Anisometropia in an adult population in rural myanmar: the Meiktila Eye Study

Prevalence of anisometropia and influencing factors among school-age children in Nantong, China: a cross-sectional study

Objective

To investigate the prevalence of anisometropia and associated parameters among school-aged children in Nantong, China.

Methods

This school-based, cross-sectional study examined students from primary schools, junior high schools, and senior high schools in an urban area of Nantong, China. Univariate and multivariate logistic regression analyses were used to investigate the specific correlations between anisometropia and related parameters. Non-cycloplegic autorefraction was assessed for each student. Anisometropia was defined as the spherical equivalent refraction (SE) difference ≥ 1.0 D between eyes.

Results

A total of 9,501 participants were validated for analyses, of which 53.2% (n = 5,054) were male, and 46.8% (n = 4,447) were female. The mean of age was 13.32 ± 3.49 years, ranging from 7-19 years. The overall prevalence of anisometropia was 25.6%. Factors such as myopia, scoliosis screening positive, hyperopia, female sex, older age, and higher weight had a significantly higher risk of anisometropia (p < 0.05).

Conclusion

There was a high prevalence of anisometropia in school-age children. Some physical examination parameters are closely related to children's anisometropia, especially myopia and scoliosis. Preventing myopia and controlling its progression may be the most important ways to reduce the prevalence of anisometropia. Correcting scoliosis may be an important factor in controlling the prevalence of anisometropia, and maintaining good reading and writing posture may be helpful in controlling the prevalence of anisometropia.

Prevalence and Associations of Myopic Anisometropia in Chinese Adults

PURPOSE

To investigate the prevalence and associations of myopic anisometropia in Chinese adults.

METHODS

A total of 3,791 Chinese refractive surgery candidates with myopia (25.15±7.09 years old, Mean±SD) were recruited. All eyes underwent a standardized ophthalmological examination. Associations between myopic anisometropia and age, gender, spherical ametropia, astigmatism, and axial length (AL) were analyzed by means of the chi-squared test, nonparametric Kruskal-Wallis or Mann-Whitney test, binomial logistic regression analyses, and multivariate logistic regression analysis.

RESULTS

The mean myopic anisometropic level was 0.96 D and prevalence of myopic anisometropia was 29.62% (defined as myopic anisometropia ≥1.00 D). The prevalence and severity of myopic anisometropia increased with age, larger interocular AL difference, and higher cylindrical power (all P<0.001). Myopic anisometropia showed a U-shaped correlation with spherical equivalent (SE) refractive error and V-shaped correlations with AL, J0 and J45. Myopic anisometropia was most strongly associated with interocular AL difference (P<0.001).

CONCLUSIONS

Compared with previous reports, this study revealed an even higher prevalence of myopic anisometropia and showed a U-shaped correlation with SE and a V-shaped correlation with AL. These results indicate that the formation of myopic anisometropia could be related to neural control in the binocular AL growth balance. Further study is needed to clarify this presumption.

Anisometropia of ocular refractive and biometric measures among 66- to 79-year-old female twins

PURPOSE

To examine the prevalence of anisometropia of spherical refraction (AnisoSR), astigmatism (AnisoAST) and spherical equivalent (AnisoSE) and their associations with spherical refraction (SR), refractive astigmatism (AST), spherical equivalent (SE) and interocular differences of ocular biometric parameters among elderly female twins.

METHODS

Refraction of 117 monozygotic (MZ) and 116 dizygotic (DZ) female twin subjects aged 66-79 years was assessed with an auto-refractor (Topcon AT) and controlled by subjective refraction. Corneal refraction, anterior chamber depth and axial length were measured with a Zeiss IOL Master. Participants with eyes operated for cataract or glaucoma were excluded, but the grade of nuclear opacity was not recorded. The associations between the absolute values of AnisoSR, AnisoAST and AnisoSE with SR, AST, SE, corneal refractive power (CR), corneal astigmatism (CAST), anterior chamber depth (ACD) and axial length (AL) and with their interocular differences were calculated. When calculating the interdependencies of the differences, the real and absolute differences between the right and left eye were used.

