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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 25  |  Issue : 2  |  Page : 105-111

Pattern of childhood visual impairment and blindness among students in schools for the visually impaired in Lagos State: An update


1 Guinness Eye Center, Lagos University Teaching Hospital, Lagos, Nigeria
2 Department of Ophthalmology, Guinness Eye Center, Lagos University Teaching Hospital, College of Medicine of the University of Lagos, Lagos, Nigeria

Date of Web Publication19-Jul-2018

Correspondence Address:
Abimbola Olayinka Olowoyeye
Guinness Eye Center, Lagos University Teaching Hospital, Idi-Araba, Lagos
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/npmj.npmj_27_18

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  Abstract 

Aim: The aim of this study was to determine the pattern of childhood visual impairment and blindness (VI and BL) among students attending schools for the visually impaired in Lagos State, with a view to providing information on avoidable causes as well as emerging trends that would be useful to policy-makers for the planning and implementation of strategies for the control of avoidable childhood BL in Lagos State. Subjects and Methods: The study was conducted among students enrolled in two schools for the visually impaired in Lagos State who developed VI/BL before the age of 16 years. Participants and their parents/guardians were interviewed to obtain medical history. Ocular and systemic examinations were also performed. Information was recorded using a modified World Health Organization/Prevention of BL Eye Examination Record for Children with BL and Low Vision and analysed using the Statistical Package for the Social Sciences version 23.0. Z-test determined differences in the proportions of the causes of VI/BL between this study and an earlier study. Results: A total of 116 students were enrolled in this study of which 65 (56.0%) were males. Avoidable causes accounted for 58.5% of VI/BL. Preventable causes predominated with measles (15; 12.9%) accounting for the largest proportion. Surgical complications (16; 13.8%) were the largest cause of VI/BL. A statistically significant decrease (P = 0.004; 95% confidence interval = 0.09–0.50) in the proportion of avoidable BL between a previous study carried out in Lagos State and this study was found. Hereditary cataract and cortical VI were the findings of this study not recorded in the previous study. Conclusion: Avoidable causes of childhood VI/BL still predominate among students in the schools for the visually impaired in Lagos State; however, there is a statistically significant decrease.

Keywords: Causes, childhood blindness, pattern, schools for the visually impaired


How to cite this article:
Olowoyeye AO, Musa KO, Aribaba OT, Onakoya AO, Akinsola FB. Pattern of childhood visual impairment and blindness among students in schools for the visually impaired in Lagos State: An update. Niger Postgrad Med J 2018;25:105-11

How to cite this URL:
Olowoyeye AO, Musa KO, Aribaba OT, Onakoya AO, Akinsola FB. Pattern of childhood visual impairment and blindness among students in schools for the visually impaired in Lagos State: An update. Niger Postgrad Med J [serial online] 2018 [cited 2020 Apr 1];25:105-11. Available from: http://www.npmj.org/text.asp?2018/25/2/105/237083


  Introduction Top


The major causes of blindness (BL) in children vary from region to region within countries and change over time within specific localities, which is determined mainly by socio-economic development and the availability of health-care and eye-care services.[1] The World Health Organization (WHO)'s VISION 2020-The Right to Sight programme launched in 1999 aims to eliminate avoidable causes of BL.[2] One of its major priorities is the control of BL in children.[2] BL in children is a priority because, of the years, they would have to live with BL (blind years)[3] and its physical, psychological and economic impact on affected individuals, their families and society.[4],[5],[6] To effectively tackle avoidable causes of childhood BL, it is necessary to monitor the pattern over time in order to recognise emerging trends so that control strategies can be developed and resources targeted towards these.

A recent study in schools for the blind in South-East Nigeria [7] found a reduction in avoidable BL and suggested that cortical visual impairment (CVI) may be an emerging cause of childhood BL in Nigeria. In view of the varying aetiologies of childhood BL in the different geographical areas in Nigeria,[7],[8] it is important for each region to identify the causes of childhood BL and monitor its evolving aetiology over time. The last study, to the best of the authors' knowledge, on the causes of childhood BL in Lagos State was undertaken in 2000.[9] Findings from that study showed that retinal causes predominated and few cases of corneal scars were found.[9]

It is now 18 years since the launch of WHO's VISION 2020 initiative that has led to increased coverage of measles immunisation, Vitamin A supplementation [7],[10] and establishment of Child Eye Health Tertiary Facilities (CEHTFs).[11] Increased awareness and improved health care have appreciable effects on the pattern of childhood VI/BL. These changes are worthy of study.

