Primary angle-closure glaucoma (ACG) is more visually destructive than open-angle glaucoma (OAG), and its prevalence increases exponentially with age.1,2 Using the National Longitudinal Health Insurance Database, the authors analyzed the incidence and prevalence of OAG and ACG in one million subjects from year 2001 to 2010. They found the prevalence of both types of glaucoma increased over the years, but OAG showed a steeper trend than ACG, making it more prevalent after the year 2005. As well, there was a significantly decreasing trend in ACG incidence over the years; more significant in woman than in men. The authors attributed these findings to the high prevalence of myopia and increasing number of cataract surgery in Taiwan.
The findings may not be surprising in a society where myopia is prevalent and healthcare is accessible and inexpensive, but cautions should be exercised before we draw conclusions. Population studies found most OAG patients are unaware of this disease before study examinations,3 and ACG also may be under-diagnosed because most cases are asymptomatic until late stage.2 In this study, ACG might be underestimated to a greater extent than OAG because ACG is more prevalent in subjects with low socioeconomic status which is a barrier to healthcare access.4,5 Another study limitation is uncertainty about accuracy of the diagnosis coding. Sometimes it is challenging to discriminate glaucomatous damage from myopic changes. Under such circumferences, physicians may opt for coding related to OAG, resulting in overestimation of its prevalence and incidence in populations prevalent with myopia.
ACG might be underestimated to a greater extent than OAG because ACG is more prevalent in subjects with low socioeconomic status which is a barrier to healthcare access
The fact that the authors used loose criteria for case selection may increase this possibility. Despite these limitations, the study results may reflect the reality that echo findings from another study which showed the incidence of primary ACG appeared to be decreasing after reaching a peak in the late 1990s.6