RESULTS

Means ± standard deviations for AnisoSR, AnisoAST and AnisoSE were 0.67 ± 0.92 D, 0.42 ± 0.41 D and 0.65 ± 0.71 D, respectively. AnisoSR, AnisoAST and AnisoSE >1.0 D were present in 14.7%, 4.2% and 17.7% of cases, respectively. Anisometropia of spherical refraction (AnisoSR), AnisoAST and AnisoSE were higher the more negative the values of SR or SE. Hyperopic ametropia did not increase these anisometropia values. The correlations of AnisoSR and AnisoSE with the absolute values of interocular differences in CR and AL were non-significant. Using the real values of the interocular differences, the respective correlations were significant. The correlation between the real interocular differences in CR and AL was negative (r = -0.258, p < 0.001). Thus, the combined effect of the real interocular differences in CR and AL was a decrease in AnisoSR and AnisoSE (emmetropization).

CONCLUSION

Higher AnisoSR and AnisoSE were associated with more myopic refraction and longer AL. Higher AnisoAST was associated with more negative SR and higher AST and CAST. The negative correlation between real interocular differences in CR and AL indicated their influence of emmetropization in AnisoSR and AnisoSE.

The prevalence of anisometropia in population base study

PURPOSE

To determine the prevalence of anisometropia and its determinants in the population of Mashhad.

METHODS

In a cross-sectional study in 2008, 4453 residents of Mashhad city between the ages of 1 and 90 years were selected using stratified cluster sampling, of which 70.4% participated in the study. All respondents had visual acuity and refraction testing. Anisometropia was defined as the absolute interocular difference in the spherical equivalent based on non-cycloplegic refraction. The prevalence rates and 95% confidence intervals (CI) of anisometropia were determined based on cut points of 0.5 diopter (D), 1.0 D, and 2.0 D or more, and we used the 1.0 D cut point to examine associations.

RESULTS

After applying exclusion criteria, data from 2947 participants were used in the analyses. Based on cut points of 0.5 D, 1.0 D, and 2.0 D or more, the prevalence of anisometropia was 17.0% (n = 451) (95% CI, 15.1-18.8), 5.6% (n = 148) (95% CI, 4.6-6.6), and 1.7% (n = 50) (95% CI, 1.2-2.2), respectively. The odds of anisometropia showed a significant increase of 2.8% with every year of aging (P < 0.001); 2.6% and 2.8% were anisomyopic and anisohyperopic, respectively. The prevalence of anisometropia was directly associated with myopia (P < 0.001) as well as a history of ocular trauma (P < 0.001). The prevalence of anisoastigmatism was 5.6% and significantly increased with age (P < 0.001).

CONCLUSION

The prevalence of anisometropia in the studied population, compared to studies conducted in the Middle Eastern Region and East Asia, is in the midrange. The prevalence of anisometropia is higher at older age, however, children should receive more attention due to the risk of amblyopia. A history of ocular trauma is a risk factor for anisometropia.

All biometric components are important in anisometropia, not just axial length

BACKGROUND

No study to date has looked into the relationship between ocular biometrics with anisometropia exclusively; therefore, the purpose of this study was to determine the relationship between anisometropia and ocular biometrics.

METHODS

In a cross-sectional study with multistage cluster sampling, 6311 people in the 40-64-year-old age group from the population of Shahroud, Iran, were selected. Of these, 5190 people participated in the study. For all participants, tests for visual acuity, cycloplegic and non-cycloplegic refraction, slit lamp test and fundoscopy were performed. All participants underwent biometric examinations using the Allegro Biograph (WaveLight AG, Erlangen, Germany).

RESULTS

Asymmetry of axial length, corneal power, vitreous chamber depth, anterior chamber depth, lens thickness and lens power were significantly more among participants who were anisometropic than those who were non-anisometropic. The correlation of anisometropia with axial length asymmetry was 0.735, 0.273 with corneal power, 0.183 with anterior chamber depth and 0.311 with lens power (p<0.001). In a multiple linear regression model, anisometropia was found to have significant associations with axial length asymmetry (standard coefficient (SC)=0.905), corneal power asymmetry (SC=0.350), lens power asymmetry (SC=0.454), nuclear opacity asymmetry (SC=0.074) and age (SC=0.28) (R(2)=85.1%). According to the linear regression model, corneal power had the strongest association with anisoastigmatism.

