Background

It has been estimated that 19 million children have vision impairment, with uncorrected refractive error (URE) affecting 12 million children [1], making it the leading cause of childhood vision impairment worldwide [2]. Although spectacles can effectively correct refractive errors, less than one-third of children who need spectacles in low-resource settings have them [3]. Studies have found that vision impairment and ocular morbidities have increased anxiety [4], reading difficulties [5,6,7], anti-social behaviour [8], quality of life issues [9] and problems with self-esteem [10].

A meta-analysis by Mavi et al. found that children with uncorrected hyperopia had lower education performance (Standardised Mean Difference [SMD] − 0.18, 95%CI − 0.27 to − 0.09) and reading skills (SMD − 0.46, 95% CI, − 0.90 to − 0.03) compared to emmetropic children [11]. Another systematic review by Li and Chan et al. found that vision-impaired children have higher depression (SMD 0.57, 95%CI 0.26–0.89) and anxiety scores (SMD 0.61, 95% CI 0.40–0.82) than normally sighted children. The same systematic review also observed myopic children having higher depression scores than normally sighted children (SMD 0.59, 95% CI 0.36–0.81) [12]. Uncorrected myopia is also shown to impact children’s mental health negatively [13]. Furthermore, many of these studies were cross-sectional [7,8,9,10, 13,14,15,16] and could not demonstrate the causal relationship between VI due to URE and aspects of well-being due to the inherent limitations of the study design.

Studies on the impact of spectacle correction on children’s well-being are rare, with most focusing on the impact on academic performance [11, 17,18,19,20]. However, child well-being is a multi-dimensional construct that explores various domains of a child’s life, including health, education, living conditions, material well-being, and interpersonal relations [21]. The scarcity of conclusive evidence makes promoting healthy well-being in children by correcting their refractive error challenging despite having a long-term impact on their later years and into adulthood, affecting their ability to actively participate in society, their communities, and their families [22].

No systematic review of the impact of spectacle correction on the broader aspects of children’s well-being has been published or registered to date. Considering the increasing evidence on the detrimental effects of vision impairment due to URE on children, we conducted a review to systematically synthesise the findings from the existing literature on the impact of spectacle correction on various aspects of children’s well-being.

Methods

This systematic review was registered on the International Prospective Register of Systematic Reviews (PROSPERO Registration number: CRD42020196847). The Preferred Reporting Items for Systematic Reviews and Meta-Analyses for Systematic Review Protocols (PRISMA-P) guidelines were used to develop and report the systematic review protocol [23].

The search strategy was adapted to each electronic database, including MEDLINE, PubMed, Embase, SCOPUS, ProQuest, Weipu Database (VIP), Chinese National Knowledge Infrastructure (CNKI) and Wanfang databases using the search terms in Supplementary file 1. The inclusion criteria were as follows: studies of any language from any geographic locations, published between 1999 and 2021, qualitative, observational or interventional studies; participants were children 18 years and younger diagnosed with vision impairment due to uncorrected refractive error, without any ocular comorbidities. No grey literature was included in the review. The intervention of interest was spectacle correction. The primary outcome was well-being according to the Organisation of Economic and Co-operative Development’s [24] Measuring What Matters for Child Well-being and Policies, which includes social health, physical health, cognitive and education and material health, in addition to physiological and mental health and quality of life.

Two reviewers (PGP and ACY) independently screened all titles and abstracts against eligibility criteria. If an article’s eligibility could not be determined based on its title and abstract, its full text was retrieved and screened by the two same reviewers. A third senior reviewer (VFC) was consulted in cases of disagreement between the two reviewers. Data were then extracted into a pre-designed Microsoft Excel Spreadsheet, capturing information on the publication date, author(s), title, geographic location, study setting, study design, sample size, sampling method, outcome measure, and key findings, limitations, strengths and recommendations. Two data extractors (PGP and ACY) checked for data errors and consistencies.

Two reviewers (PGP and ACY) independently appraised the quality of each randomised control trial (RCT) and qualitative study using the Critical Appraisal Skills Programme checklists (CASP) [25]. In contrast, cohort and cross-sectional studies were appraised using the Joanna Briggs Institute’s Critical Appraisal-Checklists (JBI) [26]. Discrepancies were resolved through discussion and consensus. A third senior reviewer (VFC) was consulted in cases of disagreement between the two reviewers.

