Objective. To classify anatomic features related to anterior chamber angles by a qualitative assessment system based on ultrasound biomicroscopy (UBM) images. Methods. Cases of primary angle-closure suspect (PACS), defined by pigmented trabecular meshwork that is not visible in two or more quadrants on static gonioscopy (cases) and systematically selected subjects (1 of every 10) who did not meet this criterion (controls) were enrolled during a population-based survey in Guangzhou, China. All subjects underwent UBM examination. A set of standard UBM images was used to qualitatively classify anatomic features related to the angle configuration, including iris thickness, iris convexity, iris angulation, ciliary body size, and ciliary process position. All analysis was conducted on right eye images. Results. Based on the qualitative grades, the difference in overall iris thickness between gonioscopically narrow eyes (n = 117) and control eyes (n = 57) was not statistically significant. The peripheral one third of the iris tended to be thicker in all quadrants of the PACS eyes, although the difference was statistically significant only in the superior quadrant (P = 0.008). No significant differences were found in the qualitative classifications of iris insertion, iris angulation, ciliary body size, and ciliary process position. The findings were similar when compared with the control group of eyes with wide angles in all quadrants. Conclusions. Basal iris thickness seems to be more relevant to narrow angle configuration than to overall iris thickness. Otherwise, the anterior rotation and size of the ciliary body, the iris insertion, and the overall iris thickness are comparable in narrow- and wide-angle eyes.

More ITC is identified on UBM imaging than by gonioscopy. Careful consideration should be given to the assessment modality regarded as the reference standard in defining anatomic risk factors for glaucomatous visual loss and the need for treatment.

Additive genetic effects had a substantial influence on phenotypic variation in PEL and RPEL, suggesting genetic rather than environmental factors play a major role in determining eye shape.

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

Repeatability is improved when larger measurement areas are chosen.