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Abstract
Background The magnitude of blindness is unevenly distributed worldwide. This systematic review aimed to study gender differences in the prevalence of blindness, cataract blindness and cataract surgical coverage in India among persons aged 50 years and above.
Methods Literature search was carried out in the Medline, Web of Science, Google Scholar, EMBASE and Trip databases. Data were abstracted and risk of bias was assessed for the selected full-text articles. Pooled prevalence, ORs and risk differences were synthesised by meta-analyses.
Results 22 studies were included in the systematic review. The pooled prevalence of blindness obtained for men was 4.17% and that for women was 5.68%. Women had 35% higher odds of being blind (OR 1.35, 95% CI 1.08 to 1.62) and 69% higher odds of being cataract blind (OR 1.69, 95% CI 1.44 to 1.95). Women had a 27% lower odds of getting cataract surgery (OR 0.73, 95% CI 0.45 to 1.01). In women, around 35% of the prevalence of blindness and 33% of the prevalence of cataract blindness are attributable to their gender.
Conclusion Marked gender differences in blindness, cataract blindness and cataract surgical coverage were seen in India, with the odds being unfavourable for women. Interventions implemented for reduction of blindness, including cataract blindness, need to consider these gender differentials in the Indian context. Further research is needed to ascertain the reasons for these differences and devise interventions to reduce these differences in order to tackle the magnitude of avoidable blindness in India.
- public health
- epidemiology
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Introduction
From the current figure of 36 million blind persons globally, it is estimated that over 114 million will be blind by 2050 if effective preventive measures are not implemented.1 Low-income and middle-income countries (LMICs) bear the greater proportion of this burden. Moreover, 81% of people who are blind or have moderate or severe vision impairment are aged more than 50 years.1
Previous studies have suggested that this disease prevalence is not gender-equal.2 It is imperative to quantify the gender difference in the magnitude of blindness and to investigate causes for its existence in order to guide future policies.
It has been demonstrated that the overall magnitude of disease morbidity is higher for women in India.3 It is imperative to bridge this difference and address its determinants in all spheres of health if the aim of universal health coverage is to be achieved in the near future.
Public health policy in India has aimed to give due importance to blindness prevention and treatment. Cataract is the most common cause of blindness in India.4 It is postulated that the gender difference in the magnitude of blindness in India may be due to differences in access and uptake of cataract surgeries.
To quantify the gender difference in the magnitude of this disease, and to assess a possible cause thereof, we undertook a systematic review and meta-analysis to investigate gender differences in the prevalence of blindness, cataract blindness and cataract surgical coverage (CSC).
Methodology
Methods
The Preferred Reporting Items for Systematic Reviews and Meta-analyses and the Meta-analysis Of Observational Studies in Epidemiology statements were adhered to in the present report.5 6
Inclusion criteria
The following inclusion criteria were used for eligibility:
Population-based studies/surveys.
Study conducted in India.
Published between year 1990 and 2018.
Gender-wise prevalence of blindness/cataract blindness/CSC estimates reported for persons aged 50 years or more.
Editorials, letters, news, reviews, expert opinions, case report and studies without original data were excluded.
If data were duplicated or shared in more than one study, the study published later or the more comprehensive report was included in the analysis.
Studies on specific disease groups (eg, patients with leprosy or diabetes) and those reporting prevalence of blindness only due to specific causes were also excluded.
Data sources and searches
Medline, Web of Science, EMBASE, Google Scholar and Turning Research Into Practice (TRIP)
Selection of studies
Titles and abstracts were screened in duplicate by two reviewers independently (MP and SM), and full texts of articles that either reviewer considered potentially eligible were obtained. The eligibility of articles was determined from the full texts. Similarly, data were abstracted by two reviewers independently and risk of bias was assessed. For all phases of the project, disagreement was resolved by discussion and, as necessary, in consultation with a third reviewer (SKG).
The systematic review included studies calculating blindness prevalence from WHO definition, that is, visual acuity of less than 3/60 in better eye and with available correction, as well as the old definition under the Indian National Programme for Control of Blindness, that is, presenting visual acuity <6/60 in better eye. For the purpose of meta-analysis, the WHO definition of blindness was used. Blindness resulting from cataract was referred to as cataract blindness.
