Epidemiology of childhood blindness

Survey of school children with visual impairment in Bradford

This work was presented as a poster at the Institute of Health Research Conference 2000: Health of Children and Young People: Research Perspectives. University of Bradford 15th of September 2000.

AIMS

The aim of this survey was to determine the prevalence and aetiology of visual impairment in school children in Bradford.

METHODS

The case notes of school children with predominantly uncomplicated visual impairment were reviewed. Data including age, sex, race and information on visual diagnosis, heredity, degree of visual impairment and additional morbidity were collected.

RESULTS

Seventy-two children between the ages of 5 and 16 years were included in this survey. The male: female ratio was 2.1: 1. Twenty-one children were Caucasian, 42 were of Pakistani and nine of other racial origin. The most common diagnoses were congenital nystagmus (19), ocular albinism (6), myopia (4), cataract (4) and microphthalmia (4). Twenty-five children had a genetically linked visual diagnosis and 31 had a family history of the same visual disorder.

CONCLUSIONS

This survey showed similar causes of visual impairment as described in other studies on children with uncomplicated visual impairment and confirmed the previously described preponderance of boys. The proportion of Pakistani children in our study population was significantly higher than that in the general Bradford population, indicating a higher prevalence of visual impairment in this group. Children of Pakistani origin were significantly more likely to have genetically linked visual disease and a positive family history of the same visual disorder than children of Caucasian origin. This is probably due to genetic factors and a higher proportion of consanguineous marriages in this population. Information about the prevalence and causes of visual impairment is important for adequate provision of special services and for developing preventive strategies.

A survey of visual impairment in children attending the Royal Blind School, Edinburgh using the WHO childhood visual impairment database

PURPOSE

To assess the aetiology and changing patterns of childhood blindness in one school for the blind in the UK and to assess the use of the World Health Organisation Prevention of Blindness (WHO/PBL) methodology and reporting form in a developed country.

METHODS

One hundred and seven children in one school for the blind and visually impaired in Edinburgh were examined using the WHO/PBL childhood blindness assessment form.

RESULTS

Of the 107 children examined, 87 (81%) were blind or severely visually impaired (corrected visual acuity of <6/60 (20/200) in the better eye). Perinatal related blindness (40%), hereditary disease (26%) and developmental factors (26%) formed the three largest aetiological categories.

CONCLUSION

The pattern of childhood blindness seen in this study was similar to reports from other developed countries. The WHO/PBL reporting form allows detailed comparisons between countries and over time. Additional fields for more detailed reporting of cerebral visual impairment and associated handicaps would increase the usefulness of the WHO/PBL form for population-based studies and for use in developed countries.

Blindness and visual impairment in the Americas and the Caribbean

AIM

To summarise available data on the prevalence and causes of visual impairment and blindness in the Americas and the Caribbean.

METHODS

The published literature was searched in Medline and LILACS using the following key words: blindness, visual impairment, prevalence. Articles were reviewed, and the references of the articles were also searched for relevant articles, which were also reviewed.

RESULTS

Using the mortality in children under the age of 5 as an indicator, the overall prevalence of childhood blindness (in the under age 15 group) for the region was estimated at 0.45/1000, with the majority (67%) living in countries with mortality of children under age 5 above 30/1000 live births. Corneal opacities were more common in countries where the under 5 year mortality are above 30/1000 live births and retinopathy of prematurity (ROP) was an important cause in countries with intermediate death rates. For adults, overall blindness rates were not estimated because of the social, economic, and ethnic diversity in the region. The primary causes of visual loss in adults in the Americas were age related eye diseases, notably cataract and glaucoma in the African-American and Hispanic populations, and age related macular degeneration in the white population. Uncorrected refractive error was a significant cause of decreased vision across ages, ethnic groups, and countries.

CONCLUSION

More data are needed on the magnitude and causes of visual loss for the Caribbean and Latin American countries. Rates of blindness and visual loss from available data within these countries are widely disparate. Prevention and control of avoidable blindness needs to be an ongoing focus in this region.

A locus for isolated cataract on human Xp

PURPOSE

To genetically map the gene causing isolated X linked cataract in a large European pedigree.

