Myopia and night lighting in children in Singapore

Potential causal associations between leisure sedentary behaviors, physical activity, sleep traits, and myopia: a Mendelian randomization study

BACKGROUND

Myopia is the most prevalent refractive error and a growing global health concern that significantly affects visual function. Researchers have recently emphasized considerably on the influence of lifestyle on myopia incidence and development. This study investigates the relationship between leisure sedentary behaviors (LSB)/physical activity (PA)/sleep traits and myopia.

METHODS

LSB, PA, and sleep trait-associated genetic variants were used as instrument variables in a Mendelian randomization (MR) study to examine their causal effects on myopia. Summary genome-wide association studies (GWASs) statistical data for LSB and PA were obtained from UK Biobank, and the data of sleep traits was obtained from UK Biobank, UK Biobank and 23andMe, and FinnGen. We used summary statistics data for myopia from MRC IEU. The MR analyses was performed using the inverse variance-weighted (IVW), MR-Egger, weighted median, and MR Pleiotropy RESidual Sum and Outlier methods.

RESULTS

Computer use was genetically predicted to increase the myopia risk [IVW odds ratio (OR) = 1.057; 95% confidence interval (CI), 1.038-1.078; P = 7.04 × 10- 9]. The self-reported moderate-to-vigorous physical activity (MVPA) (IVW OR = 0.962; 95% CI, 0.932-0.993; P = 1.57 × 10- 2) and television watching (IVW OR = 0.973; 95% CI, 0.961-0.985, P = 1.93 × 10- 5) were significantly associated with a lower myopia risk. However, genetically predicted sleep traits or accelerometer-measured physical activity had no significant associations with myopia.

CONCLUSION

Our results indicated that computer use is a risk factor for myopia, whereas television watching and MVPA may protect against myopia. These findings shed new light on possible strategies for reducing the prevalence of myopia.

Association between sleep-wake schedules and myopia among Chinese school-aged children and adolescents: a cross-sectional study

BACKGROUND

This study aimed to investigate the relationship between sleep-wake schedules and self-reported myopia in the pediatric population.

METHODS

In this cross-sectional study in 2019, school-aged children and adolescents in the Baoan District of Shenzhen City were sampled using a stratified cluster sampling approach. Sleep-wake schedules of children were determined by a self-administered questionnaire. The age that participants first reported using myopia correction glasses or contact lenses was used to identify those with myopia. Pearson χ² test was used to examine differences in myopia prevalence among participants with different characteristics. Multivariate logistic regression, adjusted for potential confounding variables, was applied to examine the relationship between sleep-wake schedule and risk of self-reported myopia, and a stratification analysis by school grade was also performed.

RESULTS

A total of 30,188 students were recruited. In this study, the overall prevalence of myopia was 49.8%, with prevalence rates of 25.6%, 62.4%, and 75.7% for primary, junior high, and senior high school students, respectively. Students with irregular sleep-wake times reported a higher prevalence of myopia than those with regular sleep-wake times. Nighttime sleep duration of < 7 hours/day (h/d) (OR = 1.27, 95%CI: 1.17-1.38), no daytime nap (OR = 1.10, 95%CI: 1.03-1.18), irregular weekday bedtime (OR = 1.11, 95%CI: 1.05-1.17), irregular weekday wake time (OR = 1.21, 95%CI: 1.12-1.30), weekend bedtime delayed > = 1 h/d (OR = 1.20, 95%CI: 1.11-1.29, P < 0.001), weekend wake time delayed > = 1 h/d (OR = 1.11, 95%CI: 1.03-1.19), irregular sleep-wake time on weekdays (OR = 1.13, 95%CI: 1.07-1.19), and social jetlag > = 1 h (OR = 1.08, 95%CI: 1.03-1.14) were likely to be associated with increased risks of self-reported myopia after adjusting age, sex, grade, parental education level, family income, parental myopia, academic record, and academic workload. When stratified by school grade, we observed that nighttime sleep duration < 7 h/d, no daytime naps, and irregular sleep-wake time on weekdays were significantly associated with self-reported myopia in primary school students.

CONCLUSION

Insufficient sleep and irregular sleep-wake schedules can increase the risk of self-reported myopia in children and adolescents.

Interventions recommended for myopia prevention and control among children and adolescents in China: a systematic review

In 2018, a consortium of government bodies in China led by the Ministry of Education released the Comprehensive Plan to Prevent Nearsightedness among Children and Teenagers (CPPNCT), aiming to reduce the incidence of myopia and control myopic progression in China. Recommendations span from home-based to school-based interventions, including time outdoors, physical activity, light exposure, near-work activity, screen time, Chinese eye exercises, diet and sleep. To date, the levels of evidence for this suite of interventions have not been thoroughly investigated. This review has summarised the evidence of the interventions recommended by the CPPNCT in myopia prevention and control. Thus, the following statements are supposed by the evidence: (1) Increasing time outdoors and reducing near-work time are effective in lowering incident myopia in school-aged children. (2) All interventions have a limited effect on myopia progression. Ongoing research may lead to a better understanding of the underlying mechanisms of myopia development, the interaction of different interventions and recommendations, confounding variables and their true effect on myopia prevention, and the identification of those most likely to respond to specific interventions. This field may also benefit from longer-term studies of the various interventions or strategies covered within this review article, to better understand the persistence of treatment effects over time and explore more novel approaches to myopia control.

Relationship between peripheral refraction, axial lengths and parental myopia of young adult myopes

PURPOSE

To determine the relationship between peripheral refraction at the horizontal retina, axial length and parental history of myopia between myopic adults who have positive parental myopia and those with negative parental myopia.

METHODS

69 males and 44 females in the age range of 18-25 years were assigned either a negative parental myopia (NPM) or positive parental myopia (PPM) group. In the corrected and uncorrected states, peripheral refractive error was measured up to 30° horizontally in 10° steps using an open field autorefractor. Axial length was measured using an Opto US1000 Fine A-Scan Ultrasonography (model US1000).

