Wenyong Huang

Refractive error and biometry in older Chinese adults: the Liwan eye study.

PURPOSE To assess the prevalence of refractive error and describe the distribution of ocular biometry and its association with refraction in adult Chinese. METHODS Random clustering sampling was used to identify adults aged > or = 50 years in Liwan District, Guangzhou. Refraction was determined by subjective refraction that achieved the best corrected vision based on monocular measurement. Ocular biometry was measured by A-mode ultrasound using a handheld applanation probe. RESULTS Among 1405 participants in the study, data from 1269 phakic right eyes were available for analysis. The prevalence of myopia (SE < -0.5 D), hyperopia (SE > +0.5 D), and astigmatism (cylinder > 0.75 D) was 32.3% (95% confidence interval [CI], 27.8%-34.6%), 40.0% (95% CI, 37.3%-42.7%), and 48.3% (95% CI, 45.6%-51.1%), respectively. The spherical equivalent tended to become hyperopic at 60 years and shifted toward myopia at 75 years. Axial length did not change with age but was consistently shorter in women. Lens thickness increased with age and tended to be greater in women. CONCLUSIONS The prevalence of myopia and biometric distribution in this urban Chinese cohort are similar to those observed in Singaporean Chinese but greater than in Mongolians and Europeans. Further studies are needed to clarify the role of environmental factors in the myopia rates.

Prevalence and Causes of Visual Impairment in Chinese Adults in Urban Southern China: The Liwan Eye Study

OBJECTIVE To assess the prevalence and causes of visual impairment and blindness in adults living in an urban area of southern China. METHODS Random cluster sampling was used to identify the adults 50 years and older living in the Liwan district of Guangzhou, China. Presenting visual acuity (PVA) with habitual correction and best-corrected visual acuity (BCVA) based on autorefraction and subjective refraction were measured using the Early Treatment Diabetic Retinopathy Study visual chart. Blindness and low vision were defined according to World Health Organization criteria. Eyes with visual impairment were assigned 1 principal cause for the impairment. RESULTS Visual acuity measurements were available for 1399 adults 50 years and older (75.3% participation rate). The prevalence of blindness and low vision based on the PVA was 0.6% (95% confidence interval, 0.2%-1.0%) and 10.1% (95% confidence interval, 8.5%-11.7%), respectively. These rates were reduced to 0.5% and 3.1% when the BCVA was considered. Based on the PVA, the principal causes for blindness were cataract (39.6%), glaucoma (11.0%), and myopic maculopathy (6.6%). The majority of low vision cases were attributable to cataract (45.3%) and uncorrected refractive error (43.9%). CONCLUSION The majority of eye diseases leading to visual impairment are potentially treatable in this population.

Anterior Chamber Depth in Elderly Chinese: The Liwan Eye Study

PURPOSE To assess the anterior chamber depth (ACD) and its variation with age, gender, and angle width in elderly Chinese in an urban area of southern China. DESIGN Cross-sectional study. PARTICIPANTS Adults 50 and older were identified using cluster random sampling in Liwan District, Guangzhou. METHODS Gonioscopy was performed before ACD measurements to estimate the geometric angle width according to the Shaffer system. ACD was measured using optical pachymetry. True ACD was calculated by subtracting central corneal thickness from the distance between the anterior corneal epithelium and the anterior lens capsule. Data were presented for the right phakic eyes. MAIN OUTCOME MEASURES Anterior chamber depth and gonioscopy. RESULTS Among 1405 participants in the study, data from 1248 right eyes were available for analysis. The mean ACD values for men and women were 2.59 mm (95% confidence interval [CI], 2.56-2.62; 25th-75th percentile, 2.37-2.82) and 2.42 mm (95% CI, 2.39-2.44; 25th-75th percentile, 2.21-2.63). Mean ACD declined by 0.09 mm (95% CI, -0.011 to -0.008) per decade (adjusted for gender) and was 0.18 mm (95% CI, -0.213 to -0.141) shallower in women than men (adjusted for age). The ACD was found to be monotonically associated with gonioscopic angle width, decreasing from 2.73 mm (standard deviation [SD], 0.26) in Shaffer grade 4 to 1.94 mm (SD, 0.27) in Shaffer grade 0. There was also a relationship between ACD and refractive error; mean spherical equivalent decreased by 0.030 mm ACD per diopter. CONCLUSIONS This study confirms an inverse association between ACD and age, female gender, and spherical refractive error. Eyes with shallower ACDs had narrower angles.

