Aim To ascertain the causes severe visual impairment and blindness (SVI/BL) in schools for the blind in southeast Nigeria and to evaluate temporal trends.
Methods All children who developed blindness at <15 years of age in all the three schools for the blind in southeast Nigeria were examined. All the data were recorded on a WHO/Prevention of Blindness (WHO/PBL) form entered into a Microsoft Access database and transferred to STATA V.12.1 for analysis. To estimate temporal trends in causes of blindness, older (>15 years) children were compared with younger (≤15 years) children.
Results 124 children were identified with SVI/BL. The most common anatomical site of blindness was the lens (33.9%). Overall, avoidable blindness accounted for 73.4% of all blindness. Exploring trends in SVI/BL between children ≤15 years of age and those >15 years old, this study shows a reduction in avoidable blindness but an increase in cortical visual impairment in the younger age group.
Conclusions The results from this study show a statistically significant decrease in avoidable blindness in children ≤15 years old. Corneal blindness appears to be decreasing but cortical visual impairment seems to be emerging in the younger age group. Appropriate strategies for the prevention of avoidable childhood blindness in Nigeria need to be developed and implemented.
- Child health (paediatrics)
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In 1999, the WHO and the International Agency for the Prevention of Blindness (IAPB) launched VISION2020—a global alliance for the elimination of avoidable blindness.1
This alliance considered childhood blindness as a priority because it has been estimated that there are 1.4 million blind children, accounting for 75 million blind years of their lives.2
The pattern and burden of childhood blindness varies from region to region and on the level of socioeconomic development of the region. Corneal disease and cataract predominate in the poorest economies, retinopathy of prematurity (ROP) in middle income economies, and neurological lesions in the affluent economies.3 Also, poorer countries are disproportionately affected with 75% of the world’s blind children living in the poorest regions of Asia and Africa.4
Nigeria is a lower middle income country(LMIC)5 and so childhood blindness patterns may exhibit features of both lower and middle income economies.
Some of the strategies for the prevention of childhood blindness include vitamin A supplementation, measles immunisation, and the development of child eye health tertiary facilities (CEHTF), 1 per 10 million population by 2020, to treat congenital cataract, glaucoma and ROP.2
In Nigeria, measles immunisation coverage has increased from 54% in 1990 to 71% in 2011 and vitamin A supplementation is 73%.6
In countries where corneal blindness is decreasing because of vitamin A supplementation and measles immunisation, cataract is becoming an important cause of childhood blindness.7
There are six geographical zones in Nigeria with varying vegetation and with different ethnicities and customs.
Recent studies from Nigeria have shown varying aetiologies of childhood blindness in different geographical areas. In school for the blind studies, the most common causes of blindness were: in the southwest zone (2008) cornea 29.1% and cataract 26.7%,8 in the northwest zone (2005) cornea 35.5%,9 and in the southeast zone (2003) cataract 30.4% and cornea 21.7%.10
These geographical differences were collaborated by population based studies using the key informant methodology- northwest zone (2008) corneal opacity 55%, cataract 15%11 and south-south zone (2011) cataract 35% and cornea 19%.12
Results from blind schools may therefore give an idea of the various aetiologies of childhood blindness in that zone. This study aims to ascertain the causes of severe visual impairment and blindness (SVI/BL) in schools for the blind in south-eastern Nigeria, to identify avoidable causes and by comparing older and younger children, and to estimate temporal trends in the causes of childhood blindness.
There are three schools for the blind in Southeast Nigeria and all were visited for this study between August 2011 and January 2012. These schools were established to cater for all the blind children in this region and also to offer vocational training/rehabilitation for those with adult onset blindness. Only those who developed blindness at ≤15 years were eligible to be enrolled in the study.
Ethical clearance for this study was obtained from the institutional research committees of both the University of Nigeria Teaching Hospital, Enugu, Nigeria and also the London School of Hygiene and Tropical Medicine. Also informed consent was obtained from the head teachers of each school and the participants. All investigations were performed according to the guidelines of the 1964 declaration of Helsinki and its later amendments. All children for whom consent was obtained were examined. A concise history on age, onset of visual loss, family history of blindness and consanguinity was taken. The presence of any associated disability was also documented. All the ocular examinations were done by one of the authors (AA).
Visual acuity (VA) was measured using Snellen’s tumbling E Chart. The vision was classified according to the WHO categories of vision.13 The anterior segment was examined with a pen torch and head mounted magnifying loupe. The posterior segment was examined by indirect ophthalmoscopy after dilating with 1% tropicamide.
All the data were recorded on a WHO/Prevention of Blindness (WHO/PBL) form. The anatomical and aetiological classifications of blindness were done using the WHO/PBL form and coding instructions.14 Those with treatable causes of blindness were referred to the nearest secondary or tertiary eye centre to them. The data were entered into a specially designed database in Microsoft Access and transferred to STATA V.12.1 (Statcorp, Texas) using STATransfer.
