Nigerian Postgraduate Medical Journal

: 2018  |  Volume : 25  |  Issue : 3  |  Page : 166--171

Visual impairment and ocular morbidities among schoolchildren in Southwest, Nigeria

Adegboyega Sunday Alabi1, Olufisayo Temitayo Aribaba2, Adewumi Olabimpe Alabi3, Olubanke Ilo2, Adeola O Onakoya2, Folasade B Akinsola2,  
1 Me Cure Eye Center; Department of Ophthalmology, Guinness Eye Centre, Lagos University Teaching Hospital (LUTH), Lagos, Nigeria
2 Department of Ophthalmology, Guinness Eye Centre, Lagos University Teaching Hospital (LUTH), Lagos, Nigeria
3 Department of Radiotherapy, LUTH, Lagos, Nigeria

Correspondence Address:
Adegboyega Sunday Alabi
Me Cure Eye Centre, Oshodi, Lagos


Aim: The purpose of this study was to determine the prevalence of visual impairment and ocular morbidities among primary and secondary schoolchildren aged 5 years to <l6 years in Ifo, Ifo Local Government Area in Ogun State, Nigeria. Materials and Methods: The study was a population-based descriptive cross-sectional study conducted among schoolchildren aged 5 years to <16 years old attending primary and secondary schools in Ifo, Ifo Local Government Area of Ogun State. Multistage sampling technique was used for the study. After enumeration and questionnaire administration, the visual acuities of all respondents were measured, followed by examination of the anterior and posterior segment structures of the eyes of the children. Results: A total of 1308 schoolchildren (574 males and 734 females) participated in the study with a mean age of 12.03 years (standard deviation = ±2.572 years). Eighty-seven (6.7%) children had visual impairment and 224 (17.1%) children had ocular morbidities. Of the 87 children with visual impairment, 61 (70.1%) had mild impairment, 19 (21.8%) had moderate impairment and 7 (8.0%) had severe impairment. The common ocular morbidities identified were refractive error 39.7%, high/asymmetrical vertical cup-to-disc ratio (suggestive of glaucomatous optic neuropathy) 33.5%, allergic conjunctivitis 19.2%, corneal opacity 2.7% and lenticular opacity 2.2%. Ocular morbidities identified among children with severe visual impairment were refractive error 5 (71.4%), allergic conjunctivitis and corneal opacity 1 (14.3%) each. Conclusion: The study concluded that with the prevalence of 6.7% of visual impairment and 17.1% of ocular morbidity, it will be beneficial to establish a sustainable school eye health services in schools in Ifo.

How to cite this article:
Alabi AS, Aribaba OT, Alabi AO, Ilo O, Onakoya AO, Akinsola FB. Visual impairment and ocular morbidities among schoolchildren in Southwest, Nigeria.Niger Postgrad Med J 2018;25:166-171

How to cite this URL:
Alabi AS, Aribaba OT, Alabi AO, Ilo O, Onakoya AO, Akinsola FB. Visual impairment and ocular morbidities among schoolchildren in Southwest, Nigeria. Niger Postgrad Med J [serial online] 2018 [cited 2022 Sep 29 ];25:166-171
Available from:

Full Text


The estimated number of people globally with visual impairment is 253 million, with 217 million having moderate-to-severe visual impairment (SVI).[1] Of these, 19 million are children under the age of 15 years. Visual impairment due to uncorrected refractive errors or inadequately corrected refractive errors accounts for 12 million among this age group.[1]

The United Nations Children's Fund defines a child as an individual aged <16 years.[2] A child with moderate visual impairment is an individual below 16 years of age who has a presenting visual acuity (VA) worse than 6/18 in the better eye.[1],[2] Presenting VA was used according to the revised World Health Organization's definition to include uncorrected refractive error.[2]

Data on the prevalence and causes of SVI in children are needed for planning and evaluating preventive and curative services including planning special education and low vision services.[2]

The amelioration of childhood blindness and visual impairment is a stated priority of vision 2020 – the right to sight, the Global initiative established by the World Health Organization and the International Agency for the Prevention of Blindness.[3],[4]

