Hyperopia: a meta-analysis of prevalence and a review of associated factors among school-aged children

The literature search was performed on MEDLINE (PubMed), Scielo, Bireme, Embase, Cochrane Library, Clinical Trials registration website and WHO databases. The following descriptors were used: refractive errors, hyperopia, prevalence and children, limited to keywords or words in the title or abstract, in either their isolated or combined form. The searches were limited to the 0-18 age range.A total of 701 records were identified and screened (including theses, journals, articles, books, book chapters and institutional reports) relating to hyperopia prevalence in children up to 18 years old. 99 of these articles were duplicated. Population-based or school-based studies assessing hyperopia through cycloplegic autorefraction or cycloplegic retinoscopy were included. 525 papers were excluded owing to their focus on: specific populations as well as publications about refractive errors in subjects with eye diseases (amblyopia, strabismus, glaucoma, corneal abnormalities, chromatic aberrations, accommodative and binocular dysfunction and asthenopia); other specific clinical diseases or conditions (intellectual disability, cerebral palsy, dyslexia and prematurity); ophthalmology/optometry outpatients; genetic and/or congenital alterations; before and/or after examinations, clinical and/or surgical treatment; cost-benefit research and geographically isolated populations. A further 44 articles were excluded due to: non-random sample of the general population and schools; determination of refractive error without cycloplegia; cycloplegia only in children with low vision; hyperopia based only on visual acuity testing, studies without specific cut-off for hyperopia, samples excluding children that were already in eye care treatment, samples based on records of clinics or mobile clinics, very small and stratified samples. 07 papers found in the references of the selected articles were included (Figure 1).

Meta-analysis was undertaken regarding prevalence of moderate hyperopia at specific ages in 6 to 15 year-olds. Out of a total of 21 articles on hyperopia prevalence at specific ages (Table 1), three had losses of more than 20% and six did not report their response rates. Fotouhi’s study showed prevalence estimates significantly different to all the other studies in various age groups, and its inclusion in the meta-analysis resulted in a statistically significant heterogeneity test (p < 0.05). Based on the heterogeneity assumption for the effect summary, Fotouhi’s study was characterized as an outlier and excluded from the meta-analysis. Following this, the heterogeneity test produced a p-value > 0.1 in all specific ages [9]. Thus the meta-analysis was based on 11 studies assessing moderate hyperopia taking ≥ +2.00D as the cut-off point and a response rate greater than 80% (Table 1).

The meta-analysis was performed using a Microsoft Excel spreadsheet [49]. Differences in the populations studied, especially ethnicity, have a non-random impact on prevalence. The random effects model was therefore used in order to obtain the effect summary and its confidence interval. The adequacy of the effect summary depends on the homogeneity assumption. Heterogeneity was measured using the Q test and was quantified using I² statistics. Heterogeneity tests having a p-value <0.1 were considered statistically significant.

This systematic review was performed according to the PRISMA [50] and MOOSE [51] Statements. The study was approved by the Federal University of Pelotas School of Medicine Research Ethics Committee and follows the Declaration of Helsinki guidelines [52].

The review included 40 cross-sectional studies on prevalence and/or assessment of risk factors for hyperopia. Eighteen studies were conducted in Asia, of which six were carried out in China and five in India. The other Asian countries were: Nepal (three studies), Malaysia (two studies), Cambodia and the Democratic Republic of Laos (one study each). Seven studies are from Europe (two were conducted in the United Kingdom; Poland and Sweden carried out two studies each and one study was conducted in Finland). Six studies are from the Middle East (Iran). Four studies were conducted in Australia, two in the United States and one study each in South Africa, Chile and Mexico.

All samples of children used in the studies were population-based or school-based, except the study that used a sample of children from a private school in Xiamen, China [13].

In most studies included in this review, the cut-off point for hyperopia was based on the Refractive Error Study in Children (RESC) protocol used in multicenter studies [53]. Spherical equivalent refraction (SE) for hyperopia was ≥ +2.00D (one or both eyes, if none the eyes are myopic). The studies used data from one or both eyes to determine prevalence. However, some studies used different cut-off points [38‐48, 54], thus underestimating or overestimating hyperopia prevalence compared to studies using the RESC protocol. Some studies performed the examination on the right eye only, thereby underestimating the prevalence of hyperopia [38, 43].

The meta-analysis indicates that hyperopia prevalence decreases as age increases, with a summary prevalence measure of 5% at age 7, 2-3% between age 9 and 14 and around 1% at age 15. Various studies of children aged 6 to 8 presented large confidence intervals. I² indicates homogeneity among the studies regarding specific age (Figure 2).

In studies using the 5-15 age group and ≥ +2.00 D (RESC) cut-off, hyperopia prevalence ranged from 2.1% [18] to 19.3% [25, 37] (Table 1).

Although there is literature indicating a direct association between AL and age, only a few studies have assessed its distribution by specific ages [40, 55].

Most studies showed no statistically significant association between gender and hyperopia (Table 2) [9, 11, 14, 17, 19, 20, 23, 25‐27, 30, 32, 34, 36, 39‐41, 46‐48, 56, 57]. With regard to ocular components, on average girls appear to have shorter AL when compared to boys [3, 30, 55, 58].

