Table of Contents  
Year : 2021  |  Volume : 29  |  Issue : 1  |  Page : 39-44

Utilization of Vision Corridor for Self-evaluation of Vision Among Secondary School Students in Igbo-Ora, Southwest Nigeria

Department of Ophthalmology, College of Medicine, University College Hospital, University of Ibadan, Ibadan, Nigeria

Date of Submission10-Oct-2020
Date of Decision13-Dec-2020
Date of Acceptance04-Jan-2021
Date of Web Publication16-Jul-2021

Correspondence Address:
Mary O Ugalahi
Department of Ophthalmology, College of Medicine, University College Hospital, University of Ibadan, Ibadan
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/njo.njo_44_20

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Introduction: Uncorrected refractive errors have been identified as a major cause of visual impairment with a high magnitude in developing countries, due to the paucity of eye care workers. To overcome this, different approaches like screening by non-eye care workers and self-assessment have been explored. This study aims to determine the utilization, reliability, and factors affecting the utilization of vision corridors among secondary school students. Material and Methods: An observational cross-sectional study conducted among students of Lasogba High School, Igbo-Ora, Southwest Nigeria. All the students received training on visual acuity assessment with the 6-meter Snellen’s chart. Thereafter, the chart with graphic instruction “Vision Corridor” was provided with a 4-week exposure period. All students who utilized the vision corridor recorded visual acuity in a register maintained by a community health extension worker. The utilization and factors that may have affected utilization were assessed after the exposure. Data were analyzed with the Statistical Package for Social Science version 15. Results: A total of 373 students completed the study; males accounted for 48.8% and females 51.2%. The mean age of the students was 15.2 (±2.2) years. A total of 151 (40.5%) students utilized the vision corridor and factors associated with utilization included being female, age ≤15 years, and being in a junior class, all of which were statistically significant. Conclusion: A moderate proportion of the students utilized the vision corridor. This approach to refractive error screening appears promising, as self-evaluation may reduce the need for skilled manpower in refractive error screening in secondary school students. Therefore, this may effectively utilize skilled eye care manpower for other eye care services in developing countries where there is a paucity of eye care workers.

Keywords: Nigeria, refractive errors, utilization, vision corridor

How to cite this article:
Ugalahi MO, Bekibele CO, Ogundipe AO. Utilization of Vision Corridor for Self-evaluation of Vision Among Secondary School Students in Igbo-Ora, Southwest Nigeria. Niger J Ophthalmol 2021;29:39-44

How to cite this URL:
Ugalahi MO, Bekibele CO, Ogundipe AO. Utilization of Vision Corridor for Self-evaluation of Vision Among Secondary School Students in Igbo-Ora, Southwest Nigeria. Niger J Ophthalmol [serial online] 2021 [cited 2022 Jan 22];29:39-44. Available from:

  Introduction Top

Uncorrected refractive error is the number one cause of visual impairment as estimated by the World Health Organization (WHO), with developing countries having a higher burden of the condition.[1] This has been demonstrated in Nigeria where hospital-based studies showed refractive error as a major reason for ophthalmic consultation among children.[2],[3]

Vision screening of school children in various communities revealed a high prevalence of uncorrected refractive error,[4],[5],[6] buttressing the need for periodic visual screening among school children. In Singapore, a cross-sectional survey of secondary school students showed a prevalence of uncorrected refractive error of 22.3%, a large proportion of which was due to myopia.[5] Similarly in a study in Nepal among urban and rural schools, the prevalence of uncorrected refractive error was 19.8%; with myopia being more prevalent in the urban students; 15.5% compared to 8.2% in the rural students. In addition, there was a higher prevalence of refractive errors in students in the urban area; 11.8% compared to 8.0%% in the rural region.[7]

In Nigeria, Abah et al.[8] in a study in Zaria, reported 8.0% prevalence of refractive error among secondary school students. Similar studies in Ogun State, Nigeria[9] and Tanzania[6] reported a prevalence of 11.6% and 6.1%, respectively, with a higher prevalence of myopia. The proportion of uncorrected refractive errors is also high among these school children. This was demonstrated by a study from Tanzania[6] reporting only about 30.3% of the children with refractive errors having spectacle correction at the time of the study.