From here frequency tables were generated. With the aim of exploring possible trends, the participants were divided into two groups (≤15 and >15 years).15 The student’s t test was used to compare the difference in quantitative variables in these two groups. Differences in causes and proportions of available blindness were analysed using the z-test statistic in STATA. Tests of significance were set at the 95% level.
There were a total of 139 eligible participants, of whom 127 were examined. Two eligible participants declined to be examined and the others were absent from the school at the time of our visits. This gives a participation rate of 91.4%. There were 65 males and 62 females.
Three of the students had visual impairment and were not included in other analyses. There were 124 children with SVI/BL. Their mean age was 16.7±4.9 years. The difference in the mean age between the >15-year-old group and ≤15-year-old group was 7.8 years (p=0.000).
About 89% of the subjects were blind while 8.7% had severe visual impairment. The WHO category of vision of the participants is presented in table 1.
The lens was the most common site of abnormality causing SVI/BL (33.9%). This was followed by whole globe lesions (28.2%, with 12.1% from glaucoma/buphthalmos). The cornea accounted for 21.8% of the lesions mainly from measles/vitamin A deficiency (VAD) (18.5%).
To test for trends in causative changes over time, the two different age groups were compared (table 2).
The greatest change between the two age groups was in the cornea, showing corneal disease as being a less frequent anatomical site in children aged ≤15 years. The main causes of corneal lesions were VAD and measles. This difference was not statistically significant (p=0.26). However, there was a trend between the two age groups in the ‘other’ category (p=0.05). There were a total of six subjects in this category. All of them had cortical visual impairment (CVI). The profiles of these subjects are presented in table 3.
Five of the six subjects were in the ≤15 years age group. Three of the subjects had associated neurological deficits (motor/cognitive/hearing loss). The subject with VAD had corneal opacities which were not visually significant. There was a history of perinatal hypoxia in subject 1.
The aetiological cause of blindness could not be determined in 49.2% of the subjects. This group comprises subjects with non-hereditary/non-traumatic cataracts, glaucoma/buphthalmos, and abnormalities since birth. Postnatal (childhood) factors were responsible for SVI/BL in 29.8% of cases. These include measles/VAD, harmful traditional eye medication (HTEM), and trauma. About 5.7% of the participants had clinical features suggestive of rubella. There was a history of cerebral hypoxia in the subject with SVI/BL of perinatal aetiology. This is presented in table 4.
Analysing aetiological causes by age groups, the greatest change was in the postnatal factor, accounting for 34.8% of blindness in the older age group and 25.4% of blindness in those ≤15 years. There was no change in the intrauterine factor as a cause of blindness. Also, the proportion of those in the two age groups with indeterminate causes was almost similar, with 49.1% in those ≤15 years and 47.8% in those >15 years. There was an increase in the relative proportions of those ≤15 years with hereditary causes of blindness (16.4%) compared with their older counterparts (10.1%). However, none of these trends was statistically significant.
There were a total of 91 participants with avoidable blindness, making this responsible for 73.4% of SVI/BL in these subjects (table 5).
Testing for trends in the causes of avoidable blindness between those ≤15 years of age and those >15 years, measles/VAD was responsible for 10.9% (6) of cases in the younger age group and 24.6% (17) in those aged >15 years (p=0.05 STATA z statistic). The proportion of children who were blind from cataract, glaucoma and HTEM did not show any statistically significant trend (p=0.5, p=0.3 and p=0.8, respectively, STATA z statistic).
Overall, there was a trend suggestive of a decrease in avoidable blindness in the younger age group, 60% (55) compared with the older age group of 84% (69) (p=0.003 STATA z statistic).
The majority of childhood blindness in developing countries is avoidable and the causes may have changed over the years. To develop or fine tune strategies for the prevention of childhood blindness, it is important for each region to identify the causes of childhood blindness and monitor its evolving aetiology over time. This is the first study of childhood blindness in Nigeria that demonstrates a significant reduction in the proportion of avoidable blindness between the older and younger age groups, suggesting a temporal change. There were trends suggesting that this effect was due to a reduction in corneal scarring from measles and VAD. A notable increase in vitamin A coverage and measles immunisation rates over the last 10 years may explain this.6
Cataract is becoming a significant cause of childhood blindness in developing countries where there are programmes for the control of VAD and measles.7 It is therefore important for strategies to be developed and implemented to combat childhood cataract blindness.
The WHO recommendation of one CEHTF per 20 million population has not been met in southeast Nigeria. There is currently no CEHTF but there are five tertiary eye centres with paediatric cataract surgery carried out by general ophthalmologists in one of them.
However, it is not enough to have a CEHTF. In Calabar, southern Nigeria, which has a CEHTF, cataract blindness is still the most common cause of avoidable blindness.12 The reasons for failure of uptake of cataract surgery in children include ignorance about the condition, ineffectual reference linkages, and financial barriers.16
This suggests that information education communication and behavioural change communication need to be carried out at the community level in a manner that is appropriate and acceptable to the community.
