Near-work activity and myopia in rural and urban schoolchildren in China

The influence of the environment and lifestyle on myopia

BACKGROUND

Myopia, commonly known as near-sightedness, has emerged as a global epidemic, impacting almost one in three individuals across the world. The increasing prevalence of myopia during early childhood has heightened the risk of developing high myopia and related sight-threatening eye conditions in adulthood. This surge in myopia rates, occurring within a relatively stable genetic framework, underscores the profound influence of environmental and lifestyle factors on this condition. In this comprehensive narrative review, we shed light on both established and potential environmental and lifestyle contributors that affect the development and progression of myopia.

MAIN BODY

Epidemiological and interventional research has consistently revealed a compelling connection between increased outdoor time and a decreased risk of myopia in children. This protective effect may primarily be attributed to exposure to the characteristics of natural light (i.e., sunlight) and the release of retinal dopamine. Conversely, irrespective of outdoor time, excessive engagement in near work can further worsen the onset of myopia. While the exact mechanisms behind this exacerbation are not fully comprehended, it appears to involve shifts in relative peripheral refraction, the overstimulation of accommodation, or a complex interplay of these factors, leading to issues like retinal image defocus, blur, and chromatic aberration. Other potential factors like the spatial frequency of the visual environment, circadian rhythm, sleep, nutrition, smoking, socio-economic status, and education have debatable independent influences on myopia development.

CONCLUSION

The environment exerts a significant influence on the development and progression of myopia. Improving the modifiable key environmental predictors like time spent outdoors and engagement in near work can prevent or slow the progression of myopia. The intricate connections between lifestyle and environmental factors often obscure research findings, making it challenging to disentangle their individual effects. This complexity underscores the necessity for prospective studies that employ objective assessments, such as quantifying light exposure and near work, among others. These studies are crucial for gaining a more comprehensive understanding of how various environmental factors can be modified to prevent or slow the progression of myopia.

Risk Factors for Myopia: A Review

Due to the myopia prevalence increase worldwide, this study aims to establish the most relevant risk factors associated with its development and progression. A review search was carried out using PubMed, Web of Science, and Scopus databases to identify the main myopia risk factors. The inclusion criteria for the articles were those related to the topic, carried out in subjects from 5 to 30 years, published between January 2000 and May 2023, in English, and with the full text available. Myopia etiology has proven to be associated with both genetic and environmental factors as well as with gene-environment interaction. The risk of developing myopia increases in children with myopic parents (one parent ×2 times, two parents ×5 times). Regarding environmental factors, education is the main risk factor correlated with myopia prevalence increase. Further, several studies found that shorter distance (<30 cm) and longer time spent (>30 min) for near work increase the risk of myopia. Meanwhile, increased outdoor activity (>40 min/day) has been shown to be a key factor in reducing myopia incidence. In conclusion, the interventional strategy suggested so far to reduce myopia incidence is an increase in time outdoors and a reduction in the time spent performing near-work tasks.

Outdoor Scene Classrooms to Arrest Myopia: Design and Baseline Characteristics

PURPOSE

This study aimed to investigate the impact on childhood myopia of classrooms with spatial properties of classrooms resembling those of outdoor environments. This article describes the design, baseline characteristics, and the acceptability of this strategy.

METHODS

Classrooms had custom-made wallpaper installed with forest and sky scenes that had spatial frequency spectra comparable with outdoor environments (i.e., outdoor scene classrooms). Acceptability of this strategy was evaluated by questionnaires. Outcomes to access the efficacy include cumulative proportion of myopia, change of cycloplegic spherical equivalent refractive error, and axial length.

RESULTS

Ten classes, comprising 520 students, were randomly assigned into outdoor scene or tradition classrooms. There was no difference in refractive status between two groups (myopia/emmetropia/hyperopia, 16.3% vs. 49.4% vs. 34.2% in outdoor scene classrooms, 18.3% vs. 49.0% vs. 32.7% in traditional classrooms; P = .83). Compared with the traditional classrooms, 88.9% of teachers and 87.5% of students felt the outdoor scene classrooms enjoyable, 22.2% of teachers and 75.3% of students reported higher concentration, and 77.8% of teachers and 15.2% of students reported no change. In addition, 44.4% of teachers and 76.0% of students reported higher learning efficiency in the outdoor scene classrooms, and 55.6% of teachers and 18.3% of students reported no change.

CONCLUSIONS

Outdoor scene classrooms are appealing to teachers and students. Outcomes of the study will inform the efficacy of this strategy in Chinese children.

Epidemiological investigation of the status of myopia in children and adolescents in Fujian Province in 2020

PURPOSE

The 2020 epidemiological investigation of myopia in children and adolescents in Fujian Province' aimed to provide reference guidelines for the prevention and control of myopia. The purpose of the present study was to address shortfalls in the epidemiological survey of myopia in Fujian and provide a basis for government decision making.

STUDY DESIGN

A cross-sectional and epidemiological investigation METHODS: Based on their levels of economic development and other economic factors, three cities in Fujian Province (Fuzhou, Xiamen, Longyan) were chosen through cluster random sampling and epidemiological investigation. Final analysis included 41,906 cases. Examinations including visual acuity and mydriatic optometry were performed on all subjects.

RESULTS

The overall proportion of myopia was 63.35% in boys and 70.55% in girls living in Fujian in 2020. The proportions of myopia in Xiamen and Longyan were similar; both cities showed a higher proportion of myopic cases than Fuzhou. The proportion of girls with myopia was higher than boys. The proportion of primary and middle school students with myopia was higher in economically developed regions compared with underdeveloped regions. The proportion of urban students with myopia was higher than in suburban students. Analysis showed that the prevalence of myopia increased with age. Interestingly, the prevalence of myopia was higher in children born in June and August than in children born in other months.

CONCLUSION

Children and adolescents in Fujian have a high rate of myopia which increases as the school grade increases. The better the economic conditions are, the higher the myopic rate. In addition, the myopic rate is higher in girls in and students born in June and August. The government, schools, hospitals, and parents should be alerted to this issue and coordinate to control the risk of myopia exacerbation and improve eyesight conditions of students in Fujian Province.

Differences in visual stimulation between reading and walking and implications for myopia development

Visual input plays an important role in the development of myopia (nearsightedness), a visual disorder that blurs vision at far distances. The risk of myopia progression increases with the time spent reading and decreases with outdoor activity for reasons that remain poorly understood. To investigate the stimulus parameters driving this disorder, we compared the visual input to the retina of humans performing two tasks associated with different risks of myopia progression, reading and walking. Human subjects performed the two tasks while wearing glasses with cameras and sensors that recorded visual scenes and visuomotor activity. When compared with walking, reading black text in white background reduced spatiotemporal contrast in central vision and increased it in peripheral vision, leading to a pronounced reduction in the ratio of central/peripheral strength of visual stimulation. It also made the luminance distribution heavily skewed toward negative dark contrast in central vision and positive light contrast in peripheral vision, decreasing the central/peripheral stimulation ratio of ON visual pathways. It also decreased fixation distance, blink rate, pupil size, and head-eye coordination reflexes dominated by ON pathways. Taken together with previous work, these results support the hypothesis that reading drives myopia progression by understimulating ON visual pathways.

