Season of birth, daylight hours at birth, and high myopia

The Onset and Progression of Myopia Slows in Chinese 15-Year-Old Adolescents Following Vocational Rather Than Academic School Pathways

Purpose

The purpose of this study was to investigate the changes in spherical equivalent (SE) and axial length (AL) and cumulative incidence of myopia and high myopia in Chinese 15-year-old adolescents entering a non-academic stream of senior high school education.

Methods

A total of 880 first-born twins with a baseline age range of 7 to 15 years were enrolled and followed annually until 18 years of age. Cycloplegic refractions and AL were examined. Educational exposure was divided into academic high school (AHS) and vocational high school (VHS) streams. A piecewise linear mixed-effects model was used to estimate the effect of education exposures on SE development, the slope before the age of 15 years (β2), and the slope change at the age of 15 years (β3) was compared between the 2 groups.

Results

The curves of refractive development in a myopic direction changed in parallel in the AHS and VHS group before 15 years. For nonmyopic children, β2 was -0.19 and -0.20 diopters (D)/year (P = 0.270), and β3 was 0.16 and 0.14 D/year (P = 0.270), in the AHS and VHS groups, respectively. Among patients with myopia, β2 was -0.52 and -0.54 D/year (P = 0.500), and β3 was 0.37 and 0.32 D/year (P = 0.004), in the AHS and VHS groups, respectively. The trends in AL were similar. The 3-year cumulative incidence of myopia was 35.3% (AHS) versus 14.7% (VHS; P < 0.001), and that of high myopia was 5.7% and 3.3% (P = 0.129).

Conclusions

Students undertaking a VHS rather than an AHS education have slower myopic shifts in refraction and less incident myopia after the age of 15 years.

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.

The Causal Effect of Education on Myopia: Evidence That More Exposure to Schooling, Rather Than Increased Age, Causes the Onset of Myopia

Purpose

To distinguish the effects of age and grade on the development of myopia.

Methods

Grade 1 (n = 1465, mean age 6.71 ± 0.29 years; 53.5% male) and Grade 2 students (n = 1381, mean age 7.76 ± 0.30 years; 52.5% male) were examined in 2018, with a follow-up examination in 2019. Cycloplegic spherical equivalent (SE) in diopter (D) was measured. Regression discontinuity (RD) analysis was used to assess the causal effects on refraction at each visit.

Results

The sample in a grade was divided into three 4-month age blocks according to their birth month, the youngest, middle, and the oldest. At the 2018 visit, within each grade, there were no significant differences in SE among age blocks (all P > 0.05), despite an age range of 12 months. However, comparing the youngest block in Grade 2 to the oldest block in Grade 1, an average age difference of four months, a significant difference in SE was found (0.82 ± 0.69 D vs. 1.05 ± 0.55 D, t-test P < 0.01). Formal RD analysis found a significant casual effect of grade increase on myopic refraction shift (β = -0.32 D; 95% CI, -0.73 to -0.01; P = 0.042). Consistent results were found using the 2019 data.

Conclusions

Increased grade, rather than increasing age, is the major cause of myopic shifts in refraction. A causal link implies that interventions aimed at reducing the myopigenic exposures experienced during a school year have the potential to markedly reduce the myopic shifts in refraction associated with a grade of schooling.

Ethnic Disparities in Risk Factors for Myopia among Han and Minority Schoolchildren in Shawan, Xinjiang, China

SIGNIFICANCE

The ethnic differences in myopia rates, ocular dimensions, and risk factors between Han and non-Han schoolchildren observed in this study may help fill the knowledge gap about ethnic minorities and are important for China and other countries to address vision-related health inequalities among different ethnic groups.

PURPOSE

This study aimed to investigate the risk factors of juvenile myopia and elucidate the disparities of risk factors among Han and non-Han school students in Xinjiang, China.

METHODS

A population-based cross-sectional study of 876 schoolchildren from grades 1 to 9 was conducted in the Anjihai Middle School in Shawan, Xinjiang Uygur Autonomous Region, China. Visual acuity and ocular biometry were assessed, and personal information, including behavior, birth status, and familial factors, was collected using self-made standardized questionnaires.

RESULTS

The myopia rate among students of Han ethnicity (50.5%) was the highest, followed by Hui (41.3%) and Uygur et al. (32.0%, P < .001). Similar patterns were observed for mean axial length. The mean axial lengths are 23.7, 23.4, and 23.3 mm, respectively ( P = .01). Overall, performing high-quality eye exercises, longer sleep duration, being born in summer, parental smoking, and consuming more food containing anthocyanins were all associated with a lower incidence of myopia. Meanwhile, Han ethnicity, intensive near task, bad eye habits, and myopic mothers were associated with higher odds of myopia. After adjusting for environmental influences pertaining to myopia, the variation in myopia prevalence between Han and Uygur et al. remained significant, whereas it changed to not significant between Han and Hui ethnicities.

