|COMMUNITY EYE CARE
|Year : 2014 | Volume
| Issue : 2 | Page : 240-245
Prevalence, causes of blindness, visual impairment and cataract surgical services in Sindhudurg district on the western coastal strip of India
Shailbala Patil1, Parikshit Gogate2, Siddharth Vora1, Sachin Ainapure1, Ramkrishna N Hingane1, Anil N Kulkarni3, BR Shammanna4
1 Lions NAB Eye Hospital, Miraj, Maharashtra, India
2 Lions NAB Eye Hospital, Miraj; Dr. Gogate's Eye Clinic, Pune, Maharashtra, India
3 Lions NAB Eye Hospital; Kulkarni Eye Hospital, Miraj, Sangli; Department of Ophthalmology, Bharti Vidyapeeth Medical College, Pune, Maharashtra, India
4 PRASHA Consultants Pvt. Ltd.; Indian Institute of Public Health, South Asia Centre for Disability, Hyderabad, Andhra Pradesh, India
|Date of Submission||31-Dec-2011|
|Date of Acceptance||11-Feb-2013|
|Date of Web Publication||11-Mar-2014|
Dr. Gogate's Eye Clinic, K-102, Tadiwala Road, Pune 411001, Maharashtra
Source of Support: Lions NAB Eye Hospital and Volkart Foundation., Conflict of Interest: None
Background : Konkan coast of India is geographically distinct and its pattern of blindness has never been mapped. Aim : To study the prevalence and causes of blindness and cataract surgical services in Sindhudurg district of West Coast. Subjects : Individual aged > 50 years. Materials and Methods: Rapid assessment of avoidable blindness used to map blindness pattern in the district. Statistical analysis: SPSS version 19. Results: Amongst those examined 1415 (51.7%) had visual acuity (VA) >20/60, 924 (33.8%, confidence interval (C.I) 30.5%-36.8%) had VA 20/200-<20/60(visual impairment), 266 (9.7%, C.I. 6.1%-13.3%) had VA < 20/200-20/400 (severe visual impairment) and 132 (4.8%, C. I. 1.1%-8.5%) had VA < 20/400 (blindness by WHO standards). There was no significant gender difference in prevalence of blindness, but blindness and visual impairment was more in older and rural residing individuals. Amongst those with presenting vision < 20/200 in better eye, 309 (82.4%) had cataract, 36 (9.7%) had corneal scars, 13 (3.5%) had diabetic retinopathyand 3 (0.8%) had glaucoma. Cataract surgical coverage for the district was only 30.5%; 32% for males and 28.4% for females. Unable to afford, lack of knowledge and lack of access to services were the commonest barriers responsible for cataract patients not seeking care. Amongst those who had undergone cataract surgery, only 50% had visual acuity ≥ 20/60.46.9% of the population had spectacles for near, but only 53.3% of the population had presenting near vision < N10. Conclusion : Cataract, refractive errors and diabetes were significant causes of visual impairment and blindness.
Keywords: Cataract surgery, near vision, prevalence of blindness, visual outcome
|How to cite this article:|
Patil S, Gogate P, Vora S, Ainapure S, Hingane RN, Kulkarni AN, Shammanna B R. Prevalence, causes of blindness, visual impairment and cataract surgical services in Sindhudurg district on the western coastal strip of India. Indian J Ophthalmol 2014;62:240-5
|How to cite this URL:|
Patil S, Gogate P, Vora S, Ainapure S, Hingane RN, Kulkarni AN, Shammanna B R. Prevalence, causes of blindness, visual impairment and cataract surgical services in Sindhudurg district on the western coastal strip of India. Indian J Ophthalmol [serial online] 2014 [cited 2020 Feb 28];62:240-5. Available from: http://www.ijo.in/text.asp?2014/62/2/240/128633
The past two decades have seen tremendous improvement in eye care services in India. , There have been large surveys looking at the prevalence and causes of blindness across different states in the country.  but they had data from a single district in each state and there are vast differences amongst the populace and services amongst the large states like Maharashtra and within districts as well. There is a need for disaggregated data at the district level for planning. Sindhudurg, nestled in the south Konkan region, the western coastal strip, has long been a neglected backwater.  It is one of the few districts in the country to have a positive gender ratio, partly due to egalitarian ethos and partly due to out-migration of men for economic opportunities.  Bordering Goa in the south, the region has long been economically underdeveloped with few eye care service providers. This survey was planned to help anon-profit organization assess need for eye care services in an area considered underserved but not evidenced and to help set up a secondary eye care centre in order to contribute to the broad objective of 'VISION 2020: The Right to Sight'.
