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Abstract
Reducing visual impairment and blindness in children in resource-poor countries is one of the key components of the major global prevention of blindness initiative, VISION 2020 the Right to Sight. Although visual impairment and blindness among children is much less common than among adults, the potential lifespan of a child means that the lifelong impact of such impairment is very large. Over 10 years ago, it was estimated that, globally, 1.4 million children were blind. Much has changed in the past 10–20 years and there is a need to reassess both the magnitude and causes of global childhood blindness and visual impairment. While the widespread implementation of vitamin A supplementation and measles immunisation programmes have led to a reduction in vitamin A deficiency-related blindness in many poor countries, retinopathy of prematurity is now undergoing a third wave of endemicity, particularly in newly industrialising countries in Latin America and Asia. Childhood cataract is better recognised as an important potentially avoidable problem, as is paediatric glaucoma and refractive error in some populations. Trained paediatric ophthalmologists, although still too few, are growing in number in poor countries. A programmatic approach with a multidisciplinary team is essential to reducing childhood blindness. The elements of such programmes and the need for planning are discussed.
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Introduction
Reducing vision loss in children in resource-poor settings has been the focus of considerable efforts by governments, non-governmental organisations, donors, public health professionals and eye care providers for the past 30 years. Research on vitamin A deficiency in Indonesia and elsewhere provided the link between specific ocular conditions and childhood morbidity and mortality.1 This body of work was instrumental in including childhood blindness in VISION 2020 Right to Sight, a broad initiative by the WHO and non-governmental organisations to eliminate avoidable blindness by the year 2020.2 3 At the launch of VISION 2020, over 10 years ago, it was estimated that 1.4 million children were blind with about half of these cases being avoidable. There are no reliable estimates of disability-adjusted life years (DALYs) lost owing to childhood blindness in low- and middle-income countries. Because of the devastating immune effects of vitamin A deficiency, it was further estimated that 60% of children die within 1 year of becoming blind.4
At the launch of VISION 2020, based on the known strong link between childhood mortality and vitamin A deficiency blindness, an estimate of overall childhood blindness and visual impairment was made using country- and region-specific under-5 deaths.5 WHO defines blindness as presenting visual acuity (better eye) of <3/60, severe visual impairment as presenting visual acuity (better eye) of <6/60 (but ≥3/60) and visual impairment as presenting visual acuity (better eye) of <6/18 (but ≥6/60 or better). Additional information on causes of blindness was provided by many systematic surveys in blind schools in developing countries, although it was always acknowledged that the children attending these schools did not necessarily represent all blind children.6 Much has changed in the past couple of decades and there has been a recent call to reassess both the magnitude and causes of childhood blindness.6
Childhood blindness is uncommon, relative to blindness in adults and thus poses a great challenge to obtaining true population-based data. However, surveys using key informants and other approaches to identify children with blindness provide some information on the likely magnitude of blindness in some settings. These surveys,7,–,12 summarised in table 1,suggest that in many resource-poor settings, the prevalence of blindness is lower than the previously suggested figures of >1/1000 children in most of sub-Saharan Africa or 0.5–0.9/1000 children in most of Asia. In addition, more recent studies in schools for the blind,13,–,16 while not providing data on blindness prevalence, have shown changing patterns in the causes of blindness, with fewer children with corneal conditions secondary to measles and vitamin A deficiency and more congenital conditions (disorders of the whole globe or retina) and inadequately treated cataract (table 2). The population-based surveys shown in table 1 also present a mixed picture, with lens-related causes and posterior segment causes being the most frequent. Causes of blindness in childhood are different in the industrialised countries and it is difficult to make direct comparisons; most surveys in resource-poor settings use a WHO form for classifying causes,17 reporting one major anatomical site responsible for blindness. On the other hand, reports from industrialised countries rely on more specialised testing and extensive history and recognise that multiple anatomical sites are often involved. An extensive study in the UK18 reported ‘lens’ as a site of abnormality in only 5% of incident cases, found that 77% of cases had additional non-ophthalmic disorders and that 75% of cases were neither preventable nor treatable.
Findings from population-based surveys of childhood blindness using key informants
Recent surveys (including more than 200 children) of causes of blindness in schools for the blind
It seems there is no longer one single leading cause of global blindness in children. We will review the major causes, then discuss programme issues relevant to reducing childhood blindness.
