We found very high prevalence rates of cataract in people aged ≥60 years in centers in both north and south India. We chose to study an older age group than previous studies in India. There has so far been much less information on the older population in India, especially in the oldest age groups. Our study included >2000 people aged ≥70 years compared with <500 in other studies in India.4,5
Additionally, an older age group was preferable for the collection of data on age related macular degeneration, the other principal outcome of the INDEYE study.
The areas in our study were chosen to represent the typical population in the catchment area of each center (excluding the city of Delhi, Gurgaon city, and Pondicherry city). Our results therefore do not apply to the city populations served by the participating hospitals where cataract surgery uptake and cataract prevalence may be different. We also cannot assume that our results are generalizable to other populations in the same area. Both the RPC and AEH have an active outreach program, which may lead to a higher cataract surgery uptake than in other areas. Nonetheless we did observe a high proportion of people in both study areas with unoperated cataracts.
The response rates were high (78%). Although nonresponse was higher in the ≥80 age group, there was no response bias in other characteristics such as socioeconomic status or gender. It is possible that the lower response rate in the oldest age group may have led to a biased prevalence estimate, but we have no information to judge the direction of any bias resulting from nonparticipants being more or less likely to have cataract. Comparing results across studies is impeded by differences in methods of measuring and grading cataract, whether the denominator for the prevalence is the study population or only those with gradable lens images, the age and gender distribution of the study population, and the precision of the results. Because very few studies have published 95% CIs, the point estimates do not include the range of possible prevalence. Comparisons by type of opacity are even more problematic because of differences in methods, definitions, and the cataract surgical rate in the surveyed populations because information on the type of cataract before operation is not usually available. Studies describing the prevalence of unoperated cataract vary according to access and uptake of cataract surgery eye care. In our study, we have reported the prevalence of both operated and unoperated cataract as an overall measure of any cataract (past or present). These points need to be borne in mind when discussing results across studies. Our results for the prevalence of all cataracts, including aphakia/pseudophakia, are similar to those reported from 2 previous large studies in India4,5
(both in south India; ; available online at http://aaojournal.org
). There were some differences in grading between the studies. Although both previous studies used LOCS III grading for nuclear cataract, our definition of nuclear cataract was more stringent. The Aravind Comprehensive Eye Study and Andhra Pradesh Eye Disease Study used a cutpoint on the LOCS III scale of nuclear ≥3, whereas we used a cutpoint of ≥4. Whereas the Aravind Comprehensive Eye Study used identical cutpoints on LOCS III for cortical and PSC as in our study, the Andhra Pradesh Eye Disease Study used the Wilmer grading scheme and cutpoints for cortical and PSC that correspond with LOCS III grade 3 cortical and grade 1 PSC. The estimates for nuclear and PSC from Andhra Pradesh Eye Disease Study are therefore based on a lower threshold than our study or Aravind Comprehensive Eye Study. Our estimates are also slightly lower than from our previous feasibility study.6
In that study, we used LOCS II with a threshold of ≥2 for nuclear cataract.
Prevalence % of cataract in the India Study of age-related eye disease (INDEYE) and published studies
Our prevalence rates of unoperated and operated cataract were similar to comparable age groups in other Asian studies. In the Tanjong Pagar study in Singapore,9
the Meiktila Eye Study in Myanmar,10
and a study in rural Indonesia,11
all using LOCS III and a classification of nuclear cataract ≥4, the prevalence in people aged ≥60 ranged from 72%10
The slightly lower proportion of cataract in Myanmar could be due to a stricter classification of cortical cataract (≥4), but the number in the older age group was small and the 95% CIs, although not reported, were likely to be wide. The lowest prevalence from the Asian studies was reported from the Shih-Pai study in Taiwan,12
even though this study used a lower threshold for nuclear opacity of ≥2. The authors of the Shih-Pai study reported that the study was conducted in a prosperous area of Taipei, and that the nonresponse rate (33%) was higher among older people, women, and those with lower education. The lower prevalence might therefore reflect both bias in the sample and a higher income setting than other studies in India and Asia. In a study pooling the results from several Western populations,3
the prevalence of unoperated cataract ranged from 15.5% in the 60- to 64-year-old group to 68% in those aged ≥80 and for any aphakia/pseudophakia from 3% to 29% (). These results suggest that cataract is more common in Asia, including India, in younger age groups (e.g., 60–64), irrespective of cataract surgery, but by the age of ≥80 years in both Western and Asian populations, the overwhelming majority of people either have a cataract or have been treated for a cataract.
