specific phenotype can be estimated by comparing the phenotypic concordance within MZ and DZ twin pairs. The purpose of this study was to estimate the distribution and heritability of peripheral refraction in young twins. SUBJECTS, MATERIALS, AND METHODS SubjectsSubjects were recruited from participants in the Guangzhou Twin Study, an ongoing prospective cohort study of 9709 twin pairs that began in 2006.21 Children older than 8 years of age who visited the Zhongshan Ophthalmic Center between

The Guangzhou Twin Project: An Update

“…We have provided additional evidence to support the genetic influences of many classical ocular traits, such as central corneal thickness, IOP, optic disc parameters, and axial length (AL). In line with the data from the Australian and UK twin registries, the heritability estimates of these traits were very high, ranging from 0.6 to 0.9 (see Table 3; Ding et al, 2012;He et al, 2008aHe et al, , 2008cHe et al, , 2008dHe et al, , 2009Shen et al, 2012;Zheng et al, 2008aZheng et al, , 2008bZheng et al, , 2009. These data suggest the consistency in levels of heritability across different ethnic groups and environments.…”

“…In doing so, we have constructed classical twin studies to estimate heritability — the proportion of individual phenotypic variation that can be explained by genetic differences among individuals in a given time in a given population. Specifically, our study is the first to identify the high heritability for many novel ocular biometric measures, including lens thickness, peripheral refraction, iris thickness, pupil size, and iridotrabecular angle width (He et al, 2008a, 2009; Ding et al 2012; Shen et al, 2012). We have provided additional evidence to support the genetic influences of many classical ocular traits, such as central corneal thickness, IOP, optic disc parameters, and axial length (AL).…”

The Guangzhou Twin Eye Study: 2019 Update

“…In this case, the saturated model is fitted with an ADE model; otherwise, the saturated model is fitted with an ACE model. Using this traditional theory, we are able to estimate myopic ocular traits such as refraction, AL, central corneal thickness, intraocular pressure, optic disk parameters, peripheral refraction and peripheral eye length, which were similarly high, ranging from 0.6 to 0.9 (Table 3) (Ding et al, 2012(Ding et al, , 2018He, Ge et al, 2008;He, Liu et al, 2008;He et al, 2009;Shen et al, 2012;Zheng, Ge et al, 2008;Zheng et al, 2009). Our results concur with previous heritability data from the Australia (Dirani et al, 2006) and the UK twin registry (Lopes et al, 2009), which suggests there is consistency in the level of heritability across different ethnic groups and environments.…”

Rationale, Design, and Demographic Characteristics of the Handan Offspring Myopia Study

“…5,[31][32][33][34][35] Results from the Guangzhou Twin Eye study strongly supported a significant genetic contribution to peripheral refraction, with genetic effects accounting for more than three-quarters of the variation in peripheral refraction. 36 Urban/rural differences in myopia rates have also been recognized, which are mainly attributable to environmental factors such as nutrition, lifestyle changes, 37 time spent doing near work, intensity of near work (continuous reading), [38][39][40][41] and outdoor activity, 42,43 or physical space of the living environment. 42,[44][45][46] In 2006-2007, we conducted a population-based eye study in adults, The Handan Eye Study (HES), in Handan, Hebei province, North China.…”