METHODS

Using the patient registers at Birmingham Women's Hospital, UK, we identified and examined 23 members of a four generation family with nuclear cataract. Four of six affected males also had complex congenital heart disease. Pedigree data were collated and leucocyte DNA extracted from venous blood. Linkage analysis by PCR based microsatellite marker genotyping was used to identify the disease locus and mutations within candidate genes screened by direct sequencing.

RESULTS

The disease locus was genetically refined to chromosome Xp22, within a 3 cM linkage interval flanked by markers DXS9902 and DXS999 (Zmax=3.64 at theta=0 for marker DXS8036).

CONCLUSIONS

This is the first report of a locus for isolated inherited cataract on the X chromosome. The disease interval lies within the Nance-Horan locus suggesting allelic heterogeneity. The apparent association with congenital cardiac anomalies suggests a possible new oculocardiac syndrome.

Visual outcome in patients with isolated autosomal dominant congenital cataract

OBJECTIVE

To determine the visual outcome and surgical complication rates of patients with isolated inherited congenital cataract.

DESIGN

Retrospective noncomparative case series.

PARTICIPANTS

Patients and their families were ascertained from the genetic eye clinic and outpatient databases of Moorfields Eye Hospital, London, and invited to participate in the study. Four hundred twenty-two individuals from 72 pedigrees with this form of autosomal dominant cataract underwent ophthalmologic assessment.

MAIN OUTCOME MEASURES

Visual acuity and surgical complications (glaucoma, retinal detachment, amblyopia).

RESULTS

In this study 49.4% of patients (46.8% of those operated) achieved a visual acuity (VA) of 20/40 or better, 35.9% (36.1% of those operated) a VA between 20/50 and 20/200, and 14.7% (17.1% of those operated) worse than 20/200. Opacities that were more diffuse or did not lie close to the visual axis were associated with a better prognosis for vision; 6.6% had glaucoma and 5.0% had retinal detachment develop.

CONCLUSIONS

Patients with isolated inherited congenital cataract have a better visual and surgical outcome than those with coexisting ocular and systemic abnormalities. The improved prognosis is related in part to the lack of other developmental abnormalities of the eye, and, because inherited cataracts are often partial at birth, surgery may be delayed to later infancy and childhood when there is a lower incidence of surgical complications and refractive correction is easier. Certain inherited phenotypes (lamellar, pulverulent, polymorphic, coralliform, and cortical) also seem to have a better prognosis, and this should be borne in mind when counseling these families. A large number of the patients in this study underwent surgery many years previously, when surgical outcomes were less favorable, and thus the results of this study establish only a minimum acuity dataset for the purposes of counseling.

Aetiology of childhood vision impairment, metropolitan Atlanta, 1991-93

Data from the population-based Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP) were used to describe the underlying causes of vision impairment (VI; corrected visual acuity in the better eye of 20/70 or worse) in young children (n = 228) in metropolitan Atlanta in 1991-93. Children with VI were identified through record review at multiple educational and medical sources. Children were categorised as having isolated VI or multiple disabilities (i.e. VI plus one or more of four additional developmental disabilities) and as having low vision (visual acuity 20/70-20/400) or blindness (visual acuity worse than 20/400). Medical conditions abstracted from MADDSP sources were reviewed to determine the probable aetiology of a child's VI. Aetiologies were assigned to one of three developmental time periods: prenatal, perinatal, or postnatal. Prenatal aetiologies were identified in 43% of the children; 38% of the prenatal aetiologies were genetic. Perinatal aetiologies were found in 27% of the children. Postnatal aetiologies were rare. Prenatal aetiologies were more common in children with isolated VI; perinatal and postnatal aetiologies were more common in children with multiple disabilities. Children with prenatal aetiologies tended to have less severe vision loss than did children with perinatal or postnatal aetiologies. The distribution varied by birthweight, but did not differ significantly by sex or race.

Causes of childhood blindness in the People's Republic of China: results from 1131 blind school students in 18 provinces

AIMS

To determine the anatomical site and underlying causes of blindness and severe visual impairment in children under 16 years of age in special education in the People's Republic of China with a view to determining potentially preventable and treatable causes.

