Dr. Praveen Vashist1, D. Vivek Gupta1, Dr. Suraj Singh Senjam1, Dr. Noopur Gupta, Dr. Atul Kumar
Author Affiliations
Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, 110029 India
Corresponding Author
Dr. Vivek Gupta
Assistant Professor, Community Ophthalmology
Dr Rajendra Prasad Centre for Ophthalmic Sciences
All India Institute of Medical Sciences,
New Delhi, 110029 India
Phone: +91 26593140
E-mail: drguptavivek@yahoo.com
Word Count of Abstract: 146
Word Count of Paper: 2900
Abstract
Background: A modern rapid survey method is being used to generate valid estimates of visual impairment and blindness in India.
Method: This survey is being conducted in 30 districts of India using Rapid Assessment of Avoidable Blindness 6 (RAAB) methodology. In each district, a sample size of 3000 individuals aged 50 years and above are to be examined across 50 clusters. Clusters are being selected using multi-stage PPS sampling and compact segment sampling for identifying households and individuals within each cluster. The survey staff including Ophthalmologist and Optometrist have been trained by RAAB certified trainer. Diabetic Retinopathy screening is additionally being done in selected districts, a first among RAAB surveys across the world.
Conclusion: The survey is intended to provide the prevalence of blindness and visual impairment, its main causes, quality of eye care services, barriers and cataract surgical coverage in the various districts of India.
Introduction
India was the first country in the world to launch National Programme for Control of Blindness (NPCB) way back in 1976. It was an evolution from the National Trachoma Control Program initiated in 1963 which was changed to National Program for Control of Visual Impairment and Prevention of Blindness and finally re-designated as NPCB. The program has evolved over the years with the launch of several initiatives along the way and changes in program strategies. The most notable of these include the initiation of the District Blindness Control Societies and the World Bank Assisted Cataract Blindness Control Project (1994-2001). The programme implementation has been guided on periodic intervals through routine data collection mechanisms and national surveys on blindness as well as other eye related diseases. The prominent earlier national level surveys include the Indian Council of Medical Research (ICMR) survey of 1971-74, the National Sample Survey of 1982, the NPCB-World Health Organization(WHO) surveyof 1986-89 and the NPCB 1999-2001National Prevalence Survey.(1)
The last representative survey from India on blindness was conducted in the form of rapid assessment of avoidable blindness survey across sixteen districts in 2006-07 among 50+ year aged population. As per this survey, the national estimate of prevalence of blindness was 3.6% (WHO’s definition of presenting Visual Acuity < 3/60 in the better eye), with the majority of causes reported to be avoidable; cataract and refractive errors were predominant causes.(2)Since then, during the Eleventh and Twelfth Five Year Plan periods (2007-2012 and 2012-17 respectively), many new initiatives have been undertaken under the programme by the Ministry of Health and Family Welfare, Government of India. The priorities under the program need to be aligned with the current needs of the population. It is well established that the prevalence of non-communicable diseases including diabetes is rapidly increasing worldwide. India too has shown a high prevalence of diabetes in recent surveys with urban prevalence of 10.9-14.2% and rural prevalence of 3.0%-7.8% among 20+ year olds and a much higher prevalence among individuals aged over 50 years. In addition, just half of the cases were aware of their diabetic status.(3)However, there is little information on the nationwide prevalence of diabetic retinopathy (DR) in our country.