According to some studies however, girls are more likely to be hyperopic when compared to boys. In Australia, girls aged 6 are more likely to be hyperopic (15.5%) (95% CI 12.7-18.4) than boys of the same age (10.9%) (95% CI 8.5-13.2) (p = 0.005), although this difference was not found among children aged 12 in the same study [29]. Similarly, studies conducted in Chile, China and Nepal with children aged 5-15 years showed that girls are more likely to be hyperopic than boys: OR = 1.21 (95% CI 1.03-1.43) [37], OR = 1.51 (95% CI 1.08-2.13) [10] and OR = 1.44 (95% CI 1.02-2.03), [18] respectively. However, in a study conducted in Poland boys aged 6-18 years showed higher hyperopia prevalence (40.3%) (95% CI 38.5-42.1) when compared to girls in the same age range (35.3%) (95% CI 33.6 - 37.0) [43].

Some studies have shown that there is no significant difference in hyperopia prevalence between Caucasian and Hispanic children [39] or between Caucasian and Middle East children [29, 30]. There is also evidence that Caucasian children are more hyperopic than African-American [39, 54, 56, 61], Black [35] and Asian (East and South Asia) children [29, 30, 35]. With regard to specific ethnic groups, there is no difference between hyperopia prevalence among Malay, Chinese and Indian children [17], although Malaysian children are more hyperopic than Singaporean (p = 0.005) [16] and Melanesian children [60]. It was also found that children of other ethnicities (not specified) are more likely to be hyperopic than Melanesian children OR = 3.72 (95%CI 1.34-10.3) [17] (Table 2).

In the South African study, hyperopia prevalence among children aged 7 years was only 2.8% [36]. The majority of the South African population is Black, followed by Asians (9.4%) and Caucasians (6.6%). In the Malay study, hyperopia prevalence among children aged 10 years was 1.4% [17]. The ethnic composition of the region is mostly Malay but approximately 28% of individuals have Chinese origin. The lowest hyperopia prevalence (0.5%) was found in a study in Guangzhou, one of the most developed cities in southern China [11].

Regarding ocular components in different ethnicities, on average it was found that AL is shorter and CC is flatter among Caucasian children [3, 30, 62].

Most of the reviewed studies showed no significant association between parental education and hyperopia in children (Table 2) [16, 17, 21, 22, 27, 36, 47]. In an Australian study, although there was no significant association between paternal education and hyperopia among children under 6 years of age, maternal education showed an inverse association with the presence of hyperopia among children aged 12 (p = 0.055) [29]. In a Chinese study the high level of parental education was a protective factor against the presence of hyperopia among children aged 5-15 years, OR = 0.81 (95% CI 0.73 - 0.81) [11].

Regarding socio-economic status, maternal employment is directly related to hyperopia in 6-year-old children in Australia (p = 0.02), although it is not associated with family income or paternal employment (p > 0.1) [29]. In the same study, an association between both parents being employed and hyperopia ≥ +2.00 D was found among 6-year-old children, after adjusting for gender, ethnicity and parental education (p = 0.02) [29].

Each of the three Indian studies with children aged 0-15 years had different cut-offs for hyperopia (≥ + 2.00D, ≥ + 1.00D and ≥ +0.5 D) but none of them showed association between socio-economic status (classified according to family income) and hyperopia [22, 41, 47].

In a study conducted in the United States, children aged 6-72 months with health insurance coverage showed a greater chance of having hyperopia when compared to those with no health insurance, OR = 1.51 (95% CI 1.12 - 1.69) [61].

There are few studies on the association between area of residence (urban or rural) and hyperopia prevalence in children. In an Indian study, children aged 0-15 years who lived in two rural areas were more likely to be hyperopic when compared to those living in urban areas, OR = 2.84 (95% CI 2.16-3.75) and OR = 1.50 (95% CI 1.17-1.92) respectively (Table 2) [47]. In another study conducted in India with children aged 7-15 years, those aged 8, 9, 12 and 13 years living in rural areas presented higher prevalence of hyperopia than those of the same age living in urban areas (Table 2) [23].

An Iranian study showed that children aged 7-15 years living in rural areas are more likely to be hyperopic than those living in urban areas, OR = 2.0 (95% CI 1.09-3.65) [9] and another study in Poland reported that children aged 6-18 years living in urban areas showed lower frequency of hyperopia when compared to children living in rural areas (p < 0.001) (Table 2) [38].

Two reviewed articles (one conducted in China with children aged 6-7 years and the other in Cambodia with children aged 12-14 years) showed no significant association between area of residence and hyperopia [13, 19] In the Cambodian study, hyperopia prevalence rates among children living in urban and rural areas were 1.4% (95% CI 0.1 - 1.7) and 0.4% (95% CI 0.1 - 1.9) respectively (Table 2) [19].

Rose et al. noted that children aged 6 and 12 years in Australia who spent more time per week doing outdoor activities (outdoor sports, picnics and walking) were more hyperopic than those who spent less time practicing these activities, adjusted for gender, ethnicity, presence of myopia in parents, near activities, and maternal and paternal education and working mothers (p = 0.009 and p = 0.0003, respectively) (Table 2) [8]. These authors also noted that there was a statistically significant trend toward greater hyperopic spherical equivalent refraction as tertiles of outdoor activities increased and tertiles of near activities decreased [8]. In the same study, Rose concluded that hyperopic spherical equivalent refraction was more common in children who dedicated less time to near activities and more time to outdoor activities [8].

Spending time engaged in outdoor activities was slightly associated with hyperopia (β = 0.03, p < 0.0001) among 12-year-old children in Australia. That study found that children who performed near activities (reported by parents), such as reading distance (<30cm), were significantly associated with less hyperopia (p < 0.0001), after adjusting for age, gender, ethnicity and type of school (Table 2) [59].

In the United States, Mutti et al. examined 366 children with mean age of 13.7 ± 0.5 years and showed (using the Wilcoxon rank-sum test) that myopic children spend more time reading for pleasure (p = 0.034) and less time playing sports (p = 0.049) compared with hyperopic children [7].