RESULTS

Relative peripheral refractive error showed more hyperopic defocus that was statistically significantly more increased in the positive parental myopia group than in the negative parental myopia group (P ≥ 0.02). The overall mean ± SD axial length of all subjects was 23.38 ± 0.32 mm (range 23.01-25.01 mm). The study showed a statistically significant difference (P = 0.005) in axial lengths of young adult myopes (23.45 ± 0.36 mm) with parental myopia compared to those with similar spherical equivalent refraction who have non-myopic parents (23.28 ± 0.19 mm).

CONCLUSION

There was significantly more hyperopic defocus at 30° N and 30° T retina in the corrected states of young adult myopes who had myopic parents compared to their counterparts with non-myopic parents.

Rapid Myopic Progression in Childhood Is Associated With Teenage High Myopia

Purpose

The purpose of this study was to evaluate the association of childhood progression of spherical equivalent (SE) with high myopia (HM) in teenagers in the Singapore Cohort of Risk factors for Myopia (SCORM).

Methods

We included 928 SCORM children followed over a mean follow-up of 6.9 ± 1.0 years from baseline (6–11 years old) until their teenage years (12–19 years old). Cycloplegic autorefraction and axial length (AL) measurements were performed yearly. The outcomes in teenagers were HM (SE ≤ −5 diopter [D)], AL ≥ 25 mm, SE and AL. Three-year SE and AL progression in childhood and baseline SE and AL with outcomes were evaluated using multivariable logistic or linear regression models, with predictive performance of risk factors assessed using the area under the curve (AUC).

Results

At the last visit, 9.8% of teenagers developed HM and 22.7% developed AL ≥ 25 mm. In multivariate regression analyses, every −0.3 D/year increase in 3-year SE progression and every 0.2 mm/year increase in 3-year AL progression were associated with a −1.14 D greater teenage SE and 0.52 mm greater teenage AL (P values < 0.001). The AUC (95% confidence interval [CI]) of a combination of 3-year SE progression and baseline SE for teenage HM was 0.97 (95% CI = 0.95 – 0.98). The AUC of 3-year AL progression and baseline AL for teenage AL ≥ 25 mm was 0.91 (95% CI = 0.89 – 0.94).

Conclusions

Three-year myopia progression in childhood combined with baseline SE or AL were good predictors of teenage HM. Clinicians may use this combination of factors to guide timing of interventions, potentially reducing the risk of HM later in life.

A synopsis of the prevalence rates and environmental risk factors for myopia

The prevalence rates of myopia are higher in urban Asian cities such as Hong Kong and Singapore. One observation over the past few decades is that the prevalence rates of myopia have been rising and there is an epidemic of myopia in Asia. The age-old question of the roles of nature and nurture in this process remains unanswered. The strongest evidence for an environmental link to myopia is near work activity. Childhood exposure to night lighting has also been explored in different studies but the results have been mixed. Twin studies, segregation analysis and association studies have demonstrated that hereditary factors play an important role in myopia development. The exact nature and interplay of genetic and environmental factors is not known and data suggest that environmental factors may interact with genetic factors to increase the risks of developing myopia. Future research is needed to identify specific modifiable lifestyle factors and genetic markers for myopia. This will enable preventive measures such as health education to be instituted.

Sleeping late is a risk factor for myopia development amongst school-aged children in China

Myopia, a leading cause of distance vision impairment, is projected to affect half of the world's population in 30 years. We analysed the relationship between certain demographic, environmental, and behavioural factors and myopia from a 2-year school-based, prospective trial conducted in Shanghai, China. This trial enrolled 6295 school-aged children at baseline and followed them up for 24 months. The relationship between abovementioned factors and myopia was examined and the role of sleep in childhood myopia development was highlighted. Our results suggest that 'sleeping late' is a risk factor for myopia prevalence at baseline (odds ratio [OR] = 1.55, p = 0.04), 2-year myopia incidence (odds ratio [OR] = 1.44, p = 0.02) and progression over 24 months (p = 0.005), after adjusting for residency area, age, gender, sleep duration, and time spent outdoors. The identification and consistency of results with late sleepers being a susceptible group to both myopia onset and progression suggests a complex relationship between circadian rhythm, indoor environment, habitual indoor activities and myopia development and progression. These results can offer new insights to future myopia aetiology studies as well as aid in decision-making of myopia prevention strategies.

An Update of Eye Shape and Myopia

Myopia is one of the most prevalent eye diseases, and its advanced form, high myopia, is a leading cause of subsequent pathologic myopia, which in turn results in an increased risk of retinal diseases. The prevalence of myopia and high myopia is 28.3% and 4.0% of the global population, respectively, and these numbers are estimated to increase to 49.8% for myopia 9.8% for high myopia by 2050, thus making myopia a severe global socioeconomic problem. The eye shape has been receiving increasing attention as a possible biomarker for myopia. Among several modalities, magnetic resonance imaging (MRI) is currently considered to be the best to measure the 3-dimensional eye shape, and one study using MRI revealed that myopic eyes became much larger in all 3 dimensions, but more so in length (0.35 mm/D) than in height (0.19 mm/D) or in width (0.10 mm/D), which fitted in global and axial elongation models. Another recent study reported that emmetropic retinas were oblate but oblateness decreased with myopia progression. According to a study to evaluate eye shapes in high myopia, although all emmetropic eyes had a blunt shape, almost half of the high myopic eyes had a pointed shape. Multiple lines of evidence suggest that abnormal eye shape changes can cause not only simple myopia but also various ocular complications through biomechanical stretching. In this review, we highlight recent findings on eye shape changes in myopic eyes and abnormal eye shapes in pathologic myopia.

Effect of Ambient Light Exposure on Ocular Fatigue during Sleep

BACKGROUND

To investigate the influence of nocturnal ambient light on visual function and ocular fatigue.

METHODS

Sixty healthy subjects (30 men and 30 women) aged 19 through 29 years with no history of ocular disease were recruited. All subjects spent 3 consecutive nights in the sleep laboratory. During the first and second nights, the subjects were not exposed to light during sleep, but during the third night, they were exposed to ambient light, measuring 5 or 10 lux at the eye level, which was randomly allocated with 30 subjects each. The visual function and ocular fatigue were assessed at 7 a.m. on the 3rd and 4th mornings, using best-corrected visual acuity, refractive error, conjunctival hyperemia, tear break-up time, maximal blinking interval, ocular surface temperature, and subjective symptoms reported on a questionnaire.