In light of foregoing, this study seeks to determine the current pattern of childhood VI/BL among students attending the schools for the visually impaired in Lagos State, with a view to identifying avoidable causes and emerging trends which would be useful to policy-makers for the planning and implementation of strategies for the control of avoidable BL in children.


  Subjects and Methods Top


This study took place over a 2-month period (June–July 2017) in two schools for the visually impaired in Lagos State. The study population included students who developed VI/BL before the age of 16 years. There are four schools for the visually impaired in Lagos State which are described as follows. Pacelli School for the Blind and Partially Sighted Children (PSB) located at Surulere is run by the Catholic Mission with additional support from charitable individuals as well as religious and corporate organisations. Students are not required to pay tuition. Federal Nigeria Society for the blind Vocational Training Center located at Oshodi is a voluntary, non-governmental and not-for-profit organisation. Students are admitted on walk-in basis. Although supported primarily by philanthropists, corporate organisations, religious bodies and well-meaning individuals, students are required to pay part-tuition. Nigeria Farm Craft Center for the Blind located at Isheri Olofin is under the auspices of the Federal Ministry of Women Affair Social Development and Rehabilitation Department. Students are admitted based on state allocated and sponsored spaces. Bethesda Home for the Blind located at Mushin is a full-tuition paying school. Nigeria Society for the Blind Vocational Training Center, PSB, and Nigeria Farm Craft Center for the Blind were the three schools chosen for this study. No student from the Nigeria Farm Craft Center for the Blind was included in the study because there was no enrolment for the 2016/2017 session due to government cutbacks. Bethesda Home for the Blind was excluded because it is a full-tuition paying school whose attendance could be influenced by the socio-economic background of the student, thereby introducing bias in the study.

Ethical approval was obtained from the Health Research Ethics Committee of the Lagos University Teaching Hospital, Idi-Araba, Lagos State (Protocol number: ADM/DCST/HREC/APP/55; approval dated from 21 December 2015 to 21 December 2016 with extension to 15 December 2016). Official approval was obtained from the school administrators. Informed consent was obtained from parents/guardians and study participants of legal age. Assent was obtained from each study participant. A sample size of 300 was calculated using the Leslie Kish formula.[12] The standard normal deviate was set at 1.96, the proportion of avoidable childhood BL among students in schools for blind in a previous study was taken as 73.4%[7] while the desired level of precision was set at 5%. Considering that this study assesses a finite population,[13] the sample size was adjusted for the finite population correction.[14] This yielded a minimum sample size of 96 which was further increased to 106 after allowance for 10% attrition. To further increase the power of the study, all willing and consenting students in the schools for the visually impaired in Lagos State who met the inclusion criteria were enrolled in the study.

Pre-survey activities included training of team members on the coding instructions for the modified WHO/Prevention of BL (PBL) Eye Examination Record for Children with BL and Low Vision to maintain standardisation.[15] A pilot study was conducted at a privately owned school for sighted children to familiarise the team members with the standard operating process and to minimise inter-observer error.

Interviews to obtain ophthalmic, medical and surgical history as well as appropriate systemic examination and visual acuity were performed by an ophthalmology resident. Ocular examination including dilated fundoscopy was performed on all study participants by the lead investigator. Refraction was performed by an optometrist. To verify information obtained from study participants and also to obtain detailed pregnancy, birth, medical, surgical and family history, parents/guardians were interviewed by the lead investigator via face-to-face contact and/or via telephone calls.

Distance visual acuity (unaided, aided and with pinhole) testing was done for each eye separately and then for both eyes using an Early Treatment Diabetic Retinopathy Study LogMAR chart at 4 m in a brightly lit room to ensure adequate illumination. Near visual acuity (unaided and aided) was tested in each eye separately and then in both eyes using a near chart held at 33 cm in a brightly lit room to ensure adequate illumination.