Due to the high heterogeneity nature of the studies, we performed narrative synthesis on the findings to report the wide range of study design, characteristics, and well-being outcomes. The quality of the studies was reported as per the criteria of the appraisal tools. The quality of the study evidence was rated as Good (fulfilled 67 to 100% of criteria), Satisfactory (fulfilled 33 to 66% of criteria) or Poor (fulfilled 0 to 33% of criteria) [27].

Results

The electronic database search yielded 692 studies. After removing 174 duplicates and 416 studies due to irrelevant titles, 102 studies were included for abstract screening. Seventy-five studies were excluded. Of the 39 studies that underwent full-text screening, 30 (76.9%) were excluded because i) they did not demonstrate the impact of spectacle correction directly or as a comparison to before the spectacle correction was used (n = 17; 43.6%) [28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44], ii) they did not measure the impact of spectacles on children’s well-being (n = 9; 23.1%) [45,46,47,48,49,50,51,52,53], iii) the population’s age was older than 18 years-old (n = 3; 7.7%) [54,55,56] and iv) it was not a published study (n = 1; 2.6%) [57]. Nine full-text studies were eligible for data extraction and appraisal [17, 18, 20, 58,59,60,61,62,63]. The study selection processes are outlined in the PRISMA flow depicted in Fig. 1.

Fig. 1
figure 1

Flow chart of results of the search strategy and study selection processes

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Characteristics of the eligible studies

The eligible studies included six randomised control trials [20, 58, 59, 61,62,63], one cohort study [18], one cross-sectional study [60] and one qualitative study [60] published between 2012 and 2020. Five were conducted in China [20, 58, 59, 61, 63], three in the United States of America (19–21) and one in the Netherlands [62] (Table 1). Data was gathered from 25 522 children, 20 parents and 25 teachers across the nine reviewed studies.

Table 1 Description of the study characteristics, population, key findings, study limitations, strengths and recommendations for studies reporting the educational impact of spectacle correction (n = 7)
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Seven studies investigated children’s cognitive and educational well-being, where four were RCTs [20, 59, 61, 62], one cohort [18], one cross-sectional [60] and one qualitative study [17]. The remaining two studies in this review explored the impact of spectacle correction on children’s psychological and mental health well-being [58] and children’s quality of life [63]. Randomisation was adopted in six of the nine studies either by township or cluster [3, 20, 59], by study participants [62, 63] or schools [58]. Two studies used purposive sampling [18, 60], and one study used convenience sampling [17].

The studies investigating the impact of spectacle correction on cognitive and educational well-being used a range of indicators, with Ma et al. [61] using only math scores; Hannum and Zhang [59] using math scores, literacy and language achievement tests; Dudovitz et al. [18] using achievement marks in math, English language arts, work habits and behaviour; Nie et al.[20] using math scores, aspirations for further schooling and school dropout rate; the studies by van Rijn et al. [62] and Harvey et al. [60] used reading speed of words and nonwords and oral reading fluency respectively. The RCT by Guan et al. [58] was the only study that explored the impact of myopic spectacle correction on children’s mental health using the validated Mental Health Test (MHT) score and its subscales of learning and physical anxiety scores. Zhou et al. [63] investigated quality of life using the validated National Eye Institute Refractive Error Quality of Life-42 (NEI-RQL-42) questionnaire. The qualitative study by Dudovitz et al. [17] used focus group interviews to explore parent, teachers and student perspectives on how spectacle correction improves child well-being and school function.

The impact of spectacle correction on children’s cognitive and educational well-being

Trials by Ma et al. [61], Nie et al. [20], and Hannum and Zhang [59] that assessed math scores as an outcome found improvement by 0.25 standard deviations (SD) (satisfactory quality evidence), 0.14 SD (good quality evidence) and 0.26 SD (good quality evidence) in math scores post spectacle correction. Dudovitz et al. [18] found that after the provision of spectacle correction, students who performed in the bottom tercile for math rank at baseline achieved a significant immediate and sustained improvement of 10 to 24 percentile points (p < 0.001) (good quality evidence).

In addition to math scores, Hannum and Zhang’s [59] trial also found an average treatment effect of 0.34 SD on literacy assessment (good quality evidence) and a 44% reduction in the chances of failing a class (p < 0.01). Dudovits et al. [17] found 4.5 percentile points improvement (p = 0.02) for English Language Arts (good quality evidence) post-correction. Harvey et al. [60] also found a mean significant improvement in oral reading frequency of 6.05 words per minute (p = 0.001) among moderate astigmats and an improvement of 1.87 words per minute (p = 0.193) with spectacle correction (good quality evidence).

