Characteristics of Astigmatism in a Population of Schoolchildren, Dezful, Iran

Prevalence and risk factors for astigmatism in 7 to 19-year-old students in Xinjiang, China: a cross-sectional study

BACKGROUND

To investigate the prevalence and risk factors for astigmatism in 7-19-year-old students in Xinjiang, China.

METHODS

A school-based, cross-sectional study was conducted on students who underwent refraction examination in Xinjiang, China, between May and December 2019. The prevalence of astigmatism was determined. Astigmatism was defined as cylinder power (C) ≤-0.75 D, undefined astigmatism as ≤-1.50 D, and high astigmatism as C ≤-3.00 D. Astigmatism types were: against-the-rule astigmatism (maximum refraction of the main meridian in 180° ± 30°), with-the-rule astigmatism (maximum refraction of the main meridian at 90°±30°), and oblique astigmatism (all other cases).

RESULTS

Of the 71,838 students examined (51.0% boys, 7 - 19 years old), 25,945 (36.1%, 95%CI: 35.52-36.68%) had astigmatism and 1267 (1.8%, 95%CI: 1.07-2.53%) had high astigmatism. The prevalence of astigmatism was greater in Han individuals (39.6%) compared with the Hui (34.0%), Kazakh (34.0%), Kyrgyz (32.1%), and Uyghur (26.4%) populations. Among the 25,945 students with astigmatism, 19,947 had with-the-rule astigmatism (76.9%), 3405 had against-the-rule astigmatism (13.1%), and 2593 had oblique astigmatism (10.0%). Multivariable logistic regression analysis showed that ethnicity (Han individuals more susceptible), male gender, age, and refractive errors (myopia and hyperopia) were independently associated with astigmatism, high astigmatism, and with-the-rule astigmatism (all P < 0.05).

CONCLUSIONS

The prevalence of astigmatism among children and adolescents in Xinjiang was 36.1%, including 1.8% of high astigmatism. In this population, astigmatism was mainly of the with-the-rule astigmatism type (76.9%). Han ethnicity, male gender, and myopia or hyperopia were independently associated with a high risk of astigmatism.

Evaluation of Ocular Residual Astigmatism in Eyes with Myopia and Myopic Astigmatism and Its Interaction with Other Forms of Astigmatism

Purpose

To evaluate the prevalence, magnitude, and direction of ocular residual astigmatism (ORA) in eyes with myopia and myopic astigmatism, and its interaction with refractive, anterior corneal, posterior corneal, and true net power astigmatism.

Patients and Methods

Refractive surgery candidates with myopia and myopic astigmatism were studied. Refractive astigmatism (RA) was measured using the Nidek^® AR-310A autorefractometer. Anterior corneal astigmatism (ACA), posterior corneal astigmatism (PCA), and true net power astigmatism (TNP) were measured using the Wavelight^® Oculyzer II. Astigmatism was converted from polar to vector notation. ORA was calculated by vector subtraction of ACA from RA vertexed to corneal plane. Compensation factor (CF) was calculated as the ratio of ORA that compensates ACA for both J₀ and J₄₅.

Results

154 eyes of 88 patients (mean age 31.7±7.1 years) were included. With-the-rule (WTR) astigmatism was the most common for both RA (55.6%) and ACA (74%), while against-the-rule (ATR) was the most common for PCA (87.7%) and ORA (74.0%). The axes of RA and ACA were within 10° of each other in 46.8% of the eyes, and within 30° of each other in 76.0%. The mean difference in value between the axis of RA and ACA was 25.6°. 71.4% of eyes in the study had an ORA ≥ 0.5D, 44.1% had ORA ≥ 0.75D and 26% had ORA ≥ 1D. There was a statistically significant difference between ACA and each of RA and TNP. Using TNP to calculate ORA instead of ACA reduced its magnitude. RA is positively correlated to ACA and more strongly to TNP. The most common pattern of compensation between ORA and ACA was under-compensation for J₀ (49%) and same-axis-augmentation for J45 (35%).

Conclusion

ORA, PCA, and the interaction between ORA and ACA can affect results during refractive planning.

Prevalence of and factors associated with astigmatism in preschool children in Wuxi City, China

PURPOSE

To investigate the status of astigmatism in preschool children in Wuxi City, and explore the risk factors related to astigmatism. The risk factors related to astigmatism development as predictors can help us identify preschool children who need vision screening at an early stage to ensure good visual quality.

METHODS

The cross-sectional study was conducted in 10 kindergartens randomly selected in five districts of Wuxi City in November 2018. All preschool children were measured by objective refractometry under non-cycloplegic refraction. The basic information of preschool children was collected. The relevant factors of astigmatism in the questionnaire were completed by parents. Spss 26. 0 software was used for univariate and multivariate correlation analysis.

RESULTS

A total of 889 preschool children participated in the study, 864 were finally included in the study. The prevalence of astigmatism was 36.0%. The risk of astigmatism in premature children was higher than that in non-premature children (adjusted odds ratio = 1.841). The prevalence of astigmatism with parents' astigmatism history was higher, compared with preschool children without parents' astigmatism history (adjusted odds ratio = 2.037). When maternal age at childbirth was older (≥ 35 years old), the risk of astigmatism increased in preschool children (adjusted odds ratio = 2.181). Compared with bottle feeding, the risk of astigmatism for mixed feeding and breastfeeding reduced in preschool children. Compared with preschool children exposed to electronic screen for less than 2 h every day, preschool children exposed to electronic screen for more than 2 h had an increased risk of astigmatism (P = 0.004).

CONCLUSION

The prevalence of astigmatism among preschool children in Wuxi City was high. Some risk factors such as premature birth, parents' astigmatism history, maternal age at childbirth, feeding pattern, and electronic screen exposure time were closely related to the occurrence of astigmatism among preschool children. For preschool children with significant risk factors, their eyesight should be checked regularly to ensure their visual quality.