Table 1: Prevalence and Proportion of blindness due to various causes among Indian population aged 50+ years
| National Blindness Survey 1999-2001(2) | National Blindness Survey 2007(1) | |
| Prevalence of Blindness (presenting visual acuity < 6/60 in better eye) among population aged 50+ years | 8.5% | 8.0% |
| Major causes of Blindness among 50+ years age group | ||
| Cataract | 62.40% | 77.50% |
| Refractive Errors (uncorrected), Aphakia uncorrected | 19.65% | 8.00% |
| Cataract Surgical complications, Posterior Capsular Opacity | 2.04% | 2.20% |
| Glaucoma | 5.83% | 3.00% |
| Trachoma and non-trachomatous corneal opacity | 0.89% | 3.90% |
| Posterior segment causes (including diabetic retinopathy, suspected AMD) | 4.72% | 2.80% |
| Other causes (includingpthisis, globe abnormalities, and undetermined cause of blindness) | 4.47% | 2.50% |
There is a felt need in the country to generate evidence regarding the magnitude of blindness across different parts of the country. As the country is advancing towards elimination of blindness, it is high time that a nationally representative survey be conducted to inform NPCB implementation in the coming years. It is in this context, a nationwide survey on blindness and visual impairment has been planned by the Ministry of Health and Family Welfare and is being operationalized all over the country by Dr Rajendra Prasad Centre for Ophthalmic Sciences, AIIMS, New Delhi.The primary objectives of the survey include (1) to determine the prevalence of blindness (including avoidable blindness) among the 50+ population in India, and (2) to identify the major causes of blindness in India. The various secondary objectives include ascertaining visual outcomes after cataract surgery amongst operated cases, estimation of cataract surgical coverage in India, barriers to uptake of cataract surgery, prevalence of diabetes and diabetic retinopathy in the study population and proportion of people with known diabetes who have had a previous fundus examination.
Methods
The current survey is being done using the Rapid Assessment of Avoidable Blindness (RAAB) methodology. RAAB survey methodology was developed in the context of Vision 2020: Right to Sight initiative as a rapid and cost-effective survey method for the assessment of avoidable blindness.The current RAAB protocol version 6 is being utilized for this survey which has laid more emphasis on VI and included recording Snellen visual acuity of 6/12 in the current protocol. Additionally, diabetes and DR assessment has been included, keeping in mind the growing burden of diabetes globally.(4)The step by step procedure for the survey is explained in Figure 2. Wherever possible, survey activities in the district are done in active partnership with local medical colleges, Vision 2020 partners and Regional Institutes of Ophthalmology.
Sample Size
For determining the sample-size, following parameters were considered:3.6% estimated prevalence of blindness (visual acuity <3/60) among 50+ as per RAAB India 2007, 25% relative precision, 95% Confidence Intervals, design effect of 1.6 for multi-stage cluster random sampling with a cluster size of 60 as per RAAB recommendations and coverage of 90%. Based on these criteria, 2924 individuals aged 50+ are required in each district. Finally, a target total sample size of 3000 by enrolling 60 individuals in 50 clusters each has been finalized. Taking into account 30 districts, the total sample size for the entire country is approximately 90,000 people.
Sampling
Multi-stage cluster sampling without stratification is being utilized. The first level sampling is that of districts (primary sampling units, PSUs), followed by sampling of villages or urban wards in the chosen districts (secondary sampling units, SSUs). Compact Segment Sampling is used to choose a cluster within each SSU. Within the cluster, households are visited from a random starting point and sixty eligible adults are identified and enrolled for the survey.
Selection of Districts: Districts comprise the primary sampling units (PSUs) for the country. The survey is being conducted in 30 randomly selected districts in the country. It has been designed to be representative of entire country, India as well as, representative at the district level in the chosen districts. The selection of districts was chosen using the probability proportionate to size (PPS) systematic random sampling methodology based on the 2011 Census of India district-wise population totals for all 640 reported districts with the total district population extrapolated to year 2015 using average exponential growth rate of 1.64% reported during the 2001-2011 decade (5). Diabetic Retinopathy (DR) survey has been planned in a sub-set of these 30 districts.
Selection of villages and wards:The list of all villages in rural areas and wards in urban areas in the chosen district is obtained from the Census 2011 population data and extrapolated to 2015. These can vary in size from very small hamlets to large urban wards. Each large village/ward (having population more than 4000) is split into smaller units of 4000 population each while the smaller villages/wards enter the sampling frame as it is.A total of 50 villages/wards are selected randomly from this sampling frame using PPS sampling and these comprise the secondary sampling units (SSUs).
Selection of districts and villages/wards is done at the central level (in RP Centre) by the statistical team. At the end of it, a list gets generated informing the field team about the number of splits done for each village or urban ward and the serial number of the SSU to the included in the survey. Subsequent selection of a cluster within the SSU is a field level activity as described below.
