This is the first report on the visual status of children in Istanbul and indicates a need for government sponsored screening programs, especially for children from lower socioeconomic backgrounds. As expected, the findings indicate that children from more privileged families are more likely to have already received eye care, more likely to experience better visual acuity regardless of whether spectacles are available to them or not, and less likely to exhibit amblyopic signs. With one in ten of children in the entire sample requiring immediate attention for relatively easily remedied visual problems, and two-thirds of these being children from a low socioeconomic background, this study underscores the imperative for vision tests to be included in community- or school-based public health screenings.
The need for eye care
The pre-eminent issues relating to eye care concern strabismus, amblyopia and refractive errors as they are the most common vision-based afflictions in children and are usually manageable such that visual acuity and visual comfort can be improved to minimise any impact on learning and lifestyle into adulthood [
31‐
34]. To date, only a small number of studies on the visual status of children have been carried out in Turkey and are reviewed and summarised in Table
1 [
9‐
12,
35,
36].
Strabismus and amblyopia. Strabismus often leads to amblyopia and can be cosmetically displeasing which leads to social isolation, but can be surgically managed and the long-term impact on the child decreased [
31,
34,
37,
38]. The current finding of 1.5% of children observed to have strabismus is at the lower end of the range previously found in Turkey, and is at the lower end of the range of prevalence studies in the Middle East, European and Asian populations [
37‐
41]. Notably however, in the current Istanbul study, the prevalence of amblyopia was found to be 3.9 times greater in children from the government school than children from the private schools. It cannot be ruled out that amblyopia may have been present at an earlier age in the private school children, but that the higher incomes of parents of higher socioeconomic status facilitated earlier identification and effective treatment. Poverty has been reported in the US as a factor in poor amblyopia treatment outcomes, as access to interventions is significantly restricted by their cost [
42‐
44]. Additionally, Unsal et al. [
12] found that the children of working women in Turkey were significantly more likely to present to a school screening with visual impairment, suggesting that the mother did not have time to take their child for eye care, or, there was insufficient family income to pay for eye care services.
Refractive error prevalence. In keeping with worldwide studies, uncorrected refractive error affects a far greater number of children in Turkey than does strabismus or amblyopia as demonstrated here and in the other Turkish studies (see Table
1). Notably, Gursoy et al. [
10] considered their finding of a comparatively high prevalence of myopia in a rural university-based city may derive from incomplete cycloplegia leaving some residual focussing capability (see ‘Note’ below Table
1), even though the RESC protocol for drug administration and refractive assessment was utilized.
Myopia is usually the first refractive error category to be considered given that the eye is at far greater risk of significant age-related ocular morbidity according to WHO standards [
45], and likely to lead to low vision or blindness. In East Asia, a doubling of the numbers of children with myopia, particularly higher degrees of myopia has occurred every decade over the last 30 years which precludes genetics as being the main determinant of whether a child develops myopia and thus implicates environmental and lifestyle factors [
13,
46‐
48]. In Shanghai, 19.5% of university students have high myopia greater than −6.00DS and are at high risk of pathological consequences that will significantly affect quality of life and employment [
45]. One may argue that Turkey does not have significant numbers of persons with myopia. Indeed, it did appear that Australia was not experiencing the shift towards higher numbers of myopic children in the early 2000’s [
49] at a time when Asian countries had already noted this. However, a decade later it is apparent that the prevalence of myopia in Australian children may be rising [
50]. Although it has been long held that factors such as parental education and hours of nearwork can be drivers for the development of myopia, more subtle aspects such as urban/rural living and the number of hours of outdoor activities have also been noted as important [
13,
20,
48]. Thus, we consider it important that well-designed baseline studies be undertaken in Istanbul to document the prevalence of myopia as a means to inform and monitor the need for public health initiatives, and also aim to better understand the many parameters driving the genesis of myopia.