A systematic review of near work and myopia: measurement, relationships, mechanisms and clinical corollaries

After decades of investigation, the role of near work in myopia remains unresolved, with some studies reporting no relationship and others finding the opposite. This systematic review is intended to summarize classic and recent literature investigating near work and the onset and progression of myopia, potential mechanisms and pertinent clinical recommendations. The impact of electronic device use is considered. PubMed and Medline were used to find peer-reviewed cross-sectional and longitudinal studies related to near work and myopia from 1980 to July 2020 using the PRISMA checklist. Studies were chosen using the Joanna Briggs Institute checklist, with a focus on studies with a sample size greater than 50. Studies were independently evaluated; conclusions were drawn per these evaluations. Numerous cross-sectional studies found increased odds ratio of myopia with increased near work. While early longitudinal studies failed to find this relationship, more recent longitudinal studies have found a relationship between myopia and near work. Rather than daily duration of near work, interest has increased regarding absolute working distance and duration of continuous near viewing. Several reports have found that shorter working distances (<30 cm) and continuous near-work activity (>30 min) are risk factors for myopia onset and progression. Novel objective continuously measuring rangefinding devices have been developed to better address these questions. The literature is conflicting, likely due to the subjective and variable nature in which near work has been quantified and a paucity of longitudinal studies. We conclude that more precise objective measures of near viewing behaviour are necessary to make definitive conclusions regarding the relationship between myopia and near work. Focus should shift to utilizing objective and continuously measuring instruments to quantify near-work behaviours in children, followed longitudinally, to understand the complex factors related to near work. A better understanding of the roles of absolute working distance, temporal properties, viewing breaks and electronic device use on myopia development and progression will aid in the development of evidence-based clinical recommendations for behavioural modifications to prevent and slow myopia.

Physical activity, time spent outdoors, and near work in relation to myopia prevalence, incidence, and progression: An overview of systematic reviews and meta-analyses

Myopia has reached epidemic levels in recent years. Stopping the development and progression of myopia is critical, as high myopia is a major cause of blindness worldwide. This overview aims at finding the association of time spent outdoors (TSO), near work (NW), and physical activity (PA) with the incidence, prevalence, and progression of myopia in children. Literature search was conducted in PubMed, Scopus, Cumulative Index to Nursing and Allied Health Literature, Cochrane Database of Systematic Reviews, ProQuest, and Web of Science databases. Systematic reviews (SR) and meta-analyses (MA) on the TSO, NW, and PA in relation to myopia were reviewed. Methodological nature of qualified studies were evaluated utilizing the Risk of Bias in Systematic Review tool. We identified four SRs out of which three had MA, which included 62 unique studies, involving >1,00,000 children. This overview found a protective trend toward TSO with a pooled odds ratio (OR) of 0.982 (95% confidence interval (CI) 0.979-0.985, I2 = 93.5%, P < 0.001) per extra hour of TSO every week. A pooled OR 1.14 (95% CI 1.08-1.20) suggested NW to be related to risk of myopia. However, studies associating myopia with NW activities are not necessarily a causality as the effect of myopia might force children to indoor confinement with more NW and less TSO. PA presented no effect on myopia. Though the strength of evidence is less because of high heterogeneity and lack of clinical trials with clear definition, increased TSO and reduced NW are protective against myopia development among nonmyopes.

The prevalence and predictors of refractive error among school children in Riyadh, Saudi Arabia

PURPOSE:

Refractive error (RE) is one of the most common ocular disorders among children worldwide. This study aimed to investigate the prevalence of RE and possible risk factors among school children in Riyadh.

METHODS:

This is a cross-sectional study using data collected at various schools. To achieve the aim of the study, we selected a random sample of 850 school children aged 6–15 years. The examination was based on the RESC protocol and included full visual assessment. Furthermore, a questionnaire was sent to the parents of the participants to ascertain information about lifestyle factors. We constructed a logistic regression model to evaluate the predictors of RE.

RESULTS:

Close to a third of the children had a RE. Of those identified as having the condition, 60% did not wear glasses (newly diagnosed). Nearly all the children (95.4%) in our sample reported using electronic devices, according to parents. No association was found between using electronic devices and having a RE (P = 0.26). Doing outdoor activities was associated with 52% lower odds of a RE (odds ratio = 1.52).

CONCLUSION:

We found a higher prevalence of uncorrected RE than previously reported in other Saudi studies. About 60% of children who had RE were not wearing glasses, highlighting the need for a standardized school screening program for early detection and management. Outdoor activities were associated with a lower likelihood of having a RE. These findings might support initiatives to encourage outdoor activities among school children.

The biological basis of myopic refractive error

Myopia is among the most common refractive errors and is associated with the greatest risk of pathological outcomes. Most animals, including humans, are born with hyperopic errors. During development, axial elongation of the eye occurs and is regulated through a vision-dependent process, known as emmetropisation The extremely rapid changes in the prevalence of myopia and the dependence of myopia on the level of education indicate that there are very strong environmental impacts on the development of myopia. This conflicts with the common occurrence of familial patterns of inheritance of myopia, which suggests a role for genetic determination. There are more than 150 defined genetic syndromes in which familial high myopia is one of the features, including some that are not associated with other syndromes. The evidence for the roles of both nature and nurture in the aetiology of myopia is discussed. This review also examines the experimentally induced refractive errors associated with form-deprivation, recovery from form deprivation and the effects of both negative and positive lenses. In addition, it looks at the local and optical control of eye growth. Finally, the various control pathways for growth are considered. These include dopamine, ZENK-glucagon, retinoic acid and retinoic acid receptors, crystallin, seratonin and melatonin, vasoactive intestinal peptide and enkephalins, nitric oxide and various growth factors.

Spectacle use and reduced unaided vision in third grade students: a comparative study in different educational settings

BACKGROUND

The development of myopia is influenced by hereditary factors, environmental factors and gene-environment interaction. Reading and near-work activity are associated with myopia and myopic progression. This study sought to determine and compare the prevalence of reduced unaided vision and spectacle use among third grade Israeli students from three different educational settings.

METHOD

A sample of 917 students (mean age 8.5 years, range seven to 10 years) was drawn from the three Israeli educational streams: secular, Orthodox and ultra-Orthodox. Children in the ultra-Orthodox education pathway begin studying at the age of three years and their daily reading involves sustained near work with increased accommodative effort accompanied by head-rocking movements. Reduced distance vision was used to indicate the likely development of or an increase in the amount of myopia. Spectacle lenses were measured to determine the prevalence of myopia.

RESULTS

Of the 917 students studied, 103 (11.2 per cent) wore spectacles (14.2 per cent of the males and eight per cent of the females); 82.5 per cent of those who wore spectacles were myopic. Males from ultra-Orthodox schools had the highest rate of reduced unaided vision (72.5 per cent) compared with males from secular schools (27.3 per cent), males from Orthodox schools (59.3 per cent) or with females from all three groups (average of 34.8 per cent, p < 0.0001, chi squared). Males had a higher rate of reduced unaided vision, especially in the Orthodox and ultra-Orthodox schools.