CONCLUSIONS

Significant disparities were found in the prevalence of myopia among various ethnic groups in Shawan, Xinjiang. Life habits, birth status, and familial factors may contribute to such variance and play different roles in the occurrence of juvenile myopia among various ethnicities.

Temporal and spatial characterization of myopia in China

Purpose

The aim of this study was to characterize the temporal and spatial distribution of myopia among students aged 7-18 years, by analyzing the aggregation area and providing the basis for the prevention and control of myopia in China.

Methods

A database for the spatial analysis of myopia in China during 1995-2014 was established using ArcGIS10.0 software as a platform for data management and presentation. A spatial autocorrelation analysis of myopia was undertaken, and a temporal and spatial scan analysis was performed using SaTScan9.5 software.

Results

Our data demonstrated that the prevalence of myopia in China in 1995, 2000, 2005, 2010, and 2014 was 35.9, 41.5, 48.7, 57.3, and 57.1%, respectively, thus indicating a gradual upward trend. The prevalence of myopia was analyzed in various provinces (municipalities and autonomous regions), and the highest was found in Jiangsu Province, with an average Moran's I index of 0.244295 in China (P ≤ 0.05). According to the local Moran's I autocorrelation analysis, there was a spatial aggregation of myopia prevalence among students in the entire country, with Shandong, Jiangsu, Anhui, and Shanghai being classified as high-high aggregation areas, while Hainan and Guangxi were classified as low-low aggregation areas. In addition, the Getis-Ord General G results of the global hotspot analysis showed a countrywide myopia prevalence index of 0.035020 and a Z score of 1.7959 (P = 0.07251). Because the myopia prevalence correlation difference was not statistically significant, there were no "positive hotspots" or "negative hotspots." The local hotspot analysis shows that Shandong and Jiangsu belong to high-value aggregation areas, while Hainan and Guizhou belong to low-value aggregation areas. Further analysis using time-space scanning showed 15 aggregation regions in five stages, with four aggregation regions having statistically significant differences (P ≤ 0.05). However, the aggregation range has changed over time. Overall, from 1995 to 2014, the aggregation areas for the myopia prevalence in Chinese students have shifted from the northwest, north, and northeast regions to the southeast regions.

Conclusion

Our data demonstrate that, from 1995 to 2014, the prevalence of myopia increased in students aged 7-18 years in China. In addition, the prevalence of myopia is randomly distributed in various provinces (municipalities and autonomous regions) and exhibits spatial aggregation. Also, the gathering area is gradually shifting to the southeast, with the existence of high-risk areas. It is, therefore, necessary to focus on this area and undertake targeted prevention and control measures.

Exposure to the Life of a School Child Rather Than Age Determines Myopic Shifts in Refraction in School Children

Purpose

The prevalence of myopia increases with both age and grade for children attending school. The current study aimed to distinguish the effects of aging and grade on myopia.

Methods

Grade 1 students (706 at baseline in 2009, mean age 6.56 ± 0.29 years, range 6.00 to 6.99 years old, 55.5% boys) were followed up until 2012. Cycloplegic spherical equivalent (SE) was measured annually.

Results

The sample in a grade was divided into three 4-month age blocks according to their birth month. Within each grade, there were no significant differences in SE between age blocks (all P > 0.05), despite an age range of one year. More myopic SE was observed in the youngest block of grade 2 compared to the oldest block of grade 1 (difference, -0.36 ± 0.08 D; P < 0.001), although age of the two blocks only differed by four months. Similarly, more myopic SE were found in the youngest block in grade 3 than the oldest block in grade 2 (differences, -0.50 ± 0.10 D; P < 0.001) and in the youngest block in grade 4 than the oldest block in grade 3 (differences, -0.82 ± 0.14 D; P < 0.001).

Conclusions

Exposure to schooling, rather than age, appears to be the major driver of refractive development, at least in the early years of schooling. Interventions during this period, involving reductions in educational pressure and increased time outdoors may have major effects on the subsequent development of myopia.

Update and guidance on management of myopia. European Society of Ophthalmology in cooperation with International Myopia Institute

The prevalence of myopia is increasing extensively worldwide. The number of people with myopia in 2020 is predicted to be 2.6 billion globally, which is expected to rise up to 4.9 billion by 2050, unless preventive actions and interventions are taken. The number of individuals with high myopia is also increasing substantially and pathological myopia is predicted to become the most common cause of irreversible vision impairment and blindness worldwide and also in Europe. These prevalence estimates indicate the importance of reducing the burden of myopia by means of myopia control interventions to prevent myopia onset and to slow down myopia progression. Due to the urgency of the situation, the European Society of Ophthalmology decided to publish this update of the current information and guidance on management of myopia. The pathogenesis and genetics of myopia are also summarized and epidemiology, risk factors, preventive and treatment options are discussed in details.

