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COMMUNITY EYE CARE
Year : 1998  |  Volume : 46  |  Issue : 2  |  Page : 117-122

Planning to reduce childhood blindness in India


Prasad Eye Institute, Hyderabad, India

Correspondence Address:
L Dandona
Prasad Eye Institute, Hyderabad
India
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Source of Support: None, Conflict of Interest: None


PMID: 9847489

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  Abstract 

Reduction of blindness in children assumes particular significance since a blind child suffers from more blind-years than a blind adult. Estimates of the number of children blind in India and the causes of blindness are relatively crude as there are little reliable epidemiologic data. As a result of this, there is no organised approach to the control of childhood blindness in India. In order to address this issue, a workshop on childhood blindness was held at the L.V. Prasad Eye Institute, Hyderabad in November 1996. The aim of this workshop was to review available data, consider possible strategies, and make recommendations concerning the control of childhood blindness in India. These recommendations along with background information about childhood blindness are presented in this paper.

Keywords: Childhood blindness, magnitude, causes, eye care, policy


How to cite this article:
Dandona L, Gilbert C E, Rahi J S, Rao G N. Planning to reduce childhood blindness in India. Indian J Ophthalmol 1998;46:117-22

How to cite this URL:
Dandona L, Gilbert C E, Rahi J S, Rao G N. Planning to reduce childhood blindness in India. Indian J Ophthalmol [serial online] 1998 [cited 2020 Feb 24];46:117-22. Available from: http://www.ijo.in/text.asp?1998/46/2/117/14963

In terms of loss to society of productive human beings due to visual impairment, childhood blindness contributes significantly since the total number of blind-years suffered by a blind child is more than those suffered by a person who becomes blind in adulthood or in old age. Though accurate data on the prevalence of childhood blindness in the developing world are not available, it is estimated that the total number of blind children is much less than the number of blind adults. However, it is estimated that the cumulative number of blind-person-years worldwide due to childhood blindness ranks second only after the cumulative number of blind-person-years due to cataract blindness.[1] This indicates a need to attempt effective control of childhood blindness.

Childhood blindness is defined as best corrected visual acuity in the better eye of <3/60 in those 𕠕15 years of age.[2] Visual acuity of counting fingers at 3 metres is considered equivalent to 3/60, though the former may be less reliable. Some children, especially the younger ones, are not able to cooperate with the usual visual acuity assessment with vision charts. In these children, fixation of light which is clearly not central, not steady and not maintained may be considered equivalent to visual acuity <3/60. Though sophisticated tests of visual acuity assessment have been developed for children not able to cooperate with vision charts, these are not easily available in the developing country setting.

The first issue that needs to be addressed when attempting control of childhood blindness is the availability of reasonably accurate estimates of prevalence rates and information on the causes of childhood blindness. To our knowledge, the only population-based estimation of the prevalence of childhood blindness from India is that reported for the rural population of West Godavari district in the state of Andhra Pradesh.[3] In this population, which included 113,514 children, the prevalence of blindness was 6.5 (95% confidence interval 5.1-8.2) per 10,000 children. The causes of childhood blindness were congenital globe anomalies (microphthalmos/anophthalmos) in 25%, retinal diseases (mostly retinitis pigmentosa) in 22.2%, optic atrophy in 16.7%, cataract/lens related in 15.3%, corneal opacities in 11.1% (including vitamin A deficiency in 5.5%), glaucoma in 4.2%, amblyopia due to high refractive error in 2.8%, and abnormality of higher visual pathway in 2.8%. The proportion of these causes of childhood blindness may be different in other parts of India. A study of 1, 318 blind school students in 9 states of India revealed that the causes of blindness and severe visual impairment varied markedly amongst the states.[4] Overall, the major causes in this study included corneal scarring (mainly due to vitamin A deficiency) in 26.4%, congenital globe anomalies in 20.7%, retinal diseases in 19.3%, cataract/lens related in 12.3%, and optic nerve disorders in 5.9%.

The above-mentioned population-based and blind school data have their limitations. The former gives childhood blindness prevalence rates and causes of blindness in only one area of a state in India. The latter gives an idea about the pattern of causes of childhood blindness in blind school students in 9 states of India, but whether the causes are similar in those blind children who do not attend blind schools is not known.

In this background of the little that is known about childhood blindness in India, the following efforts may help in planning reduction of this disability.