Ratio of torus and equivalent power to refractive cylinder and spherical equivalent in phakic lenses - a Monte-Carlo simulation study

BACKGROUND

Spherical and astigmatic powers for phakic intraocular lenses are frequently calculated using fixed ratios of phakic lens refractive power to refractive spherical equivalent, and of phakic lens astigmatism to refractive cylinder. In this study, a Monte-Carlo simulation based on biometric data was used to investigate how variations in biometrics affect these ratios, in order to improve the calculation of implantable lens parameters.

METHODS

A data set of over sixteen thousand biometric measurements including axial length, phakic anterior chamber depth, and corneal equivalent and astigmatic power was used to construct a multidimensional probability density distribution. From this, we determined the axial position of the implanted lens and estimated the refractive spherical equivalent and refractive cylinder. A generic data model resampled the density distributions and interactions between variables, and the implantable lens power was determined using vergence propagation.

RESULTS

50 000 artificial data sets were used to calculate the phakic lens spherical equivalent and astigmatism required for emmetropization, and to determine the corresponding ratios for these two values. The spherical ratio ranged from 1.0640 to 1.3723 and the astigmatic ratio from 1.0501 to 1.4340. Both ratios are unaffected by the corneal spherical / astigmatic powers, or the refractive cylinder, but show strong correlation with the refractive spherical equivalent, mild correlation with the lens axial position, and moderate negative correlation with axial length. As a simplification, these ratios could be modelled using a bi-variable linear regression based on the first two of these factors.

CONCLUSION

Fixed spherical and astigmatic ratios should not be used when selecting high refractive power phakic IOLs as their variation can result in refractive errors of up to ±0.3 D for a 8 D lens. Both ratios can be estimated with clinically acceptable precision using a linear regression based on the refractive spherical equivalent and the axial position.

Prevalence of Refractive Error and Visual Acuity Among School Children in the Plateau Region of Qinghai, China

Purpose

This study aimed to investigate the prevalence of refractive error and visual acuity among school children in the plateau region of Qinghai, China.

Methods

The school-based, cross-sectional study was performed in Menyuan, Qinghai, China. Three kindergartens and three primary schools were randomly enrolled from both rural areas and county towns. The participants had undergone ophthalmic examinations of the intraocular pressure (IOP), uncorrected visual acuity (UCVA), presenting visual acuity (PVA) and best corrected visual acuity (BCVA), cycloplegic refraction, and axial length (AL). Regression analysis was applied to investigate the potential risk factors affecting the prevalence of various refractive errors.

Results

A total of 3770 children were invited to participate, and 3524 (93.5%) had undergone examination. Among the 3524 children (51.8% boys) with a mean age of 8.3±2.3 years, 1049 (29.8%) had myopia, 30 (0.9%) had high myopia, 1692 (48.0%) had mild hyperopia, 152 (4.3%) had medium to marked hyperopia and 925 (26.2%) had astigmatism. The mean SER was −0.16±1.86 D and decreased with age. The AL increased with age from 21.80±0.59 mm at 4-years to 23.53±1.05 mm at 12-years. The myopia prevalence increased with age from 2.0% at 4 years to 62.8% at 12-years. Myopia was associated with increasing age, county town habitation and girls. Among the 723 participants with PVA 20/40 or worse in one eye, 564 (78.0%) were due to uncorrected refractive error, and 83 (22.0%) were due to undercorrected refractive error. Among the 1049 children with myopia, only 254 wore glasses, and 151 children with PVA had a worse BCVA and did not have accurate spectacles.

Conclusion

The prevalence of myopia is very high among school children in Menyuan. Only 24.2% of myopic children wore glasses, and 59.4% of children did not have accurate spectacles. Strategies to improve access to eye care and affordable glasses are needed.

Refractive and Vision Status in Down Syndrome: A Comparative Study

Objectives:

To determine the prevalence of refractive errors and visual impairment in Down syndrome (DS) patients compared to normal controls.

Materials and Methods:

Cycloplegic refraction was tested in 213 DS patients and 184 normal age- and gender-matched controls using autorefraction followed by retinoscopy. Data from the worse eye of each case were used in the analyses.

Results:

In the DS and control groups, respectively, mean age was 17.2±4.8 and 17.2±4.4 years (p=0.993) and 53.0% and 49.5% were male (p=0.473). In the DS and control groups, respectively, mean spherical equivalent (SE) was -5.13±4.47 and -4.15±3.04 diopters (D) in myopics (p=0.050) and 2.47±1.64 and 2.36±2.04 D in hyperopics (p=0.482), mean cylinder error was -2.17±1.39 and -2.05±1.57 D (p=0.451), mean J0 was -0.03±0.89 and 0.12±0.76 D (p=0.086), and mean J45 was 0.11±1.02 and -0.13±1.03 D (p=0.024). The prevalence of oblique astigmatism was higher in the DS group (20.4% vs. 6.1%) while against-the-rule astigmatism was more prevalent in the control group (84.0% vs. 71.6%) (p<0.001). The prevalence of anisometropia was not significantly different between the groups (19.4% vs. 13.8%). Visual impairment was detected in 11.7% of the DS and 0.5% of the control group (p<0.001). The prevalence of amblyopia was 36.3% and 3.8% in the DS and control groups, respectively (p<0.001). Based on the multiple model, only absolute SE inversely correlated with age and differed between males and females (all p<0.05).

Conclusion:

In DS patients, the prevalence rates of refractive errors, amblyopia, and visual impairment are higher than those in non-DS individuals, and emmetropization appears to be either defective or slow. Cylinder error is stable in this age range, but the rotation of astigmatism axis is different from normal samples.

The profile of astigmatism in 6-12-year-old children in Iran

PURPOSE

To determine the prevalence of astigmatism and its determinants in schoolchildren aged 6-12 years.

