DOI: https://doi.org/10.21203/rs.3.rs-41148/v1
Background
Visual impairment impacts negatively on quality of life. Kenya has a total fertility rate of 3.5 an indication of more younger generation. However, little is known on the prevalence and causes of visual impairment in the children population of Kenya.
Methods
This cross-sectional population-based study included 3400 (1800, 52.9% female) randomly selected children with a mean age of 12 ± 2 years (range 5–16 years) in Kenya. Visual acuity was taken using snellens chart at 6 meters. Anterior and posterior segments were assessed using slit lamp and indirect ophthalmoscope. The World Health Organization formed the baseline for calculating prevalence of visual impairment.
Results
Visual acuity measurements were available for 3240 (95.3%) participants. The prevalence of visual impairment, based on pin-hole value, using World Health Organization, was 1.7 ± 0.3%. The prevalence of visual impairment, based on presenting visual acuity value, was 2.4 ± 0.7%, using the World Health Organization definition. Multivariate analysis demonstrated that the presence of visual impairment on pin-hole, according to World Health Organization definition increased significantly with increasing age (odds ratio 1.230, P = .021) and increased astigmatism (odds ratio 0.834, P = .032), but not significantly associated with socioeconomic, ocular conditions after adjusting for age and astigmatism. Lack of refractive error correction was the most common reason for presenting visual impairment. Causes of visual impairment due to presenting visual acuity were amblyopia (24%), nystagmus (14%), myopia (49%) and hyperopia (13%).
Conclusion
The prevalence of visual impairment in Kenya increased significantly with socio-economic activities. Uncorrected refractive error remains the major causes of visual impairment.
Loss of vision remains the third most major cause of visual impairement globally and a major issue of public health concern. There are raising cases of visual impairment and the World Health Organization gives a roung estimates of 285 million people being visually impaired1. Researchers have conducted studies reporting the prevalences and causes of visual impairment among different populations from different geogoraphical regions. However, there is paucity of data on prevalence and causes of visual impairment in Kenya among the children population. Kenya has a total population of 47 million people with a total fertility rate of 3.5 and a life expectancy of 67.5 years2. Kenya comprises of 43 ethnic groups, with a rural population of 80% and urban population of 20% however the healthcare system is more advanced in the urban areas3. Kenya being a country with a modernized port, trade has resulted into entrance of different commodities which may influence the lifestyles. The healthcare system in Kenya comprises of public and private systems. While the life- style is comparable to Uganda, the healthcare system and ethnic composition remain distinct for Kenya.
The latest population-based vision survey in Kenya has never been reported. However, in 2006 a study examined 384 adults in Nakuru County age 60 years and above4. Based on presenting visual acuity, the prevalence of visual impairment (< 6/18) was 10.7%. This study was limited by the use of presenting visual acuity, instead of pin-hole acuity, when presenting visual acuity was < 6/18. The fundus was not dilated for examination. At the same time the previous study only dilated subjects who could not see (6/18), hence concluded on causes of visual impairment with information from presenting visual acuity5. Therefore this study made a conclusion with supplementary information from perimetry. Our present study attempts to provide more information on the prevalence and causes of visual impairment of children in Kenya. The information will be of significance to the public health planning.