Our finding that 6.0% of children (mean age 6.7 years) have myopia is low compared with East Asia, but not lower than that generally found in Caucasian countries for children of similar age. Even lower prevalences of myopia were found in rural Turkey where farming is common and attendance at the government school is generally just half a day [
9,
11]. On the other hand, a much higher prevalence has been found in one Turkish rural centre that is also a large university town [
10]. Considering just the older children in the current study, 16% of the 9–10 year olds were myopic, which is in keeping with our other published data of a prevalence of 17.2% for children aged 10–11 years of predominantly Lebanese background but residing in Australia and undertaking the standard Australian school curriculum [
15]. The only published study concerning myopia prevalence in adults in Turkey looked specifically at medical students in 2007 [
51] and found 32.9% had at least −0.75D myopia. Although seemingly high, this finding for Turkish medical students is low compared to the prevalence of over 90% found in east Asian medical students (using a − 0.50D cut-off) [
51]. Thus, it is important when the results of vision screenings are reported that a thorough description of the demographics of the subjects are also provided so as to aid understanding of the likely genetic predisposition and potential environmental triggers for myopigenesis.
The similarity in the prevalence of myopia between the two different types of school in the current study was unexpected. However, all schools undertake the same academic curriculum set by government and the children from the three schools have very similar ethnic backgrounds and physical locations even though they come from SES lifestyle environment extremes. The size of dwelling may also be similar, as most of the private school children apparently live in new apartment blocks in inner Istanbul. On the other hand, parental myopia and higher education are well-known risk factors and the parents from the private schools pay very high school fees necessitating a higher socioeconomic level, derived in many cases as a result of a higher educational background. The advantage of higher income has long been known worldwide to be accompanied by an increasing prevalence of myopia [
52‐
57] and has this been noted in rural centres in Turkey [
9]. Therefore, one might argue there is a greater likelihood of myopia among the private school parents compared to parents of children attending low-income government schools. Notably, in Turkey only 12% of those over the age of 15 years have tertiary education [
58]. However, this phenomenon with respect to higher parental income was not apparent in the current study, even when taking into account the dissimilar age profiles between our schools (6.7% and 6.9% for myopic children of comparable age in the private and government schools respectively). An association was also not seen in urban Iran when using father’s education as the variable [
59]. Unfortunately, the refractive status and education level of parents in the current study was not available, both of which represent limitations to interpretation of our data. Counter to these arguments, the private schools in the current study have an extensive outdoor sport program that starts earlier than the government school’s program, which may according to recent research [
20], be an ameliorating factor in the potential early onset of myopia for the private school children.
Hyperopia has traditionally received less attention than myopia as, from a medical view-point, hyperopia is seldom a risk factor for ocular complications [
60]. However, hyperopia is increasingly understood as being associated with asthenopia and less successful educational outcomes, and thus should receive greater public health intervention [
60‐
62], particularly for hyperopia that has limited or no impact on visual acuity [
63]. The current non-cycloplegic findings of 0.6% children having moderate hyperopia (> + 2.00D) and 4.1% having milder hyperopia (> + 0.75, <0.2.00D) are somewhat lower proportions than typically found in populations of lower socioeconomic background or rural location, where low to moderate hyperopia is common [
17,
38,
48,
54,
64,
65]. The use of a ‘closed box’ style autorefractor in the current study (i.e. where the child looks at a picture inside the shoe-box sized instrument positioned in front of their face, rather than looking through a semi-silvered mirror sitting on top of the instrument to a distant object across the room), may have limited the detection of children with hyperopia and somewhat minimised the degree of hyperopia detected, in that the closed-box can promote awareness of nearness and in turn inhibit the degree of hyperopia manifested [
66].
Medically, those with astigmatism are not at risk of developing ocular complications, but may experience significant asthenopia (eyestrain, headaches, blurred vision) [
61,
67,
68] and thus impaired learning. Few Turkish studies have addressed astigmatism, however our finding of 12.9% is similar to the only other Turkish study using a reliable autorefractor cut-off criterion for astigmatism [
69].
In most countries neighbouring Turkey, there is limited data (particularly in the English language literature) relating to the prevalence of refractive errors in children (see Table
1). However, in Iran there have been six significant cycloplegic refractive errors studies in the last five years (all adopting the RESC procedures with large sample size and in large cities or towns of population at least 200,000 people) [
59,
70‐
74]. All yielded a prevalence of myopia (≤ − 0.50D) under 5% in children of similar age to those in the current study. The prevalence of hyperopia ≥ + 2.00D under cycloplegia has been described as ranging from 7% to 20.9% in 5–15 year olds in Iran [
59,
70‐
74] and is far greater than that found in our study. Two Iranian studies additionally examined pre-cycloplegic data and found that, as would be expected, a far greater number of children (56% [
72] to 76% [
75]) fell in the category of low hyperopia (≥ + 0.50D but <2.00D) in the non-cyclopleged state than during cycloplegia (19% to 33% respectively).