IMI Risk Factors for Myopia

Risk factor analysis provides an important basis for developing interventions for any condition. In the case of myopia, evidence for a large number of risk factors has been presented, but they have not been systematically tested for confounding. To be useful for designing preventive interventions, risk factor analysis ideally needs to be carried through to demonstration of a causal connection, with a defined mechanism. Statistical analysis is often complicated by covariation of variables, and demonstration of a causal relationship between a factor and myopia using Mendelian randomization or in a randomized clinical trial should be aimed for. When strict analysis of this kind is applied, associations between various measures of educational pressure and myopia are consistently observed. However, associations between more nearwork and more myopia are generally weak and inconsistent, but have been supported by meta-analysis. Associations between time outdoors and less myopia are stronger and more consistently observed, including by meta-analysis. Measurement of nearwork and time outdoors has traditionally been performed with questionnaires, but is increasingly being pursued with wearable objective devices. A causal link between increased years of education and more myopia has been confirmed by Mendelian randomization, whereas the protective effect of increased time outdoors from the development of myopia has been confirmed in randomized clinical trials. Other proposed risk factors need to be tested to see if they modulate these variables. The evidence linking increased screen time to myopia is weak and inconsistent, although limitations on screen time are increasingly under consideration as interventions to control the epidemic of myopia.

Effect of Education on Myopia: Evidence from the United Kingdom ROSLA 1972 Reform

Purpose

Cross-sectional and longitudinal studies have consistently reported an association between education and myopia. However, conventional observational studies are at risk of bias due to confounding by factors such as socioeconomic position and parental educational attainment. The current study aimed to estimate the causal effect of education on refractive error using regression discontinuity analysis.

Methods

Regression discontinuity analysis was applied to assess the influence on refractive error of the raising of the school leaving age (ROSLA) from 15 to 16 years introduced in England and Wales in 1972. For comparison, a conventional ordinary least squares (OLS) analysis was performed. The analysis sample comprised 21,548 UK Biobank participants born in a nine-year interval centered on September 1957, the date of birth of those first affected by ROSLA.

Results

In OLS analysis, the ROSLA 1972 reform was associated with a -0.29 D (95% confidence interval [CI]: -0.36 to -0.21, P < 0.001) more negative refractive error. In other words, the refractive error of the study sample became more negative by -0.29 D during the transition from a minimum school leaving age of 15 to 16 years of age. Regression discontinuity analysis estimated the causal effect of the ROSLA 1972 reform on refractive error as -0.77 D (95% CI: -1.53 to -0.02, P = 0.04).

Conclusions

Additional compulsory schooling due to the ROSLA 1972 reform was associated with a more negative refractive error, providing additional support for a causal relationship between education and myopia.

Neonatal vitamin D status and myopia in young adult men

PURPOSE

The prevalence of myopia is increasing worldwide, and modifiable risk factors are thus important to identify. Season of birth has been associated with later myopia risk. Neonatal vitamin D status is highly dependent on season of birth due to maternal sun exposure late in gestation. We hypothesize that prenatal exposure to low levels of vitamin D can interfere with visual development in term-born infants and that this might contribute to adult visual dysfunction. The aim of this study was thus to compare neonatal vitamin D levels from stored dried blood spots taken shortly after birth among young term-born men with myopia (cases) and random controls with emmetropia.

METHODS

In this case-control study, we analysed neonatal 25(OH)D₃ levels of 457 myopic male cases and 1280 emmetropic male controls assessed for myopia at the mandatory Danish conscript examination. Data were analysed using logistic regression analysis and results presented as crude and adjusted for potential confounders namely maternal age, maternal ethnicity, maternal and paternal education and season of birth.

RESULTS

We did not observe a seasonal variation in myopia risk, neither did we observe increased odds of myopia in relation to low neonatal 25(OH)D₃ levels.

CONCLUSION

The rapid increase in myopia does not seem related to neonatal vitamin D status.

Origins of Refractive Errors: Environmental and Genetic Factors

Refractive errors are the product of a mismatch between the axial length of the eye and its optical power, creating blurred vision. Uncorrected refractive errors are the second leading cause of worldwide blindness. One refractive error currently attracting significant scientific interest is myopia, mostly owing to the recent rise in its prevalence worldwide and associated ocular disease burden. This increase in myopia prevalence has also been rapid, suggesting environmental influences in addition to any genetic influences on eye growth. This review defines refractive errors, describes their prevalence, and presents evidence for the influence of genetic and environmental factors related to refractive error development.

IMI - Myopia Control Reports Overview and Introduction

With the growing prevalence of myopia, already at epidemic levels in some countries, there is an urgent need for new management approaches. However, with the increasing number of research publications on the topic of myopia control, there is also a clear necessity for agreement and guidance on key issues, including on how myopia should be defined and how interventions, validated by well-conducted clinical trials, should be appropriately and ethically applied. The International Myopia Institute (IMI) reports the critical review and synthesis of the research evidence to date, from animal models, genetics, clinical studies, and randomized controlled trials, by more than 85 multidisciplinary experts in the field, as the basis for the recommendations contained therein. As background to the need for myopia control, the risk factors for myopia onset and progression are reviewed. The seven generated reports are summarized: (1) Defining and Classifying Myopia, (2) Experimental Models of Emmetropization and Myopia, (3) Myopia Genetics, (4) Interventions for Myopia Onset and Progression, (5) Clinical Myopia Control Trials and Instrumentation, (6) Industry Guidelines and Ethical Considerations for Myopia Control, and (7) Clinical Myopia Management Guidelines.