RESULTS

Three men and three women subjects failed to complete the study (4 in the 5 lux; 2 from the 10 lux). For the entire 54 subjects, tear break-up time and maximal blinking interval decreased (P = 0.015; 0.010, respectively), and nasal and temporal conjunctival hyperemia increased significantly after sleep under any ambient light (P < 0.001; 0.021, respectively). Eye tiredness and soreness also increased (P = 0.004; 0.024, respectively). After sleep under 5 lux light, only nasal conjunctival hyperemia increased significantly (P = 0.008). After sleep under 10 lux light, nasal and temporal conjunctival hyperemia, eye tiredness, soreness, difficulty in focusing, and ocular discomfort increased significantly (P < 0.05).

CONCLUSION

Nocturnal ambient light exposure increases ocular fatigue. Avoiding ambient light during sleep could be recommended to prevent ocular fatigue.

Circadian rhythms, refractive development, and myopia

PURPOSE

Despite extensive research, mechanisms regulating postnatal eye growth and those responsible for ametropias are poorly understood. With the marked recent increases in myopia prevalence, robust and biologically-based clinical therapies to normalize refractive development in childhood are needed. Here, we review classic and contemporary literature about how circadian biology might provide clues to develop a framework to improve the understanding of myopia etiology, and possibly lead to rational approaches to ameliorate refractive errors developing in children.

RECENT FINDINGS

Increasing evidence implicates diurnal and circadian rhythms in eye growth and refractive error development. In both humans and animals, ocular length and other anatomical and physiological features of the eye undergo diurnal oscillations. Systemically, such rhythms are primarily generated by the 'master clock' in the surpachiasmatic nucleus, which receives input from the intrinsically photosensitive retinal ganglion cells (ipRGCs) through the activation of the photopigment melanopsin. The retina also has an endogenous circadian clock. In laboratory animals developing experimental myopia, oscillations of ocular parameters are perturbed. Retinal signaling is now believed to influence refractive development; dopamine, an important neurotransmitter found in the retina, not only entrains intrinsic retinal rhythms to the light:dark cycle, but it also modulates refractive development. Circadian clocks comprise a transcription/translation feedback control mechanism utilizing so-called clock genes that have now been associated with experimental ametropias. Contemporary clinical research is also reviving ideas first proposed in the nineteenth century that light exposures might impact refraction in children. As a result, properties of ambient lighting are being investigated in refractive development. In other areas of medical science, circadian dysregulation is now thought to impact many non-ocular disorders, likely because the patterns of modern artificial lighting exert adverse physiological effects on circadian pacemakers. How, or if, such modern light exposures and circadian dysregulation contribute to refractive development is not known.

SUMMARY

The premise of this review is that circadian biology could be a productive area worthy of increased investigation, which might lead to the improved understanding of refractive development and improved therapeutic interventions.

Gender differences in adolescent dry eye disease: a health problem in girls

AIM

To evaluate the signs and symptoms of dry eye disease (DED) in adolescents.

METHODS

This was a cross-sectional, case-control study and outpatients aged 10 to 19y were recruited from six eye clinics of various practices and locations in Japan, and 253 non-DED subjects and 70 DED patients were enrolled. Participants were examined for DED-related signs. Patients were also interviewed to ascertain the presence or absence of six common DED-related symptoms: dryness, irritation, pain, eye fatigue, blurring, and photophobia. Main outcome measures were differences in signs and symptoms of dry eye disease between boys and girls.

RESULTS

Of the 323 adolescents recruited, 70 (21.7%) were diagnosed with DED. Significant differences between the non-DED and DED groups were found for short tear break-up time (BUT; ≤5s; P=0.000) and superficial punctate keratopathy (SPK; staining score ≥3; P=0.000). Late adolescent girls reported fewer symptoms than late adolescent boys, although their DED-related signs were worse compared to other groups. The prevalence and severity of DED were similar in the Tokyo area compared with suburban and local areas but myopic errors were worse.

CONCLUSION

We find that adolescents reported symptoms of DED similar to those found in adults, and the majority have short BUT-type DED. The prevalence and severity of DED in late adolescent girls is comparable with adults. Adolescents with DED are underserved and we believe that DED is a hidden but potentially serious health problem for this age group.

Myopia in young patients with type 1 diabetes mellitus

INTRODUCTION

This study aimed to evaluate the proportion of young patients with type 1 diabetes mellitus (T1DM) who have myopia, as well as the risk factors associated with myopia in this group.

METHODS

In this cross-sectional study, patients aged < 21 years with T1DM for ≥ 1 year underwent a comprehensive eye examination. Presence of parental myopia, and average hours of near-work and outdoor activity were estimated using a questionnaire. Annualised glycosylated haemoglobin (HbA1c), defined as the mean of the last three HbA1c readings taken over the last year, was calculated. Multivariate analysis using genetic, environmental and diabetes-related factors was done to evaluate risk factors associated with myopia.

RESULTS

Of the 146 patients (mean age 12.5 ± 3.6 years) recruited, 66.4% were Chinese and 57.5% were female. Myopia (i.e. spherical equivalent [SE] of -0.50 D or worse) was present in 96 (65.8%) patients. The proportion of patients with myopia increased from 25.0% and 53.6% in those aged < 7.0 years and 7.0-9.9 years, respectively, to 59.2% and 78.4% in those aged 10.0-11.9 years and ≥ 12.0 years, respectively. Higher levels of SE were associated with lower parental myopia (p = 0.024) and higher annualised HbA1c (p = 0.011).

CONCLUSION

Compared to the background population, the proportion of myopia in young patients with T1DM was higher in those aged < 10 years but similar in the older age group. Myopia was associated with a history of parental myopia. Environmental risk factors and poor glycaemic control were not related to higher myopia risk.