The Rapid Assessment of Avoidable Blindness (RAAB) has been developed as a simple and rapid survey methodology that can provide data on the prevalence and causes of blindness. , RAAB surveys have been conducted in several countries and given useful information for planning for blindness prevention and control. ,,,,, The main aims of this study were to estimate the prevalence and causes of avoidable blindness and visual impairment in people aged 50 and above; to assess cataract surgical coverage; to identify the main barriers to the uptake of cataract surgery, to measure outcome after cataract surgery and collect data on presbyopia services.
| Materials and Methods|| |
The extended RAAB methodology was used to collect data. , As prevalence of blindness is very low in individuals aged < 50 years, only those aged > 50 years were included in the study.  The entire population of the district was enumerated using village and town-wise tables from the district authorities. Permission was sought and obtained from the ethical committee of the institution.
Stratified cluster random sampling was used for the survey. The sampling universe consisted of all those who were living in the district (staying in the village/town for at least the previous six m). The following parameters were considered for calculating the sample size: Estimated prevalence of blindness, the estimated prevalence of avoidable blindness, power of 80%, 20% relative précision, 95% Confidence Interval and a design effect of 1.5 (maximum for clustering effects). The minimum acceptable prévalence was considered as 6.6% from previous studies.  Based on these criteria of stratified cluster random sampling, 2500 individuals aged 50 + were needed to be examined in the district. Clusters of 50 people who were 50 years and above were selected with probability proportionate to size using a multistage cluster random sampling method.A total of 55 clusters (49 rural and 6 urban) were covered, 50 individuals aged > 50 years were examined in each cluster. A total of 2750 subjects were to be examined.
Two teams of ophthalmologist, ophthalmic assistants, social workers and a manager were trained for data collection and management. A separate session was conducted for their standardization and acceptable agreement as per the RAAB details.We looked at the inter-observer variation between teams and this was done for visual acuity presenting, pin hole and lens examination and all of them were > 60%.
An Early treatment diabetic retinopathy study (ETDRS) cut out chart with E Optotypes was used for recording vision. The top row of E's corresponded to 20/60 equivalent of Snellen's charts, while the E's on the bottom row correspond to 20/200 on the Snellen's charts at 4 metres. A person had to correctly identify at least four out of five E's of one line to be considered as normal vision at that line. Vision was first recorded with the habitual correction that the person was wearing (presenting vision) and it was recorded whether the person is using glasses or not. The initial vision examination was done at home. If vision was < 20/60, the pinhole vision was recorded. All individuals with vision < 20/60 were examined at a central site, as were all cataract operated (either eye) individuals irrespective of their vision. At the central examination site/clinic, visual acuity was re-checked and an external eye examination was performed using a hand held slit-lamp by one of the two ophthalmologists. Lens status was recorded and also all probable pathology. The most probable cause of visual impairment in each eye was identified. In identifying the probable cause, the currently more treatable/preventable cause was given higher rank in the hierarchy of causes compared to an untreatable cause. The most important cause of blindness in the person was identified by comparing the cause in the right and left eye for the bilaterally blind. If on torch light and slit lamp examination, a diagnosis of uncorrected refractive error, cataract, uncorrected aphakia, corneal scar, phthisis or globe abnormality could not be made, then the pupil was dilated by using 1% Tropicamide and the fundus examined with direct ophthalmoscope.
A person was defined as blind by WHO standards if the best corrected visual acuity (BCVA) in the better eye was < 20/400. If a person had BCVA < 20/200 to 20/400, the visual disability was considered as severe visual impairment (SVI) by WHO standards but still blind by Indian standard. Moderate visual impairment (MVI) was defined as the BCVA between < 20/60 and 20/200. These definitions were to measure prevalence with presenting vision and with the best correction. If vision improved to < 20/60 with pin hole, the cause of visual disability was considered to be refractive error. Cataract impairing the vision in an eye was defined as having cataract as underlying cause of visual disability. In the absence of any other obvious cause, presence of significant pallor, cup: disc (C: D) ratio > 0.6, pigment changes and other signs such as iridectomy/blebs and C: D asymmetry of > 0.2 between the two eyes were used to define glaucoma. A person with sight threatening diabetic retinopathy was considered to have visual disability due to diabetes. In the presence of macular scar, drusen at macula, geographic atrophy, a person was categorized as having age-related macular degeneration. All persons in need of medical or surgical eye care were referred to the new secondary centre set up at Kankavli in the same district.
