Indian Journal of Ophthalmology

: 2019  |  Volume : 67  |  Issue : 5  |  Page : 583--592

Prevalence of refractive errors, uncorrected refractive error, and presbyopia in adults in India: A systematic review

Sethu Sheeladevi1, Bharani Seelam2, Phanindra B Nukella3, Rishi R Borah4, Rahul Ali4, Lisa Keay2,  
1 Division of Optometry and Visual Sciences, City University of London, London, UK
2 Injury Division, The George Institute for Global Health; UNSW Sydney, Australia
3 VISION 2020: The Right to Sight, India
4 Orbis International, India

Correspondence Address:
Dr. Sethu Sheeladevi
School of Health Sciences, City University of London, London, EC1V OHB


Purpose: The objective of this review is to estimate the prevalence of refractive errors, uncorrected refractive error (URE), and uncorrected presbyopia in adults aged ≥30 years in India. Methods: The Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines were followed. A detailed literature search was performed to include all studies published from India from the year 1990 using the Cochrane Library, Medline, and Embase. Refractive error was defined by >0.50 D ametropia. URE was defined by presenting visual acuity (PVA) worse than 6/18 improving with pinhole or spectacle correction, and uncorrected presbyopia by near vision Results: Fifteen studies were included from South India, one each from Western and Central India, and one study covered 15 states across India. The prevalence of RE of at least 0.50 D of spherical equivalent ametropia was 53.1% [(95% confidence interval (CI): 37.2–68.5), of which myopia and hyperopia was 27.7% and 22.9%, respectively. The prevalence of URE was 10.2% (95% CI: 6.9–14.8), but heterogeneity in these estimates was very high. The prevalence of uncorrected presbyopia was 33% (95% CI: 19.1–51.0). Conclusion: This review highlights the magnitude of refractive errors among adults in India. More studies are needed using standard methods in regions where there is a lack of information on UREs. Programs delivering spectacles for adults in India will need to primarily focus on reading glasses to correct presbyopia along with spectacles for hyperopia and myopia.

How to cite this article:
Sheeladevi S, Seelam B, Nukella PB, Borah RR, Ali R, Keay L. Prevalence of refractive errors, uncorrected refractive error, and presbyopia in adults in India: A systematic review.Indian J Ophthalmol 2019;67:583-592

How to cite this URL:
Sheeladevi S, Seelam B, Nukella PB, Borah RR, Ali R, Keay L. Prevalence of refractive errors, uncorrected refractive error, and presbyopia in adults in India: A systematic review. Indian J Ophthalmol [serial online] 2019 [cited 2023 Jun 8 ];67:583-592
Available from:

Full Text

Refractive error (RE) is one of the most common ocular conditions affecting all age groups and a priority under the VISION 2020 initiative. Most REs can be easily corrected at the primary care level with spectacles. Despite the availability of a cost-effective intervention to address this problem, uncorrected refractive error (URE) is a major public health challenge. Worldwide, URE is the leading cause of vision impairment and the second leading cause of blindness in developing countries, including India.[1],[2] Visual impairment and blindness caused by URE in adults can have severe impact on social and economic well-being, including limiting the educational and employment opportunities of economically active persons.[3] Globally, economic loss due to lost productivity caused by URE was estimated around $269 billion[4] and due to uncorrected presbyopia was US$11.023 billion.[5]

There has been an increase in the number of population-based studies from India in the last decade on various eye conditions, and there are many reports published with the aim of determining the prevalence of REs among various age groups across different populations in India. However, a variety of methodologies and different definitions have been used to make these estimates. The reported prevalence varies considerably between studies due to differences in the study populations, methodologies, and definitions of conditions studied. Of all the variations, the definitions used in the studies particularly influence the estimated prevalence rates. Population-based pooled estimates provide evidence for policy decisions, hence, we performed a systematic review to estimate the pooled prevalence of REs, with a uniform definition in India. The aim of this study is to determine the prevalence of REs among adults aged ≥30 years in India and the need for refractive services through estimates of the prevalence of URE and uncorrected presbyopia.


We followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for this review.