METHODS

A national study of children attending schools for the blind in China was conducted between April and June 1998 using the WHO Prevention of Blindness Programme (WHO/PBL) eye examination record for children with blindness and low vision. Eight Chinese ophthalmologists attended a training workshop before conducting the study. 36 blind schools in 18 provinces of China were included.

RESULTS

1245 children aged between 5 and 15 years were examined, of whom 1131 (91%) were blind or severely visually impaired (visual acuity less than 6/60 in the better eye). The commonest anatomical sites of visual loss were whole globe (mainly microphthalmos) 25.5% and retina (mainly dystrophies) 24.9%. Lens was the major site in 18. 8%, optic nerve in 13.6%, and glaucoma in 9%. Corneal scarring was not a major cause of visual loss. The aetiology was unknown in 52.9%, hereditary factors were responsible in 30.7%, and childhood causes in 14%. 15% of cases were considered potentially preventable and 22. 5% potentially treatable.

CONCLUSION

The pattern of childhood blindness seen in this study is likely to reflect the improved health and socioeconomic status of China but may partly reflect bias in admission to, and location of, blind schools, with higher socioeconomic groups overrepresented. Nutritional and infective causes of blindness are uncommon, and hereditary and unknown factors are now the predominant causes.

Childhood blindness in Uzbekistan

PURPOSE

To elucidate the aetiology of childhood blindness in the Republic of Uzbekistan and to assess the needs for future provision of ophthalmic services for children.

METHODS

Six hundred and seventy-one children in seven schools for the blind and visually impaired throughout Uzbekistan were examined using the WHO/PBL (World Health Organization Prevention Of Blindness) childhood blindness proforma. The locations were chosen to give a representation of the major areas of population within the country.

RESULTS

Of the 671 children examined, 506 (75.4%) were blind or severely visually impaired (corrected visual acuity of less than 6/60 (20/200) in the better eye). Cataract-related blindness (35%), retinal dystrophies (24%) and microphthalmos (23%) formed the three largest diagnostic categories.

CONCLUSIONS

The commonest avoidable cause of blindness was found to be cataract; the cause of poor vision may be due to unoperated cataract, aphakia, amblyopia or post-operative capsular fibrosis. The high proportion of retinal dystrophies may be related to the common practice of consanguineous marriage. The frequent finding of microphthalmos is discussed and compared with findings from other surveys. Glaucoma accounted for approximately 5% of the avoidable blindness.

Childhood blindness and low vision in Uganda

PURPOSE

To examine the causes and outcome of subnormal vision starting in childhood in Uganda, to aid in planning for its avoidance and for rehabilitation.

METHODS

All those seen having subnormal vision with onset from birth to 15 years (total 1135) (schools 1983-97; community 1988-97) were included in the study. Clinical examination was performed and a World Health Organisation (WHO) form completed, with analysis by its computer program. Main outcome measures were visual acuity, signs of eye pathology, outcome of treatment and refraction and low vision assessment.

RESULTS

By WHO category 14.8% had visual impairment, 6.5% severe visual impairment, 63.2% were blind and 15.2% were too young to test. The acuities and causes were similar in school and community groups, excepting cortical visual impairment and multiple impairment, which are much commoner in the community. Cataract was the largest cause of visual impairment (30.7%) and surgical outcome was unsatisfactory. Visual loss following corneal ulceration was the second commonest cause of subnormal vision (22.0%).

CONCLUSIONS

Cataract and corneal damage cause half of all subnormal vision, which is avoidable for both. Cataract surgery needs to be upgraded. To prevent corneal visual loss, primary health care should continue to be expanded, especially measles immunisation and nutrition care; rubella immunisation should be added. Special education needs to be greatly expanded. Public perceptions need changing if results are to be improved and help offered to more than the present minority.

Characteristics of a pediatric low-vision population

BACKGROUND

Assessment of the causes of childhood blindness is important to develop preventive and therapeutic strategies that can reduce the incidence of visual impairment.

METHODS

A retrospective survey of the clinical records of 395 consecutive children younger than 14 years of age who were attended by the Low Vision Service of State University of Campinas (UNICAMP) was conducted. Data on the age distribution, the causes of low vision, the types of low vision aids prescribed, the follow up of their use, and improvement in visual acuity were obtained.

