Epidemiology of blindness in children.
Summary (3 min read)
Introduction
- An estimated 1.4 million of the world’s children are blind.
- 1 4 5 The differential between the blind and non-blind child is more pronounced in developing nations: whilst 10% of UK children die in the first year following the diagnosis of blindness, in lower income countries the equivalent mortality is 60%.
- This article updates their previous review on childhood visual impairment,6 by summarising new evidence on the global epidemiology of, and the emerging therapies for, severe visual impairment and blindness (or SVI/BL, table 1.
- The evidence base regarding children is inconclusive.
- Moderate visual impairment (table 1) may impact on educational opportunities, with half of the UK’s moderately visually impaired children educated within specialised schools for children with physical or learning deficits.
Defining blindness
- The 1972 WHO taxonomy still forms the basis of the International Classification for Disease (ICD) definition (table 1) of blindness.9.
- As age and cognition may be obstacles to quantification of a child’s acuity level, childhood severe visual impairment (SVI) and blindness (BL) are often categorised together (SVI/BL).
- 16 17 Children may also fail to present to health care services because families do not recognise that there is a problem,18 or because access to health care for children is limited by their carer’s own blindness.
- KI methods enable researchers to capture a more representative study population, but are still likely to underestimate the true burden.
- The review will now summarise key developments in the epidemiology and management of the most important causes of childhood severe visual impairment / blindness (table 2), i.e. those which are responsible for the highest proportion of affected children globally, and those which carry the highest burden of avoidable blindness.
Retinopathy of prematurity (ROP)
- ROP develops when the vasoconstrictive response to hyperoxia, i.e. the immature retina of the eyes of premature children, is followed by a vasoproliferative phase which is driven by the surge in endothelial growth factors (EGFs) on the return to normal oxygenation.
- Approximately 170,000 preterm babies worldwide developed some degree of ROP in 2010, and 54,000 required treatment for potentially blinding severe disease, but only an estimated 42% of these babies received this treatment.
- This finding, consistent with others from low/middle-income countries demonstrates the power of epidemiology in determining setting-specific policy and practice.
- The required infrastructure can be a challenge in higher income settings, where approximately 55 infants are examined for every infant treated.
Cataract
- Cataract related to prenatal rubella infection is still an issue globally, for example accounting for 20% of childhood cataract in the Phillipines.45.
- For the majority of affected children with bilateral cataract (and therefore at risk of blindness), aetiology is unknown, and prevention of blindness is focused on the prompt detection and treatment of visually significant lens opacity before deprivation amblyopia becomes intractable.
- The Chinese Childhood Cataract Program , established with the support of the V2020 programme, resulted in earlier diagnosis of cases of congenital / infantile cataract, and an apparent increase in prevalence of childhood cataract, as a result of improved case detection in remote regions.
- There are still many obstacles to prompt treatment for affected children.
- In several countries patients need to supplement health costs, putting treatment beyond the means of many families.
Corneal opacity
- Corneal opacity secondary to vitamin A deficiency (VAD), infection or toxicity from traditional remedies, remains the most common cause of childhood severe visual impairment / blindness in Sub-Saharan Africa and areas of extreme deprivation,1 despite recent V2020 programmes on nutritional supplementation, measles and rubella vaccination and health education.
- Childhood corneal transplants have a high failure rate, due to rejection, new scar formation, or infection.
- The advent of hypothermia (head cooling or whole body cooling) as a therapy for HIE within the ‘golden window’ has resulted in modest improvements in neurodevelopmental outcomes.
Optic nerve anomalies
- Anterior visual pathway disorders are responsible for almost a quarter of childhood SVI/BL in some higher income settings, and optic nerve hypoplasia (ONH), is the commonest single cause of severe visual impairment / blindness in industrialised nations.
- In most cases the cause is unknown, but ONH is independently associated with younger maternal age and nulliparity.
- 56-58 59 ONH is a clinical diagnosis based on the appearance of the optic nerve, and the absence of a standardised clinical phenotype for the classification of hypoplasia limits epidemiological research.
- There is evidence of the relatively frequent co-existence of ONH and CVI, but the aetiological or clinical significance of this is unclear.
- Hand-held optical coherence tomography devices, which are non-contact diagnostic tools able to produce biomicroscopical images of the paediatric eye, are an emerging technology which may be able to aid the classification of paediatric optic nerve disease.
Inherited retinal disorders
- Photoreceptor dystrophies are the most common inherited retinal disorders amongst children with SVI/BL.5 61 These constitute the global photoreceptor dystrophy of Leber’s amarosis (LCA), dystrophies affecting rod photoreceptors more than cones (the retinitis pigmentosas), and the cone dystrophies.
- The RPE65 gene, mutations of which cause LCA type 2 and retinitis pigmentosa, has been a target for gene therapies.
