The use of rapid, small-scale column tests to determine the efficiency of bauxite residue as a low-cost adsorbent in the removal of dissolved reactive phosphorus from agricultural waters.

Bauxite residue, the by-product produced in the alumina industry, is a potential low-cost adsorbent in the removal of phosphorus (P) from aqueous solution, due to its high composition of residual iron oxides such as hematite. Several studies have investigated the performance of bauxite residue in removing P; however, the majority have involved the use of laboratory "batch" tests, which may not accurately estimate its actual performance in filter systems. This study investigated the use of rapid, small-scale column tests to predict the dissolved reactive phosphorus (DRP) removal capacity of bauxite residue when treating two agricultural waters of low (forest run-off) and high (dairy soiled water) phosphorus content. Bauxite residue was successful in the removal of DRP from both waters, but was more efficient in treating the forest run-off. The estimated service time of the column media, based on the largest column studied, was 1.08 min g-1 media for the forest run-off and 0.28 min g-1 media for the dairy soiled water, before initial breakthrough time, which was taken to be when the column effluent reached approximately 5% of the influent concentration, occurred. Metal(loid) leaching from the bauxite residue, examined using ICP-OES, indicated that aluminium and iron were the dominant metals present in the treated effluent, both of which were above the EPA parametric values (0.2 mg L-1 for both Al and Fe) for drinking water.

Conjunctival ultraviolet autofluorescence area, but not intensity, is associated with myopia.

BACKGROUND: Conjunctival ultraviolet autofluorescence (CUVAF) has been used as a biomarker of time spent outdoors. Smaller CUVAF area is associated with myopia in southern hemisphere cohorts. Further research is required to determine if this association is replicated in northern latitudes and whether average CUVAF intensity is a valuable metric. This prospective study explored the association between myopia, CUVAF (area and intensity) and additional indicators of sun exposure (vitamin D3 and self-reported sun exposure preferences) across seasons at a location of 55° north. METHODS: Young adults (age 18-20) provided blood samples biannually (March/April and September/October) over an 18-month period (four phases) for the assessment of 25-hydroxyvitamin D (25(OH)D3 ) concentrations (liquid chromatography-tandem mass spectrometry). CUVAF (total area, average intensity) and self-reported sun exposure preferences were recorded at each phase. Axial length and corneal radius were measured. Refractive error was measured by autorefractor and spherical equivalent refraction used to classify participants into refractive groups: myopic (spherical equivalent refraction ≤ -0.50 DS) or non-myopic. RESULTS: Fifty-four participants (24 myopes, 30 non-myopes) participated. CUVAF area was negatively associated with the presence of myopia (odds ratio = 0.94, 95 per cent confidence interval = 0.90-0.98, p = 0.002). Myopes = 4.5 mm2 (interquartile range [IQR] 0.95-6.4 mm2 ), non-myopes = 7.0 mm2 (IQR = 2.0-10.7 mm2 ). No significant association was found between CUVAF intensity and refractive group (p = 0.17). There was no significant association between sun exposure preferences or serum concentration of 25(OH)D3 and refractive status (all p ≥ 0.21). CUVAF measures were not associated with ocular biometry measures (all p ≥ 0.084). CUVAF area was unaffected by season (all p ≥ 0.45) and variations in CUVAF area over the study period did not exceed the repeatability of the measurement technique. CONCLUSION: Myopia was associated with smaller areas of CUVAF indicative of less cumulative ultraviolet-B exposure. These findings suggest that CUVAF measures are a useful, non-invasive biomarker of the time spent outdoors in adults in northern hemisphere populations.

Re-using bauxite residues: benefits beyond (critical raw) material recovery.

Since the world economy has been confronted with an increasing risk of supply shortages of critical raw materials (CRMs), there has been a major interest in identifying alternative secondary sources of CRMs. Bauxite residues from alumina production are available at a multi-million tonnes scale worldwide. So far, attempts have been made to find alternative re-use applications for bauxite residues, for instance in cement / pig iron production. However, bauxite residues also constitute an untapped secondary source of CRMs. Depending on their geological origin and processing protocol, bauxite residues can contain considerable amounts of valuable elements. The obvious primary consideration for CRM recovery from such residues is the economic value of the materials contained. However, there are further benefits from re-use of bauxite residues in general, and from CRM recovery in particular. These go beyond monetary values (e.g. reduced investment / operational costs resulting from savings in disposal). For instance, benefits for the environment and health can be achieved by abatement of tailing storage as well as by reduction of emissions from conventional primary mining. Whereas certain tools (e.g. life-cycle analysis) can be used to quantify the latter, other benefits (in particular sustained social and technological development) are harder to quantify. This review evaluates strategies of bauxite residue re-use / recycling and identifies associated benefits beyond elemental recovery. Furthermore, methodologies to translate risks and benefits into quantifiable data are discussed. Ultimately, such quantitative data are a prerequisite for facilitating decision-making regarding bauxite residue re-use / recycling and a stepping stone towards developing a zero-waste alumina production process. © 2018 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Myopes have significantly higher serum melatonin concentrations than non-myopes.

