Component dependent risk factors for ocular parameters in Singapore Chinese children

Outdoor activity and myopia among primary students in rural and urban regions of Beijing

OBJECTIVE

To assess associations among outdoor activity, ocular biometric parameters, and myopia among grade 1 and grade 4 primary students in Beijing.

DESIGN

School-based, cross-sectional study.

PARTICIPANTS

A total of 382 grade 1 and 299 grade 4 children participated in the study.

METHODS

The children underwent a comprehensive eye examination, including ocular biometry by optical low-coherence reflectometry and noncycloplegic refractometry. Parents and children participated in a detailed interview, including questions on time spent indoors and outdoors.

MAIN OUTCOME MEASURES

Factors associated with myopia.

RESULTS

The study included 681 children, with 382 (56.1%) students from grade 1 (mean age, 6.3 ± 0.5 years; range, 5-8 years) and 299 students from grade 4 (mean age, 9.4 ± 0.7 years; range, 8-13 years); 370 students (54.3%) lived in the urban region. The mean daily time spent outdoors was 1.6 ± 0.8 hours (range, 0.5-5.1 hours). In multivariate analysis, axial length was significantly associated with older age (P<0.001; standardized β coefficient, 0.28), taller body height (P = 0.001; β, 0.18), maternal myopia (P = 0.03; β, 0.09), and urban region of habitation (P<0.001; β, -0.21), or alternatively to the region of habitation, with less time spent outdoors (P = 0.001; β, -0.16) and more time spent indoors studying (P = 0.02; β, 0.10). The axial length-to-corneal curvature radius ratio was associated with older age, urban region of habitation, maternal and paternal myopia, and paternal level of education. Presence of myopia (defined as refractive error ≤-1 diopters in the right eye) was associated with older age (P<0.001; odds ratio [OR], 1.45; 95% confidence interval [CI], 1.24-1.69), maternal myopia (P<0.001; OR, 2.99; 95% CI, 1.94-5.35), and urban region of habitation (P<0.001; OR, 0.17; 95% CI, 0.11-0.26), or alternatively to the region of habitation, with less time spent outdoors (P<0.001; OR, 0.32; 95% CI, 0.21-0.48) and more time spent indoors studying (P<0.001; OR, 1.38; 95% CI, 1.09-1.75).

CONCLUSIONS

Less outdoor activity, more indoor studying, older age, maternal myopia, and urban region of habitation were associated with longer ocular axial length and myopia in grade 1 and grade 4 primary school children in Greater Beijing. Remaining outdoors more (e.g., during school) may reduce the high prevalence of myopia in the young generation in Beijing.

Ocular axial length and its associations in Chinese: the Beijing Eye Study

PURPOSE

To investigate the normative data of ocular axial length and its associations in Chinese.

METHOD

The population-based Beijing Eye Study 2011 is a cross-sectional study performed in Greater Beijing. The study included 3468 individuals (1963 (56.6%) women) with a mean age of 64.6±9.8 years (range: 50-93 years). A detailed ophthalmic and medical examination was performed. Axial length was measured by optical low-coherence reflectometry.

RESULTS

Axial length measurements were available for 3159 (91.1%) study participants. Mean axial length was 23.25±1.14 mm (range: 18.96-30.88 mm). In multivariate analysis, axial length was significantly associated with the systemic parameters of higher age (P<0.001), higher body height (P = 0.003), higher level of education (P<0.001) and urban region of habitation (P<0.001), and with the ocular parameters of thicker central cornea (P = 0.001), higher corneal curvature radius (P<0.001), deeper anterior chamber (P<0.001), thicker lens (P<0.001), more myopic refractive error (P<0.001), larger pupil diameter (P = 0.018), and higher best corrected visual acuity (P<0.001). It was additionally and negatively associated with the lens vault (P<0.001). In highly myopic eyes, axial length was significantly associated with lower level of education (P = 0.008), more myopic refractive error (P<0.001), and lower best corrected visual acuity (P = 0.034).

CONCLUSIONS

Mean ocular axial length in the older adult population of Greater Beijing (23.25±1.14 mm) was similar to the value measured in other urban populations and was higher than in a rural Central Indian population. The association between axial length and older age may potentially be associated with a survival artifact. The association between axial length and body height agrees with the general association between anthropomorphic measures and eye globe size. The association with the level of education and urban region of habitation confirms with previous studies. In contrast in highly myopic eyes, axial length was negatively associated with educational level and best corrected visual acuity.

Juvenile myopia progression, risk factors and interventions

The development and progression of early onset myopia is actively being investigated. While myopia is often considered a benign condition it should be considered a public health problem for its visual, quality of life, and economic consequences. Nearly half of the visually impaired population in the world has uncorrected refractive errors, with myopia a high percent of that group. Uncorrected visual acuity should be screened for and treated in order to improve academic performance, career opportunities and socio-economic status. Genetic and environmental factors contribute to the onset and progression of myopia. Twin studies have supported genetic factors and research continues to identify myopia genetic loci. While multiple myopia genetic loci have been identified establishing myopia as a common complex disorder, there is not yet a genetic model explaining myopia progression in populations. Environmental factors include near work, education levels, urban compared to rural location, and time spent outdoors. In this field of study where there continues to be etiology controversies, there is recent agreement that children who spend more time outdoors are less likely to become myopic. Worldwide population studies, some completed and some in progress, with a common protocol are gathering both genetic and environmental cohort data of great value. There have been rapid population changes in prevalence rates supporting an environmental influence. Interventions to prevent juvenile myopia progression include pharmacologic agents, glasses and contact lenses. Pharmacological interventions over 1-2 year trials have shown benefits. Peripheral vision defocus has been found to affect the emmetropization process and may be affected by wearing glasses or contacts. Accommodation accuracy also has been implicated in myopia progression. Further research will aim to assess both the role and interaction of environmental influences and genetic factors.

