Myopia and visual acuity impairment: a comparative study of Greek and Bulgarian school children

Myopia in Bulgarian school children: prevalence, risk factors, and health care coverage

Background

The prevalence of myopia has increased in recent years, with changes being dynamic and uneven in different regions. The purpose of this study is to evaluate the prevalence of visual impairment caused by myopia in Bulgarian school children, associated risk factors, and health care coverage.

Methods

A cross-sectional study among 1401 children (mean age 10.38, standard deviation 2.70) is conducted in three locations in Bulgaria from 2016 to 2020. Refractive error is measured with an auto-refractor in the absence of cycloplegia, the visual acuity is assessed without refractive error correction. A paper-based preliminary questionnaire is used to collect data on previous eye examinations, prescribed optical vision correction, regularity of wearing corrective glasses and risk factors.

Results

Children with myopic objective refraction ≤ -0.75 D and decimal visual acuity ≤ 0.8 on at least one of the eyes are 236 out of 1401 or 16.85%. The prevalence of myopia varies depending on age, geographical location, and school profile. The rate of myopic children in age group 6–10 is 14.2% compared to 19.9% in age group 11–15. The prevalence of myopic children in the urban populations is 31.4% (capital) and 19.9% (medium-sized town) respectively, and only 8.4% in the rural population. Our results show 53% increase of the prevalence of myopia in the age group 11–15 compared to a 2009 report. The analysis of data associated with health care coverage factors of all myopic pupils shows that 71.6% had a previous eye examination, 43.2% have prescription for corrective glasses, 27.5% wear their glasses regularly. Risk factors for higher odds of myopia are gender (female), age (adolescence), and parents with impaired vision. Residence in a small town and daily sport activities correspond to lower odds for myopia. The screen time (time in front of the screen calculated in hours per day) is self-reported and is not associated with increased odds of myopia when accounted for the other risk factors.

Conclusions

The prevalence of myopia in this study is higher compared to previous studies in Bulgaria. Additional studies would be helpful in planning adequate prevention and vision care.

Estimating need and coverage for five priority assistive products: a systematic review of global population-based research

INTRODUCTION

To improve access to assistive products (APs) globally, data must be available to inform evidence-based decision-making, policy development and evaluation, and market-shaping interventions.

METHODS

This systematic review was undertaken to identify studies presenting population-based estimates of need and coverage for five APs (hearing aids, limb prostheses, wheelchairs, glasses and personal digital assistants) grouped by four functional domains (hearing, mobility, vision and cognition).

RESULTS

Data including 656 AP access indicators were extracted from 207 studies, most of which (n=199, 96%) were cross-sectional, either collecting primary (n=167) or using secondary (n=32) data. There was considerable heterogeneity in assessment approaches used and how AP indicators were reported; over half (n=110) used a combination of clinical and self-reported assessment data. Of 35 studies reporting AP use out of all people with functional difficulty in the corresponding functional domains, the proportions ranged from 4.5% to 47.0% for hearing aids, from 0.9% to 17.6% for mobility devices, and from 0.1% to 86.6% for near and distance glasses. Studies reporting AP need indicators demonstrated >60% unmet need for each of the five APs in most settings.

CONCLUSION

Variation in definitions of indicators of AP access have likely led to overestimates/underestimates of need and coverage, particularly, where the relationship between functioning difficulty and the need for an AP is complex. This review demonstrates high unmet need for APs globally, due in part to disparate data across this sector, and emphasises the need to standardise AP data collection and reporting strategies to provide a comparable evidence base to improve access to APs.

Refractive errors among Saudi college students and associated risk factors

Objectives

To determine the prevalence of refractive errors among freshman students of Imam Abdulrahman Bin Faisal University (IAU), and to examine the relationship of near-work activities and outdoor activities with refractive errors.

Methods

A cross-sectional study of 338 freshman students of IAU (162 males, 176 females) was carried out. Students were selected using a simple random sampling technique. Eye examination was done including non-cycloplegic autorefraction for determining the refractive error status. Myopia was defined as spherical equivalent refraction (SER) ≤−0.75 diopters (D), and it was further divided into low myopia (SER from −0.75 D to −2.99 D), moderate myopia (SER from −3.00 to −5.99 D), and high myopia (SER ≤−6.00 D). Hyperopia was defined as SER ≥1.00 D and emmetropia as having an SER value between that of low myopia and hyperopia. SER was calculated as sphere + 1/2 cylinder. A questionnaire detailed on activities was completed by participants.