What is apparent from all these figures is that our refractive data for central Istanbul is generally consistent with these recent trends showing a higher prevalence of myopia in urban versus truly rural towns. In modern urban areas there has been a shift in society towards higher education standards for children, more urban white-collar work and less outdoor play and employment. Further evidence that argues strongly for an important role for environmental influences relating to location comes from studies examining the change in prevalence with immigration to a country of higher prevalence resulting in ethnic-related increase in prevalence [
15,
76,
77] or conversely, immigration to a country of lower prevalence resulting in ethnic-related decrease in prevalence [
76]. Although ethnicity was not pursued in the current study, it would be of value in future larger investigations.
The value of public health screening to detect those requiring eye care
The issue of how many children during a screening will be identified to require further care is of utmost importance to public health policy makers, but does depend on the scope of the screening, the age of the children, the locale, etc. The current study has also highlighted socioeconomic status as an important factor, with twice the number of children (16.3%) in the lower socioeconomic background school requiring referral compared to those in private schools (8.2%).
Measurement of vision/visual acuity is a useful screening tool (see Table
1), as presenting acuity during a screener can reliably detect refractive error [
78,
79]. Presenting distance vision is particularly useful to detect myopia, but to ascertain the presence of all three refractive errors the combination of both distance and near vision testing gives best results [
78]. However, perhaps the best indicators to develop public health policy regarding the efficacy of screening children comes through comparison of the relative proportions of children with poor vision under different conditions: (i) when uncorrected (as this identifies the total number of children affected), as against (ii) habitual vision (which, with the first item, then identifies the resourcefulness within the community to provide any necessary optical aids), and finally (iii) best corrected vision (which when considered against the first item indicates the proportion requiring spectacle correction, as well as the small proportion of children who despite best correction will always be dependent on community support to adequately survive because their vision is still quite inadequate). Thus, the cost of public health screenings should not be considered simply in monetary terms, but also against the personal burden for those experiencing visual anomalies. For example, Caca et al. [
9] showed that 13.9% of children could be raised from a status of ‘visually impaired’ to ‘normal or near-normal vision’ simply through correction of their refractive error. Furthermore, they showed that 4.1% of all children changed their designation from ‘functionally blind’ to ‘useful’ if not ‘normal’ vision simply with spectacles.
Poor best-corrected visual acuity has been found to be most likely associated with strabismus, hyperopia, astigmatism and anisometropia by Gursoy et al. [
10], hence the importance of including visual acuity status and refractive error determination in the one vision screening (particularly if children are subsequently spectacle-compliant [
71]). However, in the current study there was notably a significant difference between the proportions of government school children (6.2%) and private school children (0.5%) experiencing ‘visual impairment’ as their habitual state at school (i.e. poorer than 6/19 line of letters with their better eye). By WHO standards, this level of impairment affects quality of life and ability to hold employment, and underscores potential socioeconomic contributing factors [
80].
The current study was initiated as a pilot to obtain a public health perspective on oculo-visual status of children in Turkey’s largest city. The lack of refractive data on 19% of non-participants at each school may be perceived as an equally distributed overall bias. However, because the relative proportions of children identified with anomalies at each type of school were not equal, bias from non-participation although numerically equal may not actually be the same. It could be argued that those who did not participate had already been identified as having a visual anomaly, in which case our prevalence findings may represent an overall underestimate. Some non-participation was reported by teachers to be simply due to illness on the day of screening. The reliance of non-cycloplegic data in the current study has been mentioned and is further discussed at the foot of Table
1 (see
a). This aspect suggests also that our prevalence findings for hyperopia will be an underestimate.
Future studies of visual status of children in Turkey should use appropriate randomised cluster sampling stratified by socioeconomic status and aim to determine what true differences in schooling exist for children of differing SES covered by the study, the socioeconomic status of the family, parental education and income, and importantly, parental refractive error and compliance of children already prescribed spectacles. Whilst demographic information is customarily gathered through a questionnaire to parents, it must be recognised that educational attainment is generally poor in Turkey (prior to 1997 compulsory schooling comprised only 5 years and thereafter increased to 8 years, and in 2007 literacy for persons aged 15 and over stood at only 78.5% for females and 94.4% for males [
81]).