CONCLUSIONS

Our study suggests that Jewish ultra-Orthodox males have a higher prevalence and degree of myopia. The study habits of young children, including exposure to prolonged near tasks, high accommodative demands and possibly optical defocus induced by body sway, may contribute to the development of myopia.

Refractive error, axial length, environmental and hereditary factors associated with myopia in Swedish children

Clinical relevance: Investigation of refractive errors amongst Swedish schoolchildren will help identify risk factors associated with myopia development.Background: Genetic and hereditary aspects have been linked with the development of myopia. Nevertheless, in the case of 'school myopia' some authors suggest that environmental factors may affect gene expression, causing school myopia to soar. Additional understanding about which environmental factors play a relevant role can be gained by studying refractive errors in countries like Sweden, where prevalence of myopia is expected to be low.Methods: Swedish schoolchildren aged 8-16 years were invited to participate. Participants underwent an eye examination, including cycloplegic refraction and axial length (AL) measurements. Predictors such as time spent in near work, outdoor activities and parental myopia were obtained using a questionnaire. Myopia was defined as spherical equivalent refraction (SER) ≤ -0.50D and hyperopia as SER ≥ +0.75D.Results: A total of 128 children (70 females and 58 males) participated in this study with mean age of 12.0 years (SD = 2.4). Based on cycloplegic SER of the right eye, the distribution of refractive errors was: hyperopia 48.0% (CI95 = 38.8-56.7), emmetropia 42.0% (CI95 = 33.5-51.2) and myopia 10.0%. (CI95 = 4.4-14.9). The mean AL was 23.1 mm (SD = 0.86), there was a correlation between SER and AL, r = -0.65 (p < 0.001). Participants with two myopic parents had higher myopia and increased axial length than those with one or no myopic parents. The mean time spent in near work, outside of school, was 5.3 hours-per-day (SD = 3.1), and mean outdoor time reported was 2.6 hours-per-day (SD = 2.2) for all the participants. The time spent in near work and outdoor time were different for different refractive error categories.Conclusion: The prevalence of myopia amongst Swedish schoolchildren is low. Hereditary and environmental factors are associated with refractive error categories. Further studies with this sample are warranted to investigate how refractive errors and environmental factors interact over time.

Prevalence of ocular morbidities among school children in Raipur district, India

Purpose:

To estimate the prevalence of various ocular morbidities in school children (5–15 years) utilizing a comprehensive mobile eye unit in Central India.

Methods:

A prospective, cross-sectional, school-based observational study was carried out in Raipur, Chhattisgarh, India between December 2017 and September 2018. A total of 1557 eligible school-going children in the age group 5–15 years were evaluated. Random sampling was done to allocate schools (n = 29) and children from various urban and rural (836 vs 721) schools. The primary objective was to estimate the prevalence of ocular morbidities in school-going children in Raipur district, India. The secondary objective was to analyze whether geographical location (rural vs urban), age group, and gender led to any differences in ocular morbidity patterns.

Results:

The mean age of the study population was 10.3 ± 2.4 years. There were 691 (44.4%) boys and 866 (55.6%) girls. Ocular morbidity was present in a total of 331 (21.2%) children. Vitamin A deficiency was the most common cause of ocular morbidity, noted in 156 (10%) children, followed by refractive error (81, 5.2%). Myopia was significantly higher in urban school children (4.3%) compared to rural children (1.9%) (P = 0.002). The older age group had a higher prevalence (7.6%) of refractive error, especially myopia, compared to the younger age group (2.2%) (P < 0.001).

Conclusion:

Vitamin A deficiency prevalence was much higher indicating missed opportunities for vitamin A supplementation at a younger age. Refractive error was more prevalent in the urban population as well in the older age group (11–15 years), indicating a need for frequent eye screening.

Geographical Variation in Likely Myopia and Environmental Risk Factors: A Multilevel Cross Classified Analysis of A UK Cohort

Purpose: Previous studies have demonstrated positive associations between myopia and environmental risk factors such as urbanization. However, these have failed to account for the clustering of individuals within geographical areas, opening analyses to theoretical and statistical limitations. We demonstrate how a multilevel modelling approach can provide a more nuanced understanding of the relationship between geography and myopia. We examined longitudinal associations between onset of myopia and urban/rural status or population density.

Methods: Data were collected over 5 visits during an 8-year period for a UK cohort of 3,512 children. Associations between incident myopia (spherical equivalent ≤ −1.00 diopters) and both urban/rural status and population density were examined using discrete time multilevel hazard models which allow the partitioning of variance into different neighborhood and school areas.

Results: There was evidence for an association between myopia and higher population density (Hazard Ratio = 1.14; 95% CI = 1.032 to 1.26) after adjustment for a range of risk factors. There was no strong evidence that urban/rural status was associated with incident myopia. Only a minor amount of variation in myopia was attributable to geographical areas (<2.2%), and this was not explained by rurality or population density.

Conclusion: Our findings contrast with previous studies and raise the possibility that some of the results reported may have been driven by confounding bias whereby geographical differences in myopia are driven by lifestyle factors that are correlated with geographical setting.

Continuous Objective Assessment of Near Work

Evidence regarding the role of near work in myopia is conflicting. We developed the RangeLife, a device for continuous, objective measurement of working distance. Four devices were built, calibrated, and validated. Then, adult subjects wore the device on weekdays and weekend days, while simultaneously wearing an actigraph device for objective measurements of light exposure and activity. Subjects maintained an activity log and answered a visual activity questionnaire. RangeLife data were downloaded and binned into 0.10 m intervals. Objective diopter hours (dh), a weighted measure of near work, were calculated. Diopter hours for all subjects were significantly higher on weekdays (14.73 ± 4.67 dh) compared to weekends (11.90 ± 4.84 dh, p = 0.05). 94 ± 1.85% of near and intermediate viewing distances were recorded when the subjects were exposed to mesopic and indoor photopic light levels (<1000 lux), and 80.03 ± 2.11% during periods of sedentary physical activity (<320 counts per minute). Subjective reports of time viewing near and intermediate distances significantly overestimated objective measures (p = 0.002). The RangeLife was shown to provide reliable measures of viewing distance, and can be further utilized to understand potential influences of viewing behaviors on refractive error.

Parental attitudes to myopia: a key agent of change for myopia control?

PURPOSE

With the increasing prevalence in myopia there is growing interest in active myopia prevention. This study aims to increase our understanding of parental attitudes to myopia development and control, as a means to inform future health planning and policy. It evaluates, for the first time, the attitude of parents to myopia and its associated risks, as well as assessing the exposure of Irish children to environmental factors that may influence their risk profile for myopia development.

METHODS

Parents of 8-13 year old children in eight participating schools completed a questionnaire designed to assess their knowledge of and attitudes towards myopia and its risk factors. A structured diary was also used to capture daily activities of children in relation to myopia risk factors.