Seasonal variation in myopia progression and axial elongation: an evaluation of Japanese children participating in a myopia control trial

PURPOSE

To investigate the seasonal variations in myopia progression and axial elongation in Japanese children.

METHODS

Ninety-two children who were enrolled in a myopia-control trial and wearing single vision or progressive addition lenses were included in the analyses (mean ± SD age 11.4 ± 1.7 years, mean spherical equivalent refractive error -4.40 ± 1.38 D). Refractive error and axial length were measured every 6 months for 1.5 years by non-cycloplegic autorefraction and partial coherence interferometer, respectively. Myopia progression and axial elongation for each 6-month interval were calculated by subtracting the measure at the end of the interval from that at the beginning. Seasons were classified as summer, winter or others, based on mid-day of the 6-month period between visits.

RESULTS

Myopia progression was not significantly influenced by the season. After adjusting study groups (type of spectacles), years and age at the baseline, the mean (±SE) myopia progression was 0.35 ± 0.04 D for summer, 0.28 ± 0.06 D for winter and 0.38 ± 0.04 D for the others. In contrast, axial elongation was significantly influenced by the season, and the mean axial elongation was 0.137 ± 0.010 mm for summer, 0.170 ± 0.013 mm for winter and 0.163 ± 0.008 mm for the others. The seasonal variation in axial elongation, however, was smaller than that previously reported overseas.

CONCLUSIONS

In Japanese children myopia progression did not slow in summer. Although axial elongation slightly decreased in summer, myopia progression seems to be fairly stable throughout the year.

Validity of noncycloplegic refraction in the assessment of refractive errors: the Tehran Eye Study

PURPOSE

To determine the sensitivity and specificity of noncycloplegic autorefraction for determining refractive status compared to cycloplegic autorefraction.

METHODS

The target population was noninstitutionalized citizens of all ages, residing in Tehran in 2002, selected through stratified cluster sampling. From 6497 eligible residents, 70.3% participated in the study, from August to November 2002. Here, we report data on 3501 people over the age of 5 years who had autorefraction with and without cycloplegia (two drops of cyclopentolate 1.0% 5 min apart, with autorefraction 25 min after the second drop).

RESULTS

Overall, the sensitivity of noncycloplegic autorefraction for myopia was 99%, but the specificity was only 80.4%. In contrast, the sensitivity for hyperopia was only 47.9%, but the specificity was 99.4%. At all ages, noncycloplegic autorefraction overestimated myopia and underestimated hyperopia. Overestimation of myopia was highest in the 21-30 and 31-40 year groups. Underestimation of hyperopia was high up to the age of 50 (20-40%), but decreased with age, to about 8% after the age of 50, down to almost 0% after 70. The difference in mean spherical equivalent with and without cycloplegia fell from 0.71 dioptres (D) in the 5-10 age group to 0.14D in those over 70.

CONCLUSION

Use of noncycloplegic autorefraction in epidemiological studies leads to considerable errors relative to cycloplegic measurements, except in those over 50-60. The difference between cycloplegic and noncycloplegic measurements varies with age and cycloplegic refractive category, and there is considerable individual variation, ruling out adjusting noncycloplegic measurements to obtain accurate cycloplegic refractions.

Worldwide prevalence and risk factors for myopia

BACKGROUND

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

PURPOSE

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

RECENT FINDINGS

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

CONCLUSIONS

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

The long-term results of using low-concentration atropine eye drops for controlling myopia progression in schoolchildren

PURPOSE

The purpose of this article was to evaluate the long-term efficacy of a low-concentration (LC) atropine eye drop regimen (0.05%-0.1%) for controlling myopia progression in schoolchildren.

METHODS

This retrospective, case-control study enrolled myopic schoolchildren who had been followed-up for at least 3 years from 1999 to 2007. Children who received LC doses of atropine eye drops [initial prescription 0.05%, if progression over -0.5 diopter (D) during a 6-month follow-up then changed to 0.1% atropine] every night at bedtime were included in the LC atropine group, and untreated children served as controls.

RESULTS

A total of 117 children were included in this study. The mean age was 8.4 years. There were 97 children in the LC atropine group and 20 children in the control group. The mean follow-up duration was 4.5 years. In a mixed model analysis, the adjusted myopia progression in the LC atropine group was -0.23 D/year, significantly lower than that of the control group, which was -0.86 D/year (P<0.001). About 80% of the treatment group had slow myopia progression (less than -0.5 D progression per year). In a multivariate analysis, factors such as initial spherical refraction with less myopia and treatment with LC atropine were significantly associated with less myopia progression, but age, sex, and initial astigmatism were not significantly associated (P<0.001, P<0.001, P=0.442, 0.494, and 0.547, respectively).

CONCLUSION

The results of this study demonstrate that long-term and regular instillation of LC atropine eye drops is effective for controlling myopia progression and provides a possible strategy for an initial myopia regimen.

Association of variants in FRAP1 and PDGFRA with corneal curvature in Asian populations from Singapore

Corneal curvature (CC) is a key determinant of major eye diseases, such as keratoconus, myopia and corneal astigmatism. No prior studies have discovered the genes for CC. Here we report the findings from four genome-wide association studies of CC in 10 008 samples from three population groups in Singapore. Our discovery phase surveyed 2867 Chinese and 3072 Malays, allowing us to identify two loci that were associated with CC variation: FRAP1 on chromosome 1p36.2 and PDGFRA on chromosome 4q12. These findings were subsequently replicated in a validation study involving an additional 2953 Asian Indians and a further collection of 1116 Chinese children. The effect sizes of the identified variants were consistent across all four cohorts, with seven single nucleotide polymorphisms (SNPs) in FRAP1 (lead SNP: rs17036350, meta P-value = 4.06 × 10(-13)) and six SNPs in PDGFRA (lead SNP: rs2114039, meta P-value = 1.33 × 10(-9)) attaining genome-wide significance in the SNP-based meta-analysis of the four studies. This is the first genome-wide survey of CC variation and we have identified two implicated loci in three genetically diverse Asian populations, suggesting the presence of common genetic etiology across multiple populations.