METHODS

The students selected by stratified cluster random sampling in Shahroud, north of Iran. Optometric examination included uncorrected visual acuity, refraction with autorefractometer, manifest refraction with retinoscopy followed by subjective and cycloplegic refraction (after two drops of cyclopentolate 1% with 5min interval were instilled in each eye). A cylinder power ≥0.75diopter (D) in at least one eye was considered as astigmatism. The prevalence of astigmatism was reported based on a cylinder power higher than 0.50, 1.00, and 2.00D in cycloplegic refraction, followed by power vector analysis.

RESULTS

After applying the inclusion criteria, the data of 5528 children were analyzed. The prevalence of astigmatism was 16.7% (95% CI: 15.6-17.7) in total, 16.6% (95% CI: 15.2-18.0) in boys and 16.8% (95% CI: 15.2-18.3) in girls (p=0.920) and decreased from 21.5% in 6-year-old children to 13.7% in 10-year-olds, and then again increased to 18.3% in children aged 12 years. Moreover, 17.2% (95% CI: 16.0-18.3) of urban and 12.1% (95% CI: 10.0-14.1) of rural children had astigmatism (p<0.001). The prevalence of with-the-rule, against-the-rule, and oblique astigmatism was 14.2%, 2.1%, and 0.33%, respectively. The mean cylinder power was -1.31, -0.46, and -0.44D in children with spherical myopia, emmetropia, and hyperopia, respectively (p<0.001). Urban students had a higher J₀ and boys had a higher J₄₅.

CONCLUSION

The prevalence of astigmatism in this study was lower than previous studies. Astigmatism prevalence was markedly higher in urban children.

Prevalence of myopia among disadvantaged Australian schoolchildren: A 5-year cross-sectional study

Purpose

Myopia prevalence is influenced by environmental factors including heritability and social disadvantage. The current prevalence of myopia among disadvantaged school children in Australia has not been reported. Therefore, this study analyses refractive data for children from rural and outer suburban areas.

Methods

The records of 4,365 children aged 6–15 visiting a city-based government-school respite care center during the years 2014/2016/2018 were analyzed for right eye non-cycloplegic spherical equivalent refraction (SER). The prevalence of myopia (SER≤-0.50D) was compared with historical data.

Results

The prevalence of myopia was 3.5%, 4.4% and 4.3% in 2014, 2016 and 2018, respectively. The prevalence of myopia increased with age (P<0.0001), but was not related to sex or year of testing (all P >0.05). The overall mean SER was 0.89±0.86D, 0.62±0.89D and 0.56±0.95 in 2014, 2016 and 2018, respectively. Mean SER was associated with year of testing, age (all P <0.0001) and sex (P = 0.03). Mean SER decreased slightly from 2014 to 2018 and demonstrated a significant shift towards less hyperopia with increasing age. Mean SER of females was higher than that of males and decreased faster than in males with age (P _interaction = 0.03).

Conclusions

Myopia prevalence increased with age. The mean SER decreased slightly from 2014 to 2018. Sex differences in the rate of change with age was observed. Compared with 40 years ago, the prevalence of myopia has doubled, but it remains significantly lower than in school children of a similar age living in established urban areas that are regarded as having a higher socioeconomic status.

Prevalence of Refractive Errors in Iranian University Students in Kazerun

Purpose:

To determine the prevalence of refractive errors and visual impairment and the correlation between personal characteristics, including age, sex, weight, and height, with different types of refractive errors in a population of university students in the south of Iran.

Methods:

In this cross-sectional study, a number of university majors were selected as clusters using multi-stage sampling in all universities located in Kazerun (27 clusters of 133 clusters). Then, proportional to size, a number of students in each major were randomly selected to participate in the study. Uncorrected and corrected visual acuity, non-cycloplegic objective refraction and subjective refraction were measured in all participants.

Results:

The prevalence and 95% confidence interval (CI) of presenting visual impairment and blindness was 2.19% (1.48–3.23) and 0.27% (0.12–0.62), respectively. Refractive errors comprised 75% of the causes of visual impairment. The prevalence (95% CI) of myopia [spherical equivalent (SE) ≤ –0.5 D], hyperopia (SE ≥ 0.5 D), and astigmatism (cylinder power < –0.5 D) was 42.71% (39.71–45.77), 3.75% (2.85–4.51), and 29.46% (27.50–31.50), respectively. Totally, 49.03% (46.39–51.68) of the participants had at least one type of refractive error. There was a positive association between weight and myopia (1.01; 95% CI: 1.01–1.02), anisometropia (1.03; 95% CI: 1.01–1.06), and refractive errors (1.01; 95% CI: 1.01–1.02). In comparison with the age group 18–19 years, the odds ratio (OR) of astigmatism in the age group 26–27 years was 1.64 (95% CI: 1.03–2.61), and the OR of anisometropia in the age group ≥ 30 years was 0.21 (95% CI: 0.04–0.98).

Conclusions:

The prevalence of refractive errors, especially myopia, is higher in university students than the general population. Since refractive errors constitute a major part of visual impairment, university students should receive special services for providing corrective lenses and glasses to reduce the burden of these disorders.

Simultaneous Changes in Astigmatism with Noncycloplegia Refraction and Ocular Biometry in Chinese Primary Schoolchildren

Purpose

To assess the changing profile of astigmatism in Chinese schoolchildren and the association between astigmatism changes and ocular biometry.

Methods

We examined and followed up 1,463 children aged 6–9 years from Wenzhou, China. We measured noncycloplegic refraction twice each year and tested axial length (AL) and corneal radius of curvature (CRC) annually for two years. We defined clinically significant astigmatism (CSA) as ≤−0.75 diopter (D) and non-CSA astigmatism as ≤0 to >−0.75 D.