RESULTS

Of 329 parents, just 46% considered that myopia presented a health risk to their children, while an identical number (46%) regarded it as an optical inconvenience. Myopia was also, but less frequently, considered an expense (31% of parents), a cosmetic inconvenience (14% of parents) and, by some, as a sign of intelligence (4% of parents) 76% of parents recognised the potential of digital technology to impact the eye, particularly as a cause of eyestrain and need for spectacles. Only 14% of parents expressed concern should their child be diagnosed with myopia. Compared to non myopic parents, myopic parents viewed myopia as more of an optical inconvenience (p < 0.001), an expense (p < 0.005) and a cosmetic inconvenience (p < 0.001). There was a trend for myopic parents to limit screen time use in their household more than non-myopic parents (p = 0.05). Parents who considered myopia a health risk sought to limit screen time more than parents who did not regard myopia as a health risk to their child (p = 0.01). Children spent significantly longer performing indoor proximal tasks (255 min) compared to time spent outdoors (180 min; p < 0.0001) daily. Older (p = 0.001), urban (p = 0.0005) myopic (=0.04) children spent significantly more time at digital screens compared to younger non-myopic children from a rural background.

CONCLUSION

Parental attitudes to myopia were typically nonchalant in relation to health risk. This is of particular concern given the impact parents have on children's behaviour and choices with respect to such risk factors, demonstrating an acute need for societal sensitisation to the public health importance of myopia.

Determinants of the Progress of Myopia among Omani School Children: A Historical Cohort Study

PURPOSE

This study was conducted in 2002-2003 at selected schools of eight health regions of Oman. The authors present risk factors and predictors of progression of myopia between the 7th and 10th grades.

METHODS

This was a historical cohort study. A total of 1304 students in 10th grade, both with and without progression of myopia, were examined by the refractionists. Vision, refraction, and physical measurements of each student were recorded. The health records of all students were reviewed to note the same parameters measured when they were in 7th grade. The odds of progression in height, progression in weight, protein energy malnutrition status, sex, age, history of refractive error in parents and sibling, evidence of trachoma, and allergic conjunctivitis were calculated to associate them to the progression of myopia.

RESULTS

Mean progression of myopia was 0.37 D per year (SD = 0.27D). The mean progression of myopia among students with history of myopia in 7th grade was 0.21 D more than that of students not having myopia in 7th grade (95% CI 0.12-0.29). Multivariate regression analysis suggested that weight of student in the 7th grade (t=-2.2, p=0.031), positive history of myopia in one of the siblings (t=2.44, p=0.015), and myopia in the 7th grade (t=4.56, p<0.001) were associated with the progression of myopia.

CONCLUSIONS

Family history of myopia and myopia at younger age were predictors for progressive myopia in teenaged Omani children. However, the role of body mass index at a younger age to predict progressive myopia was not conclusive.

The Influence of Environmental Factors on the Prevalence of Myopia in Poland

Purpose

In the paper, we describe and discuss the results of epidemiological studies concerning myopia carried out in Poland.

Materials and Methods

Results from the examination of 5601 Polish school children and students (2688 boys and 2913 girls) aged 6 to 18 years were analyzed. The mean age was 11.9 ± 3.2 years. Every examined student had undergone the following examinations: distance visual acuity testing, cover test, anterior segment evaluation, and cycloplegic retinoscopy after instillation of 1% tropicamide, and a questionnaire was taken.

Results

We have found that (1) intensive near work (writing, reading, and working on a computer) leads to a higher prevalence of myopia, (2) watching television does not influence the prevalence of myopia, and (3) being outdoors decreases the prevalence of myopia.

Conclusions

The results of our study point to insufficiency of accommodation contributing to the pathogenesis of myopia.

Near work, outdoor activity, and myopia in children in rural China: the Handan offspring myopia study

BACKGROUND

The near work and outdoor activity are the most important environmental risk factors for myopia. However, data from Chinese rural children are relatively rare and remain controversial. Therefore, the purpose of this study was to evaluate the relationship of both near work and outdoor activities with refractive error in rural children in China.

METHODS

In this cross-sectional study, 572 (65.1%) of 878 children (6-18 years of age) were included from the Handan Offspring Myopia Study (HOMS). Information from the parents on these children, as well as the parent's non-cycloplegic refraction, were obtained from the database of the Handan Eye Study conducted in the years 2006-2007. A comprehensive vision examination, including cycloplegic refraction, and a related questionnaire, were assessed on all children.

RESULTS

The overall time spent on near work and outdoor activity in the children was 4.8 ± 1.6 and 2.9 ± 1.4 h per day, respectively. Myopic children spent more time on near work (5.0 ± 1.7 h vs.4.7 ± 1.6 h, p = 0.049), while no significant difference was found in outdoor activity hours (2.8 ± 1.3 h vs. 3.0 ± 1.4 h, p = 0.38), as compared to non-myopic children. In the multiple logistic analysis, in general, no association between near work and myopia was found after adjusting for the children's age, gender, parental refractive error, parental educational level, and daily outdoor activity hours [odds ratio (OR), 95% confidence interval (CI): 1.10, 0.94-1.27]. However, a weak protective effect of the outdoor activity on myopia was found (OR, 95% CI: 0.82, 0.70-0.96), after adjusting for similar confounders.

CONCLUSIONS

In general, no association between near work and myopia was found, except for the high near work subgroup with moderate outdoor activity levels. A weak protective effect of outdoor activity on myopia in Chinese rural children was observed.

Time spent in outdoor activities in relation to myopia prevention and control: a meta-analysis and systematic review

Outdoor time is considered to reduce the risk of developing myopia. The purpose is to evaluate the evidence for association between time outdoors and (1) risk of onset of myopia (incident/prevalent myopia); (2) risk of a myopic shift in refractive error and c) risk of progression in myopes only. A systematic review followed by a meta-analysis and a dose-response analysis of relevant evidence from literature was conducted. PubMed, EMBASE and the Cochrane Library were searched for relevant papers. Of the 51 articles with relevant data, 25 were included in the meta-analysis and dose-response analysis. Twenty-three of the 25 articles involved children. Risk ratio (RR) for binary variables and weighted mean difference (WMD) for continuous variables were conducted. Mantel-Haenszel random-effects model was used to pool the data for meta-analysis. Statistical heterogeneity was assessed using the I² test with I²  ≥ 50% considered to indicate high heterogeneity. Additionally, subgroup analyses (based on participant's age, prevalence of myopia and study type) and sensitivity analyses were conducted. A significant protective effect of outdoor time was found for incident myopia (clinical trials: risk ratio (RR) = 0.536, 95% confidence interval (CI) = 0.338 to 0.850; longitudinal cohort studies: RR = 0.574, 95% CI = 0.395 to 0.834) and prevalent myopia (cross-sectional studies: OR = 0.964, 95% CI = 0.945 to 0.982). With dose-response analysis, an inverse nonlinear relationship was found with increased time outdoors reducing the risk of incident myopia. Also, pooled results from clinical trials indicated that when outdoor time was used as an intervention, there was a reduced myopic shift of -0.30 D (in both myopes and nonmyopes) compared with the control group (WMD = -0.30, 95% CI = -0.18 to -0.41) after 3 years of follow-up. However, when only myopes were considered, dose-response analysis did not find a relationship between time outdoors and myopic progression (R²  = 0.00064). Increased time outdoors is effective in preventing the onset of myopia as well as in slowing the myopic shift in refractive error. But paradoxically, outdoor time was not effective in slowing progression in eyes that were already myopic. Further studies evaluating effect of outdoor in various doses and objective measurements of time outdoors may help improve our understanding of the role played by outdoors in onset and management of myopia.