Reproducibility of ocular biometry with a new noncontact optical low-coherence reflectometer in children

PURPOSE

To evaluate the reproducibility of Lenstar in the pediatric population.

METHODS

Three consecutive measurements per eye by 2 ophthalmologists with a total of 6 measurements per eye were performed using Lenstar. Axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), and corneal curvatures (K1 and K2) were measured for right and left eyes in 154 school-age children. Right and left eyes were analyzed separately. Each optical parameter obtained by 2 examiners was compared by paired samples t test. Intraobserver and interobserver correlation coefficients (r) were calculated for each variable. Significance was attributed when p<0.05.

RESULTS

Measurements could be performed in 152 of the children included. The mean measurements were not different statistically except for left AL (23.22±0.81 vs 23.21±0.82 mm; p=0.014), left CCT (548.5±32.3 vs 548.0±32.7 µm; p=0.013), and right ACD (3.19±0.25 vs 3.19±0.25 mm; p=0.033). Intraobserver r values were all above 0.957 except for left LT (r=0.786) for examiner 2. Interobserver r values were all above 0.979.

CONCLUSIONS

Although statistical significance was obtained in some variables, they were clinically negligible. The intraobserver and interobserver relation coefficients were very high for all optical parameters including the r value for left LT for examiner 2 (r=0.786). Lenstar is a highly reproducible, user independent, and tolerable instrument for ocular biometry in the pediatric population, with no anesthesia or discomfort.

An evidence-based update on myopia and interventions to retard its progression

Myopia is the most common human eye disorder. With its increasing prevalence and earlier age-of-onset in recent birth cohorts, myopia now affects almost 33% of adults in the United States, and epidemic proportions of 85% to 90% adults in Asian cities. Unlike children in Western populations, where the prevalence of myopia is very low (less than 5%), Asian children have prevalences as high as 29% in 7-year-olds. In addition to the direct economic and social burdens of myopia, associated ocular complications may lead to substantial vision loss. This workshop summarizes the current literature regarding myopia epidemiology, genetics, animal model studies, risk factors, and clinical treatments. Published treatment strategies to retard the progression of myopia in children, such as pharmacologic agents, progressive addition lenses, and neural adaptation programs, are outlined.

Effect of dual-focus soft contact lens wear on axial myopia progression in children

PURPOSE

To test the efficacy of an experimental Dual-Focus (DF) soft contact lens in reducing myopia progression.

DESIGN

Prospective, randomized, paired-eye control, investigator-masked trial with cross-over.

PARTICIPANTS

Forty children, 11-14 years old, with mean spherical equivalent refraction (SER) of -2.71 ± 1.10 diopters (D).

METHODS

Dual-Focus lenses had a central zone that corrected refractive error and concentric treatment zones that created 2.00 D of simultaneous myopic retinal defocus during distance and near viewing. Control was a single vision distance (SVD) lens with the same parameters but without treatment zones. Children wore a DF lens in 1 randomly assigned eye and an SVD lens in the fellow eye for 10 months (period 1). Lens assignment was then swapped between eyes, and lenses were worn for a further 10 months (period 2).

MAIN OUTCOME MEASURES

Primary outcome was change in SER measured by cycloplegic autorefraction over 10 months. Secondary outcome was a change in axial eye length (AXL) measured by partial coherence interferometry over 10 months. Accommodation wearing DF lenses was assessed using an open-field autorefractor.

RESULTS

In period 1, the mean change in SER with DF lenses (-0.44 ± 0.33 D) was less than with SVD lenses (-0.69 ± 0.38 D; P < 0.001); mean increase in AXL was also less with DF lenses (0.11 ± 0.09 mm) than with SVD lenses (0.22 ± 0.10 mm; P < 0.001). In 70% of the children, myopia progression was reduced by 30% or more in the eye wearing the DF lens relative to that wearing the SVD lens. Similar reductions in myopia progression and axial eye elongation were also observed with DF lens wear during period 2. Visual acuity and contrast sensitivity with DF lenses were not significantly different than with SVD lenses. Accommodation to a target at 40 cm was driven through the central distance-correction zone of the DF lens.

CONCLUSIONS

Dual-Focus lenses provided normal acuity and contrast sensitivity and allowed accommodation to near targets. Myopia progression and eye elongation were reduced significantly in eyes wearing DF lenses. The data suggest that sustained myopic defocus, even when presented to the retina simultaneously with a clear image, can act to slow myopia progression without compromising visual function.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Nature of the refractive errors in rhesus monkeys (Macaca mulatta) with experimentally induced ametropias

We analyzed the contribution of individual ocular components to vision-induced ametropias in 210 rhesus monkeys. The primary contribution to refractive-error development came from vitreous chamber depth; a minor contribution from corneal power was also detected. However, there was no systematic relationship between refractive error and anterior chamber depth or between refractive error and any crystalline lens parameter. Our results are in good agreement with previous studies in humans, suggesting that the refractive errors commonly observed in humans are created by vision-dependent mechanisms that are similar to those operating in monkeys. This concordance emphasizes the applicability of rhesus monkeys in refractive-error studies.

Family history, near work, outdoor activity, and myopia in Singapore Chinese preschool children

AIMS

To investigate the risk factors for myopia, including near work and outdoor activity, in Singapore Chinese preschool children.

METHODS

A cross-sectional study, with disproportionate random sampling by 6-month age groups, of 3009 Singapore Chinese children aged 6-72 months was performed. Information on family history, near work and outdoor activity was obtained. Spherical equivalent refraction (SER) was assessed.