Results

Prevalence of CSA at baseline was 22.4% (n = 327) and decreased to 20.3% (n = 297) at the two-year follow-up (P = 0.046). Ninety-two (8.1%) non-CSA children developed CSA. In multiple regression, after adjusting for age, gender, baseline cylinder refraction, and axis, children who had longer baseline ALs (>23.58 mm; odds ratio (OR) = 5.19, 95% confidence interval (CI): 2.72–9.90) and longer baseline AL/CRC ratio (>2.99, OR = 4.99, 95% CI: 2.37–10.51) were more likely to develop CSA after two years. Four-hundred and two (27.5%) children had increased astigmatism, 783 (53.5%) had decreased, and 278 (19.0%) had no change during the two-year follow-up. Children with increased astigmatism had longer baseline ALs (23.33 mm, P < 0.001), higher AL/CRC ratios (2.99 mm, P < 0.001), and more negative spherical equivalent refraction (SER) (−0.63 D, P < 0.001) compared with the decreased and no astigmatism change subgroups. Also, children in the increased astigmatism subgroup had more AL growth (0.68 mm, P < 0.001), higher increases in AL/CRC ratio (0.08, P < 0.001), and more negative SER change (−0.86 D, P < 0.001) compared with the decreased and no astigmatism change subgroups.

Conclusions

The prevalence of astigmatism decreased slightly over the two-year study period. Longer ALs and higher AL/CRC ratios were independent risk factors for developing CSA. Increased astigmatism was associated with AL growth, AL/CRC ratio increases, and the development of myopia. This trial is registered with ChiCTR1800019915.

Enantiomorphism and rule similarity in the astigmatism axes of fellow eyes: A population-based study

PURPOSE

To evaluate the relationship patterns between astigmatism axes of fellow eyes (rule similarity and symmetry) and to determine the prevalence of each pattern in the studied population.

METHODS

This population-based study was conducted in 2015 in Iran. All participants had tests for visual acuity, objective refraction, subjective refraction (if cooperative), and assessment of eye health at the slit-lamp. Axis symmetry was based on two different patterns: direct (equal axes) and mirror (mirror image symmetry) or enantiomorphism. Bilateral astigmatism was classified as isorule if fellow eyes had the same orientation (e.g. both eyes were with-the-rule) and as anisorule if otherwise.

RESULTS

Of the total cases of bilateral astigmatism, 80% were isorule, and in the studied population, the prevalence of isorule and anisorule astigmatism was 14.89% and 3.53%, respectively. The prevalence of isorule increased with age (p<0.001). The prevalence of both isorule and anisorule increased at higher degrees of spherical ametropia (p<0.001). Median inter-ocular axis difference was 10° in mirror symmetry and 20° in direct symmetry with no significant difference between two genders (p>0.288). Both symmetry patterns reduced with age (p<0.001). Among cases of bilateral astigmatism, 15.5% and 19.8% had exact direct and mirror symmetry, respectively.

CONCLUSION

Bilateral astigmatism is mainly isorule in the population and anisorule astigmatism is rare. The enantiomorphism is the most common pattern in the population of bilateral astigmatism.

Astigmatism and its components in 12-year-old Chinese children: the Anyang Childhood Eye Study

Purpose

To determine prevalence of refractive (RA), corneal (CA) and internal astigmatism (IA), including variation with gender and spherical equivalent refraction (SE), in a population of 12-year-old Chinese children.

Methods

A total of 1783 students with a mean age of 12.7 years (range 10.0–15.6 years) completed comprehensive eye examinations in the Anyang Childhood Eye Study. Data of cycloplegic refraction and corneal curvature were analysed.

Results

Prevalences of RA, CA and IA ≥1.0 D were 17.4% (95%CI 15.6% to 19.2%), 52.8% (50.5% to 55.1%)%) and 20.9% (19.0% to 22.8%), respectively. With different limits of astigmatism axes classification, including ±15°, ±20° and ±30°, RA and CA axes were mainly ‘with-the-rule’ (WTR) (ie, correcting axis of negative cylinders at or near 180°), while those for IA axes were mainly ‘against-the-rule’ (ATR) (ie, correcting axis of negative cylinders at or near 90°). RA was not different between the genders, but girls had higher prevalence and greater means of CA and IA. RA and CA increased in students with higher ametropia (more myopia and more hyperopia) and were the highest in a high myopic group (SE≤−6 D), while IA was stable across refraction groups. Children with RA higher than 0.50 D were more likely to have lens corrections (51%, 57%, 61% and 69% for magnitudes of ≥0.50 D, ≥0.75 D, ≥1.0 D and ≥1.5 D, respectively).

Conclusions

Prevalence of RA in the Chinese 12-year-old children was relatively high compared with other studies. RA and CA had mainly ‘WTR’ astigmatism, while IA was mainly ATR and partially compensated for CA. Girls had greater means and prevalences of CA and IA than did boys. Both RA and CA, but not IA, increased with refractive errors away from emmetropia.

Ocular residual and corneal astigmatism in a clinical population of high school students

Purpose

Total refractive astigmatism is usually the first consideration that guides the selection of contact lens type (e.g., spherical or toric), while the ocular source of the astigmatism is a second, but more important consideration, for the final clinical decision. This study was conducted to provide detailed data on this topic by evaluating astigmatic components in Chinese adolescents.

Methods

Participants were recruited from healthy high school students undergoing an annual ocular examination at a local hospital. Total astigmatism (TA), corneal astigmatism (CA), and ocular residual astigmatism (ORA) were determined by a Hartmann-Shack wavefront analyzer system (KR-1W, Topcon) with the natural pupil. The axis relationship between CA and ORA was placed into three categories: on-axis, defined as an axis with a difference of 0 ± 10°; opposite-axis, a difference of 90 ± 10°; and the rest defined as oblique-axis.

Results

The study consisted of 1,466 students (57.84% girls, age: 16.49 ± 1.05 years). ORA was present in 83.97%, 66.64%, and 45.23% of participants, according to the various criteria for astigmatism (≥ 0.50 D, ≥ 0.75 D, and ≥ 1.00 D, respectively). While with-the-rule was the most common axis orientation for both TA (76.28%) and CA (89.94%), against-the-rule predominated in ORA (93.82%; χ² = 1688.544, p < 0.001). Opposite-axis was the major type of axis difference (90.96%) of clinical significance (i.e., ≥ 1.00 D) between CA and ORA, which also prevailed in all levels of TA (range: 56.25–82.26%).