Retinopathy of prematurity
Retinopathy of prematurity (ROP) is a vasoproliferative disorder that affects premature infants. Over 50 000 children are probably blind worldwide from ROP.19 The ‘first epidemic’ of ROP took place in the 1940s and 1950s, affected larger premature infants, and was associated with unmonitored oxygen supplementation.20 21 Over the course of the following decades, supplemental oxygen was carefully titrated, and the ‘second epidemic’ affected extremely premature infants in highly developed countries who were receiving appropriate dosages of oxygen.22 With the institution of carefully timed screening examinations and treatment with cryotherapy, panretinal photocoagulation and advanced surgical techniques, the rate of blindness from ROP has dropped substantially in developed countries. As developing countries began to adopt modern neonatology techniques in the 1980s and 1990s, increasing the survival of preterm neonates, ROP began to emerge in middle-income countries (the ‘third epidemic’), where it can account for as much as 60% of childhood blindness.23 The current epidemic reveals a large amount of variability in the characteristics of affected infants because of the wide range of availability of prenatal care, advanced neonatology techniques and ROP screening and treatment. Countries with an infant mortality between 9 and 60/1000 appear to have the highest rate of blindness from ROP; currently the countries at highest risk are located in Eastern Europe, Latin America, India and China.20 There is a need worldwide to establish locally relevant and evidence-based screening guidelines, to explore use of remote screening methodologies, and to investigate the role of vascular endothelial growth factor inhibitors in conjunction with laser or as a stand alone modality in the treatment of ROP.24,–,26 Finally reducing supplemental oxygen has been shown to decrease significantly the rate of severe ROP; however, deaths may increase with reduced oxygen supplementation. Ongoing investigations are aimed at optimising oxygen management strategies to prevent ROP.27
Paediatric glaucoma
Glaucoma is a disease characterised by elevated intraocular pressure (IOP) and progressive damage to the optic nerve. Paediatric glaucoma is classified as primary when caused by a developmental anomaly of the filtration angle of the eye and secondary when aqueous outflow is impeded by another ocular disease or a systemic disorder such as anterior segment dysgenesis, aniridia or aphakia.28
Primary congenital glaucoma (PCG) is the most common glaucoma in infancy with an incidence of 1/10 000–18 000 births in North America and Western Europe; however, it can occur almost 10 times more frequently in populations where consanguinity is common.28
Surgical treatment of PCG has been shown to be associated with long-term IOP control and improvement in visual outcome in western countries. In Africa and India trabeculotomy,29,–,31 and goniotomy after removal of corneal epithelium32 have been used with limited success in patients with corneal opacity, which is characteristic of the advanced glaucoma typically found in these settings. Secondary glaucoma accounts for a similar proportion of new cases of childhood glaucoma, but is more difficult to diagnose and treat in resource-poor countries because of the absence of the overt signs that herald PCG (buphthalmos, photophobia and epiphora) and the lack of availability of pharmacological agents.28
Obstacles to effective treatment of childhood glaucoma in developing countries include limited patient and practitioner awareness about the disease, fears about surgical treatment, and limited access to isolated surgical centres and surgeons. Poor access to glaucoma drugs limits long-term management of PCG patients with residual IOP elevations in spite of successful surgical intervention and in patients with juvenile onset and secondary glaucoma. As the genetic basis for diagnosing and treating paediatric glaucoma evolves, genetic testing, counselling and treatment of high risk populations will be of paramount importance.33
Amblyopia
Amblyopia is defined as a reduction in vision caused by abnormal visual development because of abnormal visual stimulation during childhood. Common causes of amblyopia include deprivation (due to cataracts, corneal opacities or other opacities of the visual axis), strabismus and refractive errors. Children are susceptible to amblyopia until the brain reaches visual maturity around age 8 during which time treatment is most effective.34 Amblyopia is estimated to affect 1–4% of children with evidence that the prevalence is even higher in medically underserved populations.35 Overshadowed by organic causes of blindness, relatively little has been documented about the prevalence of amblyopia in resource-poor countries. However, as treatments for glaucoma, cataract and refractive error become established the effect of amblyopia is beginning to become apparent and ultimately accounts for the long-term visual impairment in many children whose primary disease was ‘successfully’ treated.33 36
Vitamin A deficiency
Vitamin A supplementation has been shown to be successful in reducing vitamin A deficiency-related blindness and overall childhood mortality.37 Children with inadequate vitamin A stores can develop xerophthalmia, corneal scarring and phthisis. Measles has been particularly implicated in leading to rapid depletion of vitamin A stores in young children. In the past 10–20 years the expansion of vitamin A supplementation efforts and a large-scale measles immunisation initiative have probably led to decreased frequency of vitamin A deficiency-related blindness in population-based studies of childhood blindness. Some school for the blind studies38 39 have shown vitamin A deficiency as a cause of blindness, however whether these studies (many being over 10 years old) reflect the current status of blindness or incident blindness in children, is unclear. That said, there are likely to be settings, such as refugee camps40 and disenfranchised focal groups19 where vitamin A deficiency-related blindness persists. Identifying these pockets for intensive intervention, alongside routine vitamin A supplementation and measles immunisation, is likely to be the approach for further reduction of vitamin A deficiency as a cause of blindness.