RESULTS

Children with two myopic parents were more likely to be myopic (adjusted OR=1.91; 95% CI 1.38 to 2.63) and to have a more myopic SER (regression coefficient=-0.35; 95% CI -0.47 to -0.22) than children without myopic parents. For each 1 cm taller height, the SER was more myopic by 0.01 dioptres. Neither near work nor outdoor activity was associated with preschool myopia.

CONCLUSIONS

A family history of myopia was the strongest factor associated with preschool myopia. In contrast, neither near work nor outdoor activity was found to be associated with early myopia. These data suggest that genetic factors may play a more substantial role in the development of early-onset myopia than key environmental factors.

Ocular axial length and its associations in an adult population of central rural India: the Central India Eye and Medical Study

PURPOSE

To investigate the normal distribution of axial length of the globe, which is a major measurement of the eye, and its associations with other ocular and systemic parameters.

DESIGN

Population-based study.

PARTICIPANTS

The Central India Eye and Medical Study is a population-based study performed in a rural region of central India. The study comprised 4711 subjects (aged 30+ years) of 5885 eligible individuals (response rate, 80.1%).

METHODS

A detailed ophthalmic and medical examination was performed. The axial length was measured sonographically.

MAIN OUTCOME MEASURES

Axial length.

RESULTS

Axial length measurements were available on 4698 study participants (99.7%). Their mean age was 49.4+/-13.4 years (range, 30-100 years), and the mean refractive error was -0.18+/-1.48 diopters (range, -20.0 to +7.25 diopters). Mean axial length was 22.6+/-0.91 mm (range, 18.22-34.20 mm). In multivariate analysis, axial length was significantly (P<0.001) associated with the systemic parameters of increased age, taller body height, greater body mass index, and higher level of education, and with the ocular parameters of lower best-corrected visual acuity, lower corneal refractive power, deeper anterior chamber, thicker lens, and more myopic spherical power and cylindrical refractive power. Within the highly myopic group, as defined by an axial length that exceeded 26.5 mm, none of these associations (except for the association between axial length and spherical refractive power) were statistically significant (P>0.15) in univariate or multivariate analysis.

CONCLUSIONS

In a rural population of central India, the mean ocular axial length was 22.6+/-0.91 mm, which was shorter than that of other populations. Axial length was associated with the systemic parameters of increased age, taller body height, greater body mass index, and a higher level of education, and with the ocular parameters of lower best-corrected visual acuity, lower corneal refractive power, deeper anterior chamber, thicker lens, and more myopic spherical and cylindrical refractive power. These associations were valid only for those eyes that were not highly myopic, whereas axial length was associated with refractive error only in highly myopic eyes.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Distribution of axial length and ocular biometry measured using partial coherence laser interferometry (IOL Master) in an older white population

PURPOSE

We aimed to describe norms for the distribution of axial length (AL) and other ocular biometric parameters in an older Caucasian population, measured using partial coherence laser interferometry (Zeiss IOL Master; Carl Zeiss AG, Oberkochen, Germany), a technique now routinely used in measuring AL before cataract surgery. We also aimed to assess age and gender relationships with these parameters and their correlations with spherical equivalent refraction (SER).

DESIGN

Cross-sectional analysis of the Blue Mountains Eye Study (BMES) cohort at the examinations (10-year follow-up examination).

PARTICIPANTS

From 2002 to 2004, 1952 persons (76% of surviving baseline BMES participants) aged 59 years or older had ocular biometry measured at the 10-year examinations.

METHODS

Spherical equivalent refraction was calculated as the sum of sphere +0.5 cylinder power, after protocol refraction. Measurements of AL, corneal curvature (K1), anterior chamber depth (ACD), and corneal diameter (WTW) were performed using the IOL Master. Only right phakic eyes (n = 1335) with biometry data were included.

MAIN OUTCOME MEASURES

Axial length distribution.

RESULTS

Mean AL was 23.44 mm (95% confidence interval [CI], 23.38-23.50) and was greater in men, 23.76 mm (CI, 23.68-23.84), than in women, 23.19 mm (CI, 23.11-23.27). The mean K1, ACD, and WTW were 43.42 diopters (D), 3.10 mm, and 12.06 mm, respectively. The AL and ACD distributions were both positively skewed and peaked, whereas the WTW and K1 distributions were near normal. From age 59 years or older, a mean reduction in AL with age was observed (P for trend = 0.005), 0.12 mm per decade (P = 0.0176) in women but only 0.02 mm per decade (P = 0.6319) in men. Mean SER was 0.58 D, and the distribution was peaked with a negative skew. The SER was negatively correlated with both AL (beta coefficient -0.688) and ACD (beta coefficient -0.222), but not with K1 or WTW.

CONCLUSIONS

These data provide normative values in the older general population for AL measured using the IOL Master. Axial length distribution was peaked and skewed, suggesting an active modulation process.

Can Information on the Purpose of Spectacle Use and Age at First Use Predict Refractive Error Type?

PURPOSE

To assess the sensitivity and specificity of predicting refractive error type using information from a four-item questionnaire on the purpose of spectacle use and age at first use.

METHODS

The Sydney Myopia Study examined 1,740 year 1 (78.9% response) and 2,353 year 7 students (75.3% response) from a random cluster sample of 34 primary and 21 secondary schools across Sydney. Parents of participants completed a four-item questionnaire that sought data on parental spectacle use, age at first use, and purpose of use (for clear distant vision, close work, or both). Prescriptions were obtained for 720 of 3,209 (22%) parents (73% of those approached) for validation. A receiver operating characteristic (ROC) curve was used to determine the optimal cutoff age for spectacle use in myopia classification.

