Accommodative anomalies are visual conditions that can affect the eye’s ability to alter its dioptric power to bring an object of regard coincident with the retina.^1,2 Clinical signs range from reduced accommodative amplitude (AA), reduced sustainability and accuracy of accommodation and difficulty maintaining clear vision when changing fixation from one point to another with associated symptoms.^1,2,3 The symptoms include blurred vision at near, transient blurred vision when looking at a distant target following performance of near work, headaches, pulling sensation around the eyes, tired eyes and reduced attention span. Because of these symptoms, individuals find themselves attempting to compensate by holding reading material too close or too far away, or simply avoiding near activities altogether.^1,2,4,5,6 These ocular discomforts can impair reading efficiency, school performance and possibly a person’s quality of life.^7,8,9

A number of studies^{3,6,9,10,11,12,13,14,15,16,17,18,19,20} have reported on the prevalence of accommodative anomalies in school-age children in different populations, especially in Caucasian children. For the specific populations indicated in Table 1, the prevalence range for different accommodative anomalies include accommodative insufficiency (AIS, 0.2% – 18.3%), accommodative excess (AE, 1.2% – 5.1%) and accommodative infacility (AIF, 2.5% – 30%). Differences in study designs including the use of single or multiple sign criteria in the definition of specific accommodative anomalies and methodological differences such as small sample sizes, convenience sampling method and exclusion criteria within studies may account for the variability in study findings. Regarding exclusion criteria, the most recurring flaws among the studies are the exclusion of children with uncorrected refractive error (RE). For the studies that did not exclude children with uncorrected RE, it was not clear whether they wore their compensating lenses during testing. This is important, as RE significantly impact the aetiology and influences the measurement and treatment of accommodative anomalies.^1,7,12

There is also a lack of information in the literature on the influence of age, gender and school level on the prevalence of accommodative anomalies.⁶ As early detection remains the best approach for the treatment of visual anomalies and considering the cost of systematic screening,¹⁸ an understanding of the association between accommodative anomalies and sample demographics will allow dedicating available resources and efforts to early detection, such as regular vision screening only on people at risk, thereby reducing the high short-term and long-term costs to the health system and to society. Presently, there are no intervention and management guidelines for accommodative and vergence anomalies in Abia State and Nigeria because the subspecialty of paediatric optometry is relatively new in the country.²¹ The clinical implication is that most eye care professionals rarely consider accommodative and vergence disorders as anomalies of interest when screening children for near vision anomalies.

Our study included an adequate and representative sample of primary and secondary schoolchildren in Abia State, Nigeria. Accommodative and binocular vision tests were performed with children wearing their compensating lenses, if prescribed. This ensured that uncorrected RE did not negatively impact on the clinical outcome measures. The present study aimed to determine the prevalence of accommodative anomalies in Abia State schoolchildren and to assess possible association with age, gender and school level. The information is expected to guide health policymakers and practitioners in implementing the most appropriate intervention and management strategies, particularly for vision problems that have been associated with educational outcomes.^8,9

This study reports on the prevalence of accommodative anomalies in a population of children of Abia State, which include AIS (3.9%), AE (2.8%) and AIF (10.1%). There was no significant difference in the distribution of the various accommodative anomalies between age group, gender or school level. The mean AA of 15.46 ± 3.44 D in our study was comparatively similar to the 15.88 ± 3.46 D reported by Ovenseri-Ogbomo and Oduntan²³ on school-age children in Nigeria.

In the present study, the prevalence of AIS (3.9%) using multiple sign criteria was higher than the 2.3% reported by Scheiman et al.¹⁷ and 0.2% by Hussaindeen et al.¹⁴ However, the value is lower than two other studies^6,9 that also utilised more than one clinical sign. The study by Shin et al.⁹ estimated AIS in symptomatic participants with a score of 20 or more on the convergence insufficiency symptom survey; hence, the reported prevalence of 18.3% may have been overestimated, while the difference of 4.5% reported by Wajuihian and Hansraj⁶ may be attributed to reduction in AA with an increase in age, as their study participants were older than the children in the present study. Further, studies that defined AIS using only one clinical sign (of reduced AA, lower than the expected age norm according to Hofstetter’s formula for minimum age) reported significantly higher prevalence rates, ranging between 10% and 24.2%.^15,16,19,20 However, to accurately interpret the accommodative status of children, it is recommended to include the assessment of other accommodative parameters such as accommodative facility and response. This is so because using only reduced AA overestimates the prevalence of AIS,^1,2 because AIS presents more as a syndrome. Moreover, the prevalence of poor monocular (7.8%) and binocular (7.3%) AA reported in this study was lower than the 10% (monocular or binocular) reported by Metsing and Ferreira¹⁵ and the 24% (monocular) and 26% (binocular) reported by Moodley¹⁶ on primary schoolchildren but higher than the 4.6% (monocular) found by Wajuihian and Hansraj⁶ in high school children. Although several factors such as sampling methods and sample sizes, inconsistent measuring techniques and diagnostic criteria can play a significant role in differences between studies, the major reason here may be interexaminer variability and age of study participants. Younger children may have more difficulty in reporting blur than older children, which is the subjective criterion for the measurement of AA.