Screening and correction of refractive errors among school children globally is a cost-effective intervention. This is most cost-effective among those aged 11 to 15 years,[10] and thus makes vision screening in school children economically rewarding. Several approaches to screening for refractive errors have been explored over the years from screening by teachers,[4],[11] nurses,[12] and the use of self-report tools.[13],[14]

In India, the use of school teachers has been explored in school eye screening. Children aged 10 to 15 years are screened annually by school teachers with a resultant reduction in workload of eye care workers and wider coverage of refractive error services.[4] Similarly, a study in Nigeria11 showed that teachers could be trained to carry out vision screening among school children. This approach however, may increase the work load of the teachers and hence the need to explore self-vision screening methods or self-reported visual impairment as alternatives.

In Sub-Saharan Africa, refractive error services in The Gambia explored the use of vision corridors among adults for screening in the community, to detect those with uncorrected refractive errors. This achieved effective use of manpower in providing refractive services.15 An unpublished report of the use of vision corridor in Lagos, Nigeria, for community eye screening is also noted. However, there is inadequate information in the literature on the utilization and reliability of the use of vision corridors in visual evaluation in children.

“Vision Corridor” can simply be described as the use of a vision chart and a poster with clear instructions on how to check vision by self.[15] Self-assessment of vision as used in this study refers to the act of checking visual acuity (VA) without an instructor while using the vision corridor.

This paper describes the utilization of vision corridors, factors that affect utilization, and the reliability of self-assessment of vision with the vision corridor.

  Materials and Methods Top

This study was an observational cross-sectional study, conducted among secondary school students. The study was conducted among students of Lasogba High school Igbo-Ora, in Ibarapa Central Local Government Area of Oyo state. There are nine secondary schools in the Local Government Area located in the two main towns, namely, Idere and Igbo-Ora. Facilities rendering eye care services were not available in the Local Government Area. The nearest eye care facility was located in Eruwa town, about an hour’s drive from Igbo-Ora. This eye hospital offers secondary level eye care services, including refractive error services.

A simple random sampling technique (balloting) was used to select Lasogba High School out of seven secondary schools in the Local Government Area. Two of the nine schools in the Local Government Area were excluded from the sampling frame; one of the schools excluded was a special science school with only senior classes and the other had the junior and senior school located in two different compounds. Lasogba High school is co-educational and nonboarding, comprising junior and senior classes with three arms each in the junior classes and two arms each in the senior classes. The school population is 450 registered students, however, there was a high rate of absenteeism.

A sample size of 386 was calculated, but in order to eliminate contamination bias, the intention was to include all the students who were present in the school during the study period. The response rate was 96.6% comprising 373 students; whose parents consented and who also gave assent. Four students who were present in school were excluded from the study on account of the refusal of consent (by parents of three of the students, whereas the fourth student refused to give assent). The study team consisted of the principal investigator, one trained assistant, and one community health extension worker. The principal investigator trained the students and conducted ocular examination, the trained assistant assessed visual acuity of the students while the community health extension worker supervised the recording of the visual acuity of students who self-assessed their vision in a register.

The program was introduced to the students by the school principal and the investigator at the assembly ground on two occasions. Thereafter, training of the students on visual acuity assessment with the 6 meters Snellen’s Chart was done by the investigator. This was carried out class by class shortly before a lesson period or immediately after a lesson period to ensure maximum attendance.

All students of the school were educated on visual acuity testing while standing at six meters in a well-illuminated outdoor area with no differential lighting. This was done for the right eye while the left eye was adequately occluded with the palm of the hand and with the left eye while the right eye was adequately occluded with the palm of the hand and then with both eyes open. This exercise took place over a period of 1 week. After the period of training, the Snellen’s alphabet chart was then placed in a strategic place in the school in an outdoor area without differential lighting, with the 6-meter distance marked on the ground with a cement cast. Instructions were written on the wall beside the chart to act as reminder on the procedure. These were written in English and the local language in simple words to avoid ambiguity. In addition, a graphical representation of the procedure was also displayed beside the visual chart [Figure 1].
Figure 1 A student utilizing the vision corridor.