Cataract
As vitamin A deficiency-related blindness has decreased, cataract in childhood has been gaining importance as a cause of vision loss; not necessarily from an increase in the incidence of cataract but probably from increased efforts to identify children and ensure that they receive surgical services. Cataract is the leading cause of surgically treatable blindness in children in many resource-poor settings41,–,43 and the growth in the number of tertiary facilities44 is driven primarily to manage cataract. It has been postulated that there are around 200 000 children blind owing to cataract.45 The aetiology of paediatric cataract can be congenital, developmental, or traumatic; congenital cataract demands more urgent intervention to reduce the possibility of secondary ambylopia. The underlying causes of congenital and developmental cataract remain generally unknown; this limits approaches at primary prevention. While recognition of congenital cataract could be carried out at time of birth the infrequency of paediatrician/doctor assisted delivery in many resource-poor settings means that congenital cataract is rarely diagnosed early. Surgery would, ideally, be carried out in the first few months of life, but delay in many resource-poor settings can be 3 years or more.46 Surgery is just one step on a long pathway to vision rehabilitation and this pathway is often interrupted or discontinued for various reasons.47
Refractive error
Refractive error refers to the mismatch between the optical components of the eye so that the retinal image is out of focus. It is correctable by wearing spectacles or contact lenses, assuming that the eye has not become amblyopic. The biggest concern is that a child who has uncorrected refractive error during the critical period development may become amblyopic. Fortunately, highly myopic (‘nearsighted’) children can hold objects very close and get a clear retinal image and the paediatric eye can also adjust considerably for hyperopia. However, if the two eyes have different uncorrected refractive errors, the potential for amblyopia in one eye is very high and bilateral amblyopia may accompany extreme refractive errors.
Myopia usually starts in childhood and it progresses with age, generally levelling off in the late teens or early twenties. It is clear that the prevalence of refractive error differs among different ethnic groups; however, epidemiological studies have often had methodological problems, making comparisons difficult. Added to this difficulty is the part played by environmental factors. The population-based Refractive Error Studies in Childhood methodology, carried out in China, Chile, South Africa and Nepal, found the prevalence of myopia (at least −0.5 D) among children age 5–15 years to be 14.9%, 5.8%, 2.9% and 0.3%, respectively.48,–,51 The variation in prevalence means that approaches to screening and intervention in resource-poor settings must be tailored for the population.
Other causes
Congenital anomalies and other conditions responsible for most childhood blindness in industrialised countries remains rare in most, but not all13 resource-poor settings. Retinoblastoma, often diagnosed late, leads to early mortality; few studies identify children blind from this condition.
The need for special programmes for children's vision health
Urgency characterises childhood vision health issues, owing to the potential for amblyopia to develop if many conditions are left untreated. The growing eye of a child requires frequent reassessment to ensure a clear retinal image. Timing is critical and there are few second chances. A multidisciplinary approach is needed to ensure good vision in children.
Preverbal children cannot complain of poor vision; it is up to adults, caregivers or health personnel to detect it, ensure that children get help, and advocate for them. This can involve a variety of health personnel, teachers, parents and community members. Once a child with visual problems is identified a team of specialists (ophthalmologist, low vision specialists, optometrists, social workers, special needs teachers) will be needed throughout childhood to ensure that the child achieves the maximum visual function possible. Parents or caregivers play a key part; without their commitment, treatment is unlikely to succeed.
Childhood blindness is relatively rare so it is essential to plan carefully in order to avoid wasting resources and to ensure that all children needing services have an equal opportunity to receive them. At a WHO meeting in 1999, the concept of a ‘Child Eye Health Tertiary Facility’ (CEHTF) was developed and described.52 It was recommended that there be one CEHTF per 10 million population in lesser developed countries with a team comprising the specialists noted above. More recently, experience in Africa has shown that a more comprehensive approach is needed.47 A recent review of the status of CEHTF in Africa has highlighted the association between having a full team, including a childhood blindness coordinator (CBC) and high productivity.44
Although too few and often poorly staffed, educational and rehabilitation institutions exist in most developing countries for children with irreversible blindness. Inexpensive low vision aids and other devices can now be obtained easily.
General activities needed to combat childhood blindness may be conveniently grouped into (1) implementing systems for early identification (2) activities at the treatment centre and (3) implementing systems for follow-up.
Counselling is a critical component of eye care for children and must be provided throughout the programme. The CBC will usually be responsible for counselling once the child reaches the hospital. The personal relationship the CBC develops with the parent is often critical in compliance.