Search strategy

We searched Medline, Embase, CINAHL, and Cochrane library from 1990 to 2018. (The date of last search was September 2018 via OVID and EBSCOHOST). The search was based on medical terms using MeSH for medical subject headline and keywords to search in the title and abstract. Broad search strategy combined terms related to epidemiology (including MeSH search using exp prevalence * and exp epidemiology * and keyword search using the words prevalence, epidemiology, incidence, rates and proportions), terms related to disease (including MeSH search using exp refractive error *, exp myopia*, exp hypermetropia*, exp astigmatism*, exp presbyopia*and keyword search using the term refractive error, myopia, hypermetropia, astigmatism and presbyopia), and terms related to population (including MeSH search using exp India * and keyword search using the words India). We also searched the reference lists of included studies to identify further studies.

Inclusion and exclusion criteria

We searched all studies focused on estimating the prevalence and/or incidence of REs and/or presbyopia among all age groups from any location within India. We defined prevalence as the number of individuals in a population that have RE at a given point in time divided by those at risk. Incidence was defined as how many new cases of RE occur within a defined period of time. We included all incidence and prevalence reports from epidemiological studies. We also reviewed all relevant National, Regional, and International reports published from 1990 onwards. We excluded studies that used only qualitative methods and review papers, as well as studies published only as an abstract or presented in conferences without full subsequent publication. We removed duplicate publications from the same study. In this systematic review, we included data reported on adults aged ≥30 years and the results related to REs in children from this search has been published previously.[6]

Definitions used

RE was defined by spherical equivalent (SE) ametropic with the two major subgroups: myopia as SE worse than −0.50 D and hyperopia as SE worse than +0.50 D. URE was defined as presenting VA <6/18 and improving to ≥6/18 on using a pinhole in either eye or with spectacle correction. Uncorrected presbyopia was defined as binocular presenting near vision Data abstraction and quality assessment

The lead reviewer (SS) conducted the detailed search and identified all relevant studies. Both the lead and second reviewers (SB) assessed the included studies independently based on the abstract and title according to the inclusion criteria and shortlisted the studies for full-text review. A detailed methodological quality assessment was done independently on the full-text of shortlisted studies, using the critical appraisal checklist developed for prevalence studies by Munn et al. 2014.[7] We developed a data extraction form to extract study characteristics such as study design, geographical location, study population, participant demographics (including age and gender), screening tools, definition used, and prevalence data. Any discrepancies between the reviewers at each stage was discussed and resolved by consensus. We attempted quantitative data synthesis using MetaXL in Microsoft office.[8]

Statistical methods

We obtained an overall estimate of prevalence and incidence across included studies after stabilizing the variance of individual studies as we expected a high degree of heterogeneity among the included studies in the design and outcome measures. This was done with the use of Freeman–Tukey double arcsine transformation[8] using MetaXL software. We assessed the heterogeneity using the χ2 test on Cochrane's Q statistic and quantified by calculating the I2.[9] The I2 statistic describes the percentage of total variation between studies that is due to heterogeneity rather than chance. A value of 0% indicates no heterogeneity and larger values indicates increasing levels of heterogeneity. Further, we also examined the overlap of confidence intervals in the forest plot and assessed the heterogeneity.

As there are various metrics used to describe refractive errors and spectacle coverage for both RE and presbyopia in the included studies, we calculated the overall prevalence under three categories: (1) prevalence of REs with subcategories of myopia and hyperopia, (2) prevalence of URE based on presenting visual acuity (PVA) improving with pinhole and/or after best correction, and (3) prevalence of uncorrected presbyopia. The prevalence of REs and spectacle coverage for distance RE and presbyopia are important for planning refractive services. Where definitions were different, data were summarized separately and not included in pooled estimates.