Information about previous cataract surgery, satisfaction with surgery and barriers to cataract surgery were collected. The respondent's near vision was recorded, with specs if they had one on them and without them for all others.
The cataract surgical coverage of people was defined as the proportion of people having undergone cataract surgery amongst those who have had cataract. 
The data was collected and entered in RAAB India software. Analysis was done by excel and SPSS version 19.
| Results|| |
Of the 2750 selected subjects aged ≥50 years, 2747 were interviewed but 10 did not allow their vision to be measured and the eye examined. [Table 1] shows the composition of population examined in survey area by gender. There was no statistically significant difference between age and gender (P = 0.061). However; in the age group 50-59yrs and 60-69 yrs females were predominant and in older age groups males were predominant.
Amongst those examined (2737individuals), 1415 (51.7%) had visual acuity (VA) > 20/60, 924 (33.8%) had VA 20/200-< 20/60 (visual impairment), 266 (9.7%) had VA < 20/200-20/400 (severe visual impairment) and 132 (4.8%) had VA < 20/400 (blindness by WHO standards). [Table 2] demonstrates the unadjusted prevalence of visual impairment and blindness amongst the populace. Amongst the rural population, 121 (5%) were blind, 358 (14.9%) severely visually impaired and 1187 (49.4%) had visual acuity < 20/60; while amongst the urban population, 11 (3.2%) were blind, 40 (11.6%) severely visually impaired and 135 (39.1%) had visual acuity < 20/60. The prevalence of blindness amongst males was 5.4% (95% CI: 1.0 - 8.5) and femaleswas4.2% (95% CI: 0.7 - 7.6). Out of these, prevalence of blindness in age group between 50-59 was 2.3% (95% CI: -0.3- 4.9), between 60-69 was 4.8% (95% CI: 1.0 -8.5), 70-79 was 9.8% (95% CI: 4.6-14.9), 80-89 was 20% (95% CI: 13-27), above 90 years of age was 6.7% (95% CI: 2.3-11). The prevalence of blindness in rural population was 5.0% (95%CI: 1.2 - 8.8) and in urban population was 3.2% (95%CI: 0.1- 6.2).The prevalence of blindness by Indian standards (< 6/60) amongst males was 132 (9.5%; 95% CI: 5.9 - 13.12) and females was 134 (9.8%; 95% CI: 6.2 - 13.5). Out of these, prevalence of blindness in age group between 50-59 was 2.9% (95% CI: 0.8- 5), between 60-69 was 11.5% (95% CI: 7.6 -15.4), 70-79 was 22% (95% CI: 16.9 -27),80-89 was 20% (95% CI: 19-29), above 90 years of age was 6.7% (95% CI: 30.7- 42.5).The prevalence of blindness in rural population was 9.8% (95% CI: 6.2 - 13.5) and in urban population was 8.4% (95% CI: 5- 11.8)
|Table 2: Prevalence of Blindness and Visual Impairment by presenting visual acuity in individuals>50 years of age|
Click here to view
The various causes of blindness are shown in [Table 3], amongst those with presenting vision < 20/200 in better eye, 309 (82.4%) had cataract, 13 (3.5%) had diabetic retinopathy, 36 (9.7%) had corneal scars and 31 (7.8%) had other pathology including uncorrected refractive errors.
Of the proportion of cataract surgeries performed166/582 (28.5%) were performed by government hospitals, 165/582 (28.3%) were by non-governmental organizations (NGO), 249/582 (42.7%) were by private surgeons and 2/582 (0.3%) was eye camp. Cataract surgery was offered free for: 211 (39.8%) out of 530, 319 (60.1%) was paid. In free surgery; 102 (48.3%) out of 211 were male and 109 (51.6%) were female whereas 161 (50.4%) out of 319 were male and 158 (49.5%) were female among the paid surgery. We did not have the details of 52 patients for cost of surgery. No details available for type of cataract surgeries in 14 individuals. Type of surgery: 9/568 (1.5%) were intra-capsular cataract surgery (ICCE); 45 (7.9%)/568 were extra-capsular cataract surgery (ECCE), 50 (8.8%) were ECCE with intra-ocular lens implant (IOL); 464 (81.7%) were manual small incision cataract surgery (SICS) or phacoemulsification with IOL. A vast majority of people who had undergone cataract surgery, 528/582 (90.7%) had received an intraocular lens.