Decreased sleep quality in high myopia children

The aim of the present study was to evaluate sleep quality in myopic children and adults. This cross sectional study surveyed 486 participants aged from 10 to 59 years with refractive errors using a questionnaire containing the Pittsburgh Sleep Quality Index (PSQI) and Hospital Anxiety and Depression Scale (HADS). Children (< 20 years) in the high myopia group exhibited the poorest PSQI scores (P < 0.01), while the adults showed no such correlations. Subscales of PSQI and HADS in children disclosed that the high myopia groups had the shortest sleep duration (P < 0.01), worst subjective sleep scores (P < 0.001), and latest bedtime (P < 0.05). Regression analyses in children significantly correlated myopic errors with PSQI (P < 0.05), sleep duration (P < 0.01), and bedtime (P < 0.01). Sleep efficacy (P < 0.05) and daytime dysfunction (P < 0.05) were significantly better in contact-lens users compared to the respective non-user groups across all participants. In conclusion, sleep quality in children was significantly correlated with myopic error, with the high myopia group worst affected.

Elevated light levels in schools have a protective effect on myopia

PURPOSE

To determine whether elevated light levels in classrooms in rural areas can protect school-age children from myopia onset or myopia progression.

METHODS

A total of 317 subjects from 1713 eligible students aged six to 14 in four schools located in northeast China participated in the study. Students received a comprehensive eye examination including cycloplegic refraction and ocular biometry, which included axial length (AL), anterior chamber depth (ACD), and corneal curvature (CC) measurement, and completed a questionnaire. The intervention arm included 178 students in two schools with rebuilt elevated lighting systems and the control arm included 139 students in which lighting systems were unchanged. Results for the two arms were compared with a Wilcoxon rank sum test, a chi-squared test or a t-test, as appropriate. Factors that might help explain any differences were explored with multivariate linear regression analysis.

RESULTS

The median average illuminance of blackboards and desks and uniformity of desk lighting were significantly improved, however, the uniformity of blackboard lighting declined after intervention. At baseline, the mean refraction, AL, CC, ACD and myopia prevalence between the two arms were not significantly different. After 1 year, compared with the control arm the intervention arm had a lower incidence of new myopia onset (4% vs 10%; p = 0.029), a smaller decrease in refractive error among no myopic subjects (-0.25 dioptre [D] vs -0.47 D; p = 0.001), and shorter axial growth for both non-myopic (0.13 vs 0.18 mm; p = 0.023) and myopic subjects (0.20 vs 0.27 mm; p = 0.0001). Multivariate linear regression analysis showed the intervention program, lower hyperopic baseline refraction, lower father's education level, longer time sleeping and less time in screen-viewing activities were associated with less refractive shift in the direction of myopia in non-myopic children. For myopic subjects, myopia progression was significantly associated with family income only. The intervention program and older age had a protective effect on axial growth for both myopic and non-myopic subjects. The father's education level and sleep duration were significantly associated with axial growth in non-myopic children.

CONCLUSIONS

Elevated light levels in classrooms have a significant effect on myopia onset, decreases in refraction, and axial growth; if the findings of lighting intervention are reproduced in future studies, the ambient light levels in schools should be improved.

Eye size and shape in newborn children and their relation to axial length and refraction at 3 years

PURPOSE

To determine if eye size and shape at birth are associated with eye size and refractive error 3 years later.

METHODS

A subset of 173 full-term newborn infants from the Growing Up in Singapore Towards healthy Outcomes (GUSTO) birth cohort underwent magnetic resonance imaging (MRI) to measure the dimensions of the internal eye. Eye shape was assessed by an oblateness index, calculated as 1 - (axial length/width) or 1 - (axial length/height). Cycloplegic autorefraction (Canon Autorefractor RK-F1) and optical biometry (IOLMaster) were performed 3 years later.

RESULTS

Both eyes of 173 children were analysed. Eyes with longer axial length at birth had smaller increases in axial length at 3 years (p < 0.001). Eyes with larger baseline volumes and surface areas had smaller increases in axial length at 3 years (p < 0.001 for both). Eyes which were more oblate at birth had greater increases in axial length at 3 years (p < 0.001). Using width to calculate oblateness, prolate eyes had smaller increases in axial length at 3 years compared to oblate eyes (p < 0.001), and, using height, prolate and spherical eyes had smaller increases in axial length at 3 years compared to oblate eyes (p < 0.001 for both). There were no associations between eye size and shape at birth and refraction, corneal curvature or myopia at 3 years.

CONCLUSIONS

Eyes that are larger and have prolate or spherical shapes at birth exhibit smaller increases in axial length over the first 3 years of life. Eye size and shape at birth influence subsequent eye growth but not refractive error development.

Disordered sleep and myopia risk among Chinese children

PURPOSE

Disordered sleep and myopia are increasingly prevalent among Chinese children. Similar pathways may be involved in regulation of both sleep cycles and eye growth. We therefore sought to examine the association between disordered sleep and myopia in this group.

METHODS

Urban primary school children participating in a clinical trial on myopia and outdoor activity underwent automated cycloplegic refraction with subjective refinement. Parents answered questions about children's sleep duration, sleep disorders (Children's Sleep Habits Questionnaire [CSHQ]), near work and time spent outdoors.

RESULTS

Among 1970 children, 1902 (96.5%, mean [standard deviation SD] age 9.80 [0.44] years, 53.1% boys) completed refraction and questionnaires. Myopia < = -0.50 Diopters was present in both eyes of 588 (30.9%) children (1329/3804 = 34.9% of eyes) and 1129 children (59.4%) had abnormal CSHQ scores (> 41). In logistic regression models by eye, odds of myopia < = -0.50D increased with worse CSHQ score (Odds Ratio [OR] 1.01 per point, 95% Confidence Interval [CI] [1.001, 1.02], P = 0.014) and more night-time sleep (OR 1.02, 95% CI [1.01, 1.04, P = 0.002], while male sex (OR 0.82, 95% CI [0.70, 0.95], P = 0.008) and time outdoors (OR = 0.97, 95% CI [0.95, 0.99], P = 0.011) were associated with less myopia. The association between sleep duration and myopia was not significant (p = 0.199) for total (night + midday) sleep.

CONCLUSIONS

Myopia and disordered sleep were both common in this cohort, but we did not find consistent evidence for an association between the two.

TRIAL REGISTRATION

clinicaltrials.gov NCT00848900.

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.

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.