Seasonality of births in horizontal strabismus: comparison with birth seasonality in schizophrenia and other disease conditions

Recent work has implicated one type of horizontal strabismus (exotropia) as a risk factor for schizophrenia. This new insight raises questions about a potential common developmental origin of the two diseases. Seasonality of births is well established for schizophrenia. Seasonal factors such as light exposure affect eye growth and can cause vision abnormalities, but little is known about seasonality of births in strabismus. We examined birth seasonality in people with horizontal strabismus in a retrospective study in Washoe County, Nevada, and re-examined similar previously obtained data from Osaka, Japan. We then compared seasonal patterns of births between strabismus, refractive error, schizophrenia and congenital toxoplasmosis. Patients with esotropia had a significant seasonality of births, with a deficit in March, then increasing to an excess in September, while patients with exotropia had a distinctly different pattern, with an excess of births in July, gradually decreasing to a deficit in November. These seasonalities were statistically significant with either χ2 or Kolmogorov-Smirnov-type statistics. The birth seasonality of esotropia resembled that for hyperopia, with an increase in amplitude, while the seasonality for myopia involved a phase-shift. There was no correlation between seasonality of births between strabismus and congenital toxoplasmosis. The pattern of an excess of summer births for people with exotropia was remarkably similar to the well-established birth seasonality of one schizophrenia subtype, the deficit syndrome, but not schizophrenia as a whole. This suggests a testable hypothesis: that exotropia may be a risk factor primarily for the deficit type of schizophrenia.

Estimating heritability of refractive error in Koreans: the Korea National Health and Nutrition Examination Survey

PURPOSE

To estimate the familial correlation and heritability of refractive error in general Korean population.

METHODS

From the Korea National Health and Nutrition Examination Survey, 13 258 subjects of 7920 families, who were aged ≥19 years, were included in the study. Using variance components analysis, the additive genetic effect, or heritability, and the common and unique environmental effects on refractive error were examined, adopting common environments shared by cohabiting family or by siblings.

RESULTS

The proportions of hyperopia, myopia and high myopia in Koreans were 0.8%, 45.2% and 5.7% respectively. The correlation coefficients of spherical equivalent (SE) were 0.257 for parent-offspring pairs, 0.410 for sibling pairs and 0.112 for spouse pairs (p < 0.001 for all). Common environment shared by siblings affected the variation of SE significantly (p < 0.001), but that shared by cohabitants did not (p = 0.395). Adopting common environment shared by siblings, the heritability, common environmental effect and unique environmental effect of refractive error were 42.1 ± 3.3%, 11.8 ± 3.5% and 46.1 ± 3.9% respectively. Heritabilities of hyperopia, myopia and high myopia were 45.7%, 44.3% and 68.9% respectively. Adjusted odds ratios of myopia among offspring were 3.78 given one parent has myopia and 4.43 when both parents have myopia.

CONCLUSION

Refractive error is influenced by common environment shared by siblings. The heritability of refractive error is higher for high myopia than for myopia or hyperopia.

Early life factors for myopia in the British Twins Early Development Study

PURPOSE

Myopia is an increasingly prevalent condition globally. A greater understanding of contemporaneous, early life factors associated with myopia risk is urgently required, particularly in younger onset myopia as this correlates with higher severity and increased complications in adult life.

METHODS

Analysis of a subset of the longitudinal, UK-based Twins Early Development Study (n=1991) recruited at birth between 1994 and 1996. Subjective refraction was obtained from the twin's optometrists; mean age 16.3 years (SD 1.7). Myopia was defined as mean spherical equivalent ≤-0.75 dioptres. A life course epidemiology approach was used to appropriately weight candidate myopia risk factors during critical periods of eye growth. Adjusted ORs for myopia were estimated using multivariable logistic regression models at each life stage, together with variance explained (r²) and area under the receiver operator characteristic curve (AUROC) statistic of predictive models.

RESULTS

Factors significantly associated with myopia included level of maternal education (OR 1.33, 95% CI 1.11 to 1.59), fertility treatment (OR 0.63, 95% CI 0.43 to 0.92), summer birth (OR 1.93, 95% CI 1.28 to 2.90) and hours spent playing computer games (OR 1.03, 95% CI 1.01 to 1.06). The total variance explained by this model was 4.4 % (p<0.001) and the AUROC was 0.68 (95% CI 0.64 to 0.72). Consistent associations were observed with socioeconomic status, educational attainment, reading enjoyment and cognitive variables, particularly verbal cognition, at multiple points over the life course.

CONCLUSIONS

This study identifies known and novel associations with myopia during childhood development; associated factors identified in early life reflect sociological and lifestyle trends such as rates of maternal education, fertility treatment, early schooling and computer games.