The CSC indicates the number of people who have received cataract surgery divided by the number that ‘require’ surgery. Thus, for instance, CSC for men is defined as the number of men operated for cataract/(number of men operated for cataract + number of men blind due to cataract). This is similarly defined for women.
Data extraction
The following data were extracted from each study: the first author’s last name, publication year, region where the study was conducted, study period, rural or urban area, sample size, mean age of study subjects, proportion of women and response rate.
Risk of bias assessment
Risk of bias was assessed using the Critical Appraisal Skills Programme checklist.7
Data synthesis and statistical analysis
Pooled prevalence estimates were calculated using random effects on Stata V.14 software for WHO definition of blindness obtained from rapid surveys. Heterogeneity was estimated using I2 statistics.
Results
Study selection
Figure 1 presents the process of identifying eligible studies and citations identified through searches in electronic databases. Based on title and abstract screening, 33 full texts were assessed, of which 22 publications were included in the systematic review, which includes published studies (17) and reports (5).8–24 Two of the published studies reported two estimates which were for two different periods,16 17 and five published reports were also included in the review.25–29 The five reports are included at the end of the online supplementary tables 1 and 2. The number of studies included in the meta-analysis of WHO definition of blindness from rapid surveys was 10 for the outcome ‘blindness’, 5 for ‘cataract blindness’ and 4 for ‘cataract surgical coverage’. Consensus on inclusion of studies on full-text screening was achieved by two authors through discussion.
Supplemental material
PRISMA flow chart for selection of studies. PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-analyses. TRIP, Turning Research Into Practice
Study characteristics and estimates reported
Online supplementary tables 1 and 2 depict the study characteristics and reported blindness, cataract blindness and CSC estimates for included studies, respectively. Majority of the studies had been conducted in Southern India, and most study areas were rural. The mean age of study participants ranged from 61 to 70 years. The response rate was satisfactory in most of the studies that reported it. The reference category for all ORs in the online supplementary table 1 is men, and all ORs are computed as female to male ratios.
Risk of bias assessment
Online supplementary table 3 depicts the risk of bias in the included studies. All except two studies mentioned a sampling methodology that allows low risk of selection bias. Apart from four studies, all reported a satisfactory response rate ranging from 80.2% to 99.7%. CIs for estimates were mentioned by all published studies except for two. Only one published report mentioned the CI along with the point estimate.
Pooled ORs, risk difference and prevalence of blindness, cataract blindness and CSC in men and women
Figure 2 depicts the strength of association between gender and blindness, cataract blindness and CSC. The odds of blindness and cataract blindness were significantly higher in women compared with men. Women had 35% higher odds of being blind (OR 1.35, 95% CI 1.08 to 1.62) and 69% higher odds of being cataract blind (OR 1.69, 95% CI 1.44 to 1.95). Women had a 27% lower odds of getting cataract surgery (OR 0.73, 95% CI 0.45 to 1.01) (figure 2).
Strength of association between gender and blindness, cataract blindness and cataract surgical coverage. AIIMS, All India Institute of Medical Sciences. RACB, Rapid Assessment of Cataract Blindness. NPCB, National Programme for Control of Blindness.
The pooled risk differences between genders for blindness and cataract blindness were −0.02 (95% CI −0.03 to −0.00) and −0.02 (95% CI −0.03 to −0.00), respectively. The pooled risk difference for CSC was 0.07 (95% CI −0.02 to 0.16) (figure 3).
Risk difference (RD) in the prevalence of blindness, cataract blindness and cataract surgical coverage between men and women. AIIMS, All India Institute of Medical Sciences. RACB, Rapid Assessment of Cataract Blindness. NPCB, National Programme for Control of Blindness.
Online supplementary figures 1, 2, and 3 depict the results of the meta-analysis of proportions using random-effects model.
The pooled prevalence of blindness obtained for men was 4.17% and that for women was 5.68%. There was high level of heterogeneity, with the value of I2 statistics being 99.7%.
The pooled prevalence of cataract blindness obtained for men was 3.92% and that for women was 6.13%. There was high level of heterogeneity, with the value of I2 statistics being 99.7%.
The pooled CSC obtained for men was 59.29% and that for women was 52.34%. There was high level of heterogeneity, with the value of I2 statistics being 99.6%.