Results

Myopia was found in 47.9% of the students (95% CI 42.7%–53.3%). The most prevalent type of myopia was low myopia (66.7%; 95% CI 59.1%–73.5%). Hyperopia and emmetropia were found in 6.5% (95% CI 4.3%–9.7%) and 45.6% (95% CI 40.3%–50.9%) of the students, respectively. Parental myopia was significantly associated with the myopic status of the students (P=0.007, Fisher’s exact test). About 6% of myopic students had a history of myopia in both parents. In addition, both parents had a history of myopia in 1.9% of emmetropic students, whereas such an association was absent in the hyperopic students. Refractive error type in both genders was not significantly predicted by the activity type.

Conclusion

Although the different types of activities did not predict the types of refractive errors, the high prevalence of myopia among the college students at this age requires further studies to explore more about the clinical characteristics and risk factors of the disease.

Myopia and orthokeratology for myopia control

The prevalence of myopia in children is increasing worldwide and is viewed as a major public health concern. This increase has driven interest in research into myopia prevention and control in children. Although there is still uncertainty in the risk factors underlying differences in myopia prevalence between ethnic groups, rates in children of East Asian descent are typically higher regardless of where they live. Mounting evidence also suggests that myopia prevalence in children increases with age. Earlier commencement and more rigorous education systems in these countries, resulting in more time spent on near-work activities and less time on outdoor activities, may be responsible for the earlier age of myopia onset. However, to date, the mechanisms regulating myopia onset and progression are still poorly understood. Findings from several studies have shown orthokeratology to be effective in slowing axial elongation and it is a well-accepted treatment, particularly in East Asian regions. While our understanding of this treatment has increased in the last decade, more work is required to answer questions, including: How long should the treatment be continued? Is there a rebound effect? Should the amount of myopia control be increased? To whom and when should the treatment be offered? Practitioners are now faced with the need to carefully guide and advise parents on whether and when to undertake a long somewhat complex intervention, which is costly, both in time and money. In the near future, a greater demand for effective prophylaxis against childhood myopia is envisaged. Other than orthokeratology, atropine therapy has been shown to be effective in slowing myopia progression. While its mechanism of control is also not fully understood, it is likely that it acts via a different mechanism from orthokeratology. Thus, a combined treatment of orthokeratology and atropine may have great potential to maximise the effectiveness of myopia control interventions.

Evidence for the need for vision screening of school children in Turkey

BACKGROUND

In many countries, access to general health and eye care is related to an individual's socioeconomic status (SES). We aimed to examine the prevalence of oculo-visual disorders in children in Istanbul Turkey, drawn from schools at SES extremes but geographically nearby.

METHODS

Three school-based vision screenings (presenting distance visual acuity, cover test, eye assessment history, colour vision, gross stereopsis and non-cycloplegic autorefraction) were conducted on 81% of a potential 1014 primary-school children aged 4-10 years from two private (high SES) schools and a nearby government (low SES) school in central Istanbul. Prevalence of refractive errors and school-based differences were analysed using parametric statistics (ANOVA). The remaining oculo-visual aspects were compared using non-parametric tests.

RESULTS

Of the 823 children with mean age 6.7 ± 2.2 years, approximately 10% were referred for a full eye examination (8.2% and 16.3% of private/government schools respectively). Vision had not been previously examined in nearly 22% of private school children and 65% of government school children. Of all children, 94.5% were able to accurately identify the 6/9.5 [LogMAR 0.2] line of letters/shapes with each eye and 86.6% the 6/6 line [LogMAR 0], while 7.9% presented wearing spectacles, 3.8% had impaired colour vision, 1.5% had grossly impaired stereo-vision, 1.5% exhibited strabismus, 1.8% were suspected to have amblyopia and 0.5% had reduced acuity of likely organic origin. Of the 804 without strabismus, amblyopia or organic conditions, 6.0% were myopic ≤ - 0.50DS, 0.6% hyperopic ≥ + 2.00DS, 7.7% astigmatic ≥1.00 DC and 6.2% anisometropic ≥1.00DS.

CONCLUSIONS

The results highlight the need for general vision screenings for all children prior to school entry given the varied and different pattern of visual problems associated with lifestyle differences in two populations raised in the same urban locale but drawn from different socioeconomic backgrounds.