PURPOSE: Experimental animal models of myopia demonstrate that higher melatonin (Mel) and lower dopamine (DA) concentrations actively promote axial elongation. This study explored the association between myopia and serum concentrations of DA and Mel in humans. METHODS: Morning serum concentrations of DA and Mel were measured by solid phase extraction-liquid chromatography-tandem mass spectrometry from 54 participants (age 19.1 ± 0.81 years) in September/October 2014 (phase 1) and March/April 2016 (phase 2). Axial length (AL), corneal radii (CR) and spherical equivalent refraction (SER) were also recorded. Participants were defined as myopic if non-cycloplegic spherical equivalent refractive error ≤-0.50 DS at phase 1. RESULTS: Nine participants were lost to follow up. Mel concentrations were measurable for all myopes (phase 1 n = 25, phase 2 n = 22) and non-myopes (phase 1 n = 29, phase 2 n = 23). SER did not change significantly between phases (p = 0.51). DA concentrations were measurable for fewer myopes (phase 1 n = 13, phase 2 n = 12) and non-myopes (phase 1 n = 23, phase 2 n = 16). Myopes exhibited significantly higher Mel concentrations than non-myopes at phase 1 (Median difference: 10 pg mL-1 , p < 0.001) and at phase 2 (Median difference: 7.3 pg mL-1 , p < 0.001) and lower DA concentrations at phase 2 (Median difference: 4.7 pg mL-1 , p = 0.006). Mel concentrations were positively associated with more negative SER (all r ≥ -0.53, all p < 0.001), longer AL (all r ≥ 0.37, all p ≤ 0.008) and higher AL/CR ratio (all r ≥ 0.51, all p < 0.001). CONCLUSION: This study reports for the first time in humans that myopes exhibit higher serum Mel concentrations than non-myopes. This may indicate a role for light exposure and circadian rhythm in the human myopic growth mechanism. Further research should focus on younger cohorts exhibiting more dynamic myopic progression and explore the profile of these neurochemicals alongside evaluation of sleep patterns in myopic and non-myopic groups.

The use of conjunctival ultraviolet autofluorescence (CUVAF) as a biomarker of time spent outdoors.

PURPOSE: Conjunctival ultraviolet autofluorescence (CUVAF) has been used in previous Southern Hemisphere myopia research as a marker for time spent outdoors. The validity of CUVAF as an indicator of time spent outdoors is yet to be explored in the Northern Hemisphere. It is unclear if CUVAF represents damage attributed to UV exposure or dry eye. This cross-sectional study investigated the association between CUVAF measures, self-reported time spent outdoors and measures of dry eye. METHODS: Participants were recruited from University staff and students (n = 50, 19-64 years; mean 41). None were using topical ocular medications (with the exception of dry eye treatments). Sun exposure and dry eye questionnaires (Ocular Surface Disease Index and McMonnies) were completed by the participant. Dryness was also assessed using slit lamp biomicroscopy and invasive tear break up time. Images of the temporal and nasal conjunctiva from the right and left eye were captured using a bespoke photography system. The total CUVAF area, average CUVAF pixel intensity per mm(2) and total CUVAF pixel intensity were analysed using MATLAB R2013a (The MathWorks Inc). RESULTS: Of the 50 participants, 42% were classified as having dry eye. Self-reported sunglasses use was negatively associated with all CUVAF measures (Kruskal Wallis total CUVAF area, p = 0.04, ptrend  = 0.03, average CUVAF pixel intensity p = 0.02, ptrend  = 0.02, total CUVAF pixel intensity: p = 0.04, ptrend  = 0.02). Time spent outdoors was positively associated with all CUVAF measures (Spearman's correlation coefficients, total CUVAF area: r = 0.37, p = 0.01, average CUVAF pixel intensity: r = 0.36, p = 0.01, total CUVAF pixel intensity: r = 0.37, p = 0.01) and remained significant when sunglasses use was controlled for (partial correlation, total CUVAF area: r = 0.32, p = 0.03, average CUVAF pixel intensity: r = 0.39, p = 0.01, total CUVAF pixel intensity: r = 0.39, p = 0.03). Neither CUVAF area nor intensity measures were associated with any dry eye measure (Ocular Surface Disease Index: all p ≥ 0.41, corneal staining: all p ≥ 0.38, McMonnies: all r ≤ 0.09 all p ≥ 0.52, slit lamp biomicroscopy: all r ≤ 0.20 all p ≥ 0.17, invasive tear break up time: all r ≤ -0.07 all p ≥ 0.31). CONCLUSIONS: CUVAF area and intensity were not associated with clinical measures of dry eye. Greater CUVAF area and intensity were associated with wearing sunglasses less frequently and spending more time outdoors. If sunglass wear is accounted for, CUVAF may be a useful biomarker of time spent outdoors in future myopia studies.