An epidemiological study of the risk factors associated with myopia in young adult men in Korea

The prevalence of myopia has been increasing worldwide. Its causes are not completely clear, although genetic and environmental factors are thought to play a role. Data were collected by the Korean Military Manpower Administration. Frequency analysis was used for comparisons of general characteristics. Pearson’s chi-square tests and logistic regression analysis were used to verify the correlations between possible risk factors and the prevalence of myopia or high myopia. The prevalence of myopia (50.6–53.0%) and high myopia (11.3–12.9%) increased each year. These tended to be the highest in patients born in spring, and decreased in the following order according to education level: 4- or 6-year university education or more, high school education or less, and 2- to 3-year college education. Moreover, the prevalence of myopia and high myopia was significantly higher in patients ≤ 60 kg and with a body mass index ≤ 18.5 kg/m². The prevalence of high myopia was significantly higher in taller patients (≥175 cm). The prevalence of myopia and high myopia increased each year in Korean young adult men and was associated with birth season, education level, height, weight, and body mass index. Tall, lean men were more likely to have high myopia.

Association of neovascular age-related macular degeneration with month and season of birth in Italy

In order to investigate the influence of season and month of birth on the risk of neovascular age-related macular degeneration (n-AMD) in Italy, we evaluated the month birth and sex of all patients, recorded in the anti-vascular endothelial growth factor (VEGF) monitoring registry of the Italian Medicines Agency, born between 1925–1944, who received intravitreal anti-VEGF injections for n-AMD between January 1, 2013 and July 29, 2015. The numbers of all births in Italy in the same years, extracted from the Italian National Institute of Statistics, were used to calculate the expected number of n-AMD cases. Overall, 45,845 patients (19,207 men, 26,638 women) received intravitreal anti-VEGF for n-AMD; in the same years, 20,140,426 people (10,334,262 male, 9,806,164 female) were born in Italy. Comparing the observed number of n-AMD cases with the expected number of n- AMD cases in each season, we found that the season-specific risk for n-AMD was 2.5% higher for those born in summer (OR=1.03, Bonferroni-corrected P=0.008) and 3% lower for those born in winter (OR=0.96, Bonferroni-corrected P=0.0004). When considering the month of birth, the risk of n-AMD was 5.9% lower for people born in January (OR=0.93, Bonferroni-corrected P=0.0012). The factors causing such differences should be determined.

Environmental Factors and Myopia: Paradoxes and Prospects for Prevention

The prevalence of myopia in developed countries in East and Southeast Asia has increased to more than 80% in children completing schooling, whereas that of high myopia has increased to 10%-20%. This poses significant challenges for correction of refractive errors and the management of pathological high myopia. Prevention is therefore an important priority. Myopia is etiologically heterogeneous, with a low level of myopia of clearly genetic origins that appears without exposure to risk factors. The big increases have occurred in school myopia, driven by increasing educational pressures in combination with limited amounts of time spent outdoors. The rise in prevalence of high myopia has an unusual pattern of development, with increases in prevalence first appearing at approximately age 11. This pattern suggests that the increasing prevalence of high myopia is because of progression of myopia in children who became myopic at approximately age 6 or 7 because age-specific progression rates typical of East Asia will take these children to the threshold for high myopia in 5 to 6 years. This high myopia seems to be acquired, having an association with educational parameters, whereas high myopia in previous generations tended to be genetic in origin. Increased time outdoors can counter the effects of increased nearwork and reduce the impact of parental myopia, reducing the onset of myopia, and this approach has been validated in 3 randomized controlled trials. Other proposed risk factors need further work to demonstrate that they are independent and can be modified to reduce the onset of myopia.

Altered spontaneous brain activity pattern in patients with high myopia using amplitude of low-frequency fluctuation: a resting-state fMRI study

OBJECTIVE

Many previous reports have demonstrated significant neural anatomy changes in the brain of high myopic (HM) patients, whereas the spontaneous brain activity changes in the HM patients at rest are not well studied. Our objective was to use amplitude of low-frequency fluctuation (ALFF) method to investigate the changes in spontaneous brain activity in HM patients and their relationships with clinical features.

METHODS

A total of 38 patients with HM (17 males and 21 females) and 38 healthy controls (HCs) (17 males and 21 females) closely matched in age, sex, and education underwent resting-state functional magnetic resonance imaging scans. The ALFF method was used to assess local features of spontaneous brain activity. The relationship between the mean ALFF signal values in many brain regions and the clinical features in HM patients was calculated by correlation analysis.

RESULTS

Compared with HCs, the HM patients had significantly lower ALFF in the right inferior and middle temporal gyrus, left middle temporal gyrus, left inferior frontal gyrus/putamen, right inferior frontal gyrus/putamen/insula, right middle frontal gyrus, and right inferior parietal lobule and higher ALFF values in the bilateral midcingulate cortex, left postcentral gyrus, and left precuneus/inferior parietal lobule. However, no relationship was found between the mean ALFF signal values of the different areas and the clinical manifestations in HM.