  I. Epidemiologic Data on Childhood Blindness Top


For effective planning of eye-care services to reduce childhood blindness, reliable population-based data are needed from different parts of India regarding the prevalence and the causes of childhood blindness. Such data are lacking at present. It is obvious that without these data effective long-term planning to reduce childhood blindness in India would probably continue to be just wishful thinking.

Since crude estimates indicate that the prevalence of childhood blindness may be relatively low, a large number of children need to be studied to reliably estimate the true prevalence of childhood blindness in a population. For example, if 7 per 10,000 children are actually blind in a population, assuming Poisson distribution for this relatively rare event,[5] 100,000 children would have to be examined to have 95% confidence that the estimate would be between 5.5 and 8.8 per 10,000. This is a huge number to deal with, and therefore, population-based estimation of the prevalence and causes of childhood blindness probably has to be linked with other on-going population-based activities. For example, the population-based assessment of childhood blindness in West Godavari district[3] was done as part of a house-to-house survey designed to provide comprehensive eye-care services to that population. A team of trained field workers went from house-to-house in the designated population to detect people with visual impairment or eye problems who were taken to the base hospital for examination by an ophthalmologist. The blind children from the designated population who resided in blind schools were also included to avoid underestimation of childhood blindness. Apart from this approach, an effort can be made to link population-based assessment of childhood blindness with other population-based activities with wide coverage, such as vaccination of children and child survival programs.

In the absence of population-based data, an idea about the pattern of the causes of blindness in children can also be obtained by examination of blind school students.[4] Repeating this exercise at intervals of 5 or 10 years would be useful in detecting changes in trends for the causes of childhood blindness. Use of a standard form, developed by the World Health Organization (WHO) for recording childhood visual impairment,[6] would help in standardisation of the data.


  II. Specific Etiology of Childhood Blindness Top


The following issues need to be addressed for reducing childhood blindness due to the various causes, categorised according to etiological classification.[6]



  1. A. Genetic/Hereditary causes


  2. A large proportion of childhood blindness in India is estimated to be due to genetic/hereditary causes.[3],[4] This includes, with varying degrees of genetic influence, anophthalmos, microphthalmos, retinal dystrophies, and optic atrophy. It is likely that consanguineous marriages, which are common in certain parts of India, contribute to these causes. Efforts are needed in the following areas in order to deal with childhood blindness due to genetic/hereditary causes:



    1. (i) Health education programs to promote awareness of the increased risk from consanguineous marriages, particularly between close relatives. Consanguinity has complex social origins, and education programs exposing the risks of consanguinity would have to be developed keeping in mind the sensitive nature of this issue. Involving people from communities with high levels of consanguinity in the development and implementation of these education programs might increase their acceptance.


    2. (ii) Genetic counselling, based on sound scientific methodology, would be helpful in informing couples of the potential risk of having a child with a certain genetic disorder if someone in the family is already affected. More widespread training in genetic counselling for the genetic causes of childhood blindness would help meet this objective.


    3. (iii) Laboratory facilities for diagnosing genetic defects in families with genetic diseases would help in the long-term in dealing with genetic causes of childhood blindness. Development of these facilities and expertise would be feasible only at a few centres, perhaps at regional centres designated to deal with childhood blindness. The cost-effectiveness and cost-benefit of this investment for the whole society would have to be taken into account when using scarce health care resources for this purpose.




  3. B. Intrauterine causes




    1. 1. A recent study from India has suggested that as much as a quarter of the cataracts in the first year of life may be due to intrauterine rubella infection.[7] Rubella infection, particularly during the first trimester of pregnancy, can give rise to a range of systemic abnormalities, including ocular anomalies. This is referred to as congenital rubella syndrome. The eye signs in this include cataract, microphthalmos, corneal opacities, retinal pigment epithelium changes, and glaucoma. The question arises whether rubella immunisation could reduce the occurrence of childhood blindness. The World Health Organization has recently recommended that rubella immunisation programs not be introduced until sound epidemiological data are available.[8] The reason for this recommendation is that if rubella immunisation rates of infants are lower than the levels of protection conferred by natural immunity, there is a risk that there may be more cases of congenital rubella, as was the case in Panama. The Indian Association of Pediatrics recommends universal immunisation of infants against rubella, but a policy decision has not been taken by the Government of India (personal communication, Dr. P.S. Murthy, November 1997). Before rubella immunisation of infants is adopted as a policy, the following issues need to be addressed
    2. :



      1. (i) How significant is congenitally acquired rubella a cause of childhood disability, including blindness, in India? This could be assessed by testing infants with congenital cataracts, microphthalmos, glaucoma, or deafness for the presence of rubella specific IgM using saliva antibody capture techniques.[7]


      2. (ii) What is the level of susceptibility to acquired rubella in women of child-bearing age in India?