RESULTS

Congenital bilateral toxoplasmic macular scars, optic atrophy, and congenital cataracts were the major causes of low vision in this population. The optical aid most frequently prescribed was a telescope. The improvement of visual acuity with the use of aids was highly significant.

Visual impairment in Swedish children. III. Diagnoses

PURPOSE

To gain an overview of the spectrum of diagnoses among Swedish visually impaired children.

METHODS

An epidemiological study of all known visually impaired children was made by review of medical records.

RESULTS AND CONCLUSION

In all we found 2373 children, 0-19 years of age, with an age-specific prevalence of 10.9/10,000. The two largest diagnostic groups included neuro-ophthalmological and retinal diseases. The most frequent disorders were cerebral visual impairment, non-hereditary optic atrophy, retinal dystrophy (when regarded as a general entity), congenital hypoplasia of the optic nerve and congenital cataract. Nystagmus secondary to brain disorder, albinism, congenital nystagmus, retinopathy of prematurity and high myopia were also found in a considerable number of patients. The leading diagnoses in children with WHO-defined childhood blindness were non-hereditary optic atrophy, cerebral visual impairment and retinopathy of prematurity. A large proportion of the children, especially in the groups with neuro-ophthalmological disorders and malformations of the posterior segment had additional impairments, emphasizing the importance of a multi-disciplinary approach when assessing multi-handicapped children.

Visual impairment in Swedish children. II. Etiological factors

The analysis of etiological factors in a group of visually impaired children is of considerable importance when trying to find guidelines for possible preventive work. In this study we present etiological data on 2373 Swedish children. Data have been obtained by reviewing medical records on all known children with visual impairment throughout the country. In accordance with similar studies from industrialised countries, the group with prenatal etiology was the predominant, comprising 64% of the material. Within this group, half the patients had a disease of genetic origin. A total of 50% of all patients with prenatal etiology had an additional impairment, but in the group with diseases of genetic origin this proportion was smaller, only 40%. On the other hand, many children with additional impairments were found among those with an unspecified prenatal influence. Peri-/neonatal etiologies were found in 20% of the patients. In this group as many as 83% had additional impairments. This was even more pronounced among children delivered at term. The group with infantile/juvenile etiologies was small, 7%, with additional impairments in 66%. In 9% of all patients the etiology was classified as unknown. Among these, 80% had additional impairments. The visual impairment tended to be more pronounced, the later the disease was acquired. A male preponderance was seen in most etiological subgroups and in the material as a whole.

Uniocular childhood blindness: a prospective study

PURPOSE

This prospective study examines uniocular blindness among children younger than 16 attending a large pediatric ophthalmology department. The aim was to identify the causes of uniocular blindness and determine how much is preventable. We defined blindness according to the World Health Organization definition of vision worse than or equal to 3/60.

METHODS

All children who attended the department and were blind in one eye during the period of the study were included. A history was taken, visual acuity was assessed by an age-appropriate method, and an ocular examination was carried out. When necessary, the child also was seen by an orthoptist or pediatrician.

RESULTS

A total of 71 patients were identified. At the time of diagnosis, the patients varied in age from a few weeks to 15 years. The causes were classified into one of the following diagnostic categories: chromosomal/genetic (8.5%), prenatal (47.9%), perinatal (7.0%), or childhood (36.6%). Many cases are prenatal in origin and are not preventable. Other causes that are difficult to prevent include retinoblastoma, toxocariasis, and trauma. One cause, amblyopia, may be preventable or treatable in most instances if detected early.

CONCLUSIONS

Most cases of uniocular blindness are not preventable; however, protective glasses should be encouraged to prevent injury to the good eye.