Out of a total of 169 potentially relevant titles/abstracts, 43 full-text articles based on population-based data were found eligible. The review strategy is summarized in [Figure 1], and details of the 25 excluded studies with reasons are presented as [Table 1].{Figure 1}{Table 1}

Study characteristics and methodological quality

Eighteen studies that reported prevalence of REs were included in the final analysis. Two studies[10],[11] presented data on both REs and presbyopia, and data from these studies were extracted under the respective categories for the analysis. In the final analysis, we included 14 studies which reported data on distance RE and URE,[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23] and 6 studies reporting data on presbyopia.[10],[11],[24],[25],[26],[27] The characteristics of these studies are presented as [Table 2], [Table 3], [Table 4].{Table 2}{Table 3}{Table 4}

All eighteen studies included in the final analysis were population-based studies using various methodologies in cross-sectional studies: Rapid Assessment of Avoidable Blindness (RAAB), Rapid Assessment of Visual Impairment (RAVI), and Rapid Assessment of Refractive Errors (RARE). [Figure 2] summarizes the results of the detailed assessment for the 18 included studies using the checklist.{Figure 2}

Fifteen studies were included from South India including nine from Andhra Pradesh and six from Tamil Nadu, one each from Western and Central India (Gujarat and Maharashtra), and one study covered 15 states across India. There was no information reported on the gender characteristics of the study participants in the two studies,[21],[28] and only two studies reported the prevalence of REs by gender.[12],[19] No data were available on the incidence of REs in India. The heterogeneity of the estimates from the included studies under the three categories was very high [Figure 3],[Figure 4],[Figure 5].{Figure 3}{Figure 4}{Figure 5}

There were four population-based studies that estimated the prevalence of RE in adults. The prevalence of RE of at least 0.50 D is 53.1% (95% CI: 37.2–68.5), of which the prevalence of myopia is 27.7% (95% CI: 18.3–39.6) and hyperopia is 22.9% (95% CI: 13.9–35.3). This was the average of estimates from four population-based studies and the range in these estimates was large (37–68%).

The prevalence of URE based on best correction or improving with pinhole is estimated at 10.2% (95% CI: 6.9–14.8). This was based on the synthesis of nine studies with equivalent definitions for URE. The pooled estimate was highly heterogeneous, and prevalence was as high as 26% in Tamil Nadu[21] in the late 1990s and 21% in Gujarat[15] in 2007. Further, we grouped the studies and analyzed the prevalence of URE using cross-sectional, RAAB, and RAVI methodology, and the pooled prevalence was 10.2 (95% CI: 4.2–22.8), 10.8 (95% CI: 8.3–14.1), and 9.6 (95% CI: 5.5–16.2), respectively.

The prevalence of uncorrected presbyopia among adults in India is estimated at 33% but the confidence limits for this estimate were very wide (95% CI: 19.1–51.0). Only two studies from Andhra Pradesh[25],[26] reported data on uncorrected presbyopia by gender and overall pooled prevalence in males and females were 50% (95% CI: 17.4–82.6) and 55% (95% CI: 24.7–82.3), respectively.

There was not enough data available to calculate the prevalence by urban vs rural and by gender, which is essential for planning strategies to address the problem in these groups.


This is the first systematic review of all population-based studies on the prevalence of REs and the need for refractive correction in adults in India. REs are relatively common in India and the prevalence of half a dioptre or more of myopia or hyperopia in adults is 53.1%. Overall, 10.2% of adults in India were estimated to have URE. Nearly one-third of adults in the country have uncorrected presbyopia. As the overall magnitude of the problem is huge, it becomes imperative to prioritize refractive services and spectacle delivery programs for policy action. Of the three estimates provided in this review, the prevalence of RE as a cause of visual impairment and blindness should be the top priority as it has a profound impact on the productivity and quality of life of the individuals. Maintaining clear near vision is also important and can be easily corrected with reading glasses.

RE causing visual impairment and blindness in our review (10.2%) is much higher than the global estimates of 5.7% (95% CI: 5.0–6.9%) in population above 50 years of age.[29] Other than the age differences in these two reports, the majority of participants in this review are from rural areas of India. The relative lack of refractive services in rural areas may be a cause for the higher reported prevalence, indicating a potential area to focus on when planning any intervention. Another probable reason for the higher prevalence of RE could be cataract-induced index myopia in the rural population.[30]

Most systematic reviews aim to arrive at a single estimate for understanding the magnitude of the given problem. However, as there are different solutions for various refractive problems, findings have been presented under three categories, which are needed to plan refractive services and spectacle delivery programs.

