Profiling the visual characteristics of school children in Abia State, Nigeria, towards the development of a vision screening protocol.

Abstract

Vision is an important factor for realization of the full learning potential and intellectual performance of a child. While the ability to perform optimally at school depends significantly on the visual status of the individual, the prevalence of common vision conditions in children in Abia State and Nigeria remains largely unknown. The focus of the limited school-based crosssectional studies on paediatric vision conditions have been mainly to quantify significant refractive errors (RE), whereas the prevalence of strabismus, amblyopia, accommodative anomalies and vergence disorders, most of which have been linked to reduced academic-related performance has not been established. It is imperative that the paucity of data on the prevalence of paediatric vision conditions in Abia State is addressed as this will ensure that common visual anomalies are identified early and treated before functional performance of children is affected. An invaluable approach will be through a coordinated and standardized paediatric vision screening delivery system. However, no standard vision screening guidelines was found for school children in Abia State and Nigeria. The purpose of this study is to characterise the visual anomalies in school children in Abia State and to develop a common and comprehensive paediatric vision screening model based on an evaluation of the current paediatric vision screening programs of individual optometrists. This was a population based observational, descriptive study, using cross-sectional design to provide quantitative data. The study consisted of two parts. In part one, a total of 550 school children between 10 and 16 years were recruited from 9 schools (public and private) through a systematic random sampling method starting from the three geographic districts to the classrooms. Data were collected by means of a symptom questionnaire and a series of vision assessment instruments including visual acuity (VA), plus lens test, stereopsis, ocular motility, color vision test, non-cycloplegic autorefraction, accommodation, binocular vision and ocular health. Thirteen children were excluded from further participation due to not satisfying the inclusion criteria. A total of 537 (97.6%) children were examined with a mean age of 13.0 ± 2.0 years and median age of 13 years. Participants were divided into two age groups namely group 1 (10 – 12 years) and group 2 (13 – 16 years). The distribution of participants according to age group, gender and school level showed that 41.9% were from age group 1, 52.5% were female and 43.6% were from primary school. The prevalence of vision conditions such as visual impairment, RE, strabismus, colour vision deficiency, cornea opacity, retinal disorder, accommodative and vergence anomalies in school children in Abia State were determined. The prevalence of presenting, uncorrected and best corrected VA of ≤ 6/12 or worse in the better eye was 3.5%, 4.1% and 0.8%, respectively. Refractive error (78.9%) was the major cause of presenting visual impairment. Other causes include amblyopia (10.5%), corneal opacity (5.3%) and retinal disorders (5.3%). The prevalence of RE was 10.6%. Among the different REs, low categories of myopia, hyperopia, and astigmatism were the most frequent with corresponding values of 88.9%, 86.4% and 82.4% respectively. None of the children had a high degree hyperopia, myopia or astigmatism. Significant differences between age groups were found in hyperopia and myopia, with the prevalence of hyperopia (p = 0.03) decreasing with age while myopia (p = 0.01) increased with age, and as expected with school level (p = 0.04). There was no significant association between gender and RE. Similarly, no significant difference was found between age group or school level and astigmatism. The prevalence of strabismus, corneal opacity, and retinal disorder was 0.2 % each. A small percentage (0.9%) of children had red-green colour vision deficiency. Four participants (additional to the baseline data of 13) who have amblyopia were further excluded from the analysis of accommodative and vergence anomalies. For accommodative anomalies the estimates were 3.9% for accommodative insufficiency, 2.8% for accommodative excess and 10.1% for accommodative infacility. There were no association based on age, gender, school level with specific types of accommodative anomalies. For vergence anomalies, the estimates for low suspect, high suspect and definite convergence insufficiencies were 9.6%, 5.8% and 4.1%, respectively. Other prevalence estimates include convergence excess (2.9%), fusional vergence dysfunction (2.6%), basic exophoria (1.7%), basic esophoria (2.8%), divergence insufficiency (0.8%) and divergence excess (0.6%). The prevalence of high suspect (p < 0.01) and definite (p < 0.01) convergence insufficiency were significantly higher in older children than younger children and as expected therefore with secondary school children than primary school children (p = 0.01). There was no statistically significant association between gender and various vergence anomalies. In part two of this study, all registered optometrists currently practising in Abia State for at least one year prior to the survey were eligible to participate. A self-administered questionnaire was distributed to the optometrists by hand or email. The questionnaire covered areas such as the optometrist’s participation in paediatric vision screening, location of the screenings, the age of children being screened, tests performed and referral criteria, as well as children seen by the optometrists in their practice who were referred from a screening program. Out of a total of 83 registered optometrists that were contacted for the survey, 64 (77.1%) responded. The majority (87.5%) of the respondents were working in the two cosmopolitan cities of Aba and Umuahia and 71.9% were working in private eye care facilities. Analysis of optometrists’ participation in paediatric vision screening showed that only 28 optometrists had participated in one or more vision screening that included children in the last one year before this study and only 10 have provided vision screening services more than four times. Visual acuity and ocular health assessment procedures were the major components of the screening battery of the optometrists. While a child with any disease abnormality was referred for evaluation, the referral criteria for a full examination were inconsistent. The follow-up of those referred for complete examination, could not be established due to lack of uniform guidelines and improper documentation. The present study has systematically characterised the prevalence of vision conditions in children in Abia State and efforts that have been made at their early detection through vision screening. The findings indicate that while the prevalence of visual impairment in school children in Abia State is low, uncorrected RE is the major cause of reduced vision in those with visual impairment. Given that children within the age group of 10 to 16 years are in stages of rapid growth and intensive education which can complicate RE progression, the high proportion of uncorrected RE in the study sample is a major concern as undetected and untreated RE may progress to sight threatening complications or permanent vision loss. On the contrary, a significant proportion of the study participants were affected by visual anomalies which do not necessarily affect VA but can negatively impact on school performance. Such visual anomalies include accommodative and vergence anomalies as well as low magnitude of hyperopia and astigmatism. Considering the public health implication, vision screening should be an immediate intervention. However, data on vision screen survey demonstrated that the existing paediatric screening programs in Abia State are irregular, unequal, unstandardized and limited in range with focus mainly on the detection of REs that are detrimental to VA. The implication is that many children with common paediatric eye conditions including those that have been linked to reduced academic achievements are not routinely screened. Overall, it appears that the current screening programs are not meeting the visual needs of the paediatric population suggesting the need for a new strategy that will increase the coverage and effectiveness of paediatric vision screening in Abia State. It is therefore expected that the public-private partnership strategy as proposed in this study will provide greater access to vision screening services across the state as well as help in the early detection of vision anomalies before functional performance of children is affected.