Causes of blindness in Irbid, Jordan

To determine the most common causes of blindness and the age of onset of these conditions among Jordanians of Irbid, a study of all registered members in two societies for the care of the blind was carried out. Of all registered members, 185 individuals were blind according to the World Health Organization definition and satisfied our inclusion criteria. It was found that genetically determined causes made up 41% of the total causes. In 57% of the subjects, blindness occurred in the first two decades of life. The specific leading causes of blindness, in the order of their frequencies, were tapetoretinal degenerations as different variants of retinitis pigmentosa (17.6%), glaucomas (16%), diabetic retinopathy (13%), post-infection corneal scarring (11.5%), congenital cataract (8.8%) and uveitis (8%). The results reflect the satisfactory achievements in primary health care levels and the challenge to make specialized tertiary health care more accessible.

Risk factors associated with retinopathy of prematurity (ROP) in northern Jutland, Denmark 1990-1993

This population-based, historical, follow-up study analysed possible risk factors for retinopathy of prematurity (ROP) and resulting visual impairment in newborns over a period of 3 1/2 years in the County of Northern Jutland, Denmark. The study subjects were 141 infants with birth weight < or = 1500 grams and gestational age < 35 completed weeks who survived to a first eye examination at 5 weeks. The incidence of ROP (all stages) was 18%, and the frequency of severe visual impairment from ROP was 14/100,000 live births. A logistic regression analysis identified low gestational age, multiple births, continuous oxygen treatment, and male sex as risk factors for ROP. The main factor in the prevention of ROP is to prevent preterm births.

Infantile cataracts

Cataracts are one of the most treatable causes of visual impairment during infancy. Recent epidemiological studies have shown that they have a prevalence of 1.2 to 6.0 cases per 10,000 infants. The morphology of infantile cataracts can be helpful in establishing their etiology and prognosis. Early surgery and optical correction have resulted in an improved outcome for infants with either unilateral or bilateral cataracts. While contact lenses continue to be the standard means of optically correcting an infant's eyes after cataract surgery, intraocular lenses are gaining in popularity as an alternative means of optically correcting these eyes. Post-operative complications occur more commonly after infantile than adult cataract surgery and many of these complications do not develop until years later. As a result, it is critical that children be followed closely on a long term basis after infantile cataract surgery.

Childhood blindness in India: causes in 1318 blind school students in nine states

It is estimated that at least 200,000 children in India have severe visual impairment or blindness and approximately 15,000 are in schools for the blind. Although this represents a small percentage of the estimated 5 million blind in India, it is significant in terms of 'blind-years'. Strategies to combat childhood blindness require accurate data on the causes to allocate resources to appropriate preventive and curative services. Since socio-economic factors vary in different areas of this industrializing country data should be representative of the country as a whole. This is the first multi-state study to be undertaken in India using the Record for Children with Blindness and Low Vision from the World Health Organization/PBL Programme. A total of 1411 children in 22 schools from nine states in different geographical zones were examined by an ophthalmologist and optometrist. Of these, 1318 children were severely visually impaired or blind (SVI/BL). The major causes of SVI/BL in this study were: (1) corneal staphyloma, scar and phthisis bulbi (mainly attributable to vitamin A deficiency) in 26.4%; (2) microphthalmos, anophthalmos and coloboma in 20.7%; (3) retinal dystrophies and albinism in 19.3%; and (4) cataract, uncorrected aphakia and amblyopia in 12.3%. This mixed pattern of causes lies in an intermediate position between the patterns seen in developing countries and those seen in industrialised countries. The causes identified indicate the importance both of preventive public health strategies and of specialist paediatric ophthalmic and optical services in the management of childhood blindness in India.

Causes of childhood blindness in Sri Lanka: results from children attending six schools for the blind

AIM

The survey aimed to identify the major treatable or preventable causes of visual loss in children attending blind schools in Sri Lanka so that appropriate control measures can be implemented.

METHOD

A total of 226 children with blindness (BL) or severe visual impairment (SVI) attending six schools for the blind were examined and details recorded using the WHO standard reporting form.

RESULTS

Cataract was responsible for 17% of BL/SVI and was the commonest 'avoidable' cause of childhood blindness. Bilateral microphthalmos accounted for one quarter of BL/SVI. Vitamin A deficiency was not a significant cause of visual morbidity.

CONCLUSION

The pattern of childhood blindness seen in this study is typical of a growing number of south east Asian countries which are developing rapidly. Childhood cataract is a major avoidable cause that can benefit from future intervention strategies.