Presenting visual outcome after surgery in aphakia was: > 20/60 in 32/54 (59.3%), 20/80- 20/200 in 11/54 (20.4%), visual acuity < 20/200-20/400 in 9/54 (16.6%), < 20/400-PLPR in 2 (3.7%). In pseudophakics, 259/528 (49%) were > 6/18; 199 (37.6%) were 20/80-20/200;visual acuity < 20/200-20/400 in 51 (9.6%); < 20/400-PLPR in 19 (3.5%).
[Table 4] shows the reasons why individuals who had cataract did not seek cataract surgery. Of them 47.7% people not undergoing cataract surgery because of unavailability, no affordability or poor quality of cataract surgery services. The Cataract surgical coverage was 30.8%, 32% for males and 28.4% for females.
652 males and 632 females were found to be having spectacles during the examination (1284/2737, 46.9%).Of these 930 were N6 for near and 153 N8 for near in either of the eyes. Rest 201 had < N10 vision in each eye even if they were wearing specs. 196 of 1453 (13.5%) not wearing spectacles were still having near vision N6 or N8, perhaps due to immature cataract. Thus 1458/2737 (53.3%) had near vision < N10, only 46.7% did not.
| Discussion|| |
RAAB Surveys have been conducted in several countries. ,,,,,,,,,, In most of the surveys conducted in or after the year 2004, the prevalence of blindness ranged from 1.10% to 8.6%. In the National Survey done in India in the year 2007, the prevalence of blindness was found to be 3.6% (WHO < 20/400), 8% (Indian Std < 20/200).  In this RAAB, however the prevalence of blindness was found to be 4.8% (WHO < 20/400) and 14.5% (Indian Std < 20/200). This is comparable to prevalence at Kenya and Oman, , but much higher than what has been reported in China, East Africa and Bangladesh. ,,, This may be due to unavailability of eye care services in the district. Sindhudurg district is geographically secluded, even though it is few hours' drive from Mumbai and is just across a creek from Goa. [Table 5] compares the results of this study with RAAB studies world-wide.
|Table 5: Comparisons of severe visual impairment and blindness with other studies|
Click here to view
Overall, cataract remains the main cause of blindness 82.4%, higher than that reported by the RAAB India study at 77.5%.  Recent Indian studies from Karnataka, Maharashtra and Gujarat also put cataract as the leading cause of blindness, accounting for almost three-fourths of the blindness burden like this study. ,, The avoidable causes of blindness like cataract, refractive errors, surgical aphakia, cataract surgery complications, trachoma, causes of corneal scarring and diabetic retinopathy constituted 95.3%, compared to 88.2% in the RAAB India study,  again stressing the need for provision of eye care services in the region. But mercifully eye camp surgery had become extinct ( < 1.5% of all cataract surgeries) though outcomes after cataract surgery still remain a cause for concern. 
An alarmingly high prevalence of diabetic retinopathy i.e., 3.5% was recorded. In previous population based studies from India, diabetes was the cause for < 1% blindness. , India is now being recognized as global capital of diabetes and unlike in past, it has now become the disease of masses. The rural population is also showing a high prevalence of diabetes and thus this may be the first study to demonstrate this fact. This could be because of the centralized examination and more detailed posterior segment examination as opposed to other RAAB methods. There is a need for services to diagnose and treat diabetic retinopathy to be integrated into general medical services. Amongst the 1284 using near vision specs, 201 needed new spectacles for clearer near vision. So if we say 100% have presbyopia, 53.1% need a spectacle as they do not have any, while 201would need a change of lenses. Near vision impairment was common in the populace. The spectacle coverage in Andhra study was 18.8% for presbyopics, 19.9% for females and 18.0% for males.  For general refractive error it was 29% in Andhra, it was 46.9% in Sindhudurg.