Global variations and time trends in the prevalence of childhood myopia, a systematic review and quantitative meta-analysis: implications for aetiology and early prevention

The aim of this review was to quantify the global variation in childhood myopia prevalence over time taking account of demographic and study design factors. A systematic review identified population-based surveys with estimates of childhood myopia prevalence published by February 2015. Multilevel binomial logistic regression of log odds of myopia was used to examine the association with age, gender, urban versus rural setting and survey year, among populations of different ethnic origins, adjusting for study design factors. 143 published articles (42 countries, 374 349 subjects aged 1–18 years, 74 847 myopia cases) were included. Increase in myopia prevalence with age varied by ethnicity. East Asians showed the highest prevalence, reaching 69% (95% credible intervals (CrI) 61% to 77%) at 15 years of age (86% among Singaporean-Chinese). Blacks in Africa had the lowest prevalence; 5.5% at 15 years (95% CrI 3% to 9%). Time trends in myopia prevalence over the last decade were small in whites, increased by 23% in East Asians, with a weaker increase among South Asians. Children from urban environments have 2.6 times the odds of myopia compared with those from rural environments. In whites and East Asians sex differences emerge at about 9 years of age; by late adolescence girls are twice as likely as boys to be myopic. Marked ethnic differences in age-specific prevalence of myopia exist. Rapid increases in myopia prevalence over time, particularly in East Asians, combined with a universally higher risk of myopia in urban settings, suggest that environmental factors play an important role in myopia development, which may offer scope for prevention.

The Association between Near Work Activities and Myopia in Children-A Systematic Review and Meta-Analysis

Myopia has a multifactorial etiology, although environmental factors are predominant in determining its current patterns. Currently, associations between near work activities and myopia have not been consistently observed. Therefore, we performed a systematic review to quantify the effect of near work activities on myopia in children. Relevant articles published between 1989 and 2014 were identified in MEDLINE, Embase, and the Cochrane Library, and the citation lists were reviewed. Twelve cohort studies and 15 cross-sectional studies were included (25,025 children aged between 6 and 18 years). The I² statistic was used to assess heterogeneity. Study-level data were pooled using a random-effects model or a fixed-effects model (when less than 5 studies were included). We found that more time spent on near work activities was associated with higher odds of myopia (odds ratio [OR] = 1.14; 95% confidence interval [CI] = 1.08–1.20) and that the odds of myopia increased by 2% (OR:1.02; 95% CI = 1.01–1.03) for every one diopter-hour (hr) more of near work per week. Therefore, the development of a strategy to reduce the impact of near work on myopia would be important for preventing myopia in children.

Rapid Assessment of Refractive Error, Presbyopia, and Visual Impairment and Associated Quality of Life in Nampula, Mozambique

Introduction

Uncorrected refractive error is the leading cause of visual impairment worldwide and leads to an impaired quality of life. This study was designed to determine the prevalence of uncorrected refractive error and presbyopia, to assess spectacle coverage, and to evaluate visual health-related quality of life among persons aged 15–50 years old in Nampula, Mozambique.

Methods

Participants were assessed using a validated rapid assessment of refractive error protocol, comprised of a demographic questionnaire, a standardized ophthalmic assessment to determine refractive status and spectacle coverage, and a modified vision-related quality of life questionnaire to assess the impact of uncorrected refractive error on participants’ visual health status.

Results

Among the 3,453 respondents, visual impairment prevalence was 3.5% (95%, CI 2.7%–4.2%), with 65.8% of those visually impaired being 35 years of age and older. Uncorrected refractive error prevalence was 2.6% (95%, CI 2.1–3.2%), and was the primary cause of visual impairment among 64.5% of cases. The spectacle coverage for uncorrected refractive error was 0%. Presbyopia prevalence was higher, at 25.8% (95%, CI 12.0–30.5%), with only 2.2% spectacle coverage. Respondents with visual impairment demonstrated statistically significantly lower quality of life scores compared to those without visual problems ( p < 0.01).

Implications for practitioners

The uncorrected refractive error problem and a distinct lack of spectacle coverage for refractive error and presbyopia indicate an urgent need for the development and delivery of a comprehensive refractive error service in the Nampula region of Mozambique.

Risk factors for and progression of myopia in young Taiwanese men

Abstract Purpose: To investigate the association between potential risk factors for myopia and its progression in young adult Taiwanese men.

METHODS

A survey of male military conscripts (aged 18-24 years) was conducted from February 2010 to March 2011 in Taiwan. Participants underwent comprehensive eye examinations, including measurements of axial length and corneal radius by optical biometry and non-cycloplegic autorefraction. Participants also provided self-reported progression of myopia and information regarding potential risk factors, including age, parental myopia, educational level, close work, outdoor activities, and urbanization.

RESULTS

Of 5145 eligible participants, 5048 (98.11%) provided refraction and questionnaire data; 2316 (45.88%) of the 5048 also had biometric measurements. The prevalence of myopia was 86.1% in this group, with a mean refractive error of -3.66 diopters (D). Of the 5048 participants, 1376 (27.3%) had experienced progression of their myopia during the past year. There were trends for a higher prevalence of myopia among older participants (p = 0.014), those with a history of parental myopia (p < 0.001), higher levels of education (p = 0.001), increased time spent reading (p < 0.001), less time outdoors (p = 0.003), and higher levels of urbanization (p = 0.010). However, only parental myopia, close work, and higher urbanization levels were significantly associated with self-reported progression of myopia.

CONCLUSION

Older age, parental myopia, higher educational level, close work, fewer outdoor activities, and higher urbanization level were associated with the prevalence of myopia in Taiwanese men.

Axial elongation associated with biomechanical factors during near work

PURPOSE

To investigate the changes occurring in the axial length, choroidal thickness, and anterior biometrics of the eye during a 10-minute near task performed in downward gaze.

METHODS

Twenty young adult subjects (10 emmetropes and 10 myopes) participated in this study. To measure ocular biometrics in downward gaze, an optical biometer was inclined on a custom-built height- and tilt-adjustable table. Baseline measures were collected after each subject performed a distance primary gaze control task for 10 minutes to provide washout period for previous visual tasks before each of three different accommodation/gaze conditions. These other three conditions included a near task (2.5 diopters [D]) in primary gaze and a near (2.5 D) and a far (0 D) accommodative task in downward gaze (25 degrees), all for 10 minutes' duration. Immediately after and then 5 and 10 minutes from the commencement of each trial, measurements of ocular biometrics (e.g., anterior biometrics, axial length, choroidal thickness, and retinal thickness) were obtained.