Conclusions

ORA is common in high school students and usually demonstrates a compensation relationship with CA, which should be taken into consideration when determining the design of contact lenses to correct refractive error.

Characteristics of astigmatism in Black South African high school children

Background

Astigmatism impairs vision at various distances and causes symptoms of asthenopia which negatively impacts reading efficiency.

Objective

The aim of conducting this study was to determine the prevalence and distribution of astigmatism and its relationship to gender, age, school grade levels and spherical ametropia.

Methods

Using a multi-stage random cluster sampling, 1589 children who included 635 (40%), males, and 954 (60%), females were selected from 13 out of a sample frame of 60 schools. Their ages ranged between 13 and 18 years with a mean of 15.81±1.56 years. The parameters evaluated included visual acuity using the LogMAR chart and refractive errors measured using an autorefractor and then refined subjectively. Axis of astigmatism was presented in the vector method where positive values of J0 indicated with-the-rule, negative values described against-the-rule and J45 represented oblique astigmatism.

Results

The mean cylinder power was −0.09 ± 0.27 and mainly with-the-rule, J0 = 0.01 ± 0.11. The overall prevalence of clinically significant astigmatism (≤ − 0.75 cylinder) in the sample was 3.1% [(95% Confidence interval = 2.1–4.1%)]. Cylinder of at least − 0.25 power was considered to classify astigmatism types. Thus, the estimated distributions of types of astigmatism were: axis- 11.5%, sphero-astigmatism 10.1% and magnitude-astigmatism 11.2% while 67.2% had no cylinder of any magnitude.

Conclusion

The prevalence of astigmatism is relatively low in this population studied. Older children and those in high school grade levels were more likely to have with-the-rule or against-the-rule astigmatism. The prevalence of astigmatism were comparable within but not across regions.

Global and regional estimates of prevalence of refractive errors: Systematic review and meta-analysis

Purpose

The aim of the study was a systematic review of refractive errors across the world according to the WHO regions.

Methods

To extract articles on the prevalence of refractive errors for this meta-analysis, international databases were searched from 1990 to 2016. The results of the retrieved studies were merged using a random effect model and reported as estimated pool prevalence (EPP) with 95% confidence interval (CI).

Results

In children, the EPP of myopia, hyperopia, and astigmatism was 11.7% (95% CI: 10.5–13.0), 4.6% (95% CI: 3.9–5.2), and 14.9% (95% CI: 12.7–17.1), respectively. The EPP of myopia ranged from 4.9% (95% CI: 1.6–8.1) in South–East Asia to 18.2% (95% CI: 10.9–25.5) in the Western Pacific region, the EPP of hyperopia ranged from 2.2% (95% CI: 1.2–3.3) in South-East Asia to 14.3% (95% CI: 13.4–15.2) in the Americas, and the EPP of astigmatism ranged from 9.8% in South-East Asia to 27.2% in the Americas. In adults, the EPP of myopia, hyperopia, and astigmatism was 26.5% (95% CI: 23.4–29.6), 30.9% (95% CI: 26.2–35.6), and 40.4% (95% CI: 34.3–46.6), respectively. The EPP of myopia ranged from 16.2% (95% CI: 15.6–16.8) in the Americas to 32.9% (95% CI: 25.1–40.7) in South-East Asia, the EPP of hyperopia ranged from 23.1% (95% CI: 6.1%–40.2%) in Europe to 38.6% (95% CI: 22.4–54.8) in Africa and 37.2% (95% CI: 25.3–49) in the Americas, and the EPP of astigmatism ranged from 11.4% (95% CI: 2.1–20.7) in Africa to 45.6% (95% CI: 44.1–47.1) in the Americas and 44.8% (95% CI: 36.6–53.1) in South-East Asia. The results of meta-regression showed that the prevalence of myopia increased from 1993 (10.4%) to 2016 (34.2%) (P = 0.097).

Conclusion

This report showed that astigmatism was the most common refractive errors in children and adults followed by hyperopia and myopia. The highest prevalence of myopia and astigmatism was seen in South-East Asian adults. The highest prevalence of hyperopia in children and adults was seen in the Americas.

Comprehensive profile of bilateral astigmatism: rule similarity and symmetry patterns of the axes in the fellow eyes

PURPOSE

To study rule similarity (isorule or anisorule) and symmetry patterns of axes (direct and mirror) in bilateral astigmatism.

METHODS

Six years of data were collected from four ophthalmology clinics in Tehran. After applying the exclusion criteria (having eye disease or history of ocular surgery), final analyses were performed on data of 160 608 cases whose mean age was 39.2 ± 15.4 years (10-80 years) and 53.7% female. All subjects had autorefraction, retinoscopy, and subjective refraction data. Rule similarity was categorised as isorule (with, against or oblique astigmatism) if the orientation type in fellow eyes was the same and anisorule if they were different.

RESULTS

The prevalence of isorule astigmatism was 82.9% and was similar in men and women (p = 0.44). The prevalence of isorule astigmatism decreased with age and increased with greater spherical ametropia (p < 0.001). The median of the absolute inter-ocular axis difference from exact symmetry was 10° under the mirror symmetry model (mirror axes). Under the direct symmetry model (equal axes), the median of the absolute inter-ocular axis difference was significantly higher, at 20° (p < 0.001). 16.4% and 10.8% had exact mirror and direct symmetry, respectively. In addition, 68.0% of cases with mirror symmetry and 47.1% with direct symmetry were within ±15 degrees of exact symmetry.

CONCLUSION

The results of the present study showed that bilateral astigmatism was mostly isorule. Bilateral symmetry of the astigmatism axes was highly prevalent and mostly of the mirror pattern. High astigmatic cases showed better symmetry.