Six Year Refractive Change among White Children and Young Adults: Evidence for Significant Increase in Myopia among White UK Children.

OBJECTIVE: To determine six-year spherical refractive error change among white children and young adults in the UK and evaluate differences in refractive profiles between contemporary Australian children and historical UK data. DESIGN: Population-based prospective study. PARTICIPANTS: The Northern Ireland Childhood Errors of Refraction (NICER) study Phase 1 examined 1068 children in two cohorts aged 6-7 years and 12-13 years. Prospective data for six-year follow-up (Phase 3) are available for 212 12-13 year olds and 226 18-20 year olds in each cohort respectively. METHODS: Cycloplegic refractive error was determined using binocular open-field autorefraction (Shin-Nippon NVision-K 5001, cyclopentolate 1%). Participants were defined by spherical equivalent refraction (SER) as myopic SER ≤-0.50D, emmetropic -0.50D

The Changing Profile of Astigmatism in Childhood: The NICER Study.

PURPOSE: We performed a prospective study of the changing profile of astigmatism in white school children in Northern Ireland. METHODS: Of the 399 6- to 7-year-old and 669 12- to 13-year-old participants in Phase 1 of the Northern Ireland Childhood Errors of Refraction (NICER) study, 302 (76%) of the younger and 436 (65%) of the older cohort were re-examined three years later (Phase 2). Stratified random cluster sampling was used. Following cycloplegia (cyclopentolate HCl 1%) refractive error was recorded by the Shin-Nippon-SRW-5000 autorefractor. Astigmatism is defined as ≥ 1.00 diopters cylinder (DC). Right eye data only are presented. RESULTS: The prevalence of astigmatism was unchanged in both cohorts: younger cohort 17.1% (95% confidence intervals [CIs], 13.3-21.6) were astigmatic at 9 to 10 years compared to 22.9% (95% CIs, 18.3-28.2) at 6 to 7 years; older cohort, 17.5% (95% CIs, 13.9-21.7) of participants were astigmatic at 15-16 years compared to 18.4% (95% CIs, 13.4-24.8) at age 12 to 13 years. Although prevalence remained unchanged, it was not necessarily the same children who had astigmatism at both phases. Some lost astigmatism (10.0%; CIs, 7.5-13.3 younger cohort and 17.4%; CIs, 13.5-22.2 older cohort); others became astigmatic (9.1%; CIs, 6.7-12.2 younger cohort and 11.6%; CIs, 8.4-15.8 older cohort). CONCLUSIONS: This study presents novel data demonstrating that the astigmatic error of white children does not remain stable throughout childhood. Although prevalence of astigmatism is unchanged between ages 6 and 7 to 15 to 16 years; during this time period individual children are developing astigmatism while other children become nonastigmatic. It is difficult to predict from their refractive data who will demonstrate these changes, highlighting the importance of all children having regular eye examinations to ensure that their visual requirements are met.

Risk Factors for Childhood Myopia: Findings From the NICER Study.