Previous reports[31],[32] suggests that subjective refraction is the better way to assess the REs compared to the method of estimating REs based on vision improvement with pin hole. Consistent with earlier findings, we found that the prevalence of URE with pinhole assessment is lesser than URE diagnosed through refraction. The prevalence of visual impairment and blindness which is resolved after refractive correction in India is 10.2% and prevalence of RE based on vision improvement with pinhole is 9.4%. However, considering the logistics, time, and resource requirements for population-based assessments, pinhole assessment with the VA cut-point of <6/18 is more convenient to use in rapid assessment surveys and community-based vision screenings.[33] One study by Marmamula and colleagues published in 2009 used the cut-point of 6/12 rather than the WHO cut-point of 6/18.[10] This study was not included in the pooled estimates as the majority of studies used 6/18 as the cut-point, which is the WHO definition. However, it could be argued that 6/12 is a more appropriate cut-point for estimating visual impairment.[34]

Heterogeneity of the included studies was quite high, almost 100%, and due to this, low confidence is given to the pooled estimates. The reasons for these differences are not apparent. Heterogeneity can be due to differences in the methodology adopted or definitions used in the included studies. However, the quality assessment on the methodology adopted in the included studies were rated very high. Moreover, very close confidence intervals reported in the included studies suggest a low variance in the sample studied. It is also possible that prevalence of RE, URE, and uncorrected presbyopia are inherently variable due to differences in socioeconomic status, urban or rural geographical location, and time period of assessment. The prevalence and types of REs is subject to temporal trends. Further, economic factors can determine spectacle coverage for both RE and presbyopia. Considering the high quality of included studies, the pooled estimates were calculated for the three categories; however, more population-based data across India are needed to further characterize the determinants of RE and spectacle coverage.

This review is dominated by studies from the southern parts of India, 15 out of 18 included studies. Considering the diversity in the demographics and the healthcare infrastructure in the country,[35] it is recommended to have prevalence data, using standard methodology from each region separately for a reliable estimate. We found no evidence on the incidence of refractive errors from India in adults. Because REs such as myopia typically emerge in childhood, most incidence studies are conducted among children. Moreover, there is very little information on the prevalence of RE in many regions. More studies are required using standard methodology in regions from where data is inadequate or not available.

Correcting REs in adults is less challenging compared to other vision impairing eye problems. Most RE correction services are offered as part of primary eye care service delivery and there are many established models for providing RE correction services within affordable prices. Given the variation in availability and uptake for RE correction across India, the high prevalence suggests that further exploration on availability of, access to, and utilization of services is needed. Individual, cultural, and social barriers that possibly prevent the utilization of existing services also require further examination.

Even though most of the included studies collected information on gender, only two studies reported data on REs by gender. Gender-based estimates are very important to determine the level of need and ensure equity in access to services. Previous studies have reported that REs and other eye conditions are higher among females compared to males.[36] Moreover, wearing spectacles causes inconvenience in certain occupations such as agricultural workers and other jobs, in which leaning forward often is a job requirement. The majority of the participants included in the studies in this review are from rural areas and agricultural activities are the predominant occupation in these communities, hence, these considerations are important in this setting.

We did not consider astigmatism in estimating the overall prevalence of REs in this review. If we include astigmatism, it would further increase the reported estimate of prevalence of refractive errors among adults in India.

Lack of uniform methodology and definitions adopted in the studies reviewed makes it challenging to arrive at a single estimate, which is ideal for policy decisions, however some estimates can be made.