Intraocular pressure was measured using a handheld Perkins tonometer after anaesthesia with topical amethocaine and staining with fluorescein. Anterior-segment examination was performed with an Amtech × 3.0 magnification, binocular, head-mounted surgical loupe and bright pen torch. Where necessary, the study participants had their pupils dilated with Appamide Plus ® (guttae tropicamide 1% and phenylephrine 2.5%) after which dilated fundoscopy was performed with a Heine Beta200 direct ophthalmoscope. Cycloplegic refraction (with guttae cyclopentolate 1%) involving retinoscopy with a Heine Beta200 retinoscope followed by subjective refraction with a LogMAR chart at 4 m and trial lens set was performed where indicated. The categories of VI and BL were defined according to the WHO Tenth Revision of the International Classification of Diseases.[16] Information obtained was recorded using a modified WHO/PBL Eye Examination Record for Children with BL and Low Vision.[15] Pedigree charts were drawn to determine the patterns of inheritance in students who had positive family history of vision loss from the same eye condition. Students requiring further medical, surgical and/or optical treatment were referred appropriately.

The data generated were entered into a computer and analysed using the IBM Statistical Package for the Social Sciences (IBM-SPSS) version 23 software program (IBM Corp., Armonk, NY, USA). Descriptive statistics were depicted using absolute numbers and simple percentages. Two proportion Z-tests were generated using EpiTools;[17] this was used to determine differences between the proportions of avoidable VI/BL found in a study on children with low vision and BL in Lagos State conducted 17 years ago (previous study)[9] and findings of this study. A 95% confidence interval (CI) was calculated. A P< 0.05 was considered statistically significant.


  Results Top


PSB had a population of 126 students in the school register, all of whom had VI/BL that occurred before 16 years. One hundred and fourteen out of the 126 students participated in the study. The remaining 12 were students who registered for admission but did not show up for unknown reasons and students absent from school during the study period. The National Society for the Blind Vocational School admits students over the age of 16 years; therefore, only 15 of the 58 students in the school register met the inclusion criteria, out of which only two participated in the study. Seven students declined to participate in the study; the reason given was disillusion with medical practice/practitioners. Six students were absent from the school during the study period due to attrition of registered students because of inability to pay the part-tuition. One hundred and forty-one students were enrolled in this study; there were 116 (82.2%) students on study completion. There were 65 males and 51 females, giving a male: female ratio of 1.3:1. The ages ranged from 7 to 28 years, with a mean age of 13.7 ± 3.2 years. The study participants belonged to the following ethnic groups: Yoruba (82; 70.7%), Igbo (18; 15.5%), Hausa (2; 1, 7%) and others (14; 12.0%). Onset of vision loss was highest from birth to <1 year (39; 33.4%), followed by the age ranges 1–5 years (37; 31.6%), 6–10 years (27; 23.1%) and then 11–15 years (7; 6.0%). One hundred and seven students (92.2%) were blind based on visual acuity assessment while seven (6.0%) had VI. Two students had severe VI while five had moderate VI. In two of the students, visual acuity was labelled as could not be tested (believed blind) because they were unable to give credible responses during visual acuity assessment which was likely due to visual agnosia. In this study, whole globe was the most common anatomic site of abnormality [Table 1] while phthisis bulbi and optic atrophy were the most common ocular abnormalities, leading to vision loss [Table 2]. CVI was found in 4 (3.4%) study participants while amblyopia was found in 5 (4.3%) [Table 2]. Aetiology of vision loss was due to post-natal causes (50; 43.1%) in majority of study participants [Table 3]. A history of prior orthodox ocular surgery was obtained in 40 (34.5%) participants, of which 32 (80.0%) were bilateral and 11 (27.5%) had more than one surgery in one or both eyes. Pseudophakia was found in 11 participants while aphakia was found in four of 26 students who had undergone cataract surgery, while corneal scar, posterior capsular opacity, disorganised globe and phthisis bulbi were found in the remaining 11 students. Two children had a history of retinal detachment (RD) surgery following cataract surgery; it could not be confirmed in either case whether the RD was a complication of surgery or pre-existing. One child had undergone unilateral glaucoma surgery following cataract surgery. In this study, 17 (14.7%) students had positive family history of vision loss from the same eye condition; however, there was no known history of consanguinity. Positive family history of congenital/developmental cataract which on pedigree chart showed that autosomal dominant inheritance patterns were found in 9 (7.8%) students with operated and un-operated cataract. Similarly, positive family history was found in 3 (2.6%) students with retinitis pigmentosa, 4 (3.4%) students with suspected Leber congenital amaurosis and 1 (0.9%) student with oculocutaneous albinism. Avoidable causes of vision loss accounted for 58.5% of VI/BL in this study; preventable causes predominated (38; 32.7%) with measles, presumed central nervous system (CNS) infections and clinically confirmed rubella accounting for the majority [Table 4]. Complications following orthodox ocular surgeries (corneal scar, aphakia, posterior capsular opacity, amblyopia and glaucoma) (16; 13.8%) were the most common treatable causes of BL in this study followed by glaucoma (8; 6.9%) and then cataract (4; 3.4%) [Table 4].
Table 1: Anatomical sites of abnormality leading to vision loss