The qualitative study by Dudovitz et al. [17] found that providing corrective lenses to children improved their school function (good quality evidence), including behaviour or focus, willingness to practise academic skills, and improved academic performance. Participants reported improved reading ability due to a greater willingness to practice academic skills, more accuracy with math-related homework, effort and task persistence, improved concentration and focus in the classroom, less disruptive behaviour in the classroom, and more engagement and ability to participate in class (good quality evidence). A minor theme noted in this study was the ease with which homework was executed after receiving glasses.

The psychological and mental health impact of spectacle correction

Guan et al. [58] found a significant decline (0.08 SD; p < 0.10) in physical anxiety among children post myopic correction (good quality evidence). There was no significant impact on learning anxiety or overall mental health (good quality evidence). The study also found spectacle correction significantly improved the MHT score (0.26 SD; p < 0.05) in students studying at a high intensity (more than two hours a day), but those who studied at a moderate degree of intensity (between half an hour to two hours a day) experienced a decline in MHT score (0.13SD; p = 0.03) (good quality evidence). Students studying at a low-intensity level (studying for less than half an hour per day) experienced an increase in Learning Anxiety (0.17SD; p < 0.05) (good quality evidence). Albeit insignificant, children also experienced a decline in learning anxiety (0.25 SD, p < 0.10); a decrease in physical anxiety (0.22 SD; p < 0.10) post-correction (good quality evidence).

Quality of life impact of spectacle correction

Zhou et al. [63] found that irrespective of the method of refraction used to determine the spectacle correction, all methods showed a significant increase in quality-of-life scores with spectacle correction ranging from 2.32 [95% CI (0.37, 4.27) p = 0.020] in the group tested by an optometrist to 4.65 [95% CI (2.45, 6.86) p < 0.001] in the group receiving ready-made spectacles (good quality evidence).

Tables 1, 2 and 3 show that irrespective of the aspect of well-being investigated, spectacle correction had a positive impact, improving well-being. However, the effect of confounding factors on the study results was unclear in most cases In four out of nine studies, the type of refractive error being corrected was not specified [17, 18, 59, 61], three studies used myopic correction, [20, 58, 63] one used hyperopic correction [62], and one study used astigmatic correction [60].

Table 2 Description of the study characteristics, population, key findings, study limitations, strengths and recommendations for studies reporting the psychological impact of spectacle correction (n = 1)
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Table 3 Description of the study characteristics, population, key findings, study limitations, strengths and recommendations for studies reporting the quality of life impact of spectacle correction (n = 1)
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Quality appraisal of studies

The results of the quality appraisal are summarised in Table 4. Seven of the nine studies (77.8%) were rated as good quality, and two (22.2%) were satisfactory [27]. All studies in the review addressed a focused issue. Among the RCTs, randomisation of the groups to either the intervention or control groups was done at the cluster or school levels to ensure that participants were blind to the interventions. However, this made blinding of investigators in these clusters or schools difficult as they could easily see which groups were provided with the interventions. Almost all RCTs (n = 4, 67.6%) did not accurately report the data; only one (16.67%) could not generalise findings beyond the study areas. In the cohort study by Dudovitz et al. [18] it was unclear if the exposure and outcomes were measured in a valid or reliable way and if the loss to follow-up was explored. It was also unclear if confounding factors were identified in the cross-sectional study to assess the impact of spectacle correction on reading fluency [60].

Table 4 The checklist results for assessing the methodological quality of the included studies
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Discussion

This systematic review summarised the literature narratively on the impact of spectacle correction on well-being in children with VI due to uncorrected refractive error. All the eight eligible studies were of good or satisfactory quality. The limited evidence suggests that spectacle correction improves children’s cognitive and education, psychological and mental health well-being and quality of life.

Even though well-being is multi-dimensional and comprises a range of aspects, [64] the review found seven studies that focused strongly on cognitive and educational well-being, with limited studies (n = 1) on psychological and mental health and quality of life (n = 1). School is a significant part of a child’s life [65], and many learning activities are visually based [66], including reading, digital media and observation, thereby creating a dependency on optimal visual function [67]. Therefore, combining the fact that academic performance is a key predictor of lifelong health [68], and the availability of standardised testing could also lead to the focus on educational impact.