Selection of a cluster:Within each village/ward, compact segment sampling is used to identify the cluster to be visited in order to enrol sixty individuals aged 50+ from that cluster. The field team reaches the village or ward, prepares a map of the area with the help of local health staff and divides the village/ward into the requisite number of SSUs and marks them on the map. The SSU as identified in the list is then selected and compact segment sampling is performed within it. The selected SSU is further mapped and divided into clusters of approximately 400-500 total population. Each of these clusters is expected to have approximately 60 eligible subjects.
Selection of Households and eligible individuals:With the selected cluster, the field team starts enumerating from one random starting point and numbers each household. A list is prepared listing the number of male and female eligible subjects in each household. Households are visited till the sample size of sixty eligible in that cluster has been achieved. In case the sample size of 60 is not achieved within that cluster, the geographically contiguous cluster is chosen and households enumerated in that cluster till the sample size is reached. In case the entire village comprises of just one cluster and does not yield the requisite sample size, the next geographically nearest village is selected and a cluster selected therein.
Eligible subjects
In each household “eligible subjects” are persons of 50 years and older, residing in the household for six months or more over the past year. “Residing in the household” is defined as sharing meals from the same kitchen with the other members of the household for at least 6 months in a year. Any visitors are excluded. Household members away for more than one night are also excluded. One RAAB Survey Record is completed for each eligible subject.
Coverage
Subjects may not be examined due to their unavailability, refusal or inability to communicate (e.g. deaf, dementia or psychiatric illness). Because people with poor vision are more likely to be at home, compared with people with good vision, using replacements may lead to over-sampling of people with impaired vision and an over-estimation of visual impairment in the survey area. To avoid such a bias, absenteeism and refusals of eligible subject is kept to a minimum and less than 10%. No replacements are done. Good publicity and strict adherence to the timetable is ensures good response rates. At least two revisits are made to find and examine the absentee. An effort is made to persuade refusers to be examined. If the person is not available for examination despite repeat visit(s), a correct estimate of the age is made by interviewing a close relative or a neighbor.
Survey Record
The standard RAAB survey record for Snellen’sOptotype is being utilized in the survey. The survey record comprises of seven sections to be completed in all districts and additional three sections to be completed in RAAB+DR districts. Section A consist of basic demographic and identification data for the district and the subject. In Section B, information about use of spectacles, presenting vision and pinhole vision is noted. Section C is about the status of lens in each eye and Section D includes information on principal cause of visual impairment in each eye and for the person. Section E is completed in case the subject is a non-responder while sections F and G include information on barriers to cataract surgery and outcomes of cataract surgery respectively.Section H includes information on known diabetes disease and random capillary blood sugar measurement. The next two sections (I and J) include questions about history of diabetes and its treatment and data on current retinal status (retinopathy, maculopathy and laser treatment scars).
Assessments
Visual Acuity Assessment
Visual Acuity is tested by trained optometrists and field investigators using the three simplified tumbling `E’ charts(‘E’ Snellen optotypes for VA of 6/12, 6/18 and 6/60) with available correction at 6 meters. VA measurement is done in full daylight, in the courtyard or on the street. Distance is measured with a special tape of 6-metre length, with a ring/knot at both ends and one in the middle (3 meters). The optotype is rotated before each reading (in varying directions) to change the direction of the open ends. The criteria for vision at a certain level are 4 correct consecutive showings, or 4 correct out of 5 showings. First the right eye is examined, while the left eye is covered with an occluder. First using a demo ‘E’ chart, procedure is explained and the examinee is instructed to point in the direction of the open ends of the ‘E’. Then the ‘E’ optotype for VA of 6/60 is shown first at a distance of 6 metres. If the E size for VA 6/60 at 6 metres is be correctly seen, VA for 6/18 and 6/12 is assessed in incremental steps while if the E size for 6/60 cannot be seen at 6 metres, the distance is reduced to 3 metres (3/60) and 1 metre (1/60) incrementally.If the subject cannot see from 1 metre then in a semi-dark condition (inside the house), perception of light is checked. Any eye with a presenting VA less than 6/12 is examined for acuity with a pinhole.The classification of visual impairment used in RAAB 6 package is in accordance with the International Classification of Diseases (ICD-10)2006revision, as normal vision, early visual impairment, moderate visual impairment, severe visual impairment and blindness. (6)
Ophthalmic Examination
The examinee is taken inside the house to create a shaded or dark area. There, the lens status is assessed by torch and by distant direct Ophthalmoscopy at 20-30 cm distance in semi-dark condition, without dilatation of the pupil by the Ophthalmologist.When the examined eye does not improve to 6/12 or better with pinhole examination, and there is no obvious lens opacity, the pupil is dilated with a short-acting mydriatic (tropicamide 0.5%) eye drop.Once dilated, the lens (intraocular lens if present), the posterior capsule and the anterior vitreous and retina are examined with direct Ophthalmoscopy and hand-held slit lamp in a semi-dark room.