PURPOSE: We explored risk factors for myopia in 12- to 13-year-old children in Northern Ireland (NI). METHODS: Stratified random sampling was performed to obtain representation of schools and children. Cycloplegia was achieved using cyclopentolate hydrochloride 1%. Distance autorefraction was measured using the Shin-Nippon SRW-5000 device. Height and weight were measured. Parents and children completed a questionnaire, including questions on parental history of myopia, sociodemographic factors, childhood levels of near vision, and physical activity to identify potential risk factors for myopia. Myopia was defined as spherical equivalent ≤-0.50 diopters (D) in either eye. RESULTS: Data from 661 white children aged 12- to 13-years showed that regular physical activity was associated with a lower estimated prevalence of myopia compared to sedentary lifestyles (odds ratio [OR] = 0.46 adjusted for age, sex, deprivation score, family size, school type, urbanicity; 95% confidence interval [CI], 0.23-0.90; P for trend = 0.027). The odds of myopia were more than 2.5 times higher among children attending academically-selective schools (adjusted OR = 2.66; 95% CI, 1.48-4.78) compared to nonacademically-selective schools. There was no evidence of an effect of urban versus nonurban environment on the odds of myopia. Compared to children with no myopic parents, children with one or both parents being myopic were 2.91 times (95% CI, 1.54-5.52) and 7.79 times (95% CI, 2.93-20.67) more likely to have myopia, respectively. CONCLUSIONS: In NI children, parental history of myopia and type of schooling are important determinants of myopia. The association between myopia and an environmental factor, such as physical activity levels, may provide insight into preventive strategies.

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

PURPOSE: To assess the validity of questionnaire use in the self-identification of refractive status. METHODS: Two hundred and forty adults (21-60 years of age) presenting for a routine eye examination at various optometric practices in Northern Ireland were asked to complete one of two questionnaires. Both questionnaires used identical questions to ascertain age, gender, current spectacle use, age of first spectacle use and level of education. For the identification of refractive status, Questionnaire 1 used layman's terminology whilst Questionnaire 2 combined optometric terminology with descriptive explanations. Current refractive status was identified by the examining optometrist who did not see the completed questionnaire. The spherical equivalent refractive error of the non-cycloplegic subjective refraction was used to categorise myopia as <0D and hyperopia as ≥+1.00D. Astigmatism was defined according to two different criteria: ≥0.50DC and ≥1.00DC. RESULTS: Questionnaire 1 had a sensitivity of 0.63 and a specificity of 0.90 for identifying myopia; a sensitivity of 0.58 and a specificity of 0.71 for identifying hyperopia; a sensitivity of 0.12 and a specificity of 0.98 for identifying astigmatism ≥0.50DC and a sensitivity of 0.19 and a specificity of 0.95 for identifying astigmatism ≥1.00DC. Questionnaire 2 had a sensitivity of 0.83 and a specificity of 0.93 for identifying myopia; a sensitivity of 0.45 and a specificity of 0.86 for identifying hyperopia; a sensitivity of 0.32 and a specificity of 0.88 for identifying astigmatism ≥0.50DC and a sensitivity of 0.50 and a specificity of 0.84 for identifying astigmatism ≥1.00DC. For both questionnaires, altering a positive self-identification of myopia to include only those who had worn spectacles prior to age 30 reduced the sensitivity and increased the specificity slightly. CONCLUSIONS: Questionnaires are a valid tool in self-identification of myopic refractive status. However, they are not an effective way of identifying hyperopia and astigmatism and objective or subjective refraction remains the most appropriate method of identifying such individuals.

A prospective study of spherical refractive error and ocular components among Northern Irish schoolchildren (the NICER study).

PURPOSE: To explore 3-year change in spherical refractive error and ocular components among white Northern Irish schoolchildren. METHODS: Baseline data were collected among 6- to 7-year-old and 12- to 13-year-old children. Three years after baseline, follow-up data were collected. Cycloplegic refractive error and ocular components measurements (axial length [AL], anterior chamber depth [ACD], corneal radius of curvature [CRC]) were determined using binocular open-field autorefraction and ocular biometry. Change in spherical equivalent refractive error (SER) and ocular components were calculated. RESULTS: A statistically significantly greater change in SER was found between 6 to 7 years and 9 to 10 years (younger cohort) compared to between 12 to 13 years and 15 to 16 years (older cohort) (-0.38 diopter [D] and -0.13 D, respectively) (P<0.001). A statistically significantly greater change in AL was found among the younger compared to the older cohort (0.48 mm and 0.14 mm, respectively) (P<0.001). Change in ACD was minimal across both groups (0.12 mm younger and 0.05 mm older cohort) as were changes in CRC. Change in SER was associated with change in AL in both age groups (both P<0.01). CONCLUSIONS: There is a greater change in both spherical refractive error and axial length in younger children when compared with teenagers. Although increase in axial length drives refractive change during childhood and teenage years, lens compensation continues to occur in an attempt to maintain emmetropia. White children living in Northern Europe demonstrate dramatically less change in spherical refractive error over a fixed period of time than their East Asian counterparts. In contrast, they appear to exhibit more rapid myopic progression than UK children studied in the mid-20th century.