Refractive Errors in Northern China Between the Residents with Drinking Water Containing Excessive Fluorine and Normal Drinking Water

The purpose of this study was to evaluate the refractive errors and the demographic associations between drinking water with excessive fluoride and normal drinking water among residents in Northern China. Of the 1843 residents, 1415 (aged ≥40 years) were divided into drinking-water-excessive fluoride (DWEF) group (>1.20 mg/L) and control group (≤1.20 mg/L) on the basis of the fluoride concentrations in drinking water. Of the 221 subjects in the DWEF group, with 1.47 ± 0.25 mg/L (fluoride concentrations in drinking water), the prevalence rates of myopia, hyperopia, and astigmatism were 38.5 % (95 % confidence interval [CI] = 32.1-45.3), 19.9 % (95 % CI = 15-26), and 41.6 % (95 % CI = 35.1-48.4), respectively. Of the 1194 subjects in the control group with 0.20 ± 0.18 mg/L, the prevalence of myopia, hyperopia, and astigmatism were 31.5 % (95 % CI = 28.9-34.2), 27.6 % (95 % CI = 25.1-30.3), and 45.6 % (95 % CI = 42.8-48.5), respectively. A statistically significant difference was not observed in the association of spherical equivalent and fluoride concentrations in drinking water (P = 0.84 > 0.05). This report provides the data of the refractive state of the residents consuming drinking water with excess amounts of fluoride in northern China. The refractive errors did not result from ingestion of mild excess amounts of fluoride in the drinking water.

Pattern of astigmatism in a clinical setting in Maldives

BACKGROUND

Patterns of refractive errors have never been reported in Maldives. This study aims to dissect astigmatism and provide a general view in context of this island country.

METHODS

A clinic based cross sectional study was designed with 277 patients, aged ≥3.5 years and with a primary astigmatism of ≥-1.00 diopters (D). They underwent complete eye examination and a vector analysis was done.

RESULTS

Mean age was 28.58 (SD 19.15) years. Astigmatic magnitude depended on age (p<0.05) but not on gender (p>0.05). Severity of visual impairment after refractive correction was very less, with only 2.2% having visual acuity ≤6/60. Mean spherical, spherical equivalent and astigmatic refraction were -1.35 (SD 2.94 D), -2.40 (SD 3.04) and -2.12 (SD 1.11 D), respectively. Between fellow eyes, refractive and corneal astigmatism highly correlated (0.83 and 0.73). Fifty eyes (18.1%) had an astigmatic error of ≥-3.00 D which peaked in the second and third decades of life (p<0.0001) and was corneal in origin (p<0.0001). Internal J45 and J0 tended to be more negative with increasing age, showing a trend toward against the rule astigmatism. Correlation between corneal and refractive J0 and J45 were 0.88 and 0.62 (p<0.0001). With the rule astigmatism was more common followed by against the rule and oblique.

CONCLUSION

In conclusion, this study inferred that among patients with relatively higher magnitude of astigmatism attending to the clinics in Maldives, younger patients are affected more, which could possibly link to the environment, genetics and nutrition. The probable association between nutrition and astigmatism needs to be investigated to fill the gap in literature.

Characteristics of Astigmatism in a Population of Tunisian School-Children

Purpose:

To evaluate the characteristics of astigmatism in a cross-sectional study of schoolchildren in Tunisia.

Materials and Methods:

A random cluster design was used to recruit children from primary schools across urban and rural settings in Tunisia, from 2008 to 2010. A total of 6192 students aged 6–14-years old were enrolled. All students whose uncorrected visual acuity was worse than 20/20 underwent a complete ophthalmic examination. Astigmatism was defined as the cylinder power of 0.75 diopter (D) or greater.

Results:

The prevalence of astigmatism was 6.67%. Mean cylinder power was - 1.89 ± 0.79D. The prevalence of astigmatism increased statistically significantly with age (P = 0.032). The prevalence of astigmatism was not significantly related to gender (P = 0.051). Of those with cylinder, 63.6%, 17.8%, and 18.6% schoolchildren had with with-the-rule, against-the-rule, and oblique astigmatism, respectively. ATR astigmatism was significantly higher in males (P = 0.033). There was no significant association between the student's area of residence and astigmatism (P = 0.059).

Conclusion:

Comparisons with other studies show that the prevalence of astigmatism in Tunisia is higher than in some countries. The prevalence of astigmatism increased with age but not gender. The majority of schoolchildren had with-the-rule astigmatism.

Correlation of major components of ocular astigmatism in myopic patients

PURPOSE

To investigate the correlation of major components of ocular astigmatism in myopic patients in an academic hospital.

METHODS

This cross-sectional study was conducted on 376 eyes of 188 patients who were referred to Farabi Eye Hospital for refractive surgery. Preoperative examinations including refraction and corneal topography were performed for all candidates to measure refractive and corneal astigmatism. Ocular residual astigmatism was calculated using vector analysis. Pearson's correlation and ANOVA analysis were used to evaluate the strength of the association between different types of astigmatism. Both eyes were defined as cluster and the Generalized Estimating Equations (GEE) analysis were performed.

RESULTS

Mean age of 119 women (63.3%) and 69 men (36.7%) was 27.8 ± 5.7 years. Mean refractive error based on spherical equivalent was -3.59 ± 1.95D (range, -0.54 to -10.22D). Mean refractive and corneal astigmatism was 1.97 ± 1.3D and 1.85 ± 1.01D, respectively. Mean amount of ORA was 0.65 ± 0.36D.There was a significant correlation between ORA and refractive astigmatism(r=0.23, p<0.001), corneal and refractive astigmatism (r=0.91, p<0.001) and a weak correlation between ORA and corneal astigmatism (r=0.13, p=0.014). There was a significant correlation between J0 and J45 values of ORA and corneal astigmatism (p<0.001).