Ocular diurnal rhythms and eye growth regulation: where we are 50 years after Lauber

Many ocular processes show diurnal oscillations that optimize retinal function under the different conditions of ambient illumination encountered over the course of the 24 h light/dark cycle. Abolishing the diurnal cues by the use of constant darkness or constant light results in excessive ocular elongation, corneal flattening, and attendant refractive errors. A prevailing hypothesis is that the absence of the Zeitgeber of light and dark alters ocular circadian rhythms in some manner, and results in an inability of the eye to regulate its growth in order to achieve emmetropia, the matching of the front optics to eye length. Another visual manipulation that results in the eye growth system going into a "default" mode of excessive growth is form deprivation, in which a translucent diffuser deprives the eye of visual transients (spatial or temporal) while not significantly reducing light levels; these eyes rapidly elongate and become myopic. It has been hypothesized that form deprivation might constitute a type of "constant condition" whereby the absence of visual transients drives the eye into a similar default mode as that in response to constant light or dark. Interest in the potential influence of light cycles and ambient lighting in human myopia development has been spurred by a recent study showing a positive association between the amount of time that children spent outdoors and a reduced prevalence of myopia. The growing eyes of chickens and monkeys show a diurnal rhythm in axial length: Eyes elongate more during the day than during the night. There is also a rhythm in choroidal thickness that is in approximate anti-phase to the rhythm in eye length. The phases are altered in eyes growing too fast, in response to form deprivation or negative lenses, or too slowly, in response to myopic defocus, suggesting an influence of phase on the emmetropization system. Other potential rhythmic influences include dopamine and melatonin, which form a reciprocal feedback loop, and signal "day" and "night" respectively. Retinal dopamine is reduced during the day in form deprived myopic eyes, and dopamine D2 agonists inhibit ocular growth in animal models. Rhythms in intraocular pressure as well, may influence eye growth, perhaps as a mechanical stimulus triggering changes in scleral extracellular matrix synthesis. Finally, evidence shows varying influences of environmental lighting parameters on the emmetropization system, such as high intensity light being protective against myopia in chickens. This review will cover the evidence for the possible influence of these various factors on ocular growth. The recognition that ocular rhythms may play a role in emmetropization is a first step toward understanding how they may be manipulated in treatment therapies to prevent myopia in humans.

The complex interactions of retinal, optical and environmental factors in myopia aetiology

Myopia is the commonest ocular abnormality but as a research topic remains at the margins of mainstream ophthalmology. The concept that most myopes fall into the category of 'physiological myopia' undoubtedly contributes to this position. Yet detailed analysis of epidemiological data linking myopia with a range of ocular pathologies from glaucoma to retinal detachment demonstrates statistically significant disease association in the 0 to -6 D range of 'physiological myopia'. The calculated risks from myopia are comparable to those between hypertension, smoking and cardiovascular disease. In the case of myopic maculopathy and retinal detachment the risks are an order of magnitude greater. This finding highlights the potential benefits of interventions that can limit or prevent myopia progression. Our understanding of the regulatory processes that guide an eye to emmetropia and, conversely how the failure of such mechanisms can lead to refractive errors, is certainly incomplete but has grown enormously in the last few decades. Animal studies, observational clinical studies and more recently randomized clinical trials have demonstrated that the retinal image can influence the eye's growth. To date human intervention trials in myopia progression using optical means have had limited success but have been designed on the basis of simple hypotheses regarding the amount of defocus at the fovea. Recent animal studies, backed by observational clinical studies, have revealed that the mechanisms of optically guided eye growth are influenced by the retinal image across a wide area of the retina and not solely the fovea. Such results necessitate a fundamental shift in how refractive errors are defined. In the context of understanding eye growth a single sphero-cylindrical definition of foveal refraction is insufficient. Instead refractive error must be considered across the curved surface of the retina. This carries the consequence that local retinal image defocus can only be determined once the 3D structure of the viewed scene, off axis performance of the eye and eye shape has been accurately defined. This, in turn, introduces an under-appreciated level of complexity and interaction between the environment, ocular optics and eye shape that needs to be considered when planning and interpreting the results of clinical trials on myopia prevention.

Time outdoors and physical activity as predictors of incident myopia in childhood: a prospective cohort study

PURPOSE

Time spent in "sports/outdoor activity" has shown a negative association with incident myopia during childhood. We investigated the association of incident myopia with time spent outdoors and physical activity separately.

METHODS

Participants in the Avon Longitudinal Study of Parents and Children (ALSPAC) were assessed by noncycloplegic autorefraction at ages 7, 10, 11, 12, and 15 years, and classified as myopic (≤-1 diopters) or as emmetropic/hyperopic (≥-0.25 diopters) at each visit (N = 4,837-7,747). Physical activity at age 11 years was measured objectively using an accelerometer, worn for 1 week. Time spent outdoors was assessed via a parental questionnaire administered when children were aged 8-9 years. Variables associated with incident myopia were examined using Cox regression.

RESULTS

In analyses using all available data, both time spent outdoors and physical activity were associated with incident myopia, with time outdoors having the larger effect. The results were similar for analyses restricted to children classified as either nonmyopic or emmetropic/hyperopic at age 11 years. Thus, for children nonmyopic at age 11, the hazard ratio (95% confidence interval, CI) for incident myopia was 0.66 (0.47-0.93) for a high versus low amount of time spent outdoors, and 0.87 (0.76-0.99) per unit standard deviation above average increase in moderate/vigorous physical activity.

CONCLUSION

Time spent outdoors was predictive of incident myopia independently of physical activity level. The greater association observed for time outdoors suggests that the previously reported link between "sports/outdoor activity" and incident myopia is due mainly to its capture of information relating to time outdoors rather than physical activity.

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.

The effect of body mass on health-related quality of life among Singaporean adolescents: results from the SCORM study

PURPOSE

To investigate the relationship between body mass and health-related quality of life (HRQOL) among Singaporean adolescents. Variation in this relationship by age, gender and ethnicity, and association of HRQOL with change in body mass over time and with demographic, socioeconomic and health variables were also assessed.