Random Capillary Blood Sugar
Random capillary blood glucose (RBG) is assessed using a digital glucose meter (Freestyle Optimum, Abbott Healthcare) and the appropriate glucose test strips for that meter by a trained laboratory technician or a health worker in these activities. The same model is used by all teams. Using single-use disposable lancets, finger-prick blood samples are obtained after cleaning the finger-tips with spirit swab. Lancets and test strips are disposed of in a sharps disposal container. Blood Sugar is measured in mg/dl units.
Retina Evaluation of Patients with Diabetes
Any subject with RBG of >= 200 mg/dl (newly diagnosed diabetes) or a prior diagnosis of diabetes (known diabetes) undergoes retinal evaluation.Pupils are dilated with a short-acting mydriatic (tropicamide 0.5%) eye drop after a minimum of 30 minutes to achieve pupillary dilatation. The retina is examined first with the indirect Ophthalmoscope and 20 diopter lens. The Ophthalmologist looks for retinal hemorrhages, or exudates, and evidence of previous laser treatment. With direct ophthalmoscope, the examiner inspects the optic disc, looking for new vessels, and the macula. The major retinal vessels are then examined. The Scottish DR grading system is used for classification of retinopathy and maculopathy in each eye.(7) Presence of laser scars is noted separately.
Data Management and Analysis
The data collected in the field is entered into the specially designed RAAB6 software package on the same day as the survey is done. The software has in-built validation and consistency checks to ensure accurate data entry. Transcription errors are minimized through a dual-data entry and comparison with the initial field entered data. The second data entry being done by an independent operator in the department after the field-work in a district is over.The final corrected dataset is then analyzed using the inbuilt routines of the software. Age and sex standardized prevalence estimates for each district are obtained. The data is exported as comma separated files for further uni-variate and multi-variate analysis using dedicated statistical software.For all point estimates, 95% confidence intervals are calculated and the critical significance value has been fixed as p < 0.05.
Ethical Issues
The study protocol has been approved by the Institute Ethics Committee of the All India Institute of Medical Sciences, New Delhi, India. Approvals from state and district level health authorities are obtained before initiating survey activities. Written informed consent is obtained from each individual survey participant. Any participants requiring primary eye care are provided treatment in the field or in liaison with the local district health system. Participants requiring specialized Ophthalmic care are offered referral to the nearest centre (government or voluntary organization run) where appropriate treatment can be provided.
Discussion
It has been proven that population based survey restricted to 50 years and above age group provide valid information on causes of blindness and visual impairment in the total population which is useful for programmatic planning while having the advantage of smaller sample sizes, and at the same time being less expensive. The approach for assessment of diabetic retinopathy within context of RAAB surveys too has been validated in several smaller surveys in Suriname, Moldova, Jordan, Mexico, and Saudi Arabia. (8–12) The protocol adopted for this nationwide survey in India also includes assessment of diabetic retinopathy which is important for future planning as this disease is likely to become more and more important as cataract control interventions bear fruit and the prevalence of diabetes in India is expected to increase. (13)Using a standardized methodology such as RAAB also enables valid international comparisons across countries and regions and thereby has a global appeal as well. (14) Use of similar survey methods over time also provides accurate information about time-trends. (15) Using the RAAB survey methodology, the present survey will be able to generate valid estimates for current status of prevalence and causes of blindness and visual impairment in India.
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Figure1. Districts in which National Survey of Prevalence and Causes of Blindness and Visual Impairment Among 50+ Population (2015-2018) India is being conducted
Figure 2: Procedure for assessment of a survey participant