CONCLUSION

There is a significant correlation between ORA and refractive astigmatism, refractive and corneal astigmatism and a weak correlation between ORA and corneal astigmatism in refractive surgery candidates. Identifying the type of astigmatism and preoperative measurement of ocular residual astigmatism is highly recommended prior to any refractive surgery, especially in cases with significant astigmatism.

Astigmatism among myopics and its changes from childhood to adult age: a 23-year follow-up study

PURPOSE

To study the prevalence of and changes in astigmatism from the onset of myopia at school age.

METHODS

Two hundred and forty myopic schoolchildren (mean age 10.9 years), with no previous spectacles, were recruited during 1983-1984 to a randomized 3-year clinical trial of bifocal treatment of myopia. Three annual examinations with subjective cycloplegic refraction were performed for 237-238 subjects. Subsequent examinations were performed at the mean ages of 23.2 and 33.9 years for 178 and 163 subjects, and the last examination, including data from prescriptions of different ophthalmologists, for 32 subjects. Corneal topography was studied at baseline, at the 3-year follow-up and at the two adulthood follow-ups. Prevalence and changes in refractive astigmatism (RA), in its polar values J0 and J45, and corneal astigmatism (CA) were studied.

RESULTS

Mean RA of the right eye increased during follow-up from 0.26 D (SD) ± 0.30 to 0.79 D ± 0.74. Mean CA was 1.07 D ± 0.74 at study end. The prevalence of RA ≥0.25 or ≥1.00 D increased from 54.9 and 3.8% to 83.4 and 34.4%, respectively. The main direction of the axis of RA and its polar value J0 and CA changed mainly through sphericity, from against the rule (ATR) to with the rule during the follow-up. There was a negative correlation between RA and spherical refraction in the ATR group at end of follow-up. Changes in RA were associated with increase in myopia and with changes in CA.

CONCLUSIONS

The prevalence and mean amount of RA associated with CA increased, and the axis of astigmatism changed among myopics during the 23-year follow-up.

Eye problems in children with hearing impairment

PURPOSE

To compare the prevalence of refractive errors, amblyopia, and strabismus between hearing-impaired and normal children (7-22 years old) in Mashhad.

METHODS

In this cross-sectional study, cases were selected from hearing-impaired children in Mashhad. The control group consisted of children with no hearing problem. The sampling was done utilizing the cluster sampling method. All of the samples underwent refraction, cover test, and visual examinations.

RESULTS

254 children in the hearing-impaired group (case) and 506 children in the control group were assessed. The mean spherical equivalent was 1.7 ± 1.9 D in the case group, which was significantly different from the control group (0.2 ± 1.5) (P < 0.001). The prevalence of hyperopia was 57.15% and 21.5% in deaf and normal children, respectively, but myopia was mostly seen in the control group (5.5% versus 11.9%, P = 0.007). The mean cylinder was 0.65 ± 1.3 D and 0.43 ± 0.62 D in deaf and normal subjects, respectively (P = 0.002). 12.2% of deaf subjects and 1.2% of normal subjects were amblyopic (P < 0.001), and the prevalence of strabismus was 3.1% in the case group and 2.6% in the control group (P = 0.645).

CONCLUSION

In a comparison of children of the same ages, hearing-impaired children have significantly more eye problems; therefore, a possible relation between deafness and eye problems must exist. Paying attention to eye health assessment in hearing-impaired children may help prevent adding eye problems to hearing difficulties.

The prevalence of astigmatism and its determinants in a rural population of Iran: the "Nooravaran Salamat" mobile eye clinic experience

Purpose:

The prevalence of astigmatism, and the astigmatic axis, and their determinants were evaluated in a rural population of Iran.

Materials and Methods:

In a cross-sectional study conducted from May to August 2011, 13 villages in the vicinity of the city of Khaf in northeast Iran were investigated in this study. All the examinations including visual acuity, refraction, slit-lamp biomicroscopy and fundoscopy were performed in a Mobile Eye Clinic. Written informed consent was obtained from all participants. Only phakic eye that could be reliably refracted without a previous history of ocular surgery were included.

Results:

Out of 2635 participants who were screened, 2124 were analysed for this study of whom 52% were female. The prevalence of astigmatism was 32.2% (95% confidence intervals (CI): 30.2-34.2). Astigmatism significantly increased from 14.3% in the under 15-year-old age group to 67.2% in the age group of over 65-years old (P < 0.001). The prevalence of With-The-Rule (WTR), Against-The-Rule (ATR), and oblique astigmatism was 11.7%, 18.1%, and 2.4 %, respectively. ATR significantly increased with age (P < 0.001). The mean corneal astigmatism was 0.73 D which linearly increased with age (P < 0.001).

Conclusion:

Attention must be paid to astigmatism in rural areas due to the high prevalence. Further studies are suggested to discover the role of the environmental and genetic factors. It seems that environmental and occupational factors in the villages cause a significant increase in the prevalence of astigmatism with age. A high percentage of participants had ATR astigmatism, which was more common at older ages.

[The cornea in high axial myopia]

PURPOSE

To compare corneal characteristics of eyes with high myopia with those of eyes with no spherical ametropia using Orbscan and ultrasonic pachymetry.

METHODS

Orbscan and ultrasonic pachymetry values were prospectively recorded in a study group of 105 patients with high myopia (i.e., axial length greater than 26mm in both eyes) and in a control group of 105 patients with no spherical ametropia (absolute value of spherical equivalent less than 1.25D regardless of cylinder value). Astigmatism data were expressed by rectangular coordinates in a dioptric plane. Axis was decomposed in 2 components (WTR/ATR and oblique) which were analyzed by Cos2axis and Sin2axis trigonometric functions. Enantiomorphism (mirror-image symmetry) between fellow eyes was quantified by a Euclidean distance for the location of the thinnest point and by the difference (in absolute value) between 180° and the sum of both axes for astigmatism.