CONCLUSION

The HM patients were affected with brain dysfunction in many regions, which may indicate the presence of neurobiological changes involving deficits in language understanding and attentional control in HM patients.

Exposure to sunlight reduces the risk of myopia in rhesus monkeys

Exposure to sunlight has recently been postulated as responsible for the effect that more time spent outdoors protects children from myopia, while early life exposure to natural light was reported to be possibly related to onset of myopia during childhood. In this study, we had two aims: to determine whether increasing natural light exposure has a protective effect on hyperopic defocus-induced myopia, and to observe whether early postnatal exposure to natural light causes increased risk of refractive error in adolescence. Eight rhesus monkeys (aged 20-30 days) were treated monocularly with hyperopic-defocus (-3.0D lens) and divided randomly into two groups: AL group (n=4), reared under Artificial (indoor) Lighting (08:00-20:00); and NL group (n=4), exposed to Natural (outdoor) Light for 3 hours per day (11:00-14:00), and to indoor lighting for the rest of the light phase. After being reared with lenses for ca. 190 days, all monkeys were returned to unrestricted vision until the age of 3 years. Another eight age-matched monkeys, reared with unrestricted vision under artificial lighting since birth, were employed as controls. The ocular refraction, corneal curvature and axial dimensions were measured before lens-wearing (at 23±3 days of age), monthly during the light phase, and at the age of puberty (at 1185+3 days of age). During the lens-wearing treatment, infant monkeys in the NL group were more hyperopic than those in the AL group (F=5.726, P=0.032). Furthermore, the two eyes of most NL monkeys remained isometropic, whereas 3 of 4 AL monkeys developed myopic anisometropia more than -2.0D. At adolescence, eyes of AL monkeys showed significant myopic anisometropia compared with eyes of NL monkeys (AL vs NL: -1.66±0.87D vs -0.22±0.44D; P=0.002) and controls (AL vs Control: -1.66±0.87D vs -0.05±0.85D; P<0.0001). All differences in refraction were associated with parallel changes in axial dimensions. Our results suggest that exposure to natural outdoor light might have an effect to reduced hyperopic defocus-induced myopia. Also, the data imply that early life exposure to sunlight may help to maintain normal development of emmetropization later in life, and thus lower the risk of myopic anisometropia in adolescent monkey.

The association between season of pregnancy and birth-sex among Chinese

Objective: although numerous studies have reported the association between birth season and sex ratio, few studies have been conducted in subtropical regions in a non-Western setting. The present study assessed the effects of pregnancy season on birth sex ratio in China. Methods: We conducted a national population-based retrospective study from 2006–2008 with 3175 children-parents pairs enrolled in the Northeast regions of China. Demographics and data relating to pregnancy and birth were collected and analyzed. A multiple logistical regression model was fitted to estimate the regression coefficient and 95% confidence interval (CI) of refractive error for mother pregnancy season, adjusting for potential confounders. Results: After adjusting for parental age (cut-off point was 30 years), region, nationality, mother education level, and mother miscarriage history, there is a significant statistical different mother pregnancy season on birth-sex. Compared with mothers who were pregnant in spring, those pregnant in summer or winter had a high probability of delivering girls (p < 0.05). The birth-sex ratio varied with months. Conclusions: Our results suggested that mothers pregnant in summer and winter were more likely to deliver girls, compared with those pregnant in spring. Pregnancy season may play an important role in the birth-sex.

The relationship of season of birth with refractive error in very young children in eastern China

PURPOSE

To determine the association of season of birth and refractive error in very young Chinese children in China.

METHODS

We conducted a population-based study of Chinese children aged 0 to 3 years residing in eastern China. Refraction was determined by non-cyclopegic autorefraction using a hand-held autorefractor. Date of birth was retrieved from birth certificate of the individual subjects. A generalized linear regression model was fitted to estimate the regression coefficient and 95% confidence interval (CI) of refractive error for season of birth, adjusting for confounders.

RESULTS

Of the 1385 children eligible to participate, 1222 (88.2%) were examined. Refractive error data were available for 1219 children. The mean spherical equivalent were 1.21 diopters (D) in children born Spring, 1.24 D in those born in Summer, 1.23 D in those born in Autumn, 1.15 D in Winter. After adjusting for age, sex, father's educational level, birth weight and the number of summers between birth and examination date the children have been exposed to, children born in winter had a 0.12 D more myopic refraction compared with those born in summer (regression coefficient: -0.12; 95% CI, -0.27,-0.06; P = 0.006). The association between season of birth and cylinder power was not statistically significant.

CONCLUSIONS

In China, children born in winter had a more myopic refraction compared with those born in other seasons. The observed association between season of birth and refractive error was independent of parental educational level and birth weight, suggesting that light level may have a small impact on refractive development in early life.

Is orbital volume associated with eyeball and visual cortex volume in humans?