Profile of anisometropia and aniso-astigmatism in children: prevalence and association with age, ocular biometric measures, and refractive status.

PURPOSE: We describe the profile and associations of anisometropia and aniso-astigmatism in a population-based sample of children. METHODS: The Northern Ireland Childhood Errors of Refraction (NICER) study used a stratified random cluster design to recruit a representative sample of children from schools in Northern Ireland. Examinations included cycloplegic (1% cyclopentolate) autorefraction, and measures of axial length, anterior chamber depth, and corneal curvature. χ(2) tests were used to assess variations in the prevalence of anisometropia and aniso-astigmatism by age group, with logistic regression used to compare odds of anisometropia and aniso-astigmatism with refractive status (myopia, emmetropia, hyperopia). The Mann-Whitney U test was used to examine interocular differences in ocular biometry. RESULTS: Data from 661 white children aged 12 to 13 years (50.5% male) and 389 white children aged 6 to 7 years (49.6% male) are presented. The prevalence of anisometropia ≥1 diopters sphere (DS) did not differ statistically significantly between 6- to 7-year-old (8.5%; 95% confidence interval [CI], 3.9-13.1) and 12- to 13-year-old (9.4%; 95% CI, 5.9-12.9) children. The prevalence of aniso-astigmatism ≥1 diopters cylinder (DC) did not vary statistically significantly between 6- to 7-year-old (7.7%; 95% CI, 4.3-11.2) and 12- to 13-year-old (5.6%; 95% CI, 0.5-8.1) children. Anisometropia and aniso-astigmatism were more common in 12- to 13-year-old children with hyperopia ≥+2 DS. Anisometropic eyes had greater axial length asymmetry than nonanisometropic eyes. Aniso-astigmatic eyes were more asymmetric in axial length and corneal astigmatism than eyes without aniso-astigmatism. CONCLUSIONS: In this population, there is a high prevalence of axial anisometropia and corneal/axial aniso-astigmatism, associated with hyperopia, but whether these relations are causal is unclear. Further work is required to clarify the developmental mechanism behind these associations.

Comparison of refraction and ocular biometry in European Caucasian children living in Northern Ireland and Sydney, Australia.

PURPOSE: To compare refraction and ocular biometry in European Caucasian children aged 6 to 7 years and 12 to 13 years, living in Sydney, Australia, and Northern Ireland. METHODS: All children had a comprehensive eye examination, including cycloplegic (cyclopentolate 1%) autorefraction and ocular biometry. Hyperopia was defined as a right spherical equivalent refraction (SER) of ≥+2.00 diopters (D), myopia as ≤-0.50 D, and astigmatism as a cylindrical error of ≥1.00 D. RESULTS: The mean SER was similar at age 6 to 7 years (P = 0.9); however, at 12 to 13 years, children in Northern Ireland had a significantly less hyperopic mean SER (+0.66 D) than children in Sydney (+0.83 D, P = 0.008). The prevalence of myopia, hyperopia, and astigmatism was significantly greater in Northern Ireland than Sydney at both ages (all P < 0.03). The distribution of refraction was highly leptokurtic in both samples, but less so in Northern Ireland (kurtosis: 6-7 years of age, 7.2; 12-13 years of age, 5.9) than Sydney (kurtosis: 6-7 years of age, 15.0; 12-13 years of age, 19.5). CONCLUSIONS: European Caucasian children in Northern Ireland have a greater prevalence of myopia, hyperopia, and astigmatism when compared to children living in Sydney. Risk factors for myopia such as parental myopia, parental education, and educational standards do not appear to explain the differences. Further work on levels of near work and time spent outdoors is required.

Visual acuity measures do not reliably detect childhood refractive error--an epidemiological study.