Intraocular Pressure, Central Corneal Thickness, and Glaucoma in Chinese Adults: The Liwan Eye Study

PURPOSE To describe the distribution of central corneal thickness (CCT), intraocular pressure (IOP), and their determinants and association with glaucoma in Chinese adults. DESIGN Population-based cross-sectional study. METHODS Chinese adults aged 50 years and older were identified using cluster random sampling in Liwan District, Guangzhou. CCT (both optical [OCCT] and ultrasound [UCCT]), intraocular pressure (by Tonopen, IOP), refractive error (by autorefractor, RE), radius of corneal curvature (RCC), axial length (AL), and body mass index (BMI) were measured, and history of hypertension and diabetes (DM) was collected by questionnaire. Right eye data were analyzed. RESULTS The mean values of OCCT, UCCT, and IOP were 512 ± 29.0 μm, 542 ± 31.4 μm, and 15.2 ± 3.1 mm Hg, respectively. In multiple regression models, CCT declined with age (P < .001) and increased with greater RCC (P < .001) and DM (P = .037). IOP was positively associated with greater CCT (P < .001), BMI (P < .001), and hypertension (P < .001). All 25 persons with open-angle glaucoma had IOP <21 mm Hg. CCT did not differ significantly between persons with and without open- or closed-angle glaucoma. Among 65 persons with ocular hypertension (IOP >97.5th percentile), CCT (555 ± 29 μm) was significantly (P = .01) higher than for normal persons. CONCLUSIONS The distributions of CCT and IOP in this study are similar to that for other Chinese populations, though IOP was lower than for European populations, possibly due to lower BMI and blood pressure. Glaucoma with IOP <21 mm Hg is common in this population. We found no association between glaucoma and CCT, though power (0.3) for this analysis was low.

Heritability of Anterior Chamber Depth as an Intermediate Phenotype of Angle-Closure in Chinese: The Guangzhou Twin Eye Study

PURPOSE To assess the heritability of anterior chamber depth (ACD) and relative anterior chamber depth (ACD/axial length, rACD) in Chinese in a classic twin study. METHODS Twins aged 7 to 15 years living in two local districts were recruited from the Guangzhou Twin Registry. Anterior chamber depth and axial length were measured by partial coherence laser interferometry. Zygosity in all same-sex twin pairs was confirmed by genotyping with 16 polymorphic markers. The phenotypes of the right eyes were used in analysis. Heritability was assessed by structural variance component genetic modeling. RESULTS In total, 1126 twin participants were available for analysis, including 357 monozygotic (MZ) and 206 dizygotic (DZ) twin pairs. ACD increased with age (0.036 mm per year, P < 0.001) and 0.09 mm shallower in the girls than in the boys (P < 0.001). Age- and sex-adjusted intraclass correlation coefficients (ICCs) for ACD were 0.92 for the MZ and 0.50 for the DZ twins; those for rACD were 0.89 for the MZ and 0.52 for the DZ twins. The best-fitting model yielded 90.1% (95% CI: 88.2%-91.7%) of additive genetic and 9.9% (95% CI: 8.3%-11.8%) of unique environmental effects for ACD and 89.2% (95% CI: 87.1%-90.9%) of additive genetic and 10.8% (95% CI: 9.1%-12.9%) of unique environmental effects for rACD. CONCLUSIONS Additive genetic effects appear to be the major contributor to the variation of ACD and rACD in Chinese population. High heritability remained even when the data were corrected for the influence of myopia.

The Guangzhou Twin Project.

The Guangzhou Twin Registry, initiated in 2005, is a population-based registry of twins born between 1987 and 2000. To date, over 9700 pairs of twins, regardless of their health and medical history, were enrolled in the database using the Official Household Registry of Guangzhou City. The twins were subsequently verified by door-to-door visits based on the registry address. The primary goal of this registry is to develop a resource for genetic epidemiological studies on common diseases in the southern Chinese population. The initial focus is to distinguish the genetic and environmental determinants of eye diseases, in particular myopia and glaucoma. About 1000 pairs of twins living close to the Zhongshan Ophthalmic Center were invited for the first phenotyping examination, questionnaire administration and DNA collection in July and August 2006. An annual eye examination and other phenotype data collection have been scheduled for up to 5 years in order to investigate changes in phenotypes including the myopia progression, physical development and the changes of other eye-related phenotypes. Recruitment of adult twins aged 50 years and over is underway in the same city with the assistance of the government.

Distribution of central and peripheral corneal thickness in Chinese children and adults: the Guangzhou twin eye study.

Purpose: To describe the distribution of central and peripheral corneal thickness in children and adults by using a Scheimpflug camera. Methods: A total of 926 children 8-16 years of age and 662 adults 30-68 years of age were recruited from the Guangzhou Twin Registry. Central and peripheral corneal thicknesses were measured by using the Pentacam system with a standardized method. Regression analyses were used with the generalized estimating equation model, adjusting for the within-cluster correlation. Results: Corneal thicknesses, measured at the apex, center of pupil, superior, inferior, nasal, temporal peripheral, and the thinnest points, were 537.0 ± 29.4, 536.3 ± 29.3, 643.6 ± 37.2, 613.8 ± 32.4, 624.5 ± 35.0, 605.7 ± 33.4, and 533.2 ± 30.0 μm, respectively, in adults. In the children, these values were 550.7 ± 32.8, 550.7 ± 32.7, 656.0 ± 38.7, 627.9 ± 36.6, 642.1 ± 37.2, 612.5 ± 36.3, and 548.1 ± 32.8 μm, respectively. The thinnest point was located in the inferotemporal quadrant in 77.92% of children. All corneal thickness measurements showed no age-related change. Corneal thickness was generally thicker in boys than girls in the children, but this sex difference was not identified in adults. The discrepancy of measurements between the apex and thinnest point was small but statistically significant. Conclusions: Central and 3.0-mm peripheral corneal thicknesses were normally distributed. No age-related differences were shown. A sex difference was shown in children but not in adults. Understanding the discrepancy between the apex and thinnest point could be useful in the safe management of refractive surgery.

