The Beijing Eye Study 2011 is a population-based, cross-sectional study in Northern China.
10–12 The Medical Ethics Committee of the Beijing Tongren Hospital had approved the study protocol, all participants had given informed consent, and this study was performed according to the tenants of the Declaration of Helsinki. It was carried out in five communities in the urban district of Haidian in the North of Central Beijing and in three communities in the village area of Yufa of the Daxing District south of Beijing. The only eligibility criterion for inclusion into the study was an age of 50+ years. In 2011, the eight communities had a total population of 4403 individuals aged 50 years or older. In total, 3468 individuals (1963 [56.6%] were women) participated in the eye examination, corresponding to an overall response rate of 78.8%. The study was divided into a rural part (1633 [47.1%] subjects; 943 [57.7%] were women) and an urban part (1835 [52.9%] subjects; 1020 [55.6%] were women). The mean age was 64.6 ± 9.8 years (median, 64 years; range, 50–93 years).
All examinations were carried out in the communities, either in schoolhouses or in community houses. All study participants underwent an interview with standardized questions on their family status, level of education, income, quality of life, psychic depression, physical activity, known major systemic diseases, such as arterial hypertension and diabetes mellitus, and quality of vision. Fasting blood samples were taken for measurement of blood lipids, glucose, and glycosylated hemoglobin HbA1c. Blood pressure was measured. Body height and weight, and the circumference of the waist and hip were recorded. The ophthalmic examination included measurement of presenting visual acuity, uncorrected visual acuity, and best corrected visual acuity, tonometry, slit lamp examination of the anterior segment, optical low-coherence reflectometry (Lensstar 900 Optical Biometer; Haag-Streit, Koeniz, Switzerland) for biometry and digital photography of the cornea, lens, macula, and optic disc.
Subfoveal choroidal thickness (SFCT) was measured using a spectral domain optical coherence tomography (SD-OCT; Spectralis, Wavelength: 870nm; Heidelberg Engineering Co., Heidelberg, Germany) with enhanced depth imaging (EDI) modality (
Fig. 1) after pupil dilation.
12 Seven sections, each comprising 100 averaged scans, were obtained in an angle of 5° to 30° rectangle centered onto the fovea. The horizontal section running through the center of the fovea was selected for further analysis. SFCT was defined as the vertical distance from the hyperreflective line of the Bruch's membrane to the hyperreflective line of the inner surface of the sclera. The measurements were performed using the Heidelberg Eye Explorer software (version 5.3.3.0; Heidelberg Engineering Co.). Only the right eye of each study participant was assessed. The images were taken by one technician (CXC) and the images were assessed in a masked manner by two ophthalmologists (LS, KFD). The quality of the scans was assessed prior to the analysis and poor quality scans were rejected and repeated. The technique was described in detail recently.
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The intra-observer reproducibility was examined in a considerably smaller study group consisting of 21 healthy volunteers with no known eye disease (10 men; mean age, 63.1 ± 10.6 years; range, 50–83 years), who did not participate in the Beijing Eye Study, who were recruited from the Tongren Eye Center and who were scanned 10 times with 1 minute breaks between each measurement. The right eye of each subject was selected for the EDI-OCT analysis. The SFCT was measured in a masked manner by the same observer (LS) within 2 weeks.
Statistical analysis was performed using a commercially available statistical software package (SPSS for Windows, version 20.0; IBM-SPSS, Chicago, IL). For the interobserver study, the average of SFCT measurements obtained from both visits was compared by paired t-tests. Bland-Altman plot was used to visualize the interobserver agreement between the two observers. The intra-observer reproducibility was measured with 10 EDI-OCT images obtained from the 21 volunteers. We calculated the intra-session within subject SD (Sw), the coefficient of variation (COV, 100% × Sw/overall mean), and the intraclass correlation coefficient (ICC). Almost perfect reliability was defined as an ICC greater than 0.80. 95% confidence intervals (CI) were presented. All P values were two-sided and were considered statistically significant when the values were less than 0.05.