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The students self-evaluated their visual acuity uni-ocularly (one eye at a time) and binocularly. Students who wore spectacles were also asked to test vision with and without spectacles. Visual acuity was recorded as the last line read correctly. All the students who tested their vision were required to write their names in a register and to record their presenting acuity beside their names by themselves. This exposure period was for four uninterrupted weeks before the school holidays. After this period of exposure all the students in the school whose parents consented, were examined over a period of 2 weeks with administration of questionnaire to assess barriers and factors associated with utilization of the vision corridor.

In the school, at the venue of the examination, a trained ophthalmic assistant who was blinded checked the visual acuity at 6 meters without and with a pinhole. Visual acuity was not checked with spectacles as none of the students examined had spectacles. An ocular examination which included a pen-torch examination and a direct fundoscopy (Welch Allyn REF11720) was done. Thereafter, a non-cycloplegic refraction was done for all students with an autorefractor (XIN YUAN FA-6800). Three measurements were taken in each eye with the auto-refractor and the average recorded. Subjective refraction was done and a prescription for spectacle was given to all those who required them. Simple ocular pathologies where present (mainly allergic conjunctivitis), were treated. All other participants who required further evaluation were referred to the Mission Eye Clinic in Eruwa, a nearby town with a referral form.

Ethical approval and clearance were obtained from the Ethical Committee of the University of Ibadan/University College Hospital Ibadan. In addition, permission for the study was obtained from the State Ministry of Education and the Principal of the school while written informed consent was obtained from the parents/guardian of each student.

Data collected were entered, cleaned, and analyzed using the Statistical Package for Social Sciences (SPSS) software version 15. Means, proportions, and frequencies were calculated for descriptive summaries. Bivariate analysis using chi-square was carried out to test for associations with a level of significance set at 5% (P ≤ 0.05). The measure of agreement was analyzed with Kappa statistics.

  Results Top

A total of 373 students completed the ocular examination with a mean age of 15.2 (±2.2) years and a range of 10 to 21 years. There were 182 (48.8%) males and 191 (51.2%) females [Table 1].
Table 1 Sociodemographic characteristics

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Three hundred and seventy (99.2%) students had no history of spectacle wear and 3 (0.8 %) had a history of spectacle wear, however, none had the spectacles on them. A hundred and fifty-one (40.5%) students used the vision corridor to assess their visual acuity. The proportion of females who utilized was 55.5%. Among the male students, only 24.7% utilized the vision corridor [Table 2].
Table 2 Utilization of vision corridor

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Bivariate analysis showed students in junior classes were more likely to use the vision corridor than students in the senior classes (P < 0.0001) [Table 3].
Table 3 Bivariate analysis of utilization by class, age, and gender

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Among those who utilized the vision corridor, the proportion of children with refractive errors was 45 (29.8%), whereas among those who did not utilize it was 82 (37.1%). This. however, was not statistically significant (P = 0.15).

The main barrier to utilization of the vision corridor among the non-users was the perception of having good vision 38.0%, whereas the least reason stated for non-utilization was absenteeism from school (0.3 %) [Table 4].
Table 4 Barriers to utilization of vision corridor

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Of the 149 students who assessed their visual acuity as normal, it was confirmed by the trained ophthalmic assistant to be normal. Similarly, of the two students who assessed their visual acuity as abnormal, it was also confirmed by the trained ophthalmic assistant to be abnormal [Table 5] and [Table 6].
Table 5 Visual acuity values obtained by self-assessment and observed by the trained assistant

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Table 6 A contingency table presenting self-assessed Visual Acuity (VA) against trained observer assessed VA

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The measure of agreement between the self −assessed visual acuity and the trained ophthalmic assistant assessed visual acuity using Kappa statistics was found to be 1, which shows a strong level of agreement.

  Discussion Top

There was moderate utilization of the vision corridor by the students; less than half, 40.5% of the population did a self-assessment of vision. Although the utilization was suboptimal, it is an indication that secondary school students, if trained, could use the vision corridor to do a self-assessment of vision.