Epidemiology of Myopia

Myopia is not a simple refractive error, but an eyesight-threatening disease. There is a high prevalence of myopia, 80% to 90%, in young adults in East Asia; myopia has become the leading cause of blindness in this area. As the myopic population increases globally, the severity of its impact is predicted. Approximately one fifth of the myopic population has high myopia (≥-6 diopters), which results in irreversible vision loss such as retinal detachment, choroidal neovascularization, cataracts, glaucoma, and macular atrophy. The increasing prevalence of school myopia in the past few decades may be a result of gene-environment interactions. However, earlier school myopia onset would accompany faster myopia progression and greater risk of high myopia later in life. Recently, there have been effective interventions to delay the onset of myopia, such as outdoor activity and decreasing the duration of near work. Hyperopia (≤0.5 diopters) is a predictor of myopia. Pharmacological agents and optic interventions such as low-concentration atropine and orthokeratology may slow progression in myopic children. Novel surgeries and anti-vascular endothelial growth factor drugs could deal with some myopic complications. From available evidence, the prevention, control, and treatment of myopia seem to be promising. However, to reduce the impact of myopia in future decades, more work and effort are still needed, including that by governments and intercountry eye health organizations.

Myopia is an Adaptive Characteristic of Vision: Not a Disease or Defect

This article proposes that myopia (nearsightedness) is an adaptive characteristic of human vision. Most theories of the evolution of vision assume myopia is a disease or defect that would have resulted in decreased reproductive fitness in the absence of modern corrective lenses. In contrast, the present article argues that myopic individuals may have played important roles in hunter–gatherer groups such as making tools and weapons, and identifying medicinal plants, contributing to individual and group survival. This idea is called the “adaptive myopia hypothesis.” Evidence favoring this hypothesis is reviewed in the context of the metatheory of evolutionary psychology.

Rationale, design, and demographic characteristics of the Handan Offspring Myopia Study

PURPOSE

The Handan Offspring Myopia Study (HOMS) aims to investigate the familial associations of myopia between parents and their offspring.

METHODS

Children aged 6-18 years, residing in 6 villages where all people aged ≥30 years had participated in The Handan Eye Study in 2006-2007, were selected for the current eye study between March and June 2010. A mobile clinic was set up in the 6 villages for comprehensive eye examinations, including visual acuity, ocular biometry, cycloplegic autorefraction and retinal photography.

RESULTS

Of 1238 eligible individuals, 878 children (70.2%; 52.6% male) from 541 families were recruited. Mean age of the children was 10.5 ± 2.5 years. The prevalence of myopia (spherical equivalent refraction <-0.5 diopter) was 23.5% (males 16.8%, females 30.8%). The prevalence of low vision (presenting visual acuity ≥20/400 but <20/60) in the better eye was 7.1%. A higher number of females had low vision at the time of presentation (9.2%) compared to males (5.2%, p = 0.02). The prevalence of low vision in the worse eye was 10.6% (males 6.7%, females 14.9%, p < 0.001). The majority of visual impairment in the better-seeing (56/62, 90.3%) as well as the worse-seeing (84/93, 90.3%) eye was correctable.

CONCLUSIONS

The HOMS examined about 70% of eligible Han Chinese offspring of Handan Eye Study participants in a rural region of northern China. Results from the HOMS will provide key information about the prevalence of refractive errors and eye diseases in rural Chinese children.

Myopia and international educational performance

PURPOSE

To analyse the relationship between myopia, educational performance and engagement in after-school tutorial classes.

METHODS

Educational performance data and data on engagement in after-school tutorial classes were taken from the results of the Organisation for Economic Cooperation and Development (OECD) Program in Secondary Assessment (PISA) reports for 2009, which tested educational outcomes in representative samples of 15 year-old school children from 65 jurisdictions. High prevalence of myopia (>70%) and low prevalence of myopia (<40%) locations were identified by systematic literature search.

RESULTS

Six locations with a high prevalence of myopia were identified from among the participants in PISA 2009 - Shanghai-China, Hong Kong-China, Taiwan, Singapore, Japan and South Korea. All were ranked in the top quartile on educational performance. Other participants in the top educational performance quartile were identified as locations with a low prevalence of myopia, including Australia and Finland. The locations with a high prevalence of myopia combined high educational performance and high engagement in after-school tutorials, whereas the locations with a low prevalence of myopia combined high educational performance with little engagement in tutorials.

DISCUSSION

These results show that it is possible to achieve high educational outcomes without extensive engagement in after-school tutorials, and that the combination of high educational outcomes with extensive use of tutorials is associated with high prevalence rates of myopia. We suggest that extensive use of after-school tutorials may be a marker of educational environments which impose high educational loads. Further quantification of educational loads to include after- school educational activities, such as homework, tutorials and other after-school classes, as well as formal school classes, is desirable. Policy initiatives to decrease these loads may contribute to the prevention of myopia, perhaps, at least in part, by enabling children to spend more time outdoors.

Choice of analytic approach for eye-specific outcomes: one eye or two?