In this study, both men and women did not show significant difference in prevalence of blindness and visual impairment. The pattern of blindness was also similar in both the genders. In some Indian studies, prevalence of blindness and severe visual impairment ( < 20/200 in the better eye) was higher among females (9.2%) compared to males (6.5%). , The Konkan region of which Sindhudurg is a part of has one of the most positive gender ratios in the country with high female literacy rates in spite of relative economic deprivation. ,
Thus 291/582 (50%) subjects failed to have a vision > 20/60 post cataract surgery. This fails to meet the WHO target > 80% of eyes having good vision with available correction. The poor outcome ( < 20/200) was 81/582 (13.9%) compared to the permissible 5% by WHO norms.  Such results do not inculcate great trust in the cataract surgical services. So 13.2% of cataract patients who knew they had cataract but did not feel the need for surgery and another 9.4% had been told by health care workers to wait for their cataract to 'mature'. Another significant cause was unaware of cataract which could be due the lack of access to eye care services. The Andhra study had cataracts operated in older individuals and those undergoing free surgery as having a poorer outcome as also those operated before 2005 and illiterate individuals.  The series from Gujarat had poorer outcomes in older and illiterate individuals. 
Unable to afford cataract surgery still remains the principal barrier for its uptake. So the free and subsidized surgical services provided by the government and NGO sector are still the need of the hour. Not having anyone to accompany or having to travel too far were also listed as significant barriers; these underline the need of outreach services to bridge this gap. The cataract surgical coverage was much lower than the state average for Maharashtra, but report from tribal part of Maharashtra had even a lower cataract surgical coverage than our study. ,
While the limitations of this study are that it's a rapid assessment and not a prevalence survey. But the study is unique in terms that the pattern in Konkan region had never been mapped, the respondent rate was very high and the near vision data was collected and analyzed. The high prevalence of diabetic retinopathy is an eye opener and should result in further demographical studies.
In conclusion, the study demonstrates that still a lot more has to be done in terms of service delivery for the two common causes of visual impairment-cataract and refractive errors. Gender was not a major barrier in uptake of service but diabetes as a cause of visual impairment and blindness is on the increase. Steps must be taken to make the existing cataract and refractive services more effective and have strategies in place to tackle the newer causes of visual impairment. Sindhudurg, like many neglected backwaters in India needs a government or NGO hospital not only to increase the Cataract Surgery Coverage but will also create awareness about cataract and refractive errors and their correction.
| Acknowledgement|| |
Mr. Cyril David, Director, Volkart Foundation for funding the study. Prof. Dr. PraveenVashist, R.P.Centre, AIIMS, New Delhi for sharing the RAAB software. Dr. Ashok H. Mahadik, Medical Director, Lions NAB Eye Hospital for planning and logistics.
| References|| |
Prajna NV, Rahatmatullah R. Changing trends in intraocular lens acceptance in Tamil Nadu. Ind J Ophthalmol 1995;43:177-9.
Prajna NV, Venkataswamy G. Cataract blindness-The Indian Experience. Bull World Health Organ 2007;79:259-60.
Neena J, Rachel J, Praveen V, Murthy GV. Rapid assessment of avoidable blindness in India. PLoSOne 2008;3:e2867.
Available from: http://www.government of Maharashtra/Sindhudurg. [Last accessed on 2011 Oct 25].
Census of India.The registrar general for census government of India 2001, Sindhudurg.
Kuper H, Polack S, Limburg H. Rapid assessment of avoidable blindness. Community Eye Health 2006;19:68-69.
Dineen B, Foster A, Faal H. A proposed rapid methodology to assess the prevalence and causes of blindness and visual impairment. OphthalmicEpidemiol 2006;13:31-4.
Mathenge W, Kuper H, Limburg H, Polack S, Onyango O, Nyaga G, etal
. Rapid assessment of avoidable blindness in Nakuru district, Kenya. Ophthalmol 2007;114:599-605.
WuM, YipJL, Kuper H. Rapid assessment of avoidable blindness in Kunming, China. Ophthalmol 2008;115:969-74.
Habiyakire C, Kabona G, Courtright P, Lewallen S. Rapid assessment of avoidable blindness and cataract surgical services in Kilimanjaro region, Tanzania. Ophthalmic Epidemiol 2010;17:90-4.