RESULTS

Using the ROC curve, a cutoff age of 30 years at first spectacle use produced the highest accuracy in determining myopia. We combined information on the purpose for using spectacles (for distant and near vision) and age of first use at 30 years or younger to determine myopia, otherwise hyperopia. Validated against prescriptions, the sensitivity and specificity of these predictions were 0.89 and 0.83, respectively, for myopia. The specificity was 0.92 for hyperopia and 0.80 for astigmatism, though corresponding sensitivities were lower at 0.23 and 0.46, respectively.

CONCLUSIONS

In a sample of the parents of Sydney Myopia Study participants, information on the purpose of spectacle use with an age-at-first-use criterion can identify myopic refractive error with reasonable sensitivity and specificity. This four-item questionnaire may assist future epidemiological studies of screening for myopia.

Methods for a Population-Based Study of Myopia and Other Eye Conditions in School Children: The Sydney Myopia Study

PURPOSE

The Sydney Myopia Study will establish the prevalence of myopia and other eye diseases in a large representative sample of Sydney school children. It will also examine the relationship between myopia and potential modifiable risk factors and will assess potential gene-environment interactions by examining parents and siblings.

METHODS

The target population is a stratified random cluster sample of 1750 Year 1 (age 6 years) and 1500 Year 7 (age 12 years) students from Sydney metropolitan schools. Procedures (comprehensive parent-administered questionnaire and examination) involve standardized protocols to allow for comparison with international population-based data. Examinations include a detailed assessment of visual acuity, cover testing for strabismus, identification of amblyopia, slit-lamp examination, non-contact ocular biometry and cycloplegia (cyclopentolate) followed by autorefraction, optical coherence tomography, retinal thickness measurement, digital mydriatic retinal photography and aberrometry.

CONCLUSIONS

The Sydney Myopia Study design and methodology will ensure valid findings on ocular development and health in a large representative sample of Sydney school children, for comparison with other population-based refraction data.

Common determinants of body size and eye size in chickens from an advanced intercross line

Myopia development is characterised by an increased axial eye length. Therefore, identifying factors that influence eye size may provide new insights into the aetiology of myopia. In humans, axial length is positively correlated to height and weight, and in mice, eye weight is positively correlated with body weight. The purpose of this study was to examine the relationship between eye size and body size in chickens from a genetic cross in which alleles with major effects on eye and body size were segregating. Chickens from a cross between a layer line (small body size and eye size) and a broiler line (large body and eye size) were interbred for 10 generations so that alleles for eye and body size would have the chance to segregate independently. At 3 weeks of age, 510 chicks were assessed using in vivo high resolution A-scan ultrasonography and keratometry. Equatorial eye diameter and eye weight were measured after enucleation. The variations in eye size parameters that could be explained by body weight (BW), body length (BL), head width (HW) and sex were examined using multiple linear regression. It was found that BW, BL and HW and sex together predicted 51-56% of the variation in eye weight, axial length, corneal radius, and equatorial eye diameter. By contrast, the same variables predicted only 22% of the variation in lens thickness. After adjusting for sex, the three body size parameters predicted 45-49% of the variation in eye weight, axial length, corneal radius, and eye diameter, but only 0.4% of the variation in lens thickness. In conclusion, about half of the variation in eye size in the chickens of this broiler-layer advanced intercross line is likely to be determined by pleiotropic genes that also influence body size. Thus, mapping the quantitative trait loci (QTL) that determine body size may be useful in understanding the genetic determination of eye size (a logical inference of this result is that the 20 or more genetic variants that have recently been shown to influence human height may also be found to influence axial eye length). Furthermore, adjusting for body size will be essential in mapping pure eye size QTL in this chicken population, and may also have value in mapping eye size QTL in humans.

Do Peripheral Refraction and Aberration Profiles Vary with the Type of Myopia? - An Illustration Using a Ray-Tracing Approach

Purpose

Myopia is considered to be the most common refractive error occurring in children and young adults, around the world. Motivated to elucidate how the process of emmetropization is disrupted, potentially causing myopia and its progression, researchers have shown great interest in peripheral refraction. This study assessed the effect of the myopia type, either refractive or axial, on peripheral refraction and aberration profiles.

Methods

Using customized schematic eye models for myopia in a ray tracing algorithm, peripheral aberrations, including the refractive error, were calculated as a function of myopia type.

Results

In all the selected models, hyperopic shifts in the mean spherical equivalent (MSE) component were found whose magnitude seemed to be largely dependent on the field angle. The MSE profiles showed larger hyperopic shifts for the axial type of myopic models than the refractive ones and were evident in -4 and -6 D prescriptions. Additionally, greater levels of astigmatic component (J180) were also seen in axial-length-dependent models, while refractive models showed higher levels of spherical aberration and coma.

Conclusion

This study has indicated that myopic eyes with primarily an axial component may have a greater risk of progression than their refractive counterparts albeit with the same degree of refractive error. This prediction emerges from the presented theoretical ray tracing model and, therefore, requires clinical confirmation.

Two models of experimental myopia in the mouse

PURPOSE

The purpose of this study was to test the response of the mouse eye to two methods for the induction of experimental myopia.

METHODS

Growth patterns of eyes were determined by axial length measurements from birth to adult in eyes of both sexes of normal mice examined on post-natal day 1 to 6 months and at 1 year. For the induction of experimental myopia, Balb/cJ mice were prepared with either unilateral lid suture or by a -10D spectacle lens placed over one eye at post-natal day 10. Other mice received a plano lens as a control for lens wear. Refraction was carried out at post-natal days of 28, 42 and 56 in lid suture and spectacle lens wear group by streak retinoscopy. Axial length was measured by a combination of video image photography, digital caliper, or Optical Low Coherence Interferometry (OLCI). Corroborative optical modeling of the mouse eye was carried out using ZEMAX ray tracing software.