      3. (iii) Can high levels of rubella immunisation coverage in infants be maintained?

        Efforts to obtain epidemiological data regarding these issues would help determine if rubella immunisation can contribute significantly to the reduction of childhood blindness in India.




    3. 2. Intrauterine infection with toxoplasma or cytomegalovirus may also result in ocular abnormalities including optic atrophy. Another potential intrauterine causes of childhood blindness is optic nerve hypoplasia due to maternal use of alcohol or certain drugs during pregnancy. With limited data regarding these as causes of childhood blindness in India, the one reasonable thing at this stage to attempt would be to:




      1. (i) Include in the health education programs awareness about the deleterious effects on the fetus of maternal smoking, use of alcohol or illegal drugs during pregnancy.






  4. C. Perinatal/Neonatal causes




    1. 1. The two most common agents causing ophthalmia neonatorum, conjunctivitis during the first four weeks of life, are Neisseria gonorrheae and Chlamydia trachomatis. Infection of the newborn during passage through the birth canal of the mother infected with the former can quickly lead to corneal involvement and blindness, and that with the latter can lead to ocular and systemic morbidity. Reduction of childhood blindness due to ophthalmia neonatorum can be achieved with the following efforts:




      1. (i) Prophylaxis against ophthalmia neonatorum in the developing world is not practiced regularly. When practiced, tetracycline 1% eye ointment or silver nitrate 1% eye drops in a single dose are the common agents used. However, a recent study has shown that povidone-iodine 2.5% eye drops may be the preferred choice because of efficacy and lower cost.[9] A policy decision about providing povidone-iodine drops for as many births as possible at all levels of health care should be attempted.


      2. (ii) Training of the traditional birth attendants (daies), midwives, doctors and other personnel involved with childbirth should emphasise the ease and benefit of prophylaxis against ophthalmia neonatorum.


      3. (iii) Health education programs to make pregnant women aware of the benefits to themselves and to their to-be-born baby of getting their own and their partner's sexually transmitted disease treated should be made more effective. Education of the parents of a newborn should include making them aware that in case of purulent discharge from the eyes of the neonate immediate medical attention should be sought to reduce the risk of blindness.




    2. 2. Retinopathy of prematurity (ROP)
    3. is a condition in which abnormal retinal fibrovascular proliferation occurs in preterm infants as a result of interruption of the normal process of retinal vascularisation. The main risk factors for ROP are preterm birth, low birth weight, and fluctuating levels of blood gases (oxygen and carbon dioxide) during the first few weeks of life.[10] The advanced stages of ROP can cause childhood blindness. Large clinical trials have shown that cryotherapy to the avascular retinal periphery in high risk (threshold) cases is effective in reducing the blinding consequences by 50%.[11] Similar results are expected with laser photocoagulation. Currently, ROP is not a recognised major cause of childhood blindness in India. However, the current expansion of neonatal services in India is similar to that seen in the West in the 1940s and 1950s, which led to increased survival of preterm and low-birth-weight babies, in whom the "first epidemic" of blinding ROP was seen. It is possible that a similar situation may occur in India. There is some evidence for this, as in a recent study, 16% of babies with birth weight <2,000 gms developed severe enough ROP for which treatment was required.[12] Appropriate screening for ROP in babies at risk would minimise chances of blindness. In the West, babies with birth weight <l,500 gms and those born at <30 weeks gestational age are included in the screening programs.[13] To decrease the chances of ROP becoming a major cause of childhood blindness in India, the following issues need to be addressed
        :

      1. (i) Determine the survival rate of preterm (born before 33 weeks gestation) and low birth weight (<2,000 grams) to project the population of infants that may require screening for ROP.


      2. (ii) Determine ROP screening guidelines according to gestational age and birth weight that are appropriate for India rather than using those developed for the West.