As with other studies in Asia and Western countries, the dominant type of cataract was nuclear (). The incidence of nuclear opacities seem to be more strongly age related than cortical or PSC opacities.13–15
In the Physicians Health study, the age-specific incidence rates of nuclear cataract were approximately double that of cortical or PSC opacity.15
Using a cutpoint of LOCS III ≥3, cortical opacities were lower in our study compared with other studies in India and Asia (). If we used a cutpoint of LOCS III ≥2, our results were closer to other studies (23%). The exception was the Tanjong Pagar study, with very high rates of cortical cataract, LOCS III ≥2 (62%) in those aged 60 to 81 years. Cortical opacities in Western populations are variable; some studies report results broadly comparable with ours,16,17
whereas in others the rates seem to be higher.18,19
Results in studies of Hispanic Americans20
and African Caribbeans,21
both based on LOCS II grading definitions of ≥2, produced the highest estimates (28% of those aged 60–69 and 46% of those aged ≥70 in Hispanic Americans and 49% and 72%, respectively, in the Barbados Eye Study). The prevalence of PSC was broadly similar to other studies in India and Asia, although the prevalence rates for the Shih-Pai12
and Beijing studies22
seemed to be slightly lower. In contrast, the prevalence rates of PSC opacities in Western populations are consistently lower with rates of around 5% to 8% reported for those 60 to 69 years old and around 7% to 14% for those ≥70 years old.16–21
Differences between populations in cataract prevalence and especially in the cataract subtypes may reflect environmental or genetic factors. The evidence that ultraviolet radiation is a risk factor for cataract is strongest for cortical cataracts.23
Exposure to ultraviolet radiation depends on latitude, occupation, and behavioral factors, but it seems unlikely that the lower prevalence of cortical cataract in India, compared with Hispanic and African Caribbean populations, could be due to lower exposures to ultraviolet radiation. Genetic factors have also been most strongly identified for cortical cataract,24
although few genes have been identified. Recently variants in the EPHA2
gene have been found to be associated with cortical cataracts, and to a lesser extent with nuclear cataracts.25,26
The studies, were conducted in individuals of European ancestry and, to date, information is lacking on the association and allele prevalence in groups of other ancestral origins.
We found a higher prevalence of cataract in women compared with men. This was observed for all types of cataract, both unoperated cataracts, and for all operated cataracts. Women were more likely to have undergone cataract surgery compared with men. Many studies worldwide have reported a higher prevalence of cataract among women,3,5,27
although in some studies this varied by the type of opacity, being found only for cortical opacities,4,6,19,22
or cortical and nuclear,21
or nuclear only,20
nuclear and PSC,11
or all 3 types (cortical, nuclear, and PSC).12
Studies examining the incidence of cataract have also reported higher rates among women than men.13,14
Lower cataract surgical coverage by women has been documented in many populations27
and is a major priority focus for organizations such as Vision 2020 (available: http://www.v2020.org/
; accessed January 15, 2010). Our results suggest that the higher rates of cataract in women in our study are not explained solely by differential access to health care, but may be due to other factors such as higher levels of exposures to risk factors such as biomass cooking fuels or intrinsic differences such as hormonal factors.
We observed some differences between the centers in the prevalence of cataract types. Nuclear cataract was higher in north India (48%) compared with south India (38%). For the other types of cataract and for any unoperated cataract, although the differences in the prevalence were significant, the magnitude of the differences was much smaller. The lower prevalence of nuclear cataract in the south might partially be explained by the higher rate of cataract surgery in the south because overall there was no difference between the centers for all unoperated and operated cataract considered together. Other explanations for differences between north and south in the prevalence of type-specific cataracts include environmental, nutritional, and genetic factors. The INDEYE study has collected data on potential risk factors including diet, tobacco use, biomass fuels, and other lifestyle factors. Future analyses will examine the association of these factors with cataract in north and south India. Stored DNA will also facilitate exploration of genetic differences.