Systems for early identification
Poor advice from health personnel can contribute to delay in presentation. Any point at which young children are seen in the health system, such as during immunisation or in maternal child health clinics, provides an opportunity for identifying those with obvious eye problems, such as white pupil. Primary health workers do not have the skills to differentiate the causes of a ‘white pupil’ so it is critical that they know exactly where to send children for further examination. They must be trained to counsel parents that the condition is potentially life threatening (ie, retinoblastoma) and urgent assessment is needed. In many developing countries there is a backlog of children who need services. Clearing this through structured campaigns provides service for existing cases and generates awareness for identifying incident cases in the future. ‘Key informants’ in the community have been shown to be useful53 54 in identifying children who cannot see properly. An experienced clinician can come to a peripheral site at a defined time to examine a large number of children who have been collected in a campaign. In countries where schools for the blind admit children without an ophthalmological assessment, annual assessment by an ophthalmologist and a low vision specialist will identify children who can be helped. Advocacy for adoption of preadmission examinations is essential. Education of the general public, women's groups, community or religious leaders and education of health workers who come into contact with children regularly are the best long-term strategies to identify new cases. In most cases, transportation will be needed by the child and caregiver to get to the CEHTF and the programme may need to provide this. Simply telling a parent to take a child to hospital for assessment and surgery is often ineffective. Figure 1 shows the steps from recognition and referral to intervention and follow-up care as well as the role of the CBC throughout.
Ensuring comprehensive care for children requiring surgical services and the role of the Childhood Blindness Coordinator (CBC). Arrows show pathway of a child through from identification to surgery to follow-up and back to community. CEHTF, Child Eye Health Tertiary Facility, MCH, Maternal & Child Health.
Most vision or eye health screening programmes in resource-poor settings focus on school children. In settings where refractive error in children is high (eg, East and Southeast Asia) routine refractive error screening is recommended. In much of Africa and parts of Asia, where refractive error is uncommon school screening and the provision of spectacles is unlikely to be cost-effective.55 School screening is generally too late to address blinding conditions in children.
Treatment after identification
At the hospital the CBC will act as a ‘patient advocate’ and be responsible for counselling on admission, before and after any surgery, and at discharge. Counselling is probably the single most important factor in compliance with treatment and follow-up care.
At the time of surgery the CBC creates a tracking form, which stays at the hospital. The form is a record of what surgery was done, expected dates of follow-up and the anticipated activities at the follow-up visit. It includes contact information (cell phone of parent or neighbour) and perhaps a map to show residence.
Follow-up after treatment
Poor follow-up is not inevitable; good follow-up is possible if specific strategies are employed as part of a programme. Cell phone reminders and reimbursement of transportation expenses will help and the CBC has key responsibility for ensuring follow-up. When distances are vast, follow-up may require support from facilities external to the CEHTF. Coordination and communication with external providers, whether in general healthcare, paediatrics or eye care, is necessary; external providers will probably require training to provide follow-up services and to understand the communication necessary with the base hospital. Guidelines for follow-up have been published.56
Finally, when vision is improved some children should be able to enter mainstream education, but as this does not automatically happen57 it is the responsibility of ophthalmologists, parents, educators, paediatricians and general health workers to move this process along, ensuring that the child has as normal a life as possible.
Summary box
Visual impairment in children in low and middle income countries is due to a whole host of causes and underlying factors and summary global estimates will probably hide important differences at national and regional levels. Summary points include:
Major prevention interventions, particularly for corneal opacity secondary to vitamin A deficiency and measles, are routinely applied globally and have significantly reduced vision loss owing to vitamin A deficiency.
Retinopathy of prematurity (ROP) is emerging as a problem in middle income countries and urban areas of low income countries; few settings are ready to properly manage ROP (prevention, screening, or treatment).
Vision screening of school children may be useful in some settings for finding refractive errors but it cannot be relied upon to detect many important childhood eye conditions early enough in life.
Vision screening of school children is useful in some settings for finding refractive errors (especially in East and Southeast Asia), but has not been shown to be effective in settings where refractive error is not common (such as sub-Saharan Africa).
Screening children in the community is both costly and time consuming; the use of key informants to identify children likely to have vision loss has been shown to be effective in some settings.
Throughout most low and middle income countries, the focus of eye care service delivery is shifting to a more comprehensive approach centred on tertiary facilities that include more systematic outreach to communities, improving follow-up and strengthening low vision care.
The growing focus on low vision, rehabilitation and education means that eye care/healthcare providers need to take the lead in working with the education and rehabilitation communities.
References
Footnotes
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Funding We acknowledge an unrestricted grant from Research to Prevent Blindness to Emory University Department of Ophthalmology and financial support from Dark & Light Blind Care, Light for the World and Seva Canada to the Kilimanjaro Centre for Community Ophthalmology.
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Competing interests None.
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Provenance and peer review Commissioned; externally peer reviewed.