      3. (iii) Assess the magnitude of the need for ROP screening, and accordingly increase awareness amongst neonatologists/pediatricians and ophthalmologists of this need.


      4. (iv) Based on the assessed need for ROP screening, train ophthalmologists in evaluation and treatment of ROP.






  5. D. Infancy/Childhood causes




    1. 1. A survey of blind school students in 9 Indian states revealed that 18.6% of the blindness was due to vitamin A deficiency and another 3.2% due to measles which precipitates vitamin A deficiency.[4] On the other hand, vitamin A deficiency contributed to only 5.5% of the childhood blindness in a population-based survey in West Godavari district of Andhra Pradesh.[3] The magnitude of childhood blindness due to vitamin A deficiency probably varies considerably in different parts of India.[4] This may be related to variations in socioeconomic status. Vitamin A deficiency also contributes to child mortality,[14] which can be reduced with vitamin A supplementation.[15],[16] There are global initiatives to eliminate this public health problem in the affected areas. In India, programs include: (i) vitamin A supplementation for preschool children with the first dose being given at 9 months of age with the measles immunisation, and (ii) food-based strategy including nutrition education. There are no recent population-based data regarding the extent of vitamin A deficiency as a public health problem in India, or on the effectiveness of vitamin A supplementation and nutrition education programs. In order to deal with vitamin A deficiency as a cause of childhood blindness, effort is needed to:

    2. (i) Assess the current magnitude of vitamin A deficiency as a public health problem in the at-risk parts of India, especially those where vitamin A deficiency has previously been perceived to be a significant public health problem, using the prevalence criteria suggested by WHO to define this problem.[17]


    3. (ii) Streamline vitamin A intervention programs (supplementation and education) by making them focus more intensively on areas with significant vitamin A deficiency.


    4. (iii) Establish a surveillance system for detecting cases of keratomalacia (corneal melting due to vitamin A deficiency) in areas with vitamin A deficiency as a significant public health problem.


    5. (iv) Increase awareness amongst ophthalmologists that the preferred way to treat vitamin A deficiency is with oral supplementation rather than intramuscular injection, except in cases of severe vomiting and diarrhea.




  6. 2. Trauma most commonly causes loss of vision in one eye. Though good data on the prevalence of childhood blindness due to trauma in India are not currently available, it is felt that monocular vision loss due to trauma may not be negligible in children. Most ocular trauma in children occurs as part of everyday activities. Ocular injury with callously disposed hypodermic needles as part of hospital waste has recently been noticed with increasing frequency in children. Attempts can be made to minimise visual loss in children due to trauma by:




    1. (i) Increasing public awareness about risk of vision loss due to trauma.


    2. (ii) Legislation to restrict dangerous toys and fireworks.


    3. (iii) Legislation to impose strict hospital waste disposal regulations to prevent injury with hypodermic needles.


    4. (iv) Encouraging the public to seek early treatment for eye injuries, and training of ophthalmologists in the skills necessary to effectively manage ocular trauma.






  • E. Others - etiology indeterminate


  • In this category are causes of childhood blindness for which the etiology usually can not be determined easily. These causes include:



    1. 1. Cataract and other lens-related causes contributed to 15.3% of childhood blindness in the population-based assessment,[3] and 12.3% in the blind school study[4] mentioned previously.


    2. 2. Glaucoma was responsible for 4.2% of the childhood blindness in the population-based assessment,[3] and 2.6% in the blind school study.[4]


    3. 3. Retinoblastoma caused 1.4% of the childhood blindness in the population-based assessment.[3]




    The factors that are helpful in the management of childhood cataract, glaucoma, and retinoblastoma are:

    Early identification and referral.

    Surgical management by trained specialists.

    Long-term follow-up by specialists to manage complications.

    Effective refractive error correction to prevent amblyopia.

    To deal effectively with these causes of childhood blindness, the following issues need to be addressed:



    1. (i) Increase public awareness that a white reflex from the eye or a hazy/enlarged appearance of the front of the eye in a child requires immediate attention by an ophthalmologist.


    2. (ii) Have adequate number of trained ophthalmologists to deal with these causes based on needs assessment in India.


    3. (iii) Have reasonable pediatric support services, including anesthesia and effective refractive correction, in selected centres for managing childhood cataract, glaucoma, and retinoblastoma.


    4. (iv) Address the known etiology for some cases of cataract, for example, rubella as discussed previously.