Vision is critical for conducting activities of daily living and affects development, learning, communication, work life, health and quality of life.[5] Early vision screening helps prevent blindness and permanent impairment from most eye diseases. Eye disorders can be reduced or prevented with early detection and treatment. Therefore, vision screening is an appropriate and necessary activity from a public health standpoint.[5],[6]

Undetected ocular disorders in children may lead to academic failure and cause severe ocular disability later in life.[7],[8] Moreover, planning of the youth's career is very much dependent on vision, especially in jobs such as the military, aviation, railways and in many other professions such as accounting, medicine, surgery, engineering, architecture and surveying.[5],[6]

The benefits of a school screening programme are significant compared to a community-based or office-based screening programme.[5] There is a ready access to the target population, providing the platform for screening large number of children who might not have access to other screening venues. Several studies confirm that approximately 75% of all children with vision problems were first identified in a school setting.[9]

School-based screening programmes are aimed at providing eye care services at no extra cost to the parents and intended at identifying children at risk of visually disabling conditions that can become permanent if not detected and treated early.[5],[9]

Children in the school-going age group (6–17 years) represent about a quarter of the population in the developing countries and are, therefore, a captive population as they are easily accessible to intervention.[8] The schools are, therefore, the best place for effectively implementing eye healthcare programme among children. At present, there are no school eye health screening services being rendered in the study area and hence the need to conduct this study with the purpose of determining the pattern of visual impairment and help the visually impaired to access appropriate care, thus preventing permanent ocular morbidity and optimising academic performance among schoolchildren.

The aim of the study was to assess visual impairment and ocular morbidities among primary and secondary schoolchildren aged 5 years to <l6 years in Ifo, Ifo Local Government Area in Ogun State, Nigeria.

 Materials and Methods

The study was a population-based descriptive cross-sectional study that used a quantitative method of data collection and was carried out over a 6-week period from May to June 2013. The study was conducted among schoolchildren aged 5 years to <16 years old attending primary or secondary schools in Ifo, Ifo Local Government Area of Ogun State. Visual impairment was defined as presenting VA worse than 6/9 in the better eye and classified into mild (6/12–6/18), moderate (<6/18–6/60) and severe (<6/60–3/60).[10] Blindness was defined as best-corrected VA worse than 3/60 in the better eye.[1],[2] Refractive error was defined as unaided distant VA (DVA) worse than 6/9 in the better eye which improves with pinhole or glasses.[11],[12] Cataract was defined as any lenticular opacity irrespective of the effect on vision.[13] Glaucoma suspect was defined using vertical cup-to-disc ratio (CDR) ≥0.7 or CDR asymmetry of 0.2 or greater between the two eyes.[5],[14] Multistage sampling technique was used for the study. All the eight public secondary schools in the study area were selected; simple random sampling by balloting was used to select eight public primary schools of the 49 in the study area. The two government-approved privately owned secondary and two privately owned primary schools were selected. Thus, a total of 20 schools participated in the study.

Ethical approval was obtained from the Health Research Ethics Committee (HREC) of the Lagos University Teaching Hospital, Idi-araba, Lagos State, with protocol number ADM/DCST/HREC/97 and approval dated from 06-04-2011 to 06-04-2012. Permission and informed consent were gotten for the study from the Ogun State Ministry of Education and each of the participant's parents/guardians, respectively.

The sample size for this study was calculated using the Leslie-Kish formula,[15] with the standard normal deviate at 95% confidence level set at 1.96, the prevalence of an attribute present in the population, P was taken as 15.5% = 0.155, based on a previous study in Nigeria that reported a prevalence of 15.5% for ocular morbidity in children [16] and the desired level of precision, d was set at 2%. Thus, the minimum sample size (n) calculated when the population is >10,000 with the above parameters was 1258, and following the inclusion of attrition rate of 10%, the sample size came to 1384.

Stratified sampling technique by proportional allocation was used to select the number of students and pupils that participated in the study. A pilot survey that provided the research team with practical field experience and allowed pretesting of the questionnaire was conducted separately in a school that was not selected for this study.

The survey was carried out by a team that comprised an ophthalmologist, an ophthalmic nurse and three community health workers with ophthalmic exposure. The community health workers performed the enumeration of the respondents and assisted the ophthalmic nurse with the measurement of the VA. The ophthalmologist conducted anterior and posterior segments examination on the respondents.