Rajavi Z, Katibeh M, Ziaei H, Fardesmaeilpour N, Sehat M, Ahmadieh H, etal
. Rapid assessment of avoidable blindness in Iran. Ophthalmol 2011;118:1812-8.
Wadud Z, Kuper H, Polack S, Lindfield R, Akm MR, Choudhary KA, et al
. Rapid assessment of avoidable blindness and needs assessment of cataract surgical services in Satkhira District, Bangladesh. Br J Ophthalmol 2006;90:1225-9.
Limbert H, Foster A. Cataract surgical coverage-An indicator to measure the impact of cataract intervention programmes. Community Eye Health 1998;11:3-6.
Xiao B, Kuper H, Guan C, Bailey K, Limburg H. Rapid assessment of avoidable blindness in three counties, Jiangxi Province, China. Br J Ophthalmol 2010;94:1437-42.
Oye JE, Kuper H. Prevalence and causes of blindness and visual impairment in Limbe urban area, south west province, Cameroon. Br J Ophthalmol 2007;91:1435-9.
Eusebio C, Kuper H, Polack S, Enconado J, Tongson N, Dionio D, etal
. Rapid assessment of avoidable blindness in Negros Island and Antique district, Phillipines. Br J Ophthalmol 2007;91:1588-92.
Chiang F, KuperH, Lindfield R, Keenan T, Seyam N, Magauran D, etal
.Rapid assessment of avoidable blindness in the occupied Palestinian territories. PLoS One 2010;5:e11854.
Mathenge W, Nkurikiye J, Limburg H, Kuper H. Rapid assessment of avoidable blindness in Western Rwanda: Blindness in a post conflict setting. PLoS Med 2007;4:e217.
Khandekar R, Mohommad AJ, Raisi AA. Prevalence and causes of blindness and low vision; before and five years after 'Vision 2020' initiatives in Oman: A review. Ophthalmic Epidemiol 2007;14:9-15.
Dineen B, Bourne RR, Jadoon Z, Shah SP, Khan NA, Foster A, etal
. Causes of blindness and visual impairment in Pakistan. The Pakistan national blindness and visual impairment survey. Br J Ophthalmol 2007;91:1005-10.
Gunnlagsdottir E, Arnarsson A, Jonasson F. Prevalence and causes of visual impairment and blindness in Icelanders aged 50 years and older; the Reykjavik Eye Study. ActaOphthalmol 2008;86:778-85.
Al Gamra, Al Mansouri F, Khandekar R, Elshafei M, Al Qahtani O, Singh R, etal
. Prevalence and causes of blindness, low vision and status of cataract in 50 years and older citizens of Qatar - A community based survey.OphthalmicEpidemiol2010;17:292-300.
Bettadapura GS, Donthi K, Datti NP, Ranganath BG, Ramaswamy SB, Jayaram TS.Assessment of avoidable blindness using the rapid assessment of avoidable blindness methodology. N Am J Med Sci 2012;4:389-93.
Dhake PV, Dole K, Khandekar R, Deshpande M. Prevalence and causes of avoidable blindness and severe visual impairment in a tribal district of Maharashtra, India. Oman J Ophthalmol 2011;4:129-34.
Murthy GV, 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.
Khanna RC, Pallerla SR, Eeda SS, Gudapati BK, Cassard SD, Rani PK, etal
. Population based outcomes of cataract surgery in three tribal areas of Andhra Pradesh, India: Risk factors for poor outcomes. PLoS One2012;7:e35701.
Srinivas M, Keefe JE, Rao GN. Near vision. Uncorrected refractive errors, presbyopia and spectacle coverage: Results from rapid assessment of refractive errors survey. Ophthalmic Epidemiol 2009;16:269-74.
Nirmalan PK, Padmavati A, Thulasiraj RD.Sex in equalities in Cataract blindness burden and surgical services in South India. Br J Ophthalmol 2003;87:847-9.
Dandona L, Limburg H. what do we mean by cataract outcome. Community Eye Health J 2000;13:35-6.
Department of Health, Government of Maharashtra, Annual Report of the National Program for the Control of Blindness, 2009.
Rao GN, Khanna R, Payal A. The global burden of cataract. Curr Opin Ophthalmol 2011;22:4-9.
Murthy G, Gupta SK, John N, Vashist P. Current status of cataract blindness and Vision 2020:The right to sight initiative in India. Ind J Ophthalmol 2008;56:489-94.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]