BACKGROUND

In humans orbital volume increases linearly with absolute latitude. Scaling across mammals between visual system components suggests that these larger orbits should translate into larger eyes and visual cortices in high latitude humans. Larger eyes at high latitudes may be required to maintain adequate visual acuity and enhance visual sensitivity under lower light levels.

AIM

To test the assumption that orbital volume can accurately index eyeball and visual cortex volumes specifically in humans.

SUBJECTS AND METHODS

Structural Magnetic Resonance Imaging (MRI) techniques are employed to measure eye and orbit (n = 88) and brain and visual cortex (n = 99) volumes in living humans. Facial dimensions and foramen magnum area (a proxy for body mass) were also measured.

RESULTS

A significant positive linear relationship was found between (i) orbital and eyeball volumes, (ii) eyeball and visual cortex grey matter volumes and (iii) different visual cortical areas, independently of overall brain volume.

CONCLUSION

In humans the components of the visual system scale from orbit to eye to visual cortex volume independently of overall brain size. These findings indicate that orbit volume can index eye and visual cortex volume in humans, suggesting that larger high latitude orbits do translate into larger visual cortices.

Pharmacology of myopia and potential role for intrinsic retinal circadian rhythms

Despite the high prevalence and public health impact of refractive errors, the mechanisms responsible for ametropias are poorly understood. Much evidence now supports the concept that the retina is central to the mechanism(s) regulating emmetropization and underlying refractive errors. Using a variety of pharmacologic methods and well-defined experimental eye growth models in laboratory animals, many retinal neurotransmitters and neuromodulators have been implicated in this process. Nonetheless, an accepted framework for understanding the molecular and/or cellular pathways that govern postnatal eye development is lacking. Here, we review two extensively studied signaling pathways whose general roles in refractive development are supported by both experimental and clinical data: acetylcholine signaling through muscarinic and/or nicotinic acetylcholine receptors and retinal dopamine pharmacology. The muscarinic acetylcholine receptor antagonist atropine was first studied as an anti-myopia drug some two centuries ago, and much subsequent work has continued to connect muscarinic receptors to eye growth regulation. Recent research implicates a potential role of nicotinic acetylcholine receptors; and the refractive effects in population surveys of passive exposure to cigarette smoke, of which nicotine is a constituent, support clinical relevance. Reviewed here, many puzzling results inhibit formulating a mechanistic framework that explains acetylcholine's role in refractive development. How cholinergic receptor mechanisms might be used to develop acceptable approaches to normalize refractive development remains a challenge. Retinal dopamine signaling not only has a putative role in refractive development, its upregulation by light comprises an important component of the retinal clock network and contributes to the regulation of retinal circadian physiology. During postnatal development, the ocular dimensions undergo circadian and/or diurnal fluctuations in magnitude; these rhythms shift in eyes developing experimental ametropia. Long-standing clinical ideas about myopia in particular have postulated a role for ambient lighting, although molecular or cellular mechanisms for these speculations have remained obscure. Experimental myopia induced by the wearing of a concave spectacle lens alters the retinal expression of a significant proportion of intrinsic circadian clock genes, as well as genes encoding a melatonin receptor and the photopigment melanopsin. Together this evidence suggests a hypothesis that the retinal clock and intrinsic retinal circadian rhythms may be fundamental to the mechanism(s) regulating refractive development, and that disruptions in circadian signals may produce refractive errors. Here we review the potential role of biological rhythms in refractive development. While much future research is needed, this hypothesis could unify many of the disparate clinical and laboratory observations addressing the pathogenesis of refractive errors.

Image defocus and altered retinal gene expression in chick: clues to the pathogenesis of ametropia

PURPOSE

Because of the retina's role in refractive development, this study was conducted to analyze the retinal transcriptome in chicks wearing a spectacle lens, a well-established means of inducing refractive errors, to identify gene expression alterations and to develop novel mechanistic hypotheses about refractive development.

METHODS

One-week-old white Leghorn chicks wore a unilateral spectacle lens of +15 or -15 D for 6 hours or 3 days. With total RNA from the retina/(retinal pigment epithelium, RPE), chicken gene microarrays were used to compare gene expression levels between lens-wearing and contralateral control eyes (n = 6 chicks for each condition). Normalized microarray signal intensities were evaluated by analysis of variance, using a false discovery rate of <10% as the statistical criterion. Selected differentially expressed genes were validated by qPCR.

RESULTS

Very few retina/RPE transcripts were differentially expressed after plus lens wear. In contrast, approximately 1300 transcripts were differentially expressed under each of the minus lens conditions, with minimal overlap. For each condition, low fold-changes typified the altered transcriptome. Differentially regulated genes under the minus lens conditions included many potentially informative signaling molecules and genes whose protein products have roles in intrinsic retinal circadian rhythms.

CONCLUSIONS

Plus or minus lens wear induce markedly different, not opposite, alterations in retina/RPE gene expression. The initial retinal responses to defocus are quite different from those when the eye growth patterns are well established, suggesting that different mechanisms govern the initiation and persistence or progression of refractive errors. The gene lists identify promising signaling candidates and regulatory pathways for future study, including a potential role for circadian rhythms in refractive development.