Following enumeration and questionnaire administration, all children had their VA measured with the Snellen's chart. Subsequently, anterior segment structures were examined with a pen torch and followed by the posterior segment structures examination with the direct ophthalmoscope.

Respondents with visual impairment and/or ocular abnormality in any of the ocular structures were referred, with appropriately filled referral forms to the base hospital for further evaluation and follow-up.

The data were entered into a database and analysed using the IBM Statistical Package for the Social Sciences software version 20 (IBM SPSS, IBM Corp., Armonk, NY, USA). Data were expressed as the mean and standard deviation (SD) for continuous variable ands as frequencies and percentages for categorical variables. The analysis was conducted with the use of Chi-Square tests to evaluate the association between categorical variables.


A total of 1308 children were examined in the survey representing 94.5% of the 1384 children enrolled for the study. The mean age was 12.03 years ± 2.572 and SD 14 years was the age with the highest number of respondents examined.

[Table 1] shows the sociodemographic pattern of respondents. There were more female respondents 734 (56.1%) than male respondents 574 (43.9%), with an overall female-to-male ratio of 1.3:1. Majority of the respondents were of the Yoruba ethnic group (91.4%). One thousand and seventy one (81.9%) of the respondents attend public (government owned) schools, while 237 (18.1%) of the respondents were students or pupils in privately owned schools. Four hundred and forty six (34.1%) are pupils in primary schools while 862 (65.9%) are students in secondary schools.{Table 1}

Prevalence of visual impairment

Normal vision was recorded in 1221 (93.3%) of the respondents, while 87 (6.7%) have impaired vision. Among the respondents with impaired vision, 61 (70.1%) had mild impairment, 19 (21.8%) had moderate impairment and 7 (8.0%) had severe impairment as depicted in [Figure 1].{Figure 1}

[Table 2] shows the distribution of the visual categories of the respondents by age group. P value (0.43) showed no statistically significant association between the age groups of the respondents and visual impairment.{Table 2}

[Figure 2] shows the distribution of the visual categories by sex, with 33 (5.7%) of the 574 male respondents and 54 (7.4%) of the 734 female respondents had impaired vision. P value (0.148) showed no statistically significant association between the sex of the respondents and visual impairment.{Figure 2}

[Figure 3] shows that 25 (5.6%) of the 446 respondents in primary school and 62 (7.2%) of the 862 respondents in secondary school had impaired vision. P value (0.165) showed no statistically significant association between the level of education and visual impairment.{Figure 3}

Ocular morbidities

A total of 1084 (82.9%) respondents have normal ocular findings, while 224 (17.1%) have ocular morbidities. [Table 3] below showed that visual acuities that improved with pinhole (suggestive of refractive error) accounted for the highest (39.7%) cause of ocular morbidity among the respondents. Followed by large vertical CDR and/or asymmetry of discs that accounted for 33.5% of ocular morbidity identified among the respondents.{Table 3}

Conjunctival anomalies were responsible for 20.5% of ocular morbidities, 43 (19.2%) were due to allergy while 3 (1.3%) were presumed infective in origin. Corneal opacity and lenticular opacity were each responsible for 2.7% and 2.2% of ocular morbidities, respectively.

One respondent had bilateral moderate, and another had a left ptosis. Three (0.2%) of the respondents had ocular misalignment of which two had impaired vision that improved with pinhole and one had normal vision. Two (0.15%) respondents with impaired vision that improved with pinhole had nystagmus. A respondent had bilateral chorioretinal scars with moderately impaired vision.

[Figure 4] showed that of the 224 respondents with ocular morbidities, 137 (61.2%) had normal vision, while 87 (38.8%) had impaired vision and refractive error was the most common cause of visual impairment among the respondents with ocular morbidities.{Figure 4}

Refractive error

Seventy-seven respondents with VA worse than 6/9 improved with pinhole [10](suggestive of refractive errors) which accounted for the highest cause of visual impairment among the respondents, 55 (71.4%) had mild impairment, 17 (22.1%) had moderate impairment and 5 (6.5%) had severe impairment.