Paediatric glaucoma management in developing countries can be challenging.17 It has been estimated that there are as many as 60 000 children who are blind as a result of glaucoma in low income countries.4
In this study, 12% of blindness was attributable to glaucoma. On average, glaucoma is responsible for up to 11% of childhood blindness in Africa.18 Despite these relatively high proportions, childhood glaucoma is not getting the attention it deserves.
The key to prevention of childhood cataract and glaucoma blindness lies in early diagnosis, prompt referral, and skilled management. Early diagnosis and referral can be done by training health workers who handle newborn babies and young infants. These should include midwives, traditional birth attendants, and immunisation personnel. New and expectant mothers during routine antenatal and postnatal clinic visits should be made major stakeholders in the prevention of childhood blindness. Here, they can be trained to identify and report such lesions.
There is also the need to develop effective referral systems, skilled manpower, and appropriate facilities for the management of these conditions. Unless these issues are addressed, paediatric cataract and glaucoma blindness will remain a problem in developing economies.
Rubella was suspected in 5.7% of children with SVI/BL. An estimated 238 000 children annually are born with rubella in developing countries.19 Rubella immunisation is not routinely given in Nigeria. However, it is recommended only in countries that have achieved 80% measles vaccination coverage to prevent an exacerbation of the problem.19 ,20 There is need to improve the measles vaccination coverage in Nigeria which is currently 71%.6 Advocacy for rubella immunisation can then be done when the critical level for measles immunisation is achieved and sustained.
In this study, CVI accounted for 4.8% of blindness. Not all of the children had neurological deficits. CVI has been defined as congenital or acquired brain-based visual impairment with onset in childhood, unexplained by an ocular disorder and associated with unique visual and behavioural characteristics.21 There are often additional suggestive factors such as neurological deficits (motor and/or cognitive and/or hearing loss),14 ,22 but studies have shown that neurological deficits are not always manifest in CVI cases.22 ,23
In a recent in a school for the blind in Suriname, CVI accounted for 7.7% of childhood blindness.7 CVI seems to be on the increase. In this study it was mostly seen in the younger age group. A history of perinatal asphyxia was elicited from one of the subjects who had a close relation on the teaching staff of the school. As part of the admission policy, medical records are not required before admission, so it was not possible to access the medical history of the subjects from the school. It is possible that the other causes of CVI could have been due to perinatal causes as well. As postnatal care improves and neonatal mortality decreases, there may be an increase in neonatal morbidity as children who would otherwise have died, survive albeit with neurological deficits.
CVI develops in neonates as a result of advances in perinatal care and improved survival rates of preterm babies.23
For the same reasons, ROP is likely to emerge as a significant cause of childhood blindness in sub-Saharan Africa. Middle income countries with improved neonatal care have improved survival rates of preterm or low birthweight babies and are at risk for ROP.24
Permanent CVI may also be acquired after the neonatal period from cerebral malaria or meningitis.25 Blind school studies are very likely to underestimate the proportion of childhood blindness due to cerebral pathology because traditionally schools for the blind would not accept children with additional disabilities. Also, many children with CVI and multiple disabilities may not have access to any education, even in special schools. Furthermore, it is possible that children with CVI with additional impairments do not survive as it has been estimated that, in developing countries, the majority of children die within a few years of becoming blind.4 A hospital based survey of cerebral palsy patients from Nigeria found that 62% were blind and that optic atrophy and cerebral visual loss were the main factors.26 More research may need to be done on the aetiology of childhood CVI and appropriate strategies to prevent it.
Caution should be applied when extrapolating these results to the general population as they represent only a small percentage of blind students in southeast Nigeria. However, since inclusive basic education is yet to be implemented in this region, it is representative of all the blind children currently receiving primary education in this region.
Nevertheless, studies conducted in schools for the blind have the advantage of being able to examine many children in one location and may give an idea of the relative importance of causes of blindness in any particular region.27
The results from this study show a statistically significant decrease in avoidable blindness between children aged ≤15 years and those >15 years old, and this is encouraging.
Corneal blindness appears to be decreasing, but glaucoma and cataract blindness need to be addressed. Appropriate strategies for the prevention childhood blindness from these conditions need to be developed and implemented in Nigeria.
Also, CVI seems to be emerging in the younger age group. More research on the epidemiology of CVI in children in LMICs is required.
We thank the students and staff in the schools for the blind for their cooperation.
Contributors All the listed authors contributed to the planning and execution of the study. AA and RB analysed and interpreted the results and drafted the article. This was reviewed and corrected by all authors before submission.
Funding This work was made possible by a grant from the British Council for the Prevention of Blindness.
Competing interests None.
Ethics approval London School of Hygiene & Tropical Medicine and University of Nigeria Teaching Hospital Institutional Review Boards.
Provenance and peer review Not commissioned; externally peer reviewed.
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