Although mainland China has the largest population in the world and a substantial increase in the number of older persons is expected, reports regarding the epidemiology of AMD in mainland Chinese populations are relatively rare. A previous study carried out in another block in Shanghai in 2002 reported a higher prevalence rate of AMD (15.5% of 1023 subjects older than 50 years old had AMD and 1.9% had exudative AMD) than our results indicated.
11 However, this study applied ophthalmoscopy diagnosis and was based on the Chinese Ophthalmologic Society definition of AMD. The differences in photographic and grading techniques and the definition of AMD make it difficult to compare the two studies. To our knowledge, there are only two other population-based studies in mainland China that have reported results regarding the prevalence of AMD based on a commonly used classification and grading system (
Table 4). In the Beijing Eye Study, the crude prevalence rates of early and late AMD were 5.1% and 0.3%, respectively.
12,13 The Handan Eye Study reported a lower, crude prevalence rate of early and late AMD (3.0% for early and 0.1% for late AMD prevalence).
14 The authors suggested that Chinese populations had a relatively lower prevalence rate for AMD compared with white populations. However, the prevalence rate in our study was significantly higher than the rates in both the Beijing and Handan eye studies. Several possible reasons might explain the differences in findings between the previous two studies and our present study. First, the present study were conducted in urban populations with a higher prevalence rate of AMD, whereas the Beijing Eye Study was conducted in a partially rural population (rural part, 43.8%), and the Handan Eye Study was conducted in a rural population with the lowest prevalence rate of AMD among the four studies (
Table 4). With economic/political reforms primarily targeting large metropolitan cities, there exists a great divide between urban and rural areas in mainland China after more than 3 decades of development. Possible differences between the rural and urban populations of the same race include environmental (e.g., UV exposure), lifestyle (e.g., diet, physical activity, and education), or broader healthcare factors.
25 It has been hypothesized that people growing up in a rural and self-sustained economy are less affected by AMD compared with urban residents.
26 The present sample represents a population living in a metropolitan environment exposed to Western cultures, lifestyles, and influences; it is possible that the consequent lifestyle change and westernization of the diet may have had a marked impact on the prevalence of AMD in this urban Chinese population.
25 Second, different inclusion criteria in the studies also accounted for the discrepancy. The present study recruited participants 50 years of age and older (mean age, 64.8 years), older than those of the Beijing (mean age, 56.1 years) and Handan (mean age, 51.8 years) eye studies (
Table 4). The higher prevalence of AMD in the present study could have been anticipated, given that our study sample had a larger proportion of the old age group. Third, both the Beijing and Handan eye studies were conducted in populations living in Northern China, whereas the present study was conducted in Southeastern China. The discrepancy in AMD rate might be caused partly by regional differences in climate, environmental parameters, and lifestyle. Finally, all participants of the present study received SD-OCT examination. SD-OCT has the advantage of detecting and evaluating small changes in the morphology of the retinal layers and subretinal space, which is valuable in detecting AMD lesions.
27–29 The information offered by SD-OCT was used to assist in the identification and grading of AMD in the questioned cases (11 cases in the present study), which may also have increased the AMD rate in our study.