This review concludes that REs among the adult population is a huge public health problem which has an economic impact of lost productivity due to URE and uncorrected presbyopia in India. This potential huge loss to the national economy can be prevented if the government invests in providing RE services at a larger scale through public–private partnerships involving all stakeholders to address this problem.[59]

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


1Dandona R, Dandona L. Refractive error blindness. Bull World Health Organ 2001;79:237-43.
2Resnikoff S, Pascolini D, Mariotti SP, Pokharel GP. Global magnitude of visual impairment caused by uncorrected refractive errors in 2004. Bull World Health Organ 2008;86:63-70.
3Naidoo KS, Jaggernath J. Uncorrected refractive errors. Indian J Ophthalmol 2012;60:432-7.
4Smith TS, Frick KD, Holden BA, Fricke TR, Naidoo KS. Potential lost productivity resulting from the global burden of uncorrected refractive error. Bull World Health Organ 2009;87:431-7.
5Frick KD, Joy SM, Wilson DA, Naidoo KS, Holden BA. The global burden of potential productivity loss from uncorrected presbyopia. Ophthalmology 2015;122:1706-10.
6Sheeladevi S, Seelam B, Nukella P, Modi A, Ali R, Keay L. Prevalence of refractive errors in children in India-A systematic review. Clin Exp Optom 2018;101:495-503.
7Munn Z, Moola S, Riitano D, Lisy K. The development of a critical appraisal tool for use in systematic reviews addressing questions of prevalence. Int J Health Policy Manag 2014;3:123-8.
8Barendregt JJ, Doi SA, Lee YY, Norman RE, Vos T. Meta-analysis of prevalence. J Epidemiol Community Health 2013;67:974-8.
9Higgins JP, Thompson SG. Quantifying heterogeneity in a meta-analysis. Stat Med 2002;21:1539-58.
10Marmamula S, Keeffe JE, Rao GN. Uncorrected refractive errors, presbyopia and spectacle coverage: Results from a rapid assessment of refractive error survey. Ophthalmic Epidemiol 2009;16:269-74.
11Marmamula S, Madala SR, Rao GN. Prevalence of uncorrected refractive errors, presbyopia and spectacle coverage in marine fishing communities in South India: Rapid assessment of visual impairment (RAVI) project. Ophthalmic Physiol Opt 2012;32:149-55.
12Dandona R, Dandona L, Srinivas M, Giridhar P, McCarty CA, Rao GN. Population-based assessment of refractive error in India: The Andhra Pradesh eye disease study. Clin Exp Ophthalmol 2002;30:84-93.
13Marmamula S, Narsaiah S, Shekhar K, Khanna RC. Visual impairment among weaving communities in Prakasam district in South India. PLoS One 2013;8:e55924.
14Marmamula S, Narsaiah S, Shekhar K, Khanna RC, Rao GN. Visual impairment in the South Indian state of Andhra Pradesh: Andhra Pradesh-Rapid assessment of visual impairment (AP-RAVI) project. PLoS One 2013;8:e70120.
15Murthy GVS, Vashist P, John N, Pokharel G, Ellwein LB. Prevelence and causes of visual impairment and blindness in older adults in an area of India with a high cataract surgical rate. Ophthalmic Epidemiol 2010;17:185-95.
16Nangia V, Jonas JB, Sinha A, Matin A, Kulkarni M. Refractive error in Central India. The Central India eye and medical study. Ophthalmology 2010;117:693-9.
17Neena J, Rachel J, Praveen V, Murthy GVS. Rapid assessment of avoidable blindness in India. PLoS One 2008;3:e2867.
18Nirmalan PK, Thulasiraj RD, Maneksha V, Rahmathullah R, Ramakrishnan R, Padmavathi A, et al. A population based eye survey of older adults in Tirunelveli district of south India: Blindness, cataract surgery, and visual outcomes. Br J Ophthalmol 2002;86:505-12.
19Prema R, George R, Sathyamangalam Ve R, Hemamalini A, Baskaran M, Kumaramanickavel G, et al. Comparison of refractive errors and factors associated with spectacle use in a rural and urban South Indian population. Indian J Ophthalmol 2008;56:139-44.