RESULTS

Axial length (AL) increased linearly between post-natal day 1 to day 56, plateauing at about 140 days. After 18 days of unilateral lid suture initiated 10 days after birth, the AL of experimental eyes was 3.032+/-0.003 mm, while AL in contra-lateral control eyes was 2.981+/-0.005 mm (mean+/-sem, p<0.05, n=40), after 32 days, the AL of experimental eyes was 3.290+/-0.004 mm, and the AL of control eyes was 3.104+/-0.002 mm (p<0.001, n=60). After 46 days of lid closure AL of experimental eyes was 3.592+/-0.003 mm, while AL of control eyes was 3.363+/-0.003 mm (p<0.001, n=80). Spectacle lens wear of 46 days duration increased AL in experimental eyes to 3.721+/-0.002 mm, while AL in control eyes was 3.354+/-0.003 mm (p<0.001, n=100). Refraction and ray tracing analysis substantiated the dimensional changes to be consistent with increased AL.

CONCLUSIONS

Two procedures to induce experimental myopia, initiated at eye opening, produced significant myopic shifts corresponding to increases in axial lengths after 32 and 46 days of lid suture and after 46 days wearing a -10D spectacle lens.

An intervention of acupressure and interactive multimedia to improve visual health among Taiwanese schoolchildren

OBJECTIVE

Myopia is a significant health issue but it can be alleviated and prevented by several interventions. This study aimed to construct an intervention of acupressure and interactive multimedia for visual health and to evaluate the effect of its application on schoolchildren.

DESIGN

A pre-posttest experimental research design with a control group was used. The experimental group received a 15-week visual health intervention, whereas the control group received none.

SAMPLE

70 children with visual impairment were recruited from 1 elementary school in Taipei, Taiwan.

MEASUREMENTS

The data of demographic factors, visual health knowledge, visual acuity, and refractive error were collected before and after the intervention.

RESULTS

After the intervention, the experimental group demonstrated improvements in visual health knowledge, visual acuity, and refractive error.

CONCLUSIONS

The outcomes of using the intervention seemed to be promising, but broader studies exploring its effects on children in different school years as well as its longitudinal effects are required.

A review of current approaches to identifying human genes involved in myopia

The prevalence of myopia is high in many parts of the world, particularly among the Orientals such as Chinese and Japanese. Like other complex diseases such as diabetes and hypertension, myopia is likely to be caused by both genetic and environmental factors, and possibly their interactions. Owing to multiple genes with small effects, genetic heterogeneity and phenotypic complexity, the study of the genetics of myopia poses a complex challenge. This paper reviews the current approaches to the genetic analysis of complex diseases and how these can be applied to the identification of genes that predispose humans to myopia. These approaches include parametric linkage analysis, non-parametric linkage analysis like allele-sharing methods and genetic association studies. Basic concepts, advantages and disadvantages of these approaches are discussed and explained using examples from the literature on myopia. Microsatellites and single nucleotide polymorphisms are common genetic markers in the human genome and are indispensable tools for gene mapping. High throughput genotyping of millions of such markers has become feasible and efficient with recent technological advances. In turn, this makes the identification of myopia susceptibility genes a reality.

Refractive, biometric and topographic changes among Portuguese university science students: a 3-year longitudinal study

PURPOSE

The aim of this study was to investigate the changes in refractive, biometric and topographic ocular parameters among university students in Portugal during a 3-year period.

METHODS

A 3-year longitudinal study comprised 118 Portuguese university students from the School of Science (34 males and 84 females; mean age 20.6 +/- 2.3 years). Ocular refraction, corneal curvature (CR) and eccentricity, and A-scan biometry were conducted under cycloplegia. The sphero-cylindrical refractive results were converted into vector representations (M, J(0) and J(45)) for statistical analysis. Myopia was defined as M < or = -0.50 D, emmetropia as M > -0.50 D and < +0.50 D and hyperopia as M > or = +0.50 D.

RESULTS

At the beginning of the study sphero-cylindrical refraction (M) ranged from -6.75 to +3.00 D, with a mean value of 0.23 +/- 1.46 D [mean +/- standard deviation (S.D.)]. Eighty-three students presented astigmatism with a mean value (+/-S.D.) of -0.52 +/- 0.41 D, and a maximum of -2.25 D. After 3 years the mean refractive change for the M component was -0.29 +/- 0.38 D (p < 0.001) and non-significant changes of 0.02 +/- 0.16 D (p = 0.281) for the J(0) component and 0.01 +/- 0.09 D (p = 0.784) for the J(45) component. Prevalence of myopia increased by 5.1%, while the prevalence of hyperopia decreased by 9.4%. Myopia progression > or =0.5 D was observed in 22% of the population. Axial length, vitreous chamber depth and lens thickness increased significantly while anterior chamber depth and central CR did not change significantly.

CONCLUSIONS

This study shows a change in refraction towards myopia accompanied by a vitreous chamber elongation in a Portuguese population comprising science students during the first three years of their university course. Younger students were more likely to show clinically significant myopia progression.

Eye growth changes in myopic children in Singapore

AIMS

To assess the longitudinal changes in biometric parameters and associated factors in young myopic children aged 7--9 years followed prospectively in Singapore.

METHODS

Children aged 7--9 years from three Singapore schools were invited to participate in the SCORM (Singapore Cohort study Of the Risk factors for Myopia) study. Yearly eye examinations involving biometry measures were performed in the schools. Only myopic children (n=543) with 3 year follow up data were included in this analysis.