RESULTS

Axial length increased with accommodation and was significantly greater for downward gaze with accommodation (mean ± SD change, 23 ± 13 μm at 10 minutes) compared with primary gaze with accommodation (8 ± 15 μm at 10 minutes) (p < 0.05). A small amount of choroidal thinning was also found during accommodation that was statistically significant in downward gaze (13 ± 14 μm at 10 minutes; p < 0.05). Accommodation in downward gaze also caused greater changes in anterior chamber depth and lens thickness compared with accommodation in primary gaze.

CONCLUSIONS

Axial length, choroidal thickness, and anterior eye biometrics change significantly during accommodation in downward gaze as a function of time. These changes seem to be caused by the combined influence of biomechanical factors (i.e., extraocular muscle forces, ciliary muscle contraction) associated with near tasks in downward gaze.

Prevalence of vision impairment and refractive error in school children in Ba Ria - Vung Tau province, Vietnam

Background

To assess the prevalence of vision impairment and refractive error in school children 12–15 years of age in Ba Ria – Vung Tau province, Vietnam.

Design

Prospective, cross-sectional study.

Participants

2238 secondary school children.

Methods

Subjects were selected based on stratified multistage cluster sampling of 13 secondary schools from urban, rural and semi-urban areas. The examination included visual acuity measurements, ocular motility evaluation, cycloplegic autorefraction, and examination of the external eye, anterior segment, media and fundus.

Main Outcome Measures

Visual acuity and principal cause of vision impairment.

Results

The prevalence of uncorrected and presenting visual acuity ≤6/12 in the better eye were 19.4% (95% confidence interval, 12.5–26.3) and 12.2% (95% confidence interval, 8.8–15.6), respectively. Refractive error was the cause of vision impairment in 92.7%, amblyopia in 2.2%, cataract in 0.7%, retinal disorders in 0.4%, other causes in 1.5% and unexplained causes in the remaining 2.6%. The prevalence of vision impairment due to myopia in either eye (–0.50 diopter or greater) was 20.4% (95% confidence interval, 12.8–28.0), hyperopia (≥2.00 D) was 0.4% (95% confidence interval, 0.0–0.7) and emmetropia with astigmatism (≥0.75 D) was 0.7% (95% confidence interval, 0.2–1.2). Vision impairment due to myopia was associated with higher school grade and increased time spent reading and working on a computer.

Conclusions

Uncorrected refractive error, particularly myopia, among secondary school children in Vietnam is a major public health problem. School-based eye health initiative such as refractive error screening is warranted to reduce vision impairment.

An investigation into the validity of self-reported classification of refractive error

PURPOSE

To assess the validity of questionnaire use in the self-identification of refractive status.

METHODS

Two hundred and forty adults (21-60 years of age) presenting for a routine eye examination at various optometric practices in Northern Ireland were asked to complete one of two questionnaires. Both questionnaires used identical questions to ascertain age, gender, current spectacle use, age of first spectacle use and level of education. For the identification of refractive status, Questionnaire 1 used layman's terminology whilst Questionnaire 2 combined optometric terminology with descriptive explanations. Current refractive status was identified by the examining optometrist who did not see the completed questionnaire. The spherical equivalent refractive error of the non-cycloplegic subjective refraction was used to categorise myopia as <0D and hyperopia as ≥+1.00D. Astigmatism was defined according to two different criteria: ≥0.50DC and ≥1.00DC.

RESULTS

Questionnaire 1 had a sensitivity of 0.63 and a specificity of 0.90 for identifying myopia; a sensitivity of 0.58 and a specificity of 0.71 for identifying hyperopia; a sensitivity of 0.12 and a specificity of 0.98 for identifying astigmatism ≥0.50DC and a sensitivity of 0.19 and a specificity of 0.95 for identifying astigmatism ≥1.00DC. Questionnaire 2 had a sensitivity of 0.83 and a specificity of 0.93 for identifying myopia; a sensitivity of 0.45 and a specificity of 0.86 for identifying hyperopia; a sensitivity of 0.32 and a specificity of 0.88 for identifying astigmatism ≥0.50DC and a sensitivity of 0.50 and a specificity of 0.84 for identifying astigmatism ≥1.00DC. For both questionnaires, altering a positive self-identification of myopia to include only those who had worn spectacles prior to age 30 reduced the sensitivity and increased the specificity slightly.

CONCLUSIONS

Questionnaires are a valid tool in self-identification of myopic refractive status. However, they are not an effective way of identifying hyperopia and astigmatism and objective or subjective refraction remains the most appropriate method of identifying such individuals.

Differences in children and adolescents' ability of reporting two CVS-related visual problems

The present study examined whether children and adolescents can correctly report dry eyes and blurred distance vision, two visual problems associated with computer vision syndrome. Participants are 913 children and adolescents aged 6-17. They were asked to report their visual problems, including dry eyes and blurred distance vision, and received an eye examination, including tear film break-up time (TFBUT) and visual acuity (VA). Inconsistency was found between participants' reports of dry eyes and TFBUT results among all 913 participants as well as for all of four subgroups. In contrast, consistency was found between participants' reports of blurred distance vision and VA results among 873 participants who had never worn glasses as well as for the four subgroups. It was concluded that children and adolescents are unable to report dry eyes correctly; however, they are able to report blurred distance vision correctly. Three practical implications of the findings were discussed.

PRACTITIONER SUMMARY

Little is known about children's ability to report their visual problems, an issue critical to diagnosis and treatment of children's computer vision syndrome. This study compared children's self-reports and clinic examination results and found children can correctly report blurred distance vision but not dry eyes.

Children's accommodation during reading of Chinese and English texts

PURPOSE

Inaccurate accommodation during nearwork and subsequent accommodative hysteresis may influence myopia development. Myopia is highly prevalent in Singapore; an untested theory is that Chinese children are prone to these accommodation characteristics. We measured the accuracy of accommodation responses during and nearwork-induced transient myopia (NITM) after periods spent reading Chinese and English texts.

METHODS

Refractions of 40 emmetropic and 43 myopic children were measured with a free-space autorefractor for four reading tasks of 10-minute durations: Chinese (SimSun, 10.5 points) and English (Times New Roman, 12 points) texts at 25 cm and 33 cm. Accuracy was obtained by subtracting accommodation response from accommodation demand. Nearwork-induced transient myopia was obtained by subtracting pretask distance refraction from posttask refraction, and regression was determined as the time for the posttask refraction to return to pretask levels.

RESULTS

There were significant, but small, effects of text type (Chinese, 0.97 ± 0.32 diopters [D] vs. English, 1.00 ± 0.37 D; F1,1230 = 7.24, p = 0.007) and reading distance (33 cm, 1.01 ± 0.30 D vs. 25 cm, 0.97 ± 0.39 D; F1,1230 = 7.74, p = 0.005) on accommodation accuracy across all participants. Accuracy was similar for emmetropic and myopic children across all reading tasks. Neither text type nor reading distance had significant effects on NITM or its regression. Myopes had greater NITM (by 0.07 D) (F1,81 = 5.05, p = 0.03) that took longer (by 50s) (F1,81 = 31.08, p < 0.01) to dissipate.