20Singh N, Eeda SS, Gudapati BK, Reddy S, Kanade P, Shantha GPS, et al. Prevalence and causes of blindness and visual impairment and their associated risk factors, in three tribal areas of Andhra Pradesh, India. PloS One 2014;9:e100644.
21Thulasiraj RD, Nirmalan PK, Ramakrishnan R, Krishnadas R, Manimekalai TK, Baburajan NP, et al. Blindness and vision impairment in a rural south Indian population: The Aravind comprehensive eye survey. Ophthalmology 2003;110:1491-8.
22Thulasiraj RD, Rahamathulla R, Saraswati A, Selvaraj S, Ellwein LB. The Sivaganga eye survey: I. Blindness and cataract surgery. Ophthalmic Epidemiol 2002;9:299-312.
23Joseph S, Krishnan T, Ravindran RD, Maraini G, Camparini M, Chakravarthy U, et al. Prevalence and risk factors for myopia and other refractive errors in an adult population in southern India. Ophthalmic Physiol Opt 2018;38:346-58.
24He M, Abdou A, Naidoo KS, Sapkota YD, Thulasiraj RD, Varma R, et al. Prevalence and correction of near vision impairment at seven sites in China, India, Nepal, Niger, South Africa, and the United States. Am J Ophthalmol 2012;154:107-16.e1.
25Marmamula S, Narsaiah S, Shekhar K, Khanna RC. Presbyopia, spectacles use and spectacle correction coverage for near vision among cloth weaving communities in Prakasam district in South India. Ophthalmic Physiol Opt 2013;33:597-603.
26Nirmalan PK, Krishnaiah S, Shamanna BR, Rao GN, Thomas R. A population-based assessment of presbyopia in the state of Andhra Pradesh, south India: The Andhra Pradesh eye disease study. Invest Ophthalmol Vis Sci 2006;47:2324-8.
27Marmamula S, Khanna RC, Kunuku E, Rao GN. Near visual impairment and spectacle coverage in Telangana, India. Clin Exp Ophthalmol 2017;45:568-74.
28Murthy GVS, Gupta SK, Ellwein LB, Muñoz SR, Pokharel GP, Sanga L, et al. Refractive error in children in an urban population in New Delhi. Invest Ophthalmol Vis Sci 2002;43:623-31.
29Naidoo KS, Leasher J, Bourne RR, Flaxman SR, Jonas JB, Keeffe J, et al. Global vision impairment and blindness due to uncorrected refractive error, 1990-2010. Optom Vis Sci 2016;93:227-34.
30Pesudovs K, Elliott DB. Refractive error changes in cortical, nuclear, and posterior subcapsular cataracts. Br J Ophthalmol 2003;87:964-7.
31Attebo K, Mitchell P, Smith W. Visual acuity and the causes of visual loss in Australia. The Blue mountains eye study. Ophthalmology 1996;103:357-64.
32Loewenstein JI, Palmberg PF, Connett JE, Wentworth DN. Effectiveness of a pinhole method for visual acuity screening. Arch Ophthalmol 1985;103:222-3.
33Marmamula S, Keeffe JE, Narsaiah S, Khanna RC, Rao GN. Population-based assessment of sensitivity and specificity of a pinhole for detection of significant refractive errors in the community. Clin Exp Optom 2014;97:523-7.
34Congdon N, O'Colmain B, Klaver CC, Klein R, Munoz B, Friedman DS, et al. Causes and prevalence of visual impairment among adults in the United States. Arch Ophthalmol 2004;122:477-85.
35Purohit BC. Inter-state disparities in health care and financial burden on the poor in India. J Health Soc Policy 2004;18:37-60.
36Clayton JA, Davis AF. Sex/gender disparities and women's eye health. Current Eye Res 2015;40:102-9.
37He M, Abdou A, Ellwein LB, Naidoo KS, Sapkota YD, Thulasiraj RD, et al. Age-related prevalence and met need for correctable and uncorrectable near vision impairment in a multi-country study. Ophthalmology 2014;121:417-22.
38Dandona L, Dandona R, Srinivas M, Giridhar P, Vilas K, Prasad MN, et al. Blindness in the Indian state of Andhra Pradesh. Invest Ophthalmol Vis Sci 2001;42:908-16.