CONCLUSIONS

Axial length asymmetry has the strongest correlation with anisometropia; nonetheless, other components of ocular biometrics such as corneal power, lens opacity, lens power and anterior chamber depth are related to anisometropia as well. More than 10% of changes in anisometropia can be explained with changes in factors other than asymmetry of ocular biometrics and lens opacity.

The relationship between anisometropia and amblyopia

This review aims to disentangle cause and effect in the relationship between anisometropia and amblyopia. Specifically, we examine the literature for evidence to support different possible developmental sequences that could ultimately lead to the presentation of both conditions. The prevalence of anisometropia is around 20% for an inter-ocular difference of 0.5D or greater in spherical equivalent refraction, falling to 2-3%, for an inter-ocular difference of 3D or above. Anisometropia prevalence is relatively high in the weeks following birth, in the teenage years coinciding with the onset of myopia and, most notably, in older adults starting after the onset of presbyopia. It has about one-third the prevalence of bilateral refractive errors of the same magnitude. Importantly, the prevalence of anisometropia is higher in highly ametropic groups, suggesting that emmetropization failures underlying ametropia and anisometropia may be similar. Amblyopia is present in 1-3% of humans and around one-half to two-thirds of amblyopes have anisometropia either alone or in combination with strabismus. The frequent co-existence of amblyopia and anisometropia at a child's first clinical examination promotes the belief that the anisometropia has caused the amblyopia, as has been demonstrated in animal models of the condition. In reviewing the human and monkey literature however it is clear that there are additional paths beyond this classic hypothesis to the co-occurrence of anisometropia and amblyopia. For example, after the emergence of amblyopia secondary to either deprivation or strabismus, anisometropia often follows. In cases of anisometropia with no apparent deprivation or strabismus, questions remain about the failure of the emmetropization mechanism that routinely eliminates infantile anisometropia. Also, the chronology of amblyopia development is poorly documented in cases of 'pure' anisometropic amblyopia. Although indirect, the therapeutic impact of refractive correction on anisometropic amblyopia provides strong support for the hypothesis that the anisometropia caused the amblyopia. Direct evidence for the aetiology of anisometropic amblyopia will require longitudinal tracking of at-risk infants, which poses numerous methodological and ethical challenges. However, if we are to prevent this condition, we must understand the factors that cause it to develop.

The prevalence of anisometropia and its associated factors in an adult population from Shahroud, Iran

BACKGROUND

The aim of this study was to evaluate the prevalence of anisometropia in an urban adult population in the north of Iran.

METHODS

This cross-sectional study was conducted among the 40-64-year-old population in Shahroud, Iran. Random cluster sampling was applied to select 6,311 people. Following an interview, optometric and ophthalmologic examinations, including objective non-cycloplegic refractions, were carried out. The prevalence of anisometropia was reported according to non-cycloplegic refraction and with cut-off points of 0.50, 1.00, 2.00 and 3.00 D.

RESULTS

Of the sampled people, 5,190 (82.2 per cent) took part in the study. After considering exclusion criteria, data from 4,918 participants were included in the final analysis. Most participants were female (57.6 per cent) and the average age (with standard deviation) was 50.7 ± 6.2 years. The prevalence of anisometropia with cut-off points of 0.50, 1.00 and 2.00 D were 23.1 (95%CI: 22.0-24.3), 7.7 (95%CI: 7.0-8.4) and 3.2 per cent (95%CI: 2.7-3.7), respectively. The prevalence of severe anisometropia (3.00 D or more) was 1.9 per cent (95%CI: 1.5-2.3). The odds ratio (OR) of anisometropia was 1.06 times higher for every year of increasing age. The OR of anisometropia in participants with cataract was 2.78 times more than in those without (p < 0.001). Anisometropia was more frequent among participants with unilateral cataract (21.7 per cent) compared to those with bilateral cataract (13.4 per cent). Anisometropia of 1.00 D or more was significantly more prevalent among myopic participants compared to hyperopic participants (13.8 versus 12.7 per cent, p < 0.001) and there was a stronger association between anisometropia and myopia (OR = 2.93) than hyperopia (OR = 2.23). With increasing educational level, the prevalence of anisometropia decreased significantly (p < 0.001). The prevalence of aniso-astigmatism of 1.00 D or more was 11.1 per cent (95%CI: 10.2-11.9).