This cross-sectional study was carried out from January 2018 to February 2019. Participants were randomly selected from the 47 county referral hospitals in Kenya in the 8 provinces. The provinces includes: Nyanza, western, central, eastern, rift valley, north eastern, Nairobi and Mombasa6. The participants belonged to the cohort of children who had visited the hospitals three times consecutively. The sample was obtained from list of patients who had been visiting the facility over some time till 2017. The participants were randomly selected from 47 counties across Kenya. Only children who could be traced with a record from the hospital were included in the study. Elegibility was based on visiting the same facility frequently and having the Universal Health Coverage card registered in the facility. We excluded children with psychiatric history due to lack of concentration during ocular examination. For the randomly selected participants, a detailed invitation letter was emailed to them with details about the study. To ensure a good response rate a consistent contact follow up was adopted. Participants who agreed were given a prior call to confirm before the examination and where the examination would be carried out at. Constant reminders were made to the participants on when the examination would be conducted. The recruitment of the participants lasted for 6 months, that is from January to June 2018
After examination participants were given a bottle of soda and bread just as a form of appreciation for taking their time to participate in the study. Being that the facilities had consultant ophthalmologists, participants who required more attention were reviewed by the ophthalmologists. The team consisted of ninety four optometrists with one hundred research assistants. The ocular history was recorded by the research assistants using a structured questionnaires in Kiswahili. The parents knowledge was sought on amblyopia, nystagmus, hyperopia and refractive error. Immedietrly the participants arrived at the examination area, the history was taken followed by taking visual acuity. The visual acuity was recorded at 6 meters using the Snellens chart. For participants who could not see 6/18, a pin hole was used to confirm if it’s a pathology or refractive error. For participants whose vision improved on pin hole, Retinoscopy was done to determine the magnitude and type of refractive error they had. After Retinoscopy, slit lamp assessment was done to examine the anterior segment for any abnormality. The pupil was dilated using tropicamide 0.5% to assess the posterior part of the eye. Finally an indirent ophthalmoscopy was conducted to assess the posterior segment. Ruby lens of + 90D was used to assess the fundus. To allow for comparison with the World Health Organization, the definition of visual impairment was used8.
Statistical analysis was carried using Statistical Package for Social Sciences software (SPSS, version 17.0). Descriptive statistics was conducted which included the mean, standard deviation (SD), median and percentages. The prevalence of visual impairment was determined based on age and gender. A chi-square test was conducted to compare the prevalence of visual impairment between different gender and age groups. Logistic regression analysis was conducted to compare associations of visual impairment.
A total of 3240 (1600, 49.4% male; from 47 county referral hospitals) out of 3400 eligible subjects (response rate: 95.3%) participated in the survey from January 2018 to February 2019 Table 1. All participants were Kenyans, with a mean age of 12 ± 2 years (range 5–16 years). Visual acuity measurements were available for 3181 out of 3240 (98.2%) subjects. Those participants who had no visual acuity score were significantly different from those with visual acuity score based on gender (49.4% vs. 50.6%, P = .014) and age (5 ± 4.3 vs. 11 ± 4.7, P = .012).
| Parameters | Values |
|---|---|
| Mean age | 12 ± 6 years (range 5–16 years). |
| Gender male/female | 1600/1640 |
| Nyanza province | 340 |
| Western province | 420 |
| Rift valley province | 500 |
| North eastern province | 440 |
| Nairobi province | 600 |
| Eastern province | 450 |
| Central province | 490 |
The mean for presenting visual acuity was 0.12 ± 0.15 (range 6/36 to 6/9) snellens chart. Based on best corrected visual acuity, the prevalence of visual impairment was 6/6 ± 0.2% using World Health Organization definition. The prevalence of visual impairment in relation to best corrected visual acuity reduced significantly with gender using the World Health Organization definition (P = .46), and age (5–8 (2.4%) versus 13–16 (0.5%) using the World Health Organization definition, P = .013). (Table 2)
| Male | Female | |||
|---|---|---|---|---|
| No visual impairment | Visual impairment | No visual impairment | Visual impairment | |
| WHO Criteria: ≤6/18 | ||||
| Count (%) | Count (%) | Count (%) | Count (%) | |
| 5–8 | 1054 (31) | 81 (2.4) | 168 (4.9) | 123 (3.6) |
| 9–12 | 408 (12) | 54 (1.6) | 209 (6.1) | 342 (10.1) |
| 13–16 | 646 (19) | 17 (0.5) | 103 (3.0) | 564 (16.5) |
The mean presenting visual acuity was (0.18 ± 0.26 (2.4 ± 0.7) using snellens chart. Based on pin-hole, the prevalence of visual impairment was 1.7 ± 0.3% based on World Health Organization criteria. The prevalence of visual impairment based on presenting visual acuity reduced significantly with gender using World Health Organization criteria (P < .17). There was a significant difference between men and women (49.4% versus 50.2% using World Health Organization criteria, P = .024). A bi-variate analysis showed presence of visual impairment defined by presenting visual acuity using the World Health Organization criteria was not significantly related to age, anterior segment and gender. Visual impairment was not significantly associated with age.