RESULTS

In the study group, the mean axial length and subjective spherical equivalent were, respectively, 27.82±2.14mm (26.00 to 34.06) and -9.00±3.46D (-4.71 to -19.82). The mean corneal astigmatism was +0.92D×91.3° in the study group and +0.65D×89.3° in the control group. The mean corneal cylinder was higher in the study group (1.44D versus 0.91D; P<0.001) whereas axis showed no significant differences between both groups. The mean maximal keratometry was steeper in the study group (44.53D versus 44.13D; P=0.03) whereas the mean keratometry and minimal keratometry displayed no significant differences between both groups. No significant differences in central corneal thickness (540.2μm versus 546.9μm; P=0.10), peripheral corneal thickness, corneal diameter, corneal irregularity, asphericity, and irregular astigmatism were found between both groups. There were no significant differences in enantiomorphism parameters between both groups. In the study group, correlation with axial length was significant only for spherical equivalent (r=-0.86; P<0.001) and corneal cylinder (r=0.16; P=0.04).

CONCLUSION

High myopia exhibits corneal characteristics similar to corneas of eyes with no spherical ametropia, except for toricity. While the posterior segment elongates, development of high myopia appears not to affect corneal characteristics. Corneal toricity may be associated with evolution toward high myopia by perturbing mechanisms of emmetropization.

The visual and functional impacts of astigmatism and its clinical management

PURPOSE

To provide a comprehensive overview of research examining the impact of astigmatism on clinical and functional measures of vision, the short and longer term adaptations to astigmatism that occur in the visual system, and the currently available clinical options for the management of patients with astigmatism.

RECENT FINDINGS

The presence of astigmatism can lead to substantial reductions in visual performance in a variety of clinical vision measures and functional visual tasks. Recent evidence demonstrates that astigmatic blur results in short-term adaptations in the visual system that appear to reduce the perceived impact of astigmatism on vision. In the longer term, uncorrected astigmatism in childhood can also significantly impact on visual development, resulting in amblyopia. Astigmatism is also associated with the development of spherical refractive errors. Although the clinical correction of small magnitudes of astigmatism is relatively straightforward, the precise, reliable correction of astigmatism (particularly high astigmatism) can be challenging. A wide variety of refractive corrections are now available for the patient with astigmatism, including spectacle, contact lens and surgical options.

CONCLUSION

Astigmatism is one of the most common refractive errors managed in clinical ophthalmic practice. The significant visual and functional impacts of astigmatism emphasise the importance of its reliable clinical management. With continued improvements in ocular measurement techniques and developments in a range of different refractive correction technologies, the future promises the potential for more precise and comprehensive correction options for astigmatic patients.

Myopia screening: combining visual acuity and noncycloplegic autorefraction

PURPOSE

To explore the effectiveness of combining uncorrected visual acuity (UCVA) and noncycloplegic autorefraction (NCAR) for large-scale myopia screening in schoolchildren with a high prevalence of myopia.

METHODS

A total of 1687 children aged between 6 and 12 years, from five primary schools in the Baoshan district of Shanghai participated in the study. We measured UCVA and autorefraction before and after cycloplegia by a Topcon KR-8800. We drew receiver operating characteristic curves to achieve the best cutoff points and their corresponding sensitivities and specificities for the UCVA and NCAR, respectively. We then combined the UCVA and NCAR in serial order to explore the optimal criterion and its effectiveness. A specificity of 90% was set to compare the sensitivities among the three tests. The children were divided into three age groups (aged 6 to 7, 8 to 10, 11 to 12 years) to further examine this new method.

RESULTS

A total of 1639 children with an average age of 9.35 (SD, 1.6) years were finally included, among which 428 (26.11%) children were diagnosed as being myopic (spherical equivalent refraction (SER) less than or equal to -0.5 diopters [D]). For the UCVA, the cutoff point is 0.2 logarithm of the minimum angle of resolution (20/32), with a sensitivity and specificity of 63.6% and 94.0%, respectively. For NCAR, the cutoff point is SER less than or equal to -0.75 D, with a sensitivity and specificity of 88.6% and 86.1%, respectively. When UCVA is combined with NCAR, the best cutoff point is UCVA less than or equal to 0 logarithm of the minimum angle of resolution (20/20) and SER less than or equal to -0.75 D, with a sensitivity and specificity of 84.4% and 90.5%, respectively. At a specificity of 90%, the sensitivities are 63.55%, 78.50%, and 84.35%, respectively, for UCVA, NCAR, and the combination test. In all age groups, the combination test had the highest sensitivities among the three tests.

CONCLUSIONS

In a population with a high prevalence of myopia, combining the UCVA and NCAR in serial order achieved higher sensitivity than either of the two tests alone, when specificity was set at 90%.

Statistical guidelines for the analysis of data obtained from one or both eyes

PURPOSE

Measurements obtained from the right and left eye of a subject are often correlated whereas many statistical tests assume observations in a sample are independent. Hence, data collected from both eyes cannot be combined without taking this correlation into account. Current practice is reviewed with reference to articles published in three optometry journals, viz., Ophthalmic and Physiological Optics (OPO), Optometry and Vision Science (OVS), Clinical and Experimental Optometry (CEO) during the period 2009-2012.

RECENT FINDINGS

Of the 230 articles reviewed, 148/230 (64%) obtained data from one eye and 82/230 (36%) from both eyes. Of the 148 one-eye articles, the right eye, left eye, a randomly selected eye, the better eye, the worse or diseased eye, or the dominant eye were all used as selection criteria. Of the 82 two-eye articles, the analysis utilized data from: (1) one eye only rejecting data from the adjacent eye, (2) both eyes separately, (3) both eyes taking into account the correlation between eyes, or (4) both eyes using one eye as a treated or diseased eye, the other acting as a control. In a proportion of studies, data were combined from both eyes without correction.

SUMMARY

It is suggested that: (1) investigators should consider whether it is advantageous to collect data from both eyes, (2) if one eye is studied and both are eligible, then it should be chosen at random, and (3) two-eye data can be analysed incorporating eyes as a 'within subjects' factor.