The findings of this study on AE (2.8%) were consistent with those of Wajuihian and Hansraj⁶ on black students in South Africa. However, it should be noted that two other school-based studies in South Korea^9,13 and another in Ghana³ reported different estimates of 1.2%,¹³ 1.4%³ and 3.7%,⁹ respectively. Similarly, Darko-Takyi et al.³ and Jang and Park¹³ reported prevalences of AIF of 3.8% and 2.5%, respectively, which is lower than our finding of 10.1%. Other studies reported higher estimates when compared to the present study. A case in point: in South Korea,⁹ the prevalence of AIF was 13.4% while in South Africa⁶ it was 12.9%, and in rural and urban India¹⁴ 7% and 10.7% were determined, respectively.

Although marginal differences between groups were observed in the present study, no significant differences were found between the prevalence of AIS, AE, AIF and demographic factors including age, gender and school level, which corroborates the findings of several other studies.^3,9,13,18 The study by Scheiman et al.¹⁷ that found a significant difference in the prevalence of AIS with age was a clinic-based study that was exposed to biased data, making comparison of findings with a randomised school-based study very difficult.

Overall, the differences in relation to findings of these studies can be explained from various contexts. Although most of the studies enumerated in Table 1 were school-based studies, their sample size and sampling method varied considerably. To obtain more accurate prevalence data, it is necessary to have adequate and representative samples of the target population, with a suitable age range that will provide reliable data that can be extrapolated to the entire population. Except for three studies^3,6,13 that utilised randomised samples, all others selected their participants and only a few had an adequate sample size, with Scheiman et al.¹⁷ being a clinical study. Clinic samples and school-based studies with only symptomatic participants are characteristically biased and have the possibility of reporting higher prevalence estimates when compared to an unselected population of children.^22,24 Besides being non-representative samples, participants with complaints of visual discomfort are more prone to having actual visual anomalies.^22,24

The refractive status of the participants is another important factor to consider in assessing prevalence of an accommodative anomaly. Studies have indicated that uncorrected RE can impact the aetiology and influence accommodative anomalies, as well as their treatment options.^7,12 From this point of view, it may be possible to suggest that RE affects the prevalence and distribution of accommodative anomalies in any population.²⁵ Myopes have reduced sensitivity to blur compared to hyperopes and emmetropes.¹ Blur adaptation can cause an individual to experience sustained blur at closer distances during push-up testing, resulting in higher values of AA.^1,25 Therefore, adequate correction of RE is critical in the resolution of some accommodative conditions^12,25,26 and is likely to yield more accurate prevalence estimates.¹² To ensure that uncorrected RE does not overestimate the prevalence of accommodative anomalies in our study, children were tested with the correction; however, in some studies^9,10,11,19 information regarding the refractive status of the participants was not indicated. As such, it was not clear whether those with RE were included in the study or whether they were examined with their spectacle compensations in place. Other studies excluded participants with uncorrected VA and RE, thereby limiting the extent to which their samples can be a valid representative of the target population.

Increased variability and reduced reliability associated with accommodative testing could also be the reasons for the variations in findings among studies. Some studies applied a single criterion, while others used two or more criteria to define specific accommodative anomalies. In addition to varying diagnostic criteria, different techniques were applied in measuring the accommodative parameters. Even in studies with similar criteria and measuring techniques, different cut-off points were applied in the detection of participants with specific accommodative anomalies, making it difficult to compare results among studies. Regarding reliability of test results, the measurement of accommodative parameters involves reporting blur experience, which depends on the ability of the subjects to understand the experimental procedures and instructions. Younger children have difficulty in reporting blur experience.^6,22,23 As such the use of only younger (primary school) children by some studies may have influenced their results. With the exception of Jang and Park,¹³ school-based studies (Table 1) with younger children reported higher prevalences of AIF compared to those with older children. The difference between the findings of Jang and Park and the present study and others may be related to differences in test procedures, varying diagnostic criteria and cut-off points.

One of the limitations of the present study was the non-use of cycloplegia during refraction. Cycloplegia was contradicted because the study involves the evaluation of accommodative status, and our desire was to examine the children in their habitual state. Instead the plus lens test was applied in the assessment of latent hyperopia. Another possible limitation is that all tests were performed in test stations set up in each school, rather than an optometry clinic, which would have afforded better control over the test environment. Nevertheless, testing conditions were standardised at each test station in all the schools. In addition, validated and reliable instruments were applied in data collection, with only one examiner conducting all the vision tests. The study included an adequate sample representative of primary and secondary school children representing the learning experience and visual characteristics of these two levels of educations. Furthermore, the study protocol was adapted from recent studies^6,12,14 in this area. Altogether, data from the present study have significant indications for eye care practitioners with respect to clinical management of near vision disorders as well as education and health policymakers in terms of planning and implementation of school health programmes. Given the reported association between school performance and accommodative anomalies,^7,8,9 the accommodative status of every child who presents with near vision related complaints, particularly those having difficulty with academic performance, should be properly evaluated for possible accommodative disorder.

The present study has provided a detailed and systematic report on the prevalence of accommodative anomalies in children in Abia State, Nigeria. Our data indicate that a considerable proportion (16.8%) of schoolchildren suffer from at least one of the disorders of accommodative function, which can have a substantial influence on their learning capabilities and academic performance. This is an important finding, given that conventional vision screening programmes that only focus on VA assessment are unlikely to detect these critical visual anomalies. Therefore, the scope of paediatric vision screening programmes should be widened to include test batteries that will identify common visual anomalies, including accommodative anomalies capable of affecting school performance. Overall, the data from this study will apply towards the development of a common and broad-based vision screening strategy.