  • 4. Uncorrected refractive errors are thought to be a common cause of visual impairment during childhood in India. 2.8% of the childhood blindness in the population-based assessment in Andhra Pradesh was caused by amblyopia associated with uncorrected high refractive error.[3] In a survey of 4,029 school children in Hyderabad, uncorrected refractive errors resulted in visual acuity ≤6/60 in the better eye in 1.1%, including 0.5% who had acuity <6/60 in the better eye (equivalent to economic blindness in India).[18] All these children had visual acuity >6/60 after refractive correction. A method of screening school children for refractive errors by school teachers in India has been described, and success reported with this method.[19] The issues that need to be addressed to reduce visual impairment due to uncorrected refractive errors are:





    1. (i) Increase parental awareness that symptoms in a child suggestive of poor vision such as bringing books very close to the face or colliding with objects frequently should prompt them to consult an ophthalmologist.


    2. (ii) Make vision screening of school children more effective by increasing coverage and working out the logistics of providing spectacles to those children who need them.


    3. (iii) Make an attempt to link vision screening with other population-based activities with broad coverage of children, such as comprehensive health care and vaccination programs.







      III. Human Resource Development Top


    In order to deal effectively with childhood blindness in India, the appropriate manpower would be necessary. This would involve planning to efficiently use the existing manpower, and develop those cadres of manpower which are currently inadequate. The issues related to human resource development related to childhood blindness that need to be addressed are:



    1. A. Link surveillance for eye disorders and visual impairment in children with other programs with broad coverage such as Integrated Child Development and Child Survival Programs. This would allow utilisation of existing manpower to detect children who need ophthalmological attention. Promotion of simple concepts about eye health and nutrition education regarding vitamin A amongst mothers could also be feasible with this approach. The personnel involved in these programs at the community level would have to be given some basic training in detection of eye conditions that need to be referred, and in fundamentals of eye health. If planned properly, this basic training may not require spending of much resources.


    2. B. Increase awareness amongst health care personnel involved with maternal and child care at primary and secondary health centres about when a child should be referred to the ophthalmologist. This would involve simply framed continuing medical education that could be imparted to these personnel at their own centres. Utilisation of this existing manpower in the detection of childhood visual impairment and eye disorders could be made cost-effective if a well-planned approach is followed.


    3. C. Promote closer liaison between pediatricians, obstetricians, geneticists, nutritionists, and ophthalmologists to facilitate easier cross-referral regarding childhood eye disorders. This could be attempted at the state and national level societies of these specialities. If tangible benefits to all concerned, including the patients, could be articulated, this liaison could become a reality.


    4. D. Train an adequate number of pediatric ophthalmologists to meet the need in the country. This would involve developing structured training programs at institutions in India dealing with a large volume of childhood eye disorders. Exchange programs between academic institutions in India and those abroad where good training in pediatric ophthalmology could be imparted would also be beneficial.


    5. E. Train the required number of specialised personnel, other than pediatric ophthalmologists, necessary for comprehensive child eye care. This would include anesthetists, geneticists, orthoptists, opticians, and nursing staff having skills in dealing with pediatric eye problems. The number of these specialists would have to be justified by the assessed need in India, keeping in mind the scarce health care resources.



    6.   IV. Models for Eye Care in Children Top


      An approach to health care that is comprehensive is more likely to be effective. If models are developed for children's eye care that include preventive, curative, and rehabilitation aspects based on needs assessment of the community, they are likely to provide long-term benefit to society. Such a model would have the following components:

    7. A. Epidemiology research for realistic needs assessment.


    8. B. Community-based program aimed at prevention of causes of childhood blindness.


    9. C. Provision of curative child eye care services by a team of trained personnel.


    10. D. Community-based rehabilitation programs for incurably blind children, including low vision services for uncorrectable visual impairment.


    11. E. Basic and clinical research for better understanding of the causes of childhood blindness.




    Such models for comprehensive eye care services for children could initially be developed at the regional level in India. With the elementary knowledge that the cumulative number of blind-person-years due to childhood blindness is comparable to the leading causes of blindness in other age groups,[1],[3] it may be reasonable to start experimentation with such models in India. As more information about childhood blindness becomes available, an area that could help better understand the justification for investment of societal resources in developing these models is health economics. Cost-benefit ratio between the resources invested and the expected benefit to society in the long-term would help determine what priority these models should get in the overall context of health care in India.

