Frequency of under-corrected refractive errors in elderly Chinese in Beijing
- First Online:
- Cite this article as:
- Xu, L., Li, J., Cui, T. et al. Graefe's Arch Clin Exp Ophthalmo (2006) 244: 871. doi:10.1007/s00417-005-0206-1
- 56 Views
The aim of the study was to evaluate the prevalence of under-corrected refractive error among elderly Chinese in the Beijing area.
The population-based, cross-sectional, cohort study comprised 4,439 subjects out of 5,324 subjects asked to participate (response rate 83.4%) with an age of 40+ years. It was divided into a rural part [1,973 (44.4%) subjects] and an urban part [2,466 (55.6%) subjects]. Habitual and best-corrected visual acuity was measured. Under-corrected refractive error was defined as an improvement in visual acuity of the better eye of at least two lines with best possible refractive correction.
The rate of under-corrected refractive error was 19.4% (95% confidence interval, 18.2, 20.6). In a multiple regression analysis, prevalence and size of under-corrected refractive error in the better eye was significantly associated with lower level of education (P<0.001), female gender (P<0.001), and age (P=0.001).
Under-correction of refractive error is relatively common among elderly Chinese in the Beijing area when compared with data from other populations.
KeywordsRefractive errorVisual impairmentPoor visionBlindnessMyopiaEducationGender
One of the most frequently encountered reasons for visual impairment is under-correction of refractive errors [1–5]. Since frequency of and reasons for visual impairment may differ between regions and populations, it was the purpose of the present study to evaluate the frequency of under-correction of refractive errors in elderly Chinese in a rural population and an urban population in the area of Beijing.
The Beijing Eye Study, a population-based cohort study in Northern China, was carried out in seven communities: four communities from the Haidian urban district in the Northern part of Central Beijing, and three communities from a rural district in the village area of Yufa (Daxing District) in the South of Beijing [6–8]. The Medical Ethics Committee of the Beijing Tongren Hospital had approved the study protocol and all participants had given informed consent. Of 5,324 individuals aged 40 years or older and residing in the seven communities, 4,439 (2,505 women) participated in the study (response rate 83.4%). Data on visual acuity were available for 4,438 subjects. The study was divided into a rural part [1,972 (44.4%) subjects] and an urban part [2,466 (55.6%) subjects]. Visual acuity was measured as uncorrected visual acuity, and if spectacles were worn, additionally as habitual visual acuity with the spectacles, at a distance of 5 m. Automatic refractometry (Auto Refractometer AR-610, Nidek, Tokyo, Japan) was performed if uncorrected visual acuity was lower than 1.0. The values obtained by automatic refractometry were verified and refined by subjective refractometry. Under-corrected refractive error was defined as improvement of at least two lines in visual acuity of the better eye with best possible refractive correction compared with the habitual visual acuity.
The rate of under-corrected refractive error was 19.4% (95% confidence interval, 18.2, 20.6). In univariate analysis, under-corrected refractive error in the better eye was significantly (P<0.001) more common in women (22.2%; 95%CI 20.6, 23.8) than in men (15.8; 95%CI 14.1, 17.4). Size and prevalence of under-corrected refractive error increased significantly with age (P<0.001; r=0.26), low best-corrected visual acuity (P<0.001; r=−0.16), higher degree of nuclear cataract (P<0.001; r=0.24), astigmatic refractive error (P<0.001; r=0.40), and lower level of education (P<0.001; r=−0.14). Frequency of under-corrected refractive error did not vary significantly (P=0.79) between the rural area (19.2%; 95%CI 17.4, 20.9) and the urban region (19.5%; 95%CI 18.0, 21.1). Among the subjects with under-correction, 46.7% were myopic. Transferring the World Health Organization (WHO) standard for the definition of visual impairment and blindness from best-corrected visual acuity to habitual visual acuity, we found that 192 (22.7%) out of the 847 subjects with under-correction had visual impairment (habitual visual acuity < 20/60 and ≥ 20/400), and four (0.5%) subjects were blind (visual acuity <20/400). Three (75%) of the four blind subjects showed degenerative myopia (n=2) and corneal opacity as major morphological causes for poor vision. For one subject, under-correction may have been the principal cause for poor vision, since this subject exhibited a best-corrected visual acuity of 1.0. For the three other subjects, best-corrected visual acuity was 0.02, 0.20 and 0.40, respectively. Of the 192 subjects with visual impairment, 39 (20.3%) showed morphological causes for poor vision, including degenerative myopia (n=11; 5.8%), cataract (n=10; 5.2%), and glaucomatous optic neuropathy (n=8; 4.2%). Best-corrected visual acuity for these 39 subjects was 0.10 (n=1 subject), 0.20 (n=6), 0.25 (n=6), 0.30 (n=6), or higher. For the remaining 153 (79.7%) subjects, a morphological cause for poor vision was not detected, and their best-corrected visual acuity was 0.30 (n=2 subjects), 0.40 (n=1), 0.50 (n=23), or higher. In a multiple regression analysis the size and prevalence of under-corrected refractive error was significantly associated with lower level of education (P<0.001), female gender (P<0.001) and age (P<0.001). The association with nuclear cataract was no longer statistically significant (P=0.49).
Under-corrected refractive error has been one of the leading causes of visual impairment in recent studies on various population groups [1–5]. In Australia, the Victoria Visual Impairment Project  and the Blue Mountains Eye Study  found prevalence rates of under-corrected refractive error of approximately 7.5% to 10%. In the population-based study in the Shatin area of Hong Kong, 68.9% of visual impairment was explained by under-corrected refractive error . In the Singaporean Tanjong Pagar study, the adjusted prevalence rate of under-corrected refractive error was 17.3%, so that under-corrected refractive error was a leading contributing cause of bilateral poor vision in Singaporean Chinese persons aged 40 to 79 years . In the Tanjong Prior study, as in the present study, under-corrected refractive error rates were highest among older adults with lower educational levels. Comparable findings were observed in the Australian Victoria Visual Impairment Project  and the Blue Mountains Eye Study . The present study, in which under-corrected refractive error was a considerable problem (19.4%) among elderly less educated Chinese in mainland China extends, therefore, the observations made in other population-based investigations that under-correction of refractive errors is one of the causes of visual impairment. However, since 46.7% of under-corrected subjects were myopic, some of the under-corrected subjects may have had an almost normal visual function in daily life. Limitations of the study include, as in any population-based study, that selection bias could have accentuated some estimates and masked others. The overall participation rate in our survey was 83.4%, and it is possible that non-participants had different rates of under-correction. Compared with other population-based studies, however, the response rate in the present investigation was relatively high. Another possible limitation of the study is that the regions included into the study were not representative of the whole population. To reduce the influence of this possible selection artifact, we chose the participants from rural areas as well as from urban regions. Public strategies addressing the problem of under-correction may lead to a relatively efficient and inexpensive way to improve the overall visual function of the population.