RESULTS

The 3 year increases in axial length, anterior chamber depth, lens thickness, vitreous chamber depth, and corneal curvature were 0.89 mm, -0.02 mm, -0.01 mm, 0.92 mm, and 0.01 mm, respectively. Children who were younger, female, and who had a parental history of myopia were more likely to have greater increases in axial length. After adjustment for school, age, sex, race, parental myopia and reading in books per week, the age (p<0.001), sex (p=0.012), and parental myopia (p=0.027) remained significantly associated with the 3 year change in axial length. Reading in books per week, however, was not associated with axial length change. Children with faster rates of progression of myopia had greater increases in axial length (Pearson correlation coefficient (r)=-0.69) and vitreous chamber depth (r=-0.83).

CONCLUSIONS

The 3 year change in axial length of Singapore children aged 7--9 years at baseline was high and greater in younger children, females, and children with a parental history of myopia. Myopia progression was driven largely by vitreous chamber depth increase.

Refractive error and ocular biometry in Jordanian adults

The aim of this study was to establish the prevalence of refractive errors in Jordanian adults of working age, and to study the ocular biometric correlates of refractive error in this population. Refractive error and ocular biometry were measured in 1093 Jordanian adult subjects aged 17-40 years to determine the prevalence of refractive error, and explore structural correlations of ametropia. Refractive error was measured using a Grand-Seiko GR-3100K closed-view infrared autorefractor. Ocular component measurements were made using A-scan ultrasonography and autokeratometry. The prevalence of myopia [spherical equivalent refraction (SER) less than -0.50 DS] and hyperopia (SER greater than +0.50 DS) was 53.71 and 5.67% respectively; 40.62% of the sample was emmetropic (refraction between +0.50 D and -0.50 D inclusive in both principal meridians). The distribution of SER was found to show marked leptokurtosis, exhibiting a peak between plano and 1 D of myopia. Corneal radius, anterior chamber depth, crystalline lens thickness, vitreous chamber depth and axial length (AL) parameters were normally distributed in the population studied. AL to corneal curvature ratio was not normally distributed, and showed marked leptokurtosis. Linear regression analysis showed that AL correlated most closely with spherical equivalent refractive error. This study has established a database of refractive error prevalence and ocular biometric correlates of ametropia in a Middle Eastern population of working age.

Heritability of refractive error and familial aggregation of myopia in an elderly American population

PURPOSE

To determine the heritability of refractive error and the familial aggregation of myopia in an older population.

METHODS

Seven hundred fifty-nine siblings (mean age, 73.4 years) in 241 families were recruited from the Salisbury Eye Evaluation (SEE) Study in eastern Maryland. Refractive error was determined by noncycloplegic subjective refraction (if presenting distance visual acuity was < or =20/40) or lensometry (if best corrected visual acuity was >20/40 with spectacles). Participants were considered plano (refractive error of zero) if uncorrected visual acuity was >20/40. Preoperative refraction from medical records was used for pseudophakic subjects. Heritability of refractive error was calculated with multivariate linear regression and was estimated as twice the residual between-sibling correlation after adjusting for age, gender, and race. Logistic regression models were used to estimate the odds ratio (OR) of myopia, given a myopic sibling relative to having a nonmyopic sibling.

RESULTS

The estimated heritability of refractive error was 61% (95% confidence interval [CI]: 34%-88%) in this population. The age-, race-, and sex-adjusted ORs of myopia were 2.65 (95% CI: 1.67-4.19), 2.25 (95% CI: 1.31-3.87), 3.00 (95% CI: 1.56-5.79), and 2.98 (95% CI: 1.51-5.87) for myopia thresholds of -0.50, -1.00, -1.50, and -2.00 D, respectively. Neither race nor gender was significantly associated with an increased risk of myopia.

CONCLUSIONS

Refractive error and myopia are highly heritable in this elderly population.

School vision screening, ages 5-16 years: the evidence-base for content, provision and efficacy

The optometric profession in the UK has a major role in the detection, assessment and management of ocular anomalies in children between 5 and 16 years of age. The role complements a variety of associated screening services provided across several health care sectors. The review examines the evidence-base for the content, provision and efficacy of these screening services in terms of the prevalence of anomalies such as refractive error, amblyopia, binocular vision and colour vision and considers the consequences of their curtailment. Vision screening must focus on pre-school children if the aim of the screening is to detect and treat conditions that may lead to amblyopia, whereas if the aim is to detect and correct significant refractive errors (not likely to lead to amblyopia) then it would be expedient for the optometric profession to act as the major provider of refractive (and colour vision) screening at 5-6 years of age. Myopia is the refractive error most likely to develop during primary school presenting typically between 8 and 12 years of age, thus screening at entry to secondary school is warranted. Given the inevitable restriction on resources for health care, establishing screening at 5 and 11 years of age, with exclusion of any subsequent screening, is the preferred option.

Screening for correctable visual acuity deficits in school-age children and adolescents

BACKGROUND

Although the benefits of vision screening seem intuitive, the value of such programmes in junior and senior schools has been questioned. In addition to this there exists a lack of clarity regarding the optimum age, and frequency at which to carry out screening.

OBJECTIVES

The objective of this review is to evaluate the effectiveness of vision screening programmes carried out in schools in reducing the prevalence of undetected, correctable visual acuity deficits due to refractive error in school-age children.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials - CENTRAL (which contains the Cochrane Eyes and Vision Trials Register) on The Cochrane Library (Issue 3 2004), MEDLINE (1966 to August 2004) and EMBASE (1980 to August 2004). No language or date restrictions were placed on these searches. To date it has not been possible to carry out any manual searches but it is hoped to include these in a future update.

SELECTION CRITERIA

We planned to include randomised controlled trials including randomised cluster controlled trials.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed study abstracts identified by the electronic searches. No trials were identified that met the inclusion criteria.

MAIN RESULTS

As no trials were identified, no formal analysis was performed. A narrative synthesis of other retrieved studies was undertaken in order to explain current practice.