Myopia (49%) was the main cause of presenting visual acuity impairment among children. In relation to visual impairment of pin-hole visual acuity, that is the World Health Organization definition were hyperopia (13%), nystagmus (14%), and amblyopia (24%) (Fig. 1). There were only two children aged 6 and 9 who had bilateral blindness.
In summary the prevalence of visual impairment was 2.4% among the children population in Kenya. Kenya has a population of 47 million with majority residing in rural areas with few in urban area9. Therefore the 47 counties involved in the study had relatively different demographic characteristics specifically on socio-economic activities. Uncorrected refractive error remained the major cause of visual impairment with socio-economic activities and gender being associated with visual impairment. To ensure cases of visual impairment as a result of uncorrected refractive error are curbed, optical correction is desired. Ocular pathologies such as myopia, nystagmus, amblyopia and hyperopia contributed to visual impairment and most parents had little knowledge on the conditions. The conditions cuts across all age group, however they are more significant in children on the basis of diagnosis. There was no association between visual impairment and nystagmus.
In comparison to other studies in other regions, the prevalence of visual impairment among children aged 5–16 years in Kenya was relatively lower10. This is attributed to the improved health care system in Kenya in the last 10 years. The ophthalmic division in Kenya has improved the health care and enhanced public awareness on ocular conditions such as refractive. This is a major cause of visual impairment in Kenya. This has aided in early detection of diseases and management making the patients to regain their sight. We did not only assessed the prevalence visual impairment in children aged 5–16 years, but we also investigated the causes of visual impairment among the same children. The age group has not been investigated in developing countries due to low reports from children on ocular related complications. The prevalence of visual impairment in our study was 2.4% based on presenting visual acuity in relation to World Health Organization criterion11. The core reason for the presenting visual impairment in this age group was lack of correction for refractive error 76%, hence calling for a need for correction among the population.
The current finding is consistent with previous studies where uncorrected refractive error is the major cause of presenting visual acuity impairment. In a review of 137 studies of 78543 participants from 82 countries, uncorrected refractive error remained the core leading causes of presenting visual impairment12, 13, 14. Being that refractive error is correctable, it is unfortunate that it still remains a major cause of visual impairment in Kenya even with the increase in eye care providers. In east Africa, Kenya is considered to be relatively advanced and awareness on refractive error through heath care professionals to the public should not be a barrier15, 16. Comprehensive eye assessment is necessary as it will determine whether spectacles are required. Future studies should address the solution to this problem. Apart from uncorrected refractive error, condition such as amblyopia which ais avoidable, causes visual impairment in Kenya.
The main limitations of the study was conducting a dry Retinoscopy which could have lead to over estimation of the refractive error. Comparing the study results with the World Health Organization was major strength.
Socio-economic activities is a key determinants of visual impairment. The main cause of visual impairment was uncorrected refractive error followed by amblyopia. To ensure that vision for the population is improved, eye care providers should dispense a pair of glass at an early age. There is a need to increase the training of eye care providers in Kenya on pediatric eye care.
Not applicable
Ethics approval
Ethical approval was obtained from the institution review board of Maseno University and authority to conduct the study from National Commission for Science and Technology. Participation was voluntary, and the respondents could withdraw from the study at any time during the study period. The responses were kept confidential, and the data were de-identified before data analysis. The study adhered to the tenets of the Declaration of Helsinki. Written informed consent was obtained from the parents of all subjects and assent from the children prior to their participation in the study.
Consent for publication
Not applicable.
Availability of data and materials
The dataset for the respondents generated and analyzed during the current study are available from the corresponding author upon reasonable request.
Competing interests
SM declares that they have no competing interest related to this study.
Funding
No funding received
Author’s contributions
SM initiated the research concept, developed the proposal, did the data collection and wrote the manuscript. SO improved the research concept assisted with proposal development and reviewed the proposal, analyzed data and the manuscript. All authors contributed equally to the research work.
Acknowledgement
We wish to thank all the children and parents who participated in this study and the research assistants and the ophthalmologists who reviewed technical cases.