CONCLUSIONS

Reading Chinese text caused smaller accommodative lags than reading English text, but the small differences were not clinically significant. Myopic children had significantly greater NITM and longer regression than emmetropic children for both texts. Whether differences in NITM are a cause or consequence of myopia cannot be answered from this study.

Time outdoors and the prevention of myopia

Recent epidemiological evidence suggests that children who spend more time outdoors are less likely to be, or to become myopic, irrespective of how much near work they do, or whether their parents are myopic. It is currently uncertain if time outdoors also blocks progression of myopia. It has been suggested that the mechanism of the protective effect of time outdoors involves light-stimulated release of dopamine from the retina, since increased dopamine release appears to inhibit increased axial elongation, which is the structural basis of myopia. This hypothesis has been supported by animal experiments which have replicated the protective effects of bright light against the development of myopia under laboratory conditions, and have shown that the effect is, at least in part, mediated by dopamine, since the D2-dopamine antagonist spiperone reduces the protective effect. There are some inconsistencies in the evidence, most notably the limited inhibition by bright light under laboratory conditions of lens-induced myopia in monkeys, but other proposed mechanisms possibly associated with time outdoors such as relaxed accommodation, more uniform dioptric space, increased pupil constriction, exposure to UV light, changes in the spectral composition of visible light, or increased physical activity have little epidemiological or experimental support. Irrespective of the mechanisms involved, clinical trials are now underway to reduce the development of myopia in children by increasing the amount of time they spend outdoors. These trials would benefit from more precise definition of thresholds for protection in terms of intensity and duration of light exposures. These can be investigated in animal experiments in appropriate models, and can also be determined in epidemiological studies, although more precise measurement of exposures than those currently provided by questionnaires is desirable.

Refractive error in school children in an urban and rural setting in Cambodia

PURPOSE

To assess the prevalence of refractive error in schoolchildren aged 12-14 years in urban and rural settings in Cambodia's Phnom Penh and Kandal provinces.

METHODS

Ten schools from Phnom Penh Province and 26 schools from Kandal Province were randomly selected and surveyed in October 2010. Children were examined by teams of Australian and Cambodian optometrists, ophthalmic nurses and ophthalmologists who performed visual acuity (VA) testing and cycloplegic refraction.

RESULTS

A total of 5527 children were included in the study. The prevalence of uncorrected, presenting and best-corrected VA ≤ 6/12 in the better eye were 2.48% (95% confidence interval [CI] 2.02-2.83%), 1.90% (95% CI 1.52-2.24%) and 0.36% (95% CI 0.20-0.52%), respectively; 43 children presented with glasses whilst a total of 315 glasses were dispensed. The total prevalence of refractive error was 6.57% (95% CI 5.91-7.22%), but there was a significant difference between urban (13.7%, 95% CI 12.2-15.2%) and rural (2.5%, 95% CI 2.03-3.07%) schools (P < 0.0001). Refractive error accounted for 91.2% of visually impaired eyes, cataract for 1.7%, and other causes for 7.1%. Myopia (spherical equivalent ≤ -0.50 diopters [D] in either eye) was associated with increased age, female gender and urban schooling.

CONCLUSIONS

The prevalence of refractive error was significantly higher in urban Phnom Penh schools than rural schools in Kandal Province. The prevalence of refractive error, particularly myopia was relatively low compared to previous reports in Asia. The majority of children did not have appropriate correction with spectacles, highlighting the need for more effective screening and optical intervention.

Attempts to reduce the progression of myopia and spectacle prescriptions during childhood: a survey of eye specialists

Purpose

To determine methods tried in clinical trials to reduce the progression of myopia in children, and spectacle prescribing patterns of hospital ophthalmologists.

Methods

A multi-sectioned survey composed of Likert items relating to the methods of reducing myopia progression (orthokeratology lenses [O-K lenses], undercorrected glasses, and topical atropine) and the patterns of prescribing spectacles for children (including two cases involving a 5-year-old girl and an 8-year-old boy) were distributed to members of the Korean Ophthalmological Society, and the collected data was statistically analyzed.

Results

A total of 78 out of 130 ophthalmologists returned the survey. On a scale of 1 to 5, the mean rates of whether the ophthalmologists think O-K lenses arrest myopia progression, and whether they recommend their patients to wear O-K lenses if indicative, were 3.06 and 2.75, respectively. Moreover, the mean rates of whether they consider that wearing glasses which are undercorrected would slow down the progression of the myopia, or if they think topical atropine helps in arresting myopia progression in children, were 2.34 and 1.27, respectively. In response to the case studies, the majority of practitioners preferred to prescribe the full amount found in cycloplegic refraction to pediatric patients with myopia.

Conclusions

Ophthalmologists in clinical practice encouraged children to wear O-K lenses more than undercorrected glasses as a way to retard myopia progression. However, the application of atropine is rarely tried in clinical trials. In managing pediatric patients with myopia (case specific), the majority of the practitioners chose to prescribe glasses with full cycloplegic correction.

School Myopia in Hong Kong

The short article is about school myopia in Hong Kong and the high prevalence rates of myopia in primary school children.

A novel instrument for logging nearwork distance

PURPOSE

To validate a novel ultrasonic sensor for logging reading distances. In addition, this device was used to compare the habitual reading distances between low and high myopes.

METHODS

First, the stability and sensitivity of the ultrasonic device were determined by repeated measures using artificial targets. Then, thirty Hong Kong Chinese (20-30 years) were recruited, of whom fifteen were considered to be high myopes (mean ± S.D. = -8.7 ± 0.5 D) and 15 to be low to non-myopes (mean ± S.D. = -2.0 ± 0.2 D). Each subject read a newspaper with their habitual visual aid continuously for 10 min in two sessions at their preferred working distance(s). The reading distances were recorded continuously using a novel nearwork analyzer. The modal working distance was considered as the 'habitual' reading distance. In addition, habitual reading distance was reported orally by each subject.

RESULTS

The nearwork analyzer gave accurate and repeatable measurements over a range of distances and angles. Using this instrument, high myopes were found to have a significantly shorter reading distance than low myopes or non-myopes (mean ± S.D. = 35.9 ± 9.8 cm vs 50.9 ± 24.8 cm; two-sample t-test, p = 0.04, df = 18). The reading distances reported orally by the subjects were not correlated with those recorded by the nearwork analyzer.

CONCLUSIONS

The nearwork analyzer was found to be an effective tool for measuring nearwork reading distance in a small group of emmetropic and myopic adults over a 10 min interval. Differences between the reading distance between high myopes and low/non-myopes was detected by the device. Further study is needed to determine if a closer working distance is a cause or effect of myopia development.