- Following intraretinal injection of adenoviral delivered copies of functioning RPE65, children with LCA2 initially had improved visual function.
- This improvement was not maintained in follow up studies, due to degeneration of treated retina.
- 62 Further human trials of genetic therapeutics are underway.
Summary
- Childhood visual impairment and blindness remains an important public health issue, and alongside local or disease specific successes, there has been an emergence, or re-emergence, of other causes of early onset visual impairment, particularly retinopathy of prematurity (in middle income settings) and cerebral visual impairment (within higher income settings).
- Solebo AL, Rahi J. Epidemiology, aetiology and management of visual impairment in children.
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...Inherited retinal diseases are a frequent cause of blindness in paediatric and working age populations in many countries (Liew et al., 2014; Rahman et al., 2020; Solebo and Rahi, 2014; Solebo et al., 2017)....
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Frequently Asked Questions (16)
Q2. What is needed to improve understanding of risk factors for SVI/BL?
Population based epidemiological research, particularly on cerebral visual impairment and optic nerve hypoplasia, is needed in order to improve understanding of risk factors, and to inform and support the development of novel therapies for disorders currently considered ‘untreatable’.
Q3. What is the key to reducing the burden of avoidable blindness?
Improvements in maternal and neonatal health, and investment in and maintenance of national ophthalmic care infrastructure is key to reducing the burden of avoidable blindness.
Q4. What is the need for a population based epidemiological study?
In order to reduce the burden of childhood blindness attributable to diseases previously considered ‘untreatable’,particularly cerebral visual impairment and optic nerve hypoplasia, population based epidemiological studies are needed.
Q5. What factors are likely to play a role in the degree and duration of hyperoxia?
Genetic and environmental factors are likely to play a role in the degree and duration of hyperoxia necessary to trigger the process, the resultant surge in vascular growth factors, and the severity of disease which develops.
Q6. What is the common cause of severe visual impairment in industrialised nations?
Anterior visual pathway disorders are responsible for almost a quarter of childhood SVI/BL in some higher income settings, and optic nerve hypoplasia (ONH), is the commonest single cause of severe visual impairment / blindness in industrialised nations.
Q7. What are the current trials of adjuvant therapies to treat CVI?
There are several currently underway trials of adjuvant therapies hoped to further improve outcome, including noble gases (NCT 00934700, NCT 01545271), melatonin (NCT01862250) and erythropoietin derivatives (NCT 01913340).
Q8. What is the role of the head cooling in the treatment of HIE?
The advent of hypothermia (head cooling or whole body cooling) as a therapy for HIE within the ‘golden window’ has resulted in modest improvements in neurodevelopmental outcomes.
Q9. What is the effect of the CCPMOH on the development of cataracts?
The Chinese Childhood Cataract Program (CCPMOH), established with the support of the V2020 programme, resulted in earlier diagnosis of cases of congenital / infantile cataract, and an apparent increase in prevalence of childhood cataract, as a result of improved case detection in remote regions.
Q10. What is the definition of a global developmental sequelae to HIE?
For two thirds of children who have vision worse than 1.0 logMAR due to CVI, visual impairment is part of a global developmental sequelae to hypoxic ischaemic encephalopathy (HIE).
Q11. What is the main cause of ROP in preterm infants?
In industrialised settings CVI is a more important cause of visual impairment for a preterm child, but globally, ROP remains the major threat to vision for preterm infants.
Q12. What is the common cause of childhood blindness in lower income settings?
The constellation of causes of childhood blindness in lower income settings is shifting from infective and nutritional corneal opacities, and congenital anomalies, to more resemble the patterns seen in higher income settings.
Q13. How many children had vision worse than 3/60?
26 27 Of 231,000 children (aged under 16 years) examined as part of a major recent Indian rural population based, 8 per 10,000 had vision worse than 3/60 (95% CI 40-110/10,000).28
Q14. What is the role of a laser ablation therapy in preventing central sight loss in children?
Retinal laser ablation therapy is challenging, time consuming and implicitly destructive, but remains the gold standard intervention to prevent central sight loss in children with severe RO.
Q15. What is the impact of the new diagnosis of monocular blindness on children?
The recent creation of an additional diagnosis of ‘monocular blindness’ is important as these individuals have a lifelong increased risk of binocular blindness due to visual loss in the seeing eye,10 but the impact on global development for children with monocular blindness is unclear.
Q16. How many children are blind in Tanzania?
20Using the available estimates of childhood blindness, derived through robust population based approaches, the prevalence of blindness in individuals aged under 16 years (the definition used most consistently within the research) has been estimated at 12-15 per 10,000 children in very poor regions, and 3-4/10,000 in affluent areas (figure 2).1