Childhood blindness due to vitamin A deficiency in India: regional variations

OBJECTIVES

To investigate the importance of vitamin A deficiency as a cause of childhood blindness and severe visual impairment (SVI) in India.

DESIGN AND SETTING

Cross sectional survey of children with visual acuity less than 6/60 in the better eye (SVI/blindness), attending 22 schools for the blind in nine states of India.

MAIN OUTCOME MEASURE

Proportion of children with blindness or SVI from corneal scarring attributable to vitamin A deficiency.

RESULTS

245 of 1318 (18.6%) of children had SVI/blindness attributable to vitamin A deficiency. The proportion of SVI/blindness due to vitamin A deficiency ranged from 7.5% (7/93) in Kerala to 26.7% (27/101) in Madhya Pradesh. In Tamil Nadu, 7.5% (9/120) of children in the capital city blind school had SVI/blindness due to vitamin A deficiency, compared with 30.4% (51/168) in a blind school in a rural area of the same state.

CONCLUSION

Overall, vitamin A deficiency is the single most important cause of childhood blindness and SVI in India. There are marked variations by state and also between urban and rural locations.

Causes of blindness in children attending four schools for the blind in Thailand and the Philippines. A comparison between urban and rural blind school populations

Using WHO definitions of visual loss and a standardised methodology, 256 children were examined in schools for the blind in Thailand (1 school) and the Philippines (3 schools). 244 (95%) were blind (BL) or severely visually impaired (SVI). Causes of SVI and blindness were classified anatomically and aetiologically, and avoidable causes identified. Causes of visual loss in Khon Kaen, Thailand (n = 65) and Manila, Philippines, (n = 113) were similar, with conditions of the whole globe accounting for 27.7 and 27.4% of SVI/BL; retinal disease 29.2 and 23.0%; cataract 16.9 and 16.8%; corneal disease 12.3 and 13.4%; and optic nerve disease and glaucoma 6.2 and 8.8%. Perinatal factors accounted for 20.0 and 23.0% of SVI/BL; hereditary disease 13.8 and 17.7%; and 12.3 and 15.0% was due to events occurring during childhood. The underlying aetiology could not be determined in 50.8 and 41.6% of cases, respectively. In the two schools together twenty six children (15%) were blind from retinopathy of prematurity (ROP) and 16 (9%) from corneal scarring attributed to Vitamin A deficiency. 103 of 178 (58%) children had avoidable causes of visual loss. In the Filipino towns of Baguio and Davao (n = 66), the causes of visual loss were different from those in Khon Kaen and Manila, with 54.8 and 42.9% of SVI/BL being due to corneal disease, and only 3.2 and 8.5% to retinal disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Causes of childhood blindness: results from west Africa, south India and Chile

Using World Health Organization definitions of visual loss and a standardised methodology, 905 children were examined in Chile, West Africa and South India. Of these 806 (89%) suffered from blindness (BL) or severe visual impairment (SVI). Causes of SVI and BL were classified anatomically and aetiologically, and avoidable causes identified. In W. Africa (n = 284) the major anatomical cause of SVI/BL was corneal scar/phthisis bulbi (35.9%). Retinal disease accounted for 20.4%, cataract 15.5% and glaucoma 13.0%. Aetiologically 33.8% of SVI/BL was due to childhood factors and 21.1% to hereditary disease. In S. India (n = 305) the major anatomical cause of SVI/BL was corneal scar/phthisis bulbi (38.4%). Retinal disease accounted for 22.6%, cataract 7.4% and glaucoma 3%. Aetiologically 37.0% of SVI/BL was due to childhood factors and 29.8% to hereditary disease. In Chile (n = 217) the major anatomical cause of SVI/BL was retinal disease (47.0%). Cataract accounted for 9.2%, glaucoma 8.3% and 6.9% was due to corneal pathology. Aetiologically 30.4% of SVI/BL was due to hereditary factors, and 20.8% to perinatal factors of which four-fifths (16.6%) was due to retinopathy of prematurity. Avoidable conditions accounted for 70%, 47% and 54% of cases in W. Africa, S. India and Chile respectively.