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Table 2: Major abnormalities leading to vision loss

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Table 3: Aetiology of vision loss

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Table 4: Avoidable causes of childhood visual impairment/blindness

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There was a statistically significant decrease in the proportion of avoidable BL in this study as compared to the previous study [9] (P = 0.004, Z = 2.9, 95% CI = 0.096–0.504) [Table 5]. The comparison between the proportions of aetiologies of vision loss and anatomical sites of vision loss in the previous [9] and the current study is summarised in [Table 6] and [Table 7], respectively.
Table 5: Comparison between the proportion of avoidable vision loss in previous and current study

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Table 6: Comparison between the proportions of aetiologies of vision loss in the previous and current study

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Table 7: Comparison of proportion of anatomical sites of vision loss between previous and current study

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  Discussion Top


Earlier studies on childhood BL in Nigeria showed that avoidable causes predominated and that corneal scarring attributable to measles infection, Vitamin A deficiency (VAD) and harmful traditional eye medications were the most significant causes of childhood BL.[18],[19],[20] There was a statistically significant decrease in the proportion of avoidable BL in this study as compared to the previous study.[9] Similar findings were recorded in South-East Nigeria [7] where it was attributed to a reduction in corneal scarring from measles and VAD due to increase in Vitamin A coverage and measles immunisation rates.

Compared to the previous study,[9] a statistically significant increase in the proportion of post-natal causes of vision loss was found. An increase in measles, presumed CNS infections and surgical complications contributed to the increase in post-natal causes. Eighteen years after VISION 2020-The Right to Sight, with emphasis on increased immunisation and CEHTFs, the expectation is a decrease in post-natal causes of vision loss as was found in South-East Nigeria.[7] Therefore, while a reduction in avoidable causes of vision loss could suggest improving socio-economic development and health-care services, this should be interpreted with caution in light of the increase in post-natal causes of vision loss. A statistically significant reduction in the proportion of hereditary and intra-uterine causes of vision loss was found in this study compared to the previous study. The reduction in intra-uterine causes could be due to improved antenatal care services although this cannot be proven by this study. Furthermore, the reduction in hereditary causes cannot be adequately explained.

Measles was the most common preventable cause of childhood BL found in this study. A slight increase in the proportion of vision loss due to measles was found in this study compared to the previous study [9] although this was not statistically significant. Measles was first recorded as a significant cause of BL in students in Pacelli School for the Visually Impaired in 1974.[18] In 1993,[21] it was the leading cause of BL in students in schools for the blind and vocational rehabilitation centres in Lagos State in a study which included adult-onset BL.

Cataract was the most common hereditary condition seen in this study. A total of 9 (7.8%) students with operated and unoperated cataract had a positive family history of childhood/presenile cataract. In addition to cataract being a treatable condition, hereditary cataract could also be prevented by appropriate genetic counselling of potential parents. A statistically significant decrease in the proportion of VI/BL due to cataract was found in this study compared to the previous study.[9] Only four students with un-operated cataract were seen. The decrease in cataract BL found in this study may be due to increasing availability of paediatric cataract surgical services in Lagos.

Compared to the last known study on childhood BL in Lagos State [9] conducted in a school for the blind where prior ocular surgery was found in 19.2% of students, 34.5% of the students in this study had undergone ocular surgery. There was an increase in the proportion of students who had undergone cataract surgery from 19.2% who had bilateral cataract surgery in the previous study [9] to 20.7% who had bilateral cataract surgery and 1.7% who had unilateral cataract surgery in the current study; however, this was not statistically significant.