METHODS

HRQOL was assessed for Singaporean adolescents aged 11-18 from their own (N=1,249) and their parent’s (N=948) perspective using PedsQLTM 4.0 generic core scales. Body mass, measured as body mass index z-score based on the WHO Reference 2007, was categorized as thin, healthy weight, overweight and obese. Multiple linear regression models assessed the relationship between current body mass and HRQOL, adjusting for demographic, socioeconomic and health variables. Differences between adolescent and parent-proxy reported HRQOL were also investigated.

RESULTS

Obese adolescents (and their parents) reported significantly lower HRQOL, overall and in most domains, compared to healthy weight adolescents. Parents tended to report lower HRQOL for their adolescents than the adolescents did themselves; however, this difference was much larger and statistically significant for obese adolescents.

CONCLUSIONS

Obesity is associated with reduced HRQOL among adolescents. The effect in these Singaporean adolescents is similar to that in populations with higher rates of obesity. Awareness of this relationship can make it easier for health professionals, teachers, parents and peers to be supportive of obese adolescents.

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

PURPOSE

Mandel et al recently reported that season of birth and daylight hours (photoperiod) at birth were associated with moderate and high levels of myopia in Israeli conscripts. We sought to investigate whether these associations were evident in subjects from the United Kingdom (UK).

DESIGN

Retrospective cross-sectional study.

PARTICIPANTS

The study population comprised 74,459 subjects aged 18 to 100 years attending UK optometry practices for an eye examination.

METHODS

Data comprising non-cycloplegic spectacle prescription, sex, date of birth, and date of eye examination were collected from UK optometry practices. The average refractive error in fellow eyes was used to classify the degree of myopia in diopters (D) for each subject as follows: absent (>-0.75 D), low (-0.75 to -2.99 D), moderate (-3.00 to -5.99 D), or high (<-6.00 D). The average monthly hours of daylight for London, UK, were classified into 1 of 4 "photoperiod categories," following Mandel et al. The odds ratio (OR) for each level of severity of myopia was calculated using multivariate logistic regression with age, sex, and either season of birth or photoperiod category as risk factors.

MAIN OUTCOME MEASURES

The OR for season of birth and photoperiod category as potential risk factors for myopia.

RESULTS

Season of birth was significantly associated with the presence of high myopia: Subjects born in summer or autumn were more likely to be highly myopic compared with those born in winter (summer OR=1.17; 95% confidence interval [CI], 1.05-1.30; P=0.006; autumn OR=1.16; 95% CI, 1.04-1.30; P=0.007). However, season of birth was not a significant risk factor for low or moderate myopia. Photoperiod category was weakly associated with low myopia (OR=0.94; 95% CI, 0.89-0.99; P=0.019), but with a direction of effect opposite to that observed by Mandel et al.

CONCLUSIONS

As in Israel, a disproportionate number of UK high myopes were born in summer or autumn rather than in winter. However, unlike the situation in Israel, this association does not seem to be related to daylight hours during the postnatal period, implicating alternative physiologic influences that vary with season, such as birth weight.

Necessity of cycloplegia for assessing refractive error in 12-year-old children: a population-based study

PURPOSE

To compare pre- and postcycloplegic autorefraction in two separate age samples of Australian school children.

DESIGN

Population-based cross-sectional study of random cluster samples.

METHODS

Autorefraction was performed before and after cycloplegia, using 1% cyclopentolate, in the right eyes of 2,233 12-year-old and 210 6-year-old children.

RESULTS

The mean spherical equivalent (SEQ) difference between these measures was 0.84 diopters (D) (95% confidence interval (CI) 0.81 to 0.87 D), more hyperopic in post- than precycloplegic autorefractive assessments in the 12-year-old children and 1.18 D (95% CI 1.05 to 1.30 D) more hyperopic in the 6-year-old children. Precycloplegic autorefraction substantially overestimated the proportion of children with myopia, misclassifying 17.8% aged 12 years and 9.5% aged 6 years. Conversely, precycloplegic autorefraction did not detect moderate to high hyperopia in 2.28% of 12-year-olds and 17.14% of 6-year-olds.

CONCLUSIONS

Our findings reinforce the importance of using cycloplegic autorefraction in children up to age 12 years.

Constant light rearing disrupts compensation to imposed- but not induced-hyperopia and facilitates compensation to imposed myopia in chicks

PURPOSE

While rearing chicks in constant light (CL) inhibits anterior segment growth, these conditions also induce excessive enlargement of the vitreous chamber. The mechanisms underlying these effects are poorly understood although it has been speculated that the enlarged vitreous chambers are a product of emmetropization, a compensatory response to the altered anterior segments. We examined the ability of eyes to compensate to defocusing lenses in CL as a direct test of their ability to emmetropize. We also studied recovery responses, i.e. from lens-induced changes in CL as well as CL-induced changes alone or combined with lens-induced changes in eyes returned to normal diurnal lighting (NL).

METHODS

Hatchling White-Leghorn chicks were reared in either CL or NL (control) lighting conditions (n=36) for 2 weeks, with lenses of either +10 or -10D power fitted to one eye of all chicks at the beginning of the second week. The lenses were removed at the end of the same week, at which time some CL chicks (n=14) were shifted to NL, the rest of the chicks remaining in their respective original lighting conditions. Retinoscopy, IR photo-keratometry and high-frequency A-scan ultrasonography were used to track refractions, corneal radii of curvature and ocular axial dimensions, respectively; data were collected on experimental days 0, 7, 9, 14 and 21.

RESULTS

Under CL, eyes showed near normal, albeit slightly exaggerated responses to +10D lenses while the response to -10D lenses was disrupted. With +10D lenses, lens-wearing eyes became more hyperopic (RE), and had shorter vitreous chambers (VC) and optical axial lengths (OL) relative to their fellows by the end of the lens period [RE: +10.5+/-1.5D, CL, +8.25+/-2.5D, NL; VC: -0.363+/-0.129mm, CL; -0.306+/-0.110mm, NL; OL: -0.493+/-0.115mm, CL, -0.379+/-0.106mm, NL (mean interocular difference+/-SD)]. With -10D lenses, the NL group showed a myopic shift in RE and increased elongation of both VC depth and OL (RE: -10.75+/-2.0D; VC depth: 0.554+/-0.097mm; OL: 0.746+/-0.166mm), while the CL group showed a small hyperopic shift in RE (+4.0+/-6.0D). Nonetheless, CL eyes were able to recover from lens-induced hyperopia, whether they were left in CL or returned to NL. One week of exposure to NL was sufficient to reverse the effects of 2 weeks of CL on anterior and vitreous chamber dimensions.