There was no obvious asymmetry in the funnel plots; however, the number of studies was not enough to draw a firm conclusion through either funnel plot or Egger’s regression.
Discussion
The present systematic review found that blindness is more common in women than men in India. Moreover, the overall most common cause of blindness, that is, cataract, has resulted in a greater proportion of blindness in women than men in India. Also, CSC was found to be 27% lower in women than men.
Risk difference across genders provides a measure of attributable risk. Pooled risk difference depicts that among women, 2% out of the overall 5.68% prevalence of blindness (ie, 35% of overall blindness prevalence) is attributable to their gender. Similarly, around 33% of the overall prevalence of cataract blindness in women is attributable to their gender. CSC could be improved by 13.4% in women if the gender gap in coverage is eliminated.
There could be a number of reasons for the gender differences in the prevalence of blindness. First, the gender difference in these unadjusted estimates could be a result of greater longevity. Women, having a longer life expectancy, have higher age-related morbidities, one of them being the diseases associated with blindness, for example, age-related macular degeneration and cataract.30
Increased susceptibility to conditions that result in blindness can be postulated as another cause for this discrepancy in burden.30 This is also supported by our study findings, where women had a 69% higher odds of being cataract blind. Previous studies have demonstrated a greater susceptibility to cataract in women.31 Also, the pooled prevalence of cataract among women was higher than the pooled prevalence of blindness. This was probably due to available studies that reported cataract blindness but not total blindness.
However, biological predisposition to blindness and its causes can only explain a small proportion of the gender difference, and is unlikely to account for the large overall difference.
CSC serves a meaningful measure of access to cataract surgical services. The present study demonstrated a lower CSC in women, which could be viewed as the third cause of the discrepancy in the magnitude of cataract blindness. Previous studies have also demonstrated a lower coverage of cataract surgical rate in women in India.32 33 Meta-analyses on CSC have demonstrated a gender difference in the utilisation of cataract surgical programmes in LMICs.34
The reasons for the gender gap in the utilisation of cataract surgical services could be manifold, since this is governed by gender-defined social roles. The cost of availing surgery for cataract may be prohibitive, since this incorporates the cost of transport, loss of work of the patient and their attendant, and the cost of stay for the attendant at the hospital, among other things. Women in India have, traditionally, low disposable income and less control over the finances of the household, thus precluding their ability to spend for cataract surgery.35
Moreover, cataract surgery may require travelling outside the village they live in, something that they are less likely to do. The perceived ‘value’ of cataract surgery differs across genders.36 Finally, community education about cataract surgery may not have been undertaken efficiently or widely, and lack of awareness may be responsible for low access to these services, as has been supported by previous studies.37 38
The study by Ramke et al 39, which assessed the effect of three social determinants, including gender, on the prevalence of cataract blindness and CSC using national survey data from Pakistan and Nigeria, found the overall prevalence of cataract blindness to be higher in women. CSC was found lower in women in both countries. It was also observed that women who are illiterate and residents of rural area have a higher prevalence of cataract blindness and lower CSC.
There are several limitations to this systematic review. The pooled effect is synthesised from a limited number of studies, that is, only those that reported figures that could be used for the meta-analysis. There is high level of heterogeneity, which could not be explained but can be hypothesised to result from different methods of assessment and varied time periods.
These findings imply that women do not receive cataract surgery at the same rate as men do, and closing this gender gap may be a much needed step towards reducing the prevalence of cataract blindness. Cataract surgical programmes need to take cognisance of the fact that the utilisation of their services is not uniform across genders37 38 40; thus, consideration of gender differences is imperative when evaluating programme implementation. Public health experts and community ophthalmology practitioners must consider targeting women specifically for efforts to curb blindness and evaluate local barriers to availing services. Further implementation research in this area will be needed to ascertain barriers for women in seeking eye care services and how best health system can address these barriers to reduce gender inequity prevailing in the magnitude of blindness in India.
References
Footnotes
MP and SM contributed equally.
Contributors SM, MP and MK had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: SM, PV and SKG. Acquisition, analysis or interpretation of data: SM, MP, MK and SKG. Drafting of the manuscript: MP and SM. Critical revision of the manuscript for important intellectual content: all authors. Statistical analysis: MK, MP and SM. Study supervision: PV and SKG.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement All data relevant to the study are included in the article or uploaded as online supplementary information.
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