AUTHORS' CONCLUSIONS

At present there are no robust trials available that allow the benefits of school vision screening to be measured. The disadvantage of attending school with a visual acuity deficit also needs to be quantified. The impact of a screening programme will depend on the geographical, and socio-economic setting in which it is conducted. There is therefore clearly a need for well planned randomised controlled trials, in various settings, to be undertaken so that the potential benefits and harms of vision screening can be measured.

Ocular refraction: heritability and genome-wide search for eye morphometry traits in an isolated Sardinian population

No genes influencing oculometric phenotypes have yet been identified, despite it being well known that eye morphometry is involved in refraction and that genetics may play an important role. We have therefore performed a heritability analysis and genome-wide search (GWS) of biometric ocular traits in an isolated Sardinian population, assessing the genetic contribution and identifying the associated genetic loci. A complete eye examination including refraction and ocular biometry measurements such as axial length (AL), anterior chamber depth (ACD) and corneal curvature (CC), was performed on 789 subjects. Heritability analysis was carried out by means of parent-offspring regression and variance component models. Univariate and bivariate linkage analysis was performed by using 654 microsatellite markers spanning the genome. CC showed a mean heritability of 57%. AL and ACD were found to have significantly different variances (P<0.01) in males and females, so that heritability was calculated separately for each sex. AL had an estimated heritability in females of 31% and in males of 60%, whereas ACD had an estimated heritability of 47% in females and of 44% in males. In the GWS, the most suggestive evidence of linkage was identified on chromosome 2 for AL (LOD 2.64), on chromosome 1 for ACD (LOD 2.32) and on chromosomes 7, 2 and 3 for CC (LOD 2.50, 2.44 and 2.34, respectively). High heritability of eye morphometry traits was thus revealed. The identified loci are the first linkage signals available in ocular biometry. Notably, the observed significant differences in parental transmission deserve further study.

Repeatability of IOLMaster Biometry in Children

AIMS

This study compares the repeatability of IOLMaster (Zeiss, Oberkochen, Germany) axial dimension measurements and conventional ultrasonography in children.

METHODS

A series of IOLMaster (partial coherence interferometry, optical pachometry) and Echoscan (US 800, Nidek, Tokyo, Japan) (ultrasound) measurements were taken on 179 Chinese children (mean age, 10.6 +/- 0.8 years) taking part in a longitudinal study of myopia development, and the measurements were repeated on 37 of these subjects.

RESULTS

IOLMaster axial length measurements showed better repeatability (95% limits of agreement for repeatability, -0.047 to 0.038 mm) than Echoscan axial length measurements (95% limits of agreement for repeatability, -0.85 to 0.67 mm). IOLMaster anterior chamber depth measurements also showed better repeatability (95% limits of agreement for repeatability, -0.053 to 0.073 mm) than Echoscan anterior chamber depth measurements (95% limits of agreement for repeatability, -0.57 to 0.49 mm). IOLMaster measurements were, on average, slightly larger than Echoscan measurements for axial length (by 0.14 mm) and anterior chamber depth (0.09 mm).

CONCLUSION

Partial coherence interferometry techniques, such as that used by IOLMaster, should be considered as the standard technique for axial length measurement in children because they are noninvasive, highly precise, and easy to use.

Childhood myopia and parental smoking

AIM

To examine the relation between exposure to passive parental smoke and myopia in Chinese children in Singapore.

METHODS

1334 Chinese children from three schools in Singapore were recruited, all of whom were participants in the Singapore Cohort study Of the Risk factors for Myopia (SCORM). Information on whether the father or mother smoked, number of years smoked, and the number of cigarettes smoked per day during the child's lifetime were derived. These data were correlated with contemporaneously obtained data available in SCORM. The children's cycloplegic autorefraction, corneal curvature radius, and biometry measures were compared with reported parental smoking history.

RESULTS

There were 434 fathers (33.3%) and 23 mothers (1.7%) who smoked during their child's lifetime. There were no significant trends observed between paternal smoking and refractive error or axial length. After controlling for age, sex, school, mother's education, and mother's myopia, children with mothers who had ever smoked during their lifetime had more "positive" refractions (adjusted mean -0.28 D v -1.38 D) compared with children whose mother did not smoke (p = 0.012).

CONCLUSIONS

The study found no consistent evidence of association between parental smoking and refractive error. There was a suggestion that children whose mothers smoked cigarettes had more hyperopic refractions, but the absence of a relation with paternal smoking and the small number of mothers who smoked in this sample preclude definite conclusions about a link between passive smoking exposure and myopia.

Myopia: precedents for research in the twenty-first century

The myopic eye is generally considered to be a vulnerable eye and, at levels greater than 6 D, one that is especially susceptible to a range of ocular pathologies. There is concern therefore that the prevalence of myopia in young adolescent eyes has increased substantially over recent decades and is now approaching 10-25% and 60-80%, respectively, in industrialized societies of the West and East. Whereas it is clear that the major structural correlate of myopia is longitudinal elongation of the posterior vitreous chamber, other potential correlates include profiles of lenticular and corneal power, the relationship between longitudinal and transverse vitreous chamber dimensions and ocular volume. The most potent predictors for juvenile-onset myopia continue to be a refractive error </=+0.50 D at 5 years of age and family history. Significant and continuing progress is being made on the genetic characteristics of high myopia with at least four chromosomes currently identified. Twin studies and genetic modelling have computed a heritability index of at least 80% across the whole ametropic continuum. The high index does not, however, preclude an environmental precursor, sustained near work with high cognitive demand being the most likely. The significance of associations between accommodation, oculomotor dysfunction and human myopia is equivocal despite animal models that have demonstrated that sustained hyperopic defocus can induce vitreous chamber growth. Recent optical and pharmaceutical approaches to the reduction of myopia progression in children are likely precedents for future research, for example progressive addition spectacle lens trials and the use of the topical M1 muscarinic antagonist pirenzepine.