Birth season, photoperiod, and infancy refraction

PURPOSE

To investigate the association between birth month/photoperiod and refraction in infancy.

METHODS

Seven hundred twenty-two children with refractions measured between 1 and 3 months were included in this analysis. Non-cycloplegic near retinoscopy was performed by three experienced optometrists over a 32-year period. Photoperiod hours were calculated as the mean daylight hours 30 days after each infant's birth and then grouped into quartiles between 9.12 and 15.25 hours. Two classifications for birth season were considered: regular season (Spring: March-May, Summer: June-August, Fall: September-November, and Winter: December-February) and alternate season (Spring: February-April, Summer: May-July, Fall: August-October, and Winter: November-January).

RESULTS

The mean infant age was 2.11 ± 0.55 months. The mean spherical equivalent refraction (SER) was 0.61 ± 1.56 diopters (D). Children born in the photoperiod group with the most daylight hours had slightly lower refractions than those in the shortest photoperiod group (0.43 ± 1.60 D vs. 0.87 ± 1.43 D, p < 0.05). In the longest photoperiod group, the percentage of infants with SER ≤-0.25 D was significantly higher (51/179 = 28.49%) than in the shortest photoperiod group (31/177 = 17.51%) (p = 0.02). Similar patterns were observed using the alternate season classification, with (1) lower mean SER in infants born in the summer vs. the winter and (2) a higher percentage of SER ≤-0.25 D in infants born in the summer vs. the winter. However, by regular seasons, the mean SERs were similar between summer and winter.

CONCLUSIONS

A small, statistically significant lower refraction was found in infants with the most vs. the least daylight soon after birth, suggesting that light might play a small role in the refractive error of newborns.

Dependency between light intensity and refractive development under light-dark cycles

The emmetropization process involves fine-tuning the refractive state by altering the refractive components toward zero refraction. In this study, we provided light-dark cycle conditions at several intensities and examined the effect of light intensity on the progression of chicks' emmetropization. Chicks under high-, medium-, and low-light intensities (10,000, 500, and 50 lux, respectively) were followed for 90 days by retinoscopy, keratometry, as well as ultrasound measurements. Emmetropization was reached from days 30-50 and from days 50-60 for the low- and medium-intensity groups, respectively. On day 90, most chicks in the low-intensity group were myopic, with a mean refraction of -2.41D (95% confidence interval (CI) -2.9 to -1.8D), whereas no chicks in the high-intensity group developed myopia, but they exhibited a stable mean hyperopia of +1.1D. The medium-intensity group had a mean refraction of +0.03D. The low-intensity group had a deeper vitreous chamber depth and a longer axial length compared with the high-intensity group, and shifted refraction to the myopic side. The low-intensity group had a flatter corneal curvature, a deeper anterior chamber, and a thinner lens compared with the high-intensity group, and shifted refraction to the hyperopic side. In all groups the corneal power was correlated with the three examined levels of log light intensity for all examined times (e.g., day 20 r = 0.6 P < 0.0001, day 90 r = 0.56 P < 0.0001). Thus, under light-dark cycles, light intensity is an environmental factor that modulates the process of emmetropization, and the low intensity of ambient light is a risk factor for developing myopia.

Gene profiling in experimental models of eye growth: clues to myopia pathogenesis

To understand the complex regulatory pathways that underlie the development of refractive errors, expression profiling has evaluated gene expression in ocular tissues of well-characterized experimental models that alter postnatal eye growth and induce refractive errors. Derived from a variety of platforms (e.g. differential display, spotted microarrays or Affymetrix GeneChips), gene expression patterns are now being identified in species that include chicken, mouse and primate. Reconciling available results is hindered by varied experimental designs and analytical/statistical features. Continued application of these methods offers promise to provide the much-needed mechanistic framework to develop therapies to normalize refractive development in children.

Risk factor analysis of 167 patients with high myopia

AIM

To analyze the risk factors of age, sex, course, best corrected visual acuity (BCVA), diopter and fundus features of high myopes with progressive high myopia.

METHODS

A total of 167 patients with high myopes were categorized into four groups: group 1, age 10-29 years; group 2, age 30-49 years; group 3, age 50-69 years and group 4, age 70-89 years. The refractive errors of all patients were measured without cycloplegia with an autorefractometer. Data of the spherical equivalent (SE) of the refractive errors in diopters (D) and fundus examined by direct ophthalmoscope were used in statistical analysis.

RESULTS

The number of female was statistically larger than that of male (P<0.01), also the disease course was correlated to the age. The visual acuity of high myopes significantly decreased as they grew older including the higher incidence of lacquer cracker, submacular hemorrhage, Fuchs spots, chorioretinal atrophy.

CONCLUSION

Female maybe a risk factor of high myopia, advanced age is an important factor of visual acuity decreased. High myopes ought to be treated early to delay the progress of myopia and development of macular degeneration.