Visual Impairment in Children in Middle- and Lower-income Countries
Abstract and Introduction
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.
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. 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.
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. 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. 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.
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 uggest 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, 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 UK 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.
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.