Shared Genetic Determinant of Axial Length, Anterior Chamber Depth, and Angle Opening Distance: The Guangzhou Twin Eye Study

PURPOSE To estimate the extent to which common genetic and environmental effects contribute to covariances among axial length, anterior chamber depth, and angle-opening distance. METHODS The study participants were recruited from the Guangzhou Twin Registry. Anterior segment optical coherence tomography and custom software were used to quantify the angle opening distance (AOD) at the location 500 microm anterior to the scleral spur. Anterior chamber depth (ACD) and axial length (AL) were measured using laser interferometry. Cross-trait, cross-twin correlations for monozygotic (MZ) and dizygotic (DZ) twins and the Cholesky model were used to quantify shared genetic and environmental effects for AL, ACD, and AOD after adjusting for age and sex. RESULTS A group of 459 pairs of twins (304 MZ and 155 DZ) aged 8 to 16 years were available for analysis. The phenotypic correlations among AL, ACD, and AOD ranged from 0.39 to 0.64. Cross-twin, cross-trait correlations for these three phenotypes for MZ twins were consistently greater than the corresponding correlations for DZ twins. The results of the Cholesky model-fitting analyses can be summarized as follows: first, of 70% of additive genetic factors for AOD, 23% and 13% were those shared with ACD and AL, respectively, whereas the remaining 34% were those unique to AOD. Second, of 89% of additive genetic factors for ACD, 25% were those shared with AL, whereas 64% were those unique to ACD. Third, random environmental influences on covariances among AL, ACD, and AOD were very small. CONCLUSIONS Analyses of Chinese children twin data suggest that shared genes are responsible for the significant phenotypic correlations found for AL ACD, and AOD.

Outcomes of Cataract Surgery in Urban Southern China: The Liwan Eye Study

PURPOSE The outcomes of cataract surgery have been well reported in rural China; however, the situation in the urban population remains unclear. This study assessed the outcomes of cataract surgery in urban southern China. METHODS Data were gathered from the Liwan Eye Study, a population-based, cross-sectional study conducted in people aged 50 years or more in the Liwan District of Guangzhou. Presenting and best corrected visual acuity and a detailed eye examination were performed. For all aphakic and pseudophakic participants identified, information on the date, setting, type, and complications of cataract surgery were recorded. RESULTS Of the 1405 participants, 62 people (90 eyes) had undergone cataract surgery. Of those, 54.4% underwent the phacoemulsification (Phaco) technique, 33.3% extracapsular cataract extraction (ECCE) with intraocular lens (IOL) implantation, and 11.1% ECCE without IOL; 1 patient had intracapsular cataract extraction (ICCE). Presenting visual acuity (PVA) was >6/18 in 56 (62.2%) eyes, <6/18 to >6/60 in 20 (22.2%) eyes, <6/60 to >3/60 in 3 (3.3%) eyes, and <3/60 in 11(12.3%) eyes. Of the 34 eyes with PVA less than 6/18, the principal causes were 26.5% retinal abnormalities, 20.6% glaucoma, 35.3% uncorrected aphakia or refractive error, and 14.5% posterior capsule opacification (PCO). CONCLUSIONS ECCE or Phaco with IOL are the major surgical techniques used in urban southern China. More than half of the eyes with poor outcomes due to uncorrected aphakia, refractive error, or PCO are potentially treatable. This result suggests a pressing need for improved surgical training and postoperative care.

Shared genetic determinants of axial length and height in children: the Guangzhou twin eye study.

OBJECTIVES To describe the association between axial length (AL) and height and to estimate the extent to which shared genetic or environmental factors influence this covariance. METHODS Study participants were recruited from the Guangzhou Twin Registry. Axial length was measured using partial coherence laser interferometry. Height was measured with the participants standing without shoes. We computed twin pairwise correlations and cross-twin cross-trait correlations between AL and height for monozygotic and dizygotic twins and performed model-fitting analyses using a multivariate Cholesky model. The right eye was arbitrarily selected to represent AL of participants. RESULTS Five hundred sixty-five twin pairs (359 monozygotic and 206 dizygotic) aged 7 to 15 years were available for analysis. Phenotypic correlation between AL and height was 0.46 but decreased to 0.19 after adjusting for age, sex, and age × sex interaction. Bivariate Cholesky model-fitting analyses revealed that 89% of phenotypic correlation was due to shared genetic factors and 11% was due to shared random environmental factors, which includes measurement error. CONCLUSIONS Covariance of AL and height is largely attributable to shared genes. Given that AL is a key determinant of myopia, further work is needed to confirm gene sharing between myopia and stature.