     
      References Top

    1.
    Foster A. Worldwide blindness, increasing but avoidable. Semin Ophthalmol 1993;8:166-70.  Back to cited text no. 1
        
    2.
    Foster A. Childhood blindness in India and Sri Lanka. Indian J Ophthalmol 1996;44:57-60.  Back to cited text no. 2
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    3.
    Dandona L, Williams JD, Williams BC, Rao GN. Population-based assessment of childhood blindness in southern India. Arch Ophthalmol 1998;116:545-46.  Back to cited text no. 3
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    4.
    Rahi JS, Sripathi S, Gilbert CE, Foster A. Childhood blindness in India: causes in 1318 blind school students in nine states. Eye 1995;9:545-50.  Back to cited text no. 4
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    5.
    Rosner B. Fundamentals of Biostatistics. 2nd edition. Boston : PWS Publishers; 1986. p 84-92.  Back to cited text no. 5
        
    6.
    Gilbert C, Foster A, Negrel AD, Thylefors B. Childhood blindness: a new form for recording causes of visual loss in children. Bull World Health Organ 1993;71:485-89.  Back to cited text no. 6
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    7.
    Eckstein MB, Brown DWG, Foster A, Richards AF, Gilbert CE, Vijayalakshmi P. Congenital rubella in south India: diagnosis using saliva from infants with cataract. Br Med J 1996;312:161.  Back to cited text no. 7
        
    8.
    Special Advisory Group of Experts of the Children' s Vaccine Initiative and the Global Programme for Vaccines and Immunisation. New vaccines, new vaccination approaches, and the vaccination target groups. Weekly Epidem Rec WHO 1996;71:269-76.  Back to cited text no. 8
        
    9.
    Isenberg SJ, Apt L, Wood M. A controlled trial of povidone-iodine as prophylaxis against ophthalmia neonatorum. N Engl J Med 1995;332:562-66.  Back to cited text no. 9
        
    10.
    Cunningham S, Fleck BW, Elton RA, Mclntosh N. Transcutaneous oxygen levels in retinopathy of prematurity. Lancet 1995;346:1464-65.  Back to cited text no. 10
        
    11.
    Cryotherapy for Retinopathy of Prematurity Co-operative Group. Multicenter trial of cryotherapy for retinopathy of prematurity: Snellen acuity and structural outcome at 5[] years after randomization. Arch Ophthalmol 1996;114:417-24.  Back to cited text no. 11
        
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    Gopal L, Sharma T, Ramachandran S, Shanmugasundaram R, Asha V, Retinopathy of prematurity: a study. Indian J Ophthalmol 1995;43:59-61.  Back to cited text no. 12
        
    13.
    The Royal College of Ophthalmologists and British Association of Perinatal Medicine. Report of the Joint Working Party. Retinopathy of prematurity: guidelines for screening and treatment. London: Royal College of Ophthalmologists; 1995.  Back to cited text no. 13
        
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    Sommer A, Tarwotjo I, Hussaini G, Susanto D. Increased mortality in children with mild Vitamin A deficiency. Lancet 1983;ii:585-88.  Back to cited text no. 14
        
    15.
    Sommer A, Tarwotjo I, Djunaedi E, West Jr KP, Loeden AA, Tilden R, et al. Impact of Vitamin A supplementation on childhood mortality: a randomised controlled community trial. Lancet 1986;i:1169-73.  Back to cited text no. 15
        
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    Rahmathullah L, Underwood B, Thulasiraj RD, Milton RC, Ramaswamy K, Rahmathullah R, et al. Reduced mortality among children in southern India receiving small weekly dose of Vitamin A. N Engl J Med 1990;323:929-35.  Back to cited text no. 16
        
    17.
    Control of Vitamin A Deficiency and Xerophthalmia. WHO Technical Report Series No 672. Geneva: World Health Organization; 1982.  Back to cited text no. 17
        
    18.
    Kalikivayi V, Naduvilath TJ, Bansal AK, Dandona L. Visual impairment in school children in southern India. Indian J Ophthalmol 1997;45:129-34.  Back to cited text no. 18
        
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    Limburg H, Vaidyanathan K, Dalai HP. Cost-effective screening of school children for refractive errors. World Health Forum 1995;16:173-78.  Back to cited text no. 19
        




     

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