CONCLUSION

CL impairs emmetropization. Specifically, it disrupts compensation to lens-imposed hyperopia but not imposed myopia. However, CL eyes are able to recover from lens-induced hyperopia, suggesting that the mechanisms underlying the compensatory responses to defocusing lenses are different from those involved in recovery responses. The ocular growth effects of CL on young eyes are reversible under NL.

Protecting children from myopia: a PMT perspective for improving health marketing communications

This research examined the predictive utility of the protection motivation theory (PMT) model for myopia prevention amongst children. An integrative model for myopia prevention behavior of parents was first developed in the context of theory and survey instruments then refined using information gathered from two focus groups. Empirical data then was collected from parents of primary school children in Singapore, a country with one of the highest rates of myopia in the world, and analyzed using structural equation modeling (SEM). Our findings revealed that coping appraisal variables were more significantly associated with protection motivation, relative to threat appraisal variables. In particular, perceived self-efficacy was the strongest predictor of parental intention to enforce good visual health behaviors, while perceived severity was relatively weak. Health marketing communications and public policy implications are discussed.

Near work, education, family history, and myopia in Greek conscripts

AIMS

To investigate potential factors associated with the presence of myopia in a cohort of young adult men carrying out their military service in Greece.

METHODS

A nested case-control study of 200 conscripts (99 myopes and 101 non-myopes). The cohort consisted of approximately 1000 conscripts in compulsory national service. All cohort members had been screened for refractive errors by Snellen visual acuity measurement at presentation to military service; individuals not achieving visual activity 6/6 underwent noncycloplaegic refraction. The study sample consisted of the first 99 myopic and 101 nonmyopic conscripts who attended the study. In-person interviews of these 200 conscripts were conducted to obtain information on family history, occupation, level of education, near-work activities, and sleeping behaviour. chi(2) and Mann-Whitney tests were used as univariate analysis methods to identify the potential factors associated with the presence of myopia. Multiple logistic regression was used to estimate the adjusted relative risk of myopia.

RESULTS

Univariate analysis showed that parental family history (P<0.001), older age (P<0.001), tertiary education (P<0.001), hours of reading per day (P<0.001), hours of computer use per day (P<0.001), and higher social classes (P<0.001) were associated with myopia. Sleeping in artificial or ambient light was not associated with myopia (P=0.75). Multiple logistic regression analysis showed that older age (OR=1.25, 95% CI 1.05-1.49), tertiary education (OR=12.67, 95% CI 3.57-44.88) and parental family history (OR=3.39, 95% CI 1.56-7.36) were independently associated with myopia.

CONCLUSION

In young Greek conscripts, parental family history, older age, and education level are independently associated with myopia.

Emmetropisation under continuous but non-constant light in chicks

It has been suggested that ambient lighting at night influences eye growth and might play a causal role in human myopia. To test this hypothesis, we reared newly hatched chicks under 12 hr light-dark or light-dim cycles with a light phase intensity of 1500 microW/cm(2) and variable dim phase intensities between 0.01 and 500 microW/cm(2). Other chicks were reared under constant light conditions with intensities between 1 and 1500 microW/cm(2). After three weeks, the chicks were examined by refractometry, ultrasound and caliper measurements of enucleated eyes. To relate ocular parameters with a retinal neurotransmitter likely involved in eye growth control, retinal and vitreal levels of dopamine and its principal metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), were measured by high performance liquid chromatography with electrochemical detection in the light, dark and dim phases. Diurnal fluctuations in axial length and choroidal thickness also were measured twice daily by partial coherence interferometry (PCI) in chicks under light-dark and the two brightest light-dim conditions. The eyes of chicks reared under most light-dim conditions had refractions and ocular dimensions comparable to those reared under light-dark conditions. At dim phase light intensities of 10 microW/cm(2) and above, the day-night changes in retinal dopamine metabolism were not observed. The daily fluctuations of axial length and choroidal thickness were altered with rearing under the two brightest dim light intensities, compared to the light-dark condition. Rearing under constant light with intensities ranging between 1 and 1500 microW/cm(2) produced a shallow anterior chamber and other eye alterations previously described for constant light rearing even though rearing under continuous light that fluctuated between these same intensities generally permitted normal eye growth. Thus, continuous but fluctuating light exerts different developmental effects on the eye than constant non-fluctuating light. Light-dim rearing may be more relevant to daily human light exposures than other laboratory lighting conditions and may provide an opportunity to study developmental interactions of visual quality (e.g. blur, defocus, etc.) and features of the light-dark cycle under conditions that perturb daily rhythms in dopamine metabolism and ocular dimensions. Such studies also could provide mechanistic insights into whether and how daily rhythms in retinal dopamine metabolism, axial length or choroidal thickness modulate refractive development.

The relation between birth size and the results of refractive error and biometry measurements in children

AIM

To examine the association of birth parameters with biometry and refraction in Singapore Chinese schoolchildren.

METHODS

Chinese children aged 7-9 years (n = 1413) from three schools in Singapore were recruited. Birth parameter information on birth weight, head circumference, length at birth, and gestational age were obtained from standard hospital records. Cycloplegic autorefraction, keratometry and biometry measures (axial length, vitreous chamber depth, lens thickness, and anterior chamber depth) were obtained.

RESULTS

Across the normal birthweight range (2.0-4.9 kg), children with birth weights > or =4.0 kg had longer axial lengths (adjusted mean 23.65 mm versus 23.16 mm), compared with children with birth weights <2.5 kg, after controlling for age, sex, school, height, parental myopia, and gestational age. For every 1 cm increment in head circumference at birth, the axial length was longer by 0.05 mm. For every 1 cm increment in birth length, the axial length was longer by 0.02 mm in multivariate analysis. Additional week increases in gestational age till 46 weeks resulted in axial lengths that were longer by 0.04 mm, controlling for age, sex, school, parental myopia, and height. Children with larger birth weights, head circumferences, birth lengths, or gestational ages had deeper vitreous chambers and larger corneal curvature radii; however, there were no significant associations with refraction.