The frequency of ocular surgery in this study is higher than the findings in Ondo State, Nigeria,[22] where 17.7% of the study participants had a history of ocular surgery. The high rate of surgeries among the students in this study could be explained by the fact that Lagos State has one of the two most active and equipped CEHTFs in Nigeria.[11] Increase in the rate of cataract surgery among students in the schools for the visually impaired was also found among students in schools for the visually impaired in South-East Nigeria [23] and East Africa.[24]

Surgical complications including corneal scar, aphakia, posterior capsular opacity, amblyopia and glaucoma were the most common aetiologies of vision loss among the participants in this study. Amblyopia was found in 5 (4.3%) students in this study; however, it was not reported in the previous study.[9] All five students with amblyopia were pseudophakic, four out of these five had late surgery. This emphasises the importance of early intervention and optimal refractive correction after surgery in children within the amblyopic age who have cataract.

Compared to the findings 17 years ago,[9] there was an increase in the proportion of students with optic atrophy although this was not statistically significant. Optic nerve disorders rank among the most common causes of childhood BL in high-income countries; however, these are mostly due to unavoidable causes.[25] In this study, optic atrophy was the only optic nerve disorder observed [Table 2]. The cause of optic atrophy was unknown in 50% of cases while the majority of the remaining half was presumed to be sequel to CNS infections based on diagnosis of meningitis given to the parents by supposed trained medical personnel. In addition, optic atrophy was attributed to one case, each of cerebral malaria and measles encephalitis. A study in Port Harcourt, Nigeria, reported CNS infections as the third most common cause of neurological disorders in children, most of which were due to bacterial and tuberculous meningitis.[26]Haemophilus influenzae type b (Hib) has been found to be the leading pathogen in a study on childhood bacterial meningitis in Ibadan.[27] There are available and effective vaccines for the control of Hib as well as some other pathogenic causes of meningitis.[28] This once again highlights the need to increase efforts at improving immunisation coverage.

There was a statistically significant decrease in the proportion of vision loss attributable to retinal causes in this study compared to the previous study.[9] While retinitis pigmentosa accounted for the majority of retinal diseases found in the previous study, suspected Leber congenital amaurosis was the most common retinal disease found in this study. CVI was not reported in the previous study,[9] while it was seen in four students (3.4% of VI/BL) in this study, which is comparable to the findings of Aghaji et al.,[7] where it was suggested that CVI could be an emerging cause of childhood VI/BL. The causes of CVI ascertained in this study were cerebral malaria and a case of stroke on computed tomography scan, for which the cause was not found.

By exploring differences in the pattern of childhood VI/BL between studies conducted 17 years apart, this study has been able to demonstrate temporal trends and show emerging causes of childhood VI/BL among students in schools for the visually impaired in Lagos State.

However, there are limitations to this study. First, schools for the blind/partially sighted have criteria for admission which may eliminate children with certain types of visual loss; hence, findings from this study may not be directly extrapolated to the general population. Second, the schools selected for this study are located in urban areas; therefore, blind children from poor, remote rural areas may be under-represented. Finally, in the absence of documented medical and surgical records, history was insufficient to make a diagnosis in 38.8% of students.


  Conclusion Top


This study showed that avoidable causes of childhood VI/BL still predominate among students in schools for the visually impaired in Lagos State although there is a statistically significant decrease. It also demonstrates that a large proportion of vision loss among these students is caused by diseases associated with significant paediatric morbidity and mortality (measles, presumed CNS infections and rubella) which are vaccine preventable. This underscores the importance of primary health-care strengthening and maintenance in efforts to eradicate childhood BL. It is hoped that with intense campaigns and increased coverage of measles immunisation and Vitamin A supplementation, this significant cause of childhood BL can be successfully eradicated. Furthermore, there is a need for a larger study with national outlook to determine the burden of childhood BL due to rubella in order to be able to make an evidence-based recommendation for Measles Mumps and Rubella (MMR) vaccine. Amblyopia is a significant finding of this study which was not reported in previous studies in schools for the visually impaired in Lagos State.

This study recommends as follows:First, intensified efforts to increase the coverage of immunization. Second, there is need for awareness campaigns to educate the public on the importance of early intervention in children with cataract. Third, adequate counselling of caregivers on the challenges and peculiarities of ocular surgery in children should be adopted to ensure adequate follow-up and compliance with treatment. Finally, there is a need for a proper pro forma to enable recording of causes of VI/BL in the children being admitted to schools for the visually impaired.

Acknowledgement

Special thanks to the parents and staff and students of Pacelli School for the Visually Impaired, Surulere, Lagos State, and National Society for the Blind Vocational School, Oshodi, Lagos State.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]



 

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