39Dandona L, Dandona R, Naduvilath TJ, McCarty CA, Srinivas M, Mandal P, et al. Burden of moderate visual impairment in an urban population in southern India. Ophthalmology 1999;106:497-504.
40Dandona R, Dandona L, Srinivas M, Giridhar P, Prasad MN, Vilas K, et al. Moderate visual impairment in India: The Andhra Pradesh eye disease study. Br J Ophthalmol 2002;86:373-7.
41Marmamula S, Keeffe JE, Narsaiah S, Khanna RC, Rao GN. Changing trends in the prevalence of visual impairment, uncorrected refractive errors and use of spectacles in Mahbubnagar district in South India. Indian J Ophthalmol 2013;61:755-8.
42Sharma M, Singh A. Pattern of treatment compliance among eye patients in a North Indian town. Ann Ital Chir 2008;79:341-6.
43Marmamula S, Keeffe JE, Raman U, Rao GN. Population-based cross-sectional study of barriers to utilisation of refraction services in South India: Rapid assessment of refractive errors (RARE) study. BMJ Open 2011;1:e000172.
44Dandona R, Dandona L, Kovai V, Giridhar P, Prasad MN, Srinivas M. Population-based study of spectacles use in southern India. Indian J Ophthalmol 2002;50:145-55.
45Vijaya L, George R, Asokan R, Velumuri L, Ramesh SV. Prevalence and causes of low vision and blindness in an urban population: The Chennai Glaucoma study. Indian J Ophthalmol 2014;62:477-81.
46Krishnaiah S, Srinivas M, Khanna RC, Rao GN. Prevalence and risk factors for refractive errors in the South Indian adult population: The Andhra Pradesh eye disease study. Clinical Ophthalmol 2009;3:17-27.
47Raju P, Ramesh SV, Arvind H, George R, Baskaran M, Paul PG, et al. Prevalence of refractive errors in a rural South Indian population. Invest Ophthalmol Vis Sci 2004;45:4268-72.
48Marmamula S, Madala SR, Rao GN. Rapid assessment of visual impairment (RAVI) in marine fishing communities in South India--study protocol and main findings. BMC Ophthalmol 2011;11:26.
49Dandona R, Dandona L, Naduvilath TJ, Srinivas M, McCarty CA, Rao GN. Refractive errors in an urban population in southern India: The Andhra Pradesh eye disease study. Invest Ophthalmol Vis Sci 1999;40:2810-8.
50Marmamula S, Khanna RC, Rao GN. Unilateral visual impairment in rural south India-Andhra Pradesh eye disease study (APEDS). Int J Ophthalmol 2016;9:763-7.
51Shrote VK, Thakr SS, Lanjewar AG, Brahmapurkar KP, Khakse GM. Ocular morbid conditions in the rural area of central India. Int J Collab Res Inter Med Public Health 2012;4:1692-702.
52Perkins ES. Cataract: Refractive error, diabetes, and morphology. Br J Ophthalmol 1984;68:293-7.
53Singh MC, Murthy GV, Venkatraman R, Nayar S. Epidemiological aspects of visual impairment above 50 years in a rural area. J Indian Med Assoc 1994;92:361-3, 365.
54Wong TY, Loon SC, Saw SM. The epidemiology of age related eye diseases in Asia. Br J Ophthalmol 2006;90:506-11.
55Thakur R, Banerjee A, Nikumb V. Health problems among the elderly: A cross-sectional study. Ann Med Health Sci Res 2013;3:19-25.
56Bandrakalli P, Ganekal S, Jhanji V, Liang YB, Dorairaj S. Prevalence and causes of monocular childhood blindness in a rural population in southern India. J Pediatric Ophthalmol Strabismus 2012;49:303-7.
57Singh MM, Murthy GV, Venkatraman R, Rao SP, Nayar S. A study of ocular morbidity among elderly population in a rural area of central India. Indian J Ophthalmol 1997;45:61-5.
58Dandona R, Dandona L, Srinivas M, Sahare P, Narsaiah S, Munoz SR, et al. Refractive error in children in a rural population in India. Invest Ophthalmol Vis Sci 2002;43:615-22.
59Nirmalan PK, Vijayalakshmi P, Sheeladevi S, Kothari MB, Sundaresan K, Rahmathullah L. The Kariapatti pediatric eye evaluation project: Baseline ophthalmic data of children aged 15 years or younger in Southern India. Am J Ophthalmol 2003;136:703-9.