PURPOSE

To investigate the use of analytic approaches for eye-specific outcomes in ophthalmology publications.

DESIGN

A review of analytic approaches used in original research articles published in ophthalmology journals.

METHODS

All 161 research articles published in 5 ophthalmology journals in the first 2 months of 2008 were considered. Publications were categorized according to analytic approach: 1 eye selected, both eyes contribute, or per-individual outcome. Studies were considered suboptimal when criteria for eye selection were not provided or when measurements from both eyes were included without interocular correlation being considered. Visual impairment prevalence data were used to illustrate analytic approach choices.

RESULTS

Measurements from both eyes were included in 38% of the 112 studies that used statistical inferential techniques. In 31 (74%), there was no mention of possible correlation. Only 7% used statistical methods appropriate for correlated outcomes. In 35 studies (31%), measurements from 1 eye were selected; 31% of these did not provide selection criteria. In 67%, only univariate tests were used. A review of 47 articles published in 2011 produced similar findings. Characteristics of studies were not found to differ according whether the studies were suboptimal. Using a test appropriate for correlated outcomes resulted in a P value 3.5 times that obtained ignoring the correlation.

CONCLUSIONS

Between-eye correlation seems not to be assessed commonly in ophthalmology publications, although its knowledge aids the choice of analytic approach when eye-specific variables are of interest. Statistical methods appropriate for correlated ocular outcome data are not being applied widely.

Worldwide prevalence and risk factors for myopia

BACKGROUND

Myopia, the most common type of refractive error, is a complex trait including both genetic and environmental factors. Numerous studies have tried to elucidate the aetiology of myopia. However, the exact aetiology of myopia is still unclear.

PURPOSE

To summarize the worldwide patterns and trends for the prevalence of myopia and to evaluate the risk factors for myopia in population-based studies.

RECENT FINDINGS

The prevalences of myopia vary across populations of different regions and ethnicities. In population-based studies on children, the prevalence of myopia has been reported to be higher in urban areas and Chinese ethnicity. The regional and racial difference is not so obvious in adult populations aged over 40 years. More time spent on near work, less time outdoors, higher educational level and parental history of myopia have been reported to increase the risk of myopia.

CONCLUSIONS

Environmental factors play a crucial role in myopia development. The effect of gene-environment interaction on the aetiology of myopia is still controversial with inconsistent findings in different studies. A relatively hyperopic periphery can stimulate compensating eye growth in the centre. Longitudinal cohort studies or randomized clinical trials of community-based health behaviour interventions should be conducted to further clarify the aetiology of myopia.

Childhood ethnic differences in ametropia and ocular biometry: the Aston Eye Study

PURPOSE

To describe the methodology, sampling strategy and preliminary results for the Aston Eye Study (AES), a cross-sectional study to determine the prevalence of refractive error and its associated ocular biometry in a large multi-racial sample of school children from the metropolitan area of Birmingham, England.

METHODS

A target sample of 1700 children aged 6-7 years and 1200 aged 12-13 years is being selected from Birmingham schools selected randomly with stratification by area deprivation index (a measure of socio-economic status). Schools with pupils predominantly (>70%) from a single race are excluded. Sample size calculations account for the likely participation rate and the clustering of individuals within schools. Procedures involve standardised protocols to allow for comparison with international population-based data. Visual acuity, non-contact ocular biometry (axial length, corneal radius of curvature and anterior chamber depth) and cycloplegic autorefraction are measured in both eyes. Distance and near oculomotor balance, height and weight are also assessed. Questionnaires for parents and older children will allow the influence of environmental factors on refractive error to be examined.

RESULTS

Recruitment and data collection are ongoing (currently N=655). Preliminary cross-sectional data on 213 South Asian, 44 black African Caribbean and 70 white European children aged 6-7 years and 114 South Asian, 40 black African Caribbean and 115 white European children aged 12-13 years found myopia prevalence of 9.4% and 29.4% for the two age groups respectively. A more negative mean spherical equivalent refraction (SER) was observed in older children (-0.21 D vs +0.87 D). Ethnic differences in myopia prevalence are emerging with South Asian children having higher levels than white European children 36.8% vs 18.6% (for the older children). Axial length, corneal radius of curvature and anterior chamber depth were normally distributed, while SER was leptokurtic (p<0.001) with a slight negative skew.

CONCLUSIONS

The AES will allow ethnic differences in the ocular characteristics of children from a large metropolitan area of the UK to be examined. The findings to date indicate the emergence of higher levels of myopia by early adolescence in second and third generation British South Asians, compared to white European children. The continuation of the AES will allow the early determinants of these ethnic differences to be studied.