PURPOSE: To investigate the utility of uncorrected visual acuity measures in screening for refractive error in white school children aged 6-7-years and 12-13-years. METHODS: The Northern Ireland Childhood Errors of Refraction (NICER) study used a stratified random cluster design to recruit children from schools in Northern Ireland. Detailed eye examinations included assessment of logMAR visual acuity and cycloplegic autorefraction. Spherical equivalent refractive data from the right eye were used to classify significant refractive error as myopia of at least 1DS, hyperopia as greater than +3.50DS and astigmatism as greater than 1.50DC, whether it occurred in isolation or in association with myopia or hyperopia. RESULTS: Results are presented from 661 white 12-13-year-old and 392 white 6-7-year-old school-children. Using a cut-off of uncorrected visual acuity poorer than 0.20 logMAR to detect significant refractive error gave a sensitivity of 50% and specificity of 92% in 6-7-year-olds and 73% and 93% respectively in 12-13-year-olds. In 12-13-year-old children a cut-off of poorer than 0.20 logMAR had a sensitivity of 92% and a specificity of 91% in detecting myopia and a sensitivity of 41% and a specificity of 84% in detecting hyperopia. CONCLUSIONS: Vision screening using logMAR acuity can reliably detect myopia, but not hyperopia or astigmatism in school-age children. Providers of vision screening programs should be cognisant that where detection of uncorrected hyperopic and/or astigmatic refractive error is an aspiration, current UK protocols will not effectively deliver.

Cup-to-disc and arteriole-to-venule ratios in children aged 6-7 and 12-13 years.

PURPOSE: Little data exist detailing the normal cup-to-disc (CD) ratios and arteriole-to-venule (A/V) ratios of school age children. In addition, controversy exists in the literature regarding associations between CD and A/V ratios and visual and biometric parameters. The present study investigates the success rates of obtaining useable optic disc images from the portable Nidek Handheld Non-Mydriatic Fundus Camera (NM-200D) from school-age children and describes the distribution of CD ratios and A/V ratios in children aged 6-7 years of age and 12-13 years of age. In addition, the present study explores associations between CD and A/V ratios and a range of visual function and biometric parameters in children. METHODS: Fundus images were obtained from 195 6-7 year old children and 227 12-13 year old children participating in a wider study of visual function in childhood (Northern Ireland Childhood Errors of Refraction Study or NICER). ImageJ software was used to obtain CD and A/V ratios from the digital images. Visual function measures and biometric parameters were also available for all participants including; cycloplegic refractive error, vision, corneal curvature, axial length, height and weight. RESULTS: One hundred and eighty fundus images (92.3%) from the 6-7 year olds and 194 images (85.5%) from the 12-13 year olds children were considered useable. Analysis (one way anova) demonstrated statistically significant differences between CD ratios and A/V ratios between the age groups. Participants aged 12-13 years had larger CD ratios and smaller A/V ratios (mean CD ratio 0.37 ± 0.09, mean A/V ratio 0.75 ± 0.10) than 6-7 year old participants (mean CD ratio 0.30 ± 0.09, mean A/V ratio 0.78 ± 0.12). No significant associations were noted between CD ratios and A/V ratio and any visual, ocular or biometric parameters. CONCLUSIONS: The present study provides novel normative data on CD and A/V ratios in UK school age children for clinicians in practice.

Refractive and corneal astigmatism in white school children in northern ireland.

PURPOSE: To study the prevalence of and relation between refractive and corneal astigmatism in white school children in Northern Ireland and to describe the association between refractive astigmatism and refractive error. METHODS: Stratified random clustering was used to recruit 1053 white children, 392 aged 6-7 years and 661 aged 12-13 years. Eye examinations included cycloplegic autorefraction and ocular biometric measures of axial length and corneal curvature. RESULTS: The prevalence of refractive astigmatism (≥ 1 DC) did not differ significantly between 6- to 7-year-old children (24%; 95% confidence interval [CI], 19-30) and 12- to 13-year-old children (20%; 95% CI, 14-25). The prevalence of corneal astigmatism (≥ 1 DC) also did not differ significantly between 6- to 7-year-old children (29%; 95% CI, 24-34) and 12- to 13-year-old children (25%; 95% CI, 21-28). While levels of refractive astigmatism and corneal astigmatism were similar, refractive astigmatism was predominantly oblique (76%; 95% CI, 67-85, of 6- to 7-year-olds; 59%; 95% CI, 48-70, of 12- to 13-year-olds), but corneal astigmatism was predominantly with-the-rule (80%; 95% CI, 72-87, of 6- to 7-year-olds; 82%; 95% CI, 74-90, of 12- to 13-year-olds). The prevalence of refractive astigmatism was associated with increasing myopia and hyperopia. CONCLUSIONS: This study is the first to provide robust population-based data on the prevalence of astigmatism in white school children in the United Kingdom. The prevalence of refractive astigmatism and corneal astigmatism is stable between 6 and 7 years and 12 and 13 years, although this finding would need to be confirmed by prospective studies. There is a high prevalence of refractive and corneal astigmatism which is associated with ametropia.