CONCLUSIONS

Children who were born heavier, had larger head sizes or lengths at birth, or who were born more mature had longer axial lengths, and deeper vitreous chambers; but there were no differences in refraction at ages 7-9 years, possibly because of the observed compensatory flattening of the cornea.

Continuous ambient lighting and lens compensation in infant monkeys

PURPOSE

Protracted daily lighting cycles do not promote abnormal ocular enlargement in infant monkeys as they do in a variety of avian species. However, observations in humans suggest that ambient lighting at night may reduce the efficiency of the emmetropization process in primates. To test this idea, we investigated the ability of infant monkeys reared with continuous light to compensate for optically imposed changes in refractive error.

METHODS

Beginning at about 3 weeks of age, a hyperopic or myopic anisometropia was imposed on 12 infant rhesus monkeys by securing either a -3 D or +3 D lenses in front of one eye and a zero-powered lens in front of the fellow eye. Six of these monkeys were reared with the normal vivarium lights on continuously, whereas the other six lens-reared monkeys were maintained on a 12-h-light/12-h-dark lighting cycle. The ocular effects of the lens-rearing procedures were assessed periodically during the treatment period by cycloplegic retinoscopy, keratometry, and A-scan ultrasonography.

RESULTS

Five of six animals in each of the lighting groups demonstrated clear evidence for compensating anisometropic growth. In both lighting groups, eyes that experienced optically imposed hyperopic defocus (-3 D lenses) exhibited faster axial growth rates and became more myopic than their fellow eyes. In contrast, eyes treated with +3 D lenses showed relatively slower axial growth rates and developed more hyperopic refractive errors. The average amount of compensating anisometropia (continuous light, 1.6 +/- 0.5 D vs. control, 2.3 +/- 0.5 D), the structural basis for the refractive errors, and the ability to recover from the induced refractive errors were also not altered by continuous light exposure.

CONCLUSION

Ambient lighting at night does not appear to overtly compromise the functional integrity of the vision-dependent mechanisms that regulate emmetropization in higher primates.

Sensitivity and specificity of visual acuity screening for refractive errors in school children

PURPOSE

To examine the optimal cutoff point for the use of the visual acuity test to screen for refractive errors in schoolchildren.

METHODS

In a sample of schoolchildren between 7 and 9 years old, visual acuity testing was performed using modified ETDRS charts monocularly without optical aids by trained personnel. Cycloplegic autorefraction was performed in each eye. The screening efficacy of using various cutoff points for referring children for further optometric/ ophthalmic assessment was studied. Myopia was defined as a spherical equivalent of at least -0.5 D, hyperopia a spherical equivalent of at least +2.0 D, and astigmatism a cylinder of at least -1.0 D in at least one eye. The sensitivity, specificity, and predictive values were calculated using each patient as a case; a receiver operator curve was plotted.

RESULTS

A total of 1,028 children were tested. A satisfactory sensitivity/specificity profile was obtained using a referral criterion of visual acuity worse than or equal to 0.28 logarithm of the minimum angle of resolution in at least one eye. In this scenario, the sensitivity and specificity of this screening test were 72% (95% confidence interval [CI], 68 to 76) and 97% (95%CI, 95 to 98), respectively. The positive and negative predictive values were 96% (95%CI, 93 to 98) and 78% (95%CI, 75 to 82), respectively.

CONCLUSIONS

The modified ETDRS visual acuity chart can be used to predict refractive errors in schoolchildren in Singapore in a sensitive and specific manner using a referral criterion of worse than or equal to 0.28 logarithm of the minimum angle of resolution.

A multiple regression approach to study optical components of myopia in Singapore school children

PURPOSE

Previous studies on the optical components of childhood myopia adjusted only for age and gender or reported only the change of individual components with time. We perform a study to assess the association of the optical components of the eye contributing to the degree of myopia by building a statistical model which can better assess the individual effects of each optical component.

METHODS

Children 6-12 years old with myopia of -1 to -6 D were used in this study. Autokeratometry was performed to determine the mean corneal power in two perpendicular meridia. Ultrasonography was used to determine the vitreous chamber depth (VCD). Ultrasonography and Scheimflug biometry were used to determine lens thickness (LT) and anterior chamber depth. A stepwise multiple linear regression was used to determine statistically significant independent variables that explain the variation in the mean spherical equivalent of the left eye. The independent variables investigated were anterior chamber length, LT, VCD, mean corneal power, age and gender. The first regression model used measurements of anterior chamber depth and LT from ultrasonography, while the second model used measurements from Scheimflug photography. Statistical significance was set at p < 0.05.

RESULTS

Both statistical models have the same significant independent variables - VCD, LT and gender, with similar estimates. In both models, VCD was found to have the strongest partial association with mean spherical equivalent, followed by gender and LT. A more myopic refractive error was associated with (1) a longer eye, (2) an increased LT, and (3) female gender.

CONCLUSIONS

Myopia was associated with a longer vitreous chamber. This remained the primary determinant of myopia in Chinese children after consideration of other optical components. The effect of gender and LT on myopia requires further study. These results are in agreement with multiple regression analyses in Singapore adults.

Corneal and refractive error astigmatism in Singaporean schoolchildren: a vector-based Javal's rule

BACKGROUND

Traditional approaches to Javal's rule do not use data from subjects with oblique astigmatism and have not been used to make predictions about subjects with oblique astigmatism. Vector approaches to analyzing refractive error can circumvent these problems.

METHODS

Subjects were 993 Singaporean schoolchildren. We performed linear regression of refractive error astigmatism on corneal astigmatism, using J0 vectors to describe with-the-rule and against-the-rule astigmatism and J45 vectors to describe oblique astigmatism.

RESULTS

We obtained the following statistically significant regression relationships: RJ0 = 0.931 x CJ0 - 0.276 and RJ45 = 0.638 x CJ45 + 0.010, where R and C denote refractive error astigmatism and corneal astigmatism, respectively.

CONCLUSION

Our vector-based Javal's rule gives closer predictions of refractive astigmatism than the original Javal's rule and the simplified Javal's rule and can be applied in cases of corneal oblique astigmatism.