Visually significant cataract: a global challenge

Cataract is often considered a conquered disease because of the widely available, relatively safe and cost-efficient surgical solution. However, cataract still accounts for a significant amount of blindness and vision impairment, affecting 46 million people worldwide. The impact of visual loss, especially in an elderly population, is significant and can markedly affect the quality of life because individuals will have trouble with their daily activities of living. More importantly, recent studies have shown an increased mortality in older persons with cataract, after accounting for known mortality risk factors. In 2010, cataract was responsible for 33% of global blindness and 18% of global vision impairment. The proportion of blindness caused by cataract was lowest in the high-income regions (<15%) and highest in South and Southeast Asia (>40%). From 1990 to 2010, the worldwide age-standardized prevalence of cataract-related blindness and vision impairment was reduced by half. Such a substantial decline may reflect the efforts of World Health Organization and the International Agency for the Prevention of Blindness for placing cataract as one of the priorities for Vision 2020 at the elimination of avoidable blindness. Despite major improvements in terms of reduction of prevalence, cataract remains the single largest cause of global blindness. Data on the incidence of visually significant cataract is very limited from the developing countries. In this edition of Clinical and Experimental Ophthalmology, Panday et al. investigated the incidence of visually significant cataract in an urban south Indian population and compared with a rural population. Data from this longitudinal cohort study showed that the 6-year incident rates of visually significant cataract and cataract surgery were 7.4% and 4.6%, respectively. Compared to the studies involving whites, the incidence of visually significant cataract was 2 to 3 times more common in the Chennai Eye Disease Incidence Study. Do Asians have greater risks of developing cataract compared to Caucasians? As rightly commented by Panday et al., direct comparisons among these populations is difficult because of differences in cataract grading system and definition. Studies such as Beaver Dam Eye Study and the Blue Mountains Eye Study have mostly used the lens photography based Wisconsin Cataract Grading System whereas the current study have graded lens opacity using the clinical based Lens Opacity Classification System II. However, a recent study in Singapore had the unique opportunity to compare the cataract prevalence using the same standardized method and shown that cataract was 1.5 to 2 times more common in Asians and began 10years earlier than in Caucasians. Apart from incidence rates, the study reported that people living in rural areas were 2.5 times more likely to have visually significant cataract than people in urban areas. People living in rural areas may be disproportionately affected by cataractrelated vision loss because they are in circumstances with fewer chances of getting the cataract surgical services, as seen by the lower incident of cataract surgery rates in rural areas. Apart from poor access to surgical care, the large magnitude of cataract may also be because of environmental risk factors such as ultraviolet light exposure or exposure to biomass cooking fuels. There are a few important considerations that need to be kept in mind while interpreting these study results. First, income-based disparities can exist within urban areas, where the inequalities between the poor and the rich can be striking. A subgroup of urban dwellers may also have a higher cataract risk as a result of socioeconomic constraints. In fact, having a low income was a crucial barrier for refusal of cataract surgery in India. Consistently, having either low income or poor education was an important risk factor of cataract for persons of Indian origins living in Singapore. The authors have not given details of either the income level or the housing tenure. Including the data of socioeconomic indicators in the analysis could have provided more reliable and appropriate results. Second, studies showed that people with poorer literacy have a lower uptake of cataract surgical services, particularly in rural areas. The authors did not account for rural–urban geographical location when examining literacy as a risk for cataract. A detailed analysis of the relationship between literacy and cataract