The ocular morbidities identified among the seven respondents with SVI [10] were refractive errors (suggested by improved VA with pinhole) 5 (71.4%), allergic conjunctivitis 1 (14.3%) and corneal opacity 1 (14.3%).


The place of good vision as a criterion for learning cannot be overemphasised, thus schoolchildren may require higher level of the sense of sight than the majority of the population.[5],[6] Therefore, using presenting VA worse than 6/18 in the better eye for the definition of visual impairment may be inappropriate and inadequate when carrying out visual impairment surveys among schoolchildren.[17]

Furthermore, children with mild visual impairment and ocular morbidities that could lead to blindness if not treated early could be missed during school eye screening that used presenting VA worse than 6/18 to define visual impairment.

The study recorded 94.5% participation among recruited children due to the absence of some children from school on the day of the study and refusal of some parents to give consent for their ward to participate in the study.

The prevalence of 6.7% of visual impairment in our study is similar to a study conducted in Ibadan where 7.4% was obtained.[18] However, in Ilesha, Southwestern Nigeria, also in the same geopolitical zone where our study was conducted, Ajaiyeoba et al.[16] found a prevalence of 1.3% of visual impairment. The difference in diagnostic criteria where the study in Ilesha used VA worse than 6/18 to define visual impairment as against this study that used VA worse than 6/9 to define [11] visual impairment may explain the disparity.

The prevalence of 17.1% of ocular morbidity in our study is similar to 15.5% reported in Ibadan.[18] Unlike, the 19.3% reported by the Jos Plateau study [19] and a prevalence of 22.5% of previously undetected eye disorders in the Ile-Ife study.[20] This may be due to different diagnostic criteria, methodology and possible ethnic variations.[11]

Improvement of DVA with pinhole which suggests refractive error, high vertical CDR and/or CDR asymmetry, allergic conjunctivitis, corneal opacity and cataract was the common ocular morbidities identified by our study. These findings somewhat bear similarity to other previous studies in Nigeria. Allergic conjunctivitis, refractive error, lid disorders, corneal scarring and cataract were seen in the Ilesha study,[16] while allergic conjunctivitis, refractive error, infective conjunctivitis and chalazion were reported by workers in Ile Ife.[20]

Furthermore, in Jos Plateau,[19] refractive error and corneal opacity top the list of common causes of ocular morbidity, whereas the workers in Kaduna [21] found allergic conjunctivitis, refractive error and infective conjunctivitis as the common causes of ocular morbidity among schoolchildren.

The prevalence of childhood visual impairment and ocular morbidities between Western nations and developing countries differs significantly.[2] This could be as a result of quality of healthcare, poverty, absence of compulsory screening programme for pre-schoolers and school-going children and late disease detection.

However, the prevalence of 6.7% of visual impairment in our study is similar to what the United States preventive services task force reported, with visual impairment affecting 5%–10% of young children captured in their study.[5],[6] Furthermore, in a study by Rose et al., they recorded the prevalence of 19.8% ocular morbidity, not so different from the prevalence of 17.1% in our study.[22]

The factors that may explain the high rate of respondents with high vertical CDR and/or CDR asymmetry in our study include the study definition used, racial variation in the prevalence of the disease and possibility that there may be a lot of false positives, hence the use of the term 'glaucoma suspect' and referral of all suspects to base hospital for detailed evaluation.

This study showed there was no statistically significant association between the age, sex and level of education (primary or secondary) of the respondents and the presence of visual impairment.[13]

The ocular morbidities found among respondents in our study are either preventable or treatable, thus visual impairment or blindness that can result from these conditions are avoidable. This supports the report in the literature that about 80% of all visual impairment globally can be prevented or cured.[1],[2] Furthermore, the knowledge that most ocular morbidities identified among schoolchildren in our study area are preventable or treatable should encourage the setting up of school eye health programme to ensure early diagnosis and prompt treatment.


This study demonstrates the need for the establishment of eye health programme in schools. The study further demonstrates that ocular morbidity can be present in the absence of visual impairment and stressing the need for early detection and treatment before vision and academic performance are affected. Information provided by the study could assist the government (state and local) and the schools in planning and incorporating school eye health screening into their sustainable health programs.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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