CONCLUSION

In the present study, the prevalence of anisometropia in Iran was not negligible; however, it is less than in Eastern Asia. Myopia, cataract, age and educational level were associated with anisometropia.

Prevalence and risk factors for anisometropia in the Tehran eye study, Iran

PURPOSE

To determine the prevalence of anisometropia and its determinants in a population-based sample.

METHODS

In a cross-sectional population-based study, stratified cluster sampling was carried out from the population of Tehran. Respondents were transferred to a clinic for an interview and ophthalmic examinations including tests for visual acuity with and without correction, cycloplegic refraction, the slit lamp examination, fundoscopy, and lensometry. Anisometropia was defined as unequal spherical equivalent cycloplegic refractions in the two eyes.

RESULTS

Of 4565 participants, cycloplegic refraction was performed in both eyes of 3519 people. The mean age of the examinees was 31.5 ± 18.0 (range, 5-86) years. The mean anisometropia was 0.34 diopter (D) (95% Confidence Interval (CI): 0.31-0.37). The prevalence rates of anisometropia more than 0.5, 1.0, 1.5 and 2.0 D were 18.5% (95% CI: 17.0-19.9), 6.7% (95% CI: 5.8-7.7), 3.8% (95% CI: 3.1-4.5) and 2.6% (95% CI: 2.1-3.1). The inter-gender difference in the prevalence of anisometropia ≥ 1.0D was not statistically significant (P = 0.952). The prevalence of anisometropia increased after the age of 45 years. Overall, 15.7% of the examinees had anisomyopia and 4.7% had anisohypermetropia equal to or more than 1.0D. Anisometropia was more prevalent among patients with cataracts, amblyopia, and pseudophakia. The prevalence rates of spherical and cylindrical anisometropia in the studied sample were 8.0% and 7.1%, respectively.

CONCLUSIONS

The prevalence of anisometropia in the population of Tehran is beyond negligible. It showed a significant increase with age. Results also indicate that myopic patients are more likely to have anisometropia.

Causes of blindness in rural Myanmar (Burma): Mount Popa Taung-Kalat Blindness Prevention Project

Purpose

This study is a review of the major causes of visual impairment (VI) and severe visual impairment/blindness (SVI/BL) in Mount Popa Taung-Kalat, a rural region in Myanmar (Burma).

Methods

A review of our clinical records of consecutive patients attending clinics was conducted. Participants of all ages (n = 650) of the population of Mount Popa Taung-Kalat and villages in its vicinity underwent ophthalmic interview and a detailed dilated ocular evaluation by trained Australian ophthalmologists and ophthalmic nurses. This evaluation included anterior segment examination with a slit lamp, intraocular pressure recording, and direct or indirect ophthalmoscopy. VI and SVI/BL were defined by the World Health Organization (WHO) criteria.

Results

Six hundred fifty subjects were screened, with a mean age of 49.0 ± 20.6 years (range, 1–99). One hundred five patients (16.2%) were children (ages 1–18). Five hundred thirty-one eyes of the total 1,300 eyes (39.5%) had VI/SVI/BL, and 40 eyes of the children (38.1%) (average age 15.3 ± 13.3) had VI/SVI/BL. The leading causes of VI/SVI/BL were cataract with 288 cases (54.2%), glaucoma with 84 cases (15.8%), and corneal pathology with 78 cases (14.7%). Of all the VI/SVI/BL cases, 8.4% were preventable, 81.9% were treatable, and total of 90.5% were avoidable.

Conclusions

In the current study, cataracts were the major cause of blindness and visual impairment, and most of the ophthalmic pathology causing blindness is avoidable. These results highlight the lack of basic ophthalmologist eye care and optician resources in rural regions in Myanmar.