Refractive errors in students from Middle Eastern backgrounds living and undertaking schooling in Australia

BACKGROUND

  Environmental factors associated with schooling systems in various countries have been implicated in the rising prevalence of myopia, making the comparison of prevalence of refractive errors in migrant populations of interest. This study aims to determine the prevalence of refractive errors in children of Middle Eastern descent, raised and living in urban Australia but actively maintaining strong ties to their ethnic culture, and to compare them with those in the Middle East where myopia prevalence is generally low.

METHODS

  A total of 354 out of a possible 384 late primary/early secondary schoolchildren attending a private school attracting children of Middle Eastern background in Melbourne were assessed for refractive error and visual acuity. A Shin Nippon open-field NVision-K5001 autorefractor was used to carry out non-cycloplegic autorefraction while viewing a distant target. For statistical analyses students were divided into three age groups: 10-11 years (n = 93); 12-13 years (n = 158); and 14-15 years (n = 102).

RESULTS

  All children were bilingual and classified as of Middle Eastern (96.3 per cent) or Egyptian (3.7 per cent) origin. Ages ranged from 10 to 15 years, with a mean of 13.17 ± 0.8 (SEM) years. Mean spherical equivalent refraction (SER) for the right eye was +0.09 ± 0.07 D (SEM) with a range from -7.77 D to +5.85 D. The prevalence of myopia, defined as a spherical equivalent refraction 0.50 D or more of myopia, was 14.7 per cent. The prevalence of hyperopia, defined as a spherical equivalent refraction of +0.75 D or greater, was 16.4 per cent, while hyperopia of +1.50 D or greater was 5.4 per cent. A significant difference in SER was seen as a function of age; however, no significant gender difference was seen.

CONCLUSIONS

  This is the first study to report the prevalence of refractive errors for second-generation Australian schoolchildren coming from a predominantly Lebanese Middle Eastern Arabic background, who endeavour to maintain their ethnic ties. The relatively low prevalence of myopia is similar to that found for other metropolitan Australian school children but higher than that reported in the Middle East. These results suggest that lifestyle and educational practices may be a significant influence in the progression of myopic refractive errors.

Nature and nurture: the complex genetics of myopia and refractive error

The refractive errors, myopia and hyperopia, are optical defects of the visual system that can cause blurred vision. Uncorrected refractive errors are the most common causes of visual impairment worldwide. It is estimated that 2.5 billion people will be affected by myopia alone within the next decade. Experimental, epidemiological and clinical research has shown that refractive development is influenced by both environmental and genetic factors. Animal models have showed that eye growth and refractive maturation during infancy are tightly regulated by visually guided mechanisms. Observational data in human populations provide compelling evidence that environmental influences and individual behavioral factors play crucial roles in myopia susceptibility. Nevertheless, the majority of the variance of refractive error within populations is thought to be because of hereditary factors. Genetic linkage studies have mapped two dozen loci, while association studies have implicated more than 25 different genes in refractive variation. Many of these genes are involved in common biological pathways known to mediate extracellular matrix (ECM) composition and regulate connective tissue remodeling. Other associated genomic regions suggest novel mechanisms in the etiology of human myopia, such as mitochondrial-mediated cell death or photoreceptor-mediated visual signal transmission. Taken together, observational and experimental studies have revealed the complex nature of human refractive variation, which likely involves variants in several genes and functional pathways. Multiway interactions between genes and/or environmental factors may also be important in determining individual risks of myopia, and may help explain the complex pattern of refractive error in human populations.

Relationship of retinal vascular caliber with optic disc and macular structure

PURPOSE

To examine the relationships of retinal vascular caliber with optic disc, macular, and retinal nerve fiber layer (RNFL) characteristics as measured with optical coherence tomography (OCT).

DESIGN

Observational cross-sectional study.

METHODS

This study included a subset of healthy children enrolled in the Singapore Cohort Study of the Risk Factors of Myopia (SCORM). Optic disc, macular, and RNFL morphology were measured with Stratus OCT 3. Digital retinal photography was performed and retinal arteriolar and venular caliber measured using validated imaging software.

RESULTS

One hundred and four children (mean age 11.51 +/- 0.52 years; 50% male) were included. In multivariate analyses, smaller horizontal integrated rim width and rim area were associated with narrower retinal arterioles and venules (all P < .05), and shorter horizontal rim length was associated with narrower venules (P = .04). Optic disc diameter was not associated with arteriolar or venular caliber. Larger vertical cup-to-disc ratios and cup-to-disc-area ratios were associated with narrower venules but not arterioles (P = .01 and P = .003, respectively). A thinner average RNFL measurement was associated with narrower arterioles and venules, and smaller total macular volume was associated with narrower venules.

CONCLUSIONS

Thinner optic disc rims and RNFL measurements were associated with narrower retinal arterioles and venules, and larger cup-to-disc ratios with narrower venules. These findings suggest that retinal vessel caliber varies systematically with morphologic differences in the optic nerve head, retina, and macula.

Prevalence of myopia in urban and rural children in mainland China

It has been well recognized that myopia more likely affects East Asians, particularly the Japanese and Chinese population. Although some studies have reported the prevalence of myopia in children living in mainland China, most of these studies are based on subjects with unknown representativeness, non-uniform definition, and measurement methods. A higher prevalence of myopia in urban settings, compared with rural settings, has been consistently suggested in several studies. This article intends to review the available data on the prevalence of myopia in Chinese children living in China; particular consideration is given to the evidence of urban-rural differences and their implications.

The prevalence of visual impairment in school children of upper-middle socioeconomic status in Kathmandu

PURPOSE

Assess visual impairment in school children of upper-middle socioeconomic status in Kathmandu for comparison with rural Jhapa District.

METHODS

Random selection of classes from secondary private schools in Kathmandu was used to identify the study sample. Children in 130 classes at 43 schools were enumerated using school records and examined between January-May 2006. Examinations included visual acuity testing, ocular motility evaluation, cycloplegic refraction, and examination of the external eye, anterior segment, media, and fundus. The principal cause was determined for eyes with uncorrected visual acuity < or = 20/40.

RESULTS

A total of 4,501 children in grades 5-9 were enumerated; 4282 (95.1%) were examined. The prevalence of uncorrected, presenting, and best-corrected visual impairment (< or = 20/40) in the better eye was 18.6%, 9.1%, and 0.86%, respectively. Refractive error was a cause in 93.3% of children with uncorrected visual impairment, amblyopia 1.8%, retinal disorders 1.3%, other causes 0.3%, and unexplained causes 4.4%. Among children correctable in at least one eye, 46.3% presented without the necessary spectacles. Visual impairment with myopia (-0.50 diopters) ranged from 10.9% in 10 year-olds to 27.3% in 15 year-olds, compared to 0.5%-3.0% in rural Jhapa District. Myopic visual impairment was associated with grade level, female gender, parental education, parental spectacle usage, and Mongol ethnicity.

CONCLUSIONS

Visual impairment with myopia among upper-middle socioeconomic school children in Kathmandu is higher than that in rural Nepal, and a public health problem because nearly half are without corrective spectacles. Effective strategies are needed to eliminate this easily treatable cause of visual impairment.