Overall, there was good quality [18, 20, 59, 60, 63] and satisfactory quality evidence [17, 61, 62] that spectacle correction can improve cognitive and educational well-being. Nie et al. [20], Ma et al. [61], and Hannum and Zhang’s [59] trials and, Dudovits et al.’ s [18] cohort study, has sufficient power to strongly suggest that spectacle correction can improve mathematic scores. Most of these studies were conducted in China and may limit the ability to apply their findings to other contexts. However, seeing almost half of the children in the world with VI due to URE live in Asia [69], with almost 80% of myopic adolescents living in East Asia having distance vision impairment, these findings are critically relevant in this geographic location. The scarcity of evidence outside of China also highlighted the opportunities for further research in other parts of the world.

Furthermore, despite Ma et al.’ s [61] argument that change in mathematics scores is a more valid and sensitive outcome for spectacle correction, other studies also suggest improvement in literacy, English, and reading tests. Wang et al. [70] suggested that poor academic performance in subjects such as math and English could be attributed to reduced capacity for children to perform optimally on visually demanding tasks in a modern classroom. The quantitative findings were also supported by the focus group findings from Dudovits et al.’ s [17] qualitative research that explained the perceived causal pathway of improving school function. Qualitative research on this topic is rare, but it allows a deeper understanding of experiences, phenomena, and context and explains the quantitative findings to understand human experience.

Children were at a higher risk of developing poor vision by spending more time on learning [70], and increased near work due to academic pressures has also been implicated in the increase in refractive error, particularly myopia [71]. Hence, it is not surprising that while our review shows that the positive impact of spectacle correction on psychological and mental health well-being was found among Chinese children, the greatest effect was found among children who studied for longer periods in the day [58]. We hypothesise that poorer vision prior to correction is likely to yield a greater perceived impact of the correction on the visually demanding tasks associated with the academic environment.

Numerous studies investigate the impact of uncorrected refractive error and vision impairment on aspects of quality of life in children, finding the decreased quality of life in individuals with vision impairment or uncorrected refractive error [9, 72,73,74,75]. Furthermore, numerous tools quantitatively assess the refractive error-related quality of life [76]. However, there is a paucity of studies investigating the impact of spectacle correction on the quality of life in children. The study by Zhou et al. [63] provides good evidence that quality-of-life scores increase with spectacle correction. The strength of this study is noted in the use of a self-reported measure of the quality of life (NEI-RQL-42) recommended over parental proxy reporting [77]. However, Kaphle emphasised that refractive correction may not address all quality of life issues related to URE.

While spectacle correction provides a convenient and, in many cases, cost-effective method of refractive correction, it is met with poor compliance, in many cases attributed to stigma and misconceptions [27]. Our review can be used to allay these misconceptions and educate spectacles users ahead of time as it clearly shows the positive impact of spectacle correction on academic performance, mental health and quality of life.

The limitations of this review must be acknowledged. One, the restriction to only published studies which have excluded unpublished reports, such as grey literature and programme evaluations, often provide a wealth of information that published studies do not capture [78]. These evaluation reports usually focus on the implementation effectiveness and provide a wealth of information on effective spectacle provision implementation strategies but often, lack methodological rigour to capture the impact of spectacle correction on children’s well-being. Future research could strive to incorporate these valuable sources of information without compromising on rigor by using an effectiveness-implementation hybrid designs in the programme evaluation. Two, due to the mutlifaceted factors contributing to uncorrected refractive error which could significantly impact the outcomes of spectacle correction, it reduces the generalizability of the results. These factors may include physical factors (inadequate access to routine eye examinations or a lack of trained eye care professionals, especially in rural or underserved areas, leading to a lack of diagnosis) and geographical, socioeconomic, and cultural factors (geographical constraints, and lack of awareness about the importance of spectacle correction can impede access to corrective measures). Consequently, future research should aim to capture these varied contexts and factors to allow comprehensive understanding of the impacts of spectacle correction, ensuring that the benefits observed can be appropriately generalised and applied to various settings and populations. Three, we also did not conduct a meta-analysis in this review due to the great variation in study methodologies and outcomes.

Conclusion

This review found that the limited studies touched the surface of the complex well-being construct regarding the impact of spectacle correction on children. The findings suggest that children have improved cognitive and educational well-being, psychological and mental health well-being and quality of life. More research is needed in different geographical locations to explore the impact of spectacle correction on the wider array of well-being constructs.