Despite evidence that the use of school teachers has been demonstrated to offer a wide coverage[4],[11] in school eye health screening; some questions have been raised concerning increasing the workload of the teachers and time spent away from school for training.[4] An alternative method may be found in the use of vision corridor as has been demonstrated. This, however, requires further research on improving the utilization. To the best of our knowledge, no literature exists on the uptake of vision corridors among students in secondary schools in Nigeria. A similar study[16] in India conducted among school children aged 10 to 19 years reported better utilization at 99%. This may be attributed to the established school eye health program in this area of India studied, compared to our study location where there were no existing refractive error services.

There was higher utilization among the female students which was found to be statistically significant with a P-value < 0.0001. No reason was found for this disparity; however, it may be due to the fact that young girls in this age group are more likely to obey instructions than boys. There was also higher utilization by students in junior classes and ages 15 years and less. Reasons for this may also be due to the probability of younger students obeying instructions better than older students. Furthermore, among an adult population in Australia being male was reported as a barrier to utilization of eye care services.[17]

The main identified barrier to utilization of the vision corridor in this study was the perception of having good vision by the students. Kovai et al.[18] noted that one of the main barriers to utilization of routine eye examination services was perception of being able to see adequately.

Lack of awareness was also reported as a barrier to utilization of the vision corridor despite the 1-week period of sensitization and about one month of exposure to the vision corridor. This may be an indication of a need for an increased creation of awareness on visual health among secondary school students in rural locations where there is a paucity of eye care workers. In this era of technology and increased use of smartphones, messages designed for this age group are worth exploring.

Other barriers identified were a lack of “felt need” and a feeling of nothing being wrong with the eyes which may connote an ignorance of ocular status. Studies[18],[19] have shown that a lack of felt need, lack of awareness, and lack of access are barriers to uptake of refractive error services. However, a lack of access was not a barrier in this study as the services were made available to the students in their school for a reasonable period of time. Some of the students were discouraged by friends, whereas a few failed to test their vision for fear of discovering they have poor vision, this has also been reported as a barrier to utilization of refractive error services.[20] These barriers identified underscore a need for an improved and sustainable health education program on visual health needs among school children. Self-assessed visual acuity was found to have a strong level of agreement with visual acuity assessed by a trained ophthalmic assistant, as it was able to detect the presence or absence of visual impairment in the students. This is similar to findings in a study[16] in India where there was good agreement between self-evaluated and supervised assessment of visual acuity. There are not many reports on the use of vision corridor in the literature however studies on self-reported visual status in an adult population[14],[21] have also found a good correlation with supervised visual acuity.

This strong agreement makes the use of vision corridor in school vision screening promising especially in areas with paucity and disproportionate distribution of eye care workers.

It is important to note that there was a discordance in the self-assessed visual acuity and that assessed by the trained ophthalmic assistant, as the students with poor vision, self-assessed their vision to be better than it was. Though this did not affect the overall reliability, it points to a need for refining the tool to reduce memorizing the chart by the students. Similarly, in the study[16] in India, they observed some underestimation and overestimation of visual acuity among the students. There were no other studies in a similar population to compare these findings, further emphasizing the need for more studies to be conducted in self-evaluation of vision among adolescents in Nigeria

Limitations of the study

The short duration of exposure of one month may have adversely affected the utilization of the vision corridor.

  Conclusion Top

There was moderate utilization of the vision corridor among the student populations. Utilization may be improved if some of the barriers identified in our study are addressed. We recognize that a booster health education may have encouraged better utilization; thus, further research on the use of vision corridor in school vision screening is advocated with adequate provision for a subsequent eye test and corrective spectacles as a reward for those who use the facility and found to be in need, especially in rural areas where there is low awareness of visual needs of adolescents and availability of facilities for eye care.


M.O.U. is supported by Consortium for Advanced Research Training in Africa (CARTA) that is funded by the Carnegie Corporation of New York (Grant No–B 8606.R02), Sida (Grant No:54100029), the DELTAS Africa Initiative (Grant No: 107768/Z/15/Z).

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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  [Figure 1]

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


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