Changes in refractive trends and optical components of Hong Kong Chinese aged over 40 years

Large-scale study in Chengdu, China: The prevalence of myopia full-correction decreased with increasing myopia in adolescents

Myopia is an increasingly serious health issue among children and adolescents worldwide. This study investigated the situation related to myopia among students in Chengdu, a city in western China, and analyzed the prevalence of myopia spectacle wear and myopia full-correction and their influencing factors to understand the current status of myopia prevention. This school-based cross-sectional study investigated 1582 schools in seven districts of Chengdu City, China, enrolling a total of 417,337 students aged 6-18 years (elementary, middle, and high school) from 2020 to 2022. Examination items included uncorrected visual acuity (UCVA), slit lamp examination and non-cycloplegic autorefraction. Myopia was defined as non-cycloplegic SE ≤ -0.50 D + UCVA> 0 log MAR (age ≥6). The prevalence of myopia spectacle wear is defined as the number of people wearing glasses for myopia/the number of people with myopia (%) within the study population, and myopia full-correction is defined as normal vision after wearing glasses for myopia (≤0 log MAR for 6 years and above). With the support of the government, this programme is conducted 1-2 times a year. Statistical analyses are conducted to determine the association between myopia and various parameters. The average age of the entire survey population was 10.96 ± 3.5 years, and the overall prevalence of myopia was 48.7%, myopia spectacle wear was 65.7%, and myopia full-correction was 50.5%. With increasing age and educational levels, the prevalence of moderate to high myopia, the prevalence of myopia spectacle wear, and the prevalence of myopia full-correction all rise. The prevalence of mild myopia full-correction (46.5%) was higher than that for moderate myopia (47.1%) and even higher than that for high myopia (39.6%). The correct utilization rate of myopic spectacles was 33.17%, increasing with age and education levels, with the highest correct utilization rate of 40.7% among those with moderate myopia. The prevalence of myopia among children and adolescents in Chengdu is relatively low, and the prevalence of myopia spectacle wear and myopia full-correction need to be improved, and it was found that with the increase of myopia, the prevalence of myopia full-correction among adolescents decreased instead.

Birth Year-Dependent Increase in Axial Length of Japanese Adult

PURPOSE

To determine whether the correlations between the axial length and the aging-dependent and birth year-dependent age are significant.

DESIGN

Retrospective cross-sectional study.

METHODS

This study included Japanese patients ≥50 years who had undergone cataract surgery at numerous clinics from 2002 to 2020. Only 1 eye/patient was analyzed. The axial length was measured with the IOL Master. The age-dependent changes were determined by the significance of the correlation between the axial length and age by the birth year. The birth year-dependent changes were determined by the significance of the correlation between the axial length and birth year in the different age groups. The age refers to the age at the time of the cataract surgery. Spearman correlations were calculated. The turning points were identified by the LOESS, NLIN, and HPMIXED procedures.

RESULTS

A total of 62,362 eyes (35,508 women, 26,854 men) were studied. The mean age was 72.9 ± 8.4 (standard deviation) years (range, 50-101 years), and the mean axial length was 23.90 ± 1.66 mm (standard deviation) (range, 19.20-37.07 mm). The birth year ranged from 1908 to 1970. Analyses of the birth year-dependent changes showed significant positive correlations in 48 of 81 (59.3%) groups for women and men. The increase in the axial length was birth year-dependent, and the turning point was 1939.4 for women and 1936.7 for men.

CONCLUSIONS

The negative and significant correlation between the axial length and age is due to birth year-dependent changes. A birth year-dependent increase in axial length might have continued for several decades from the birth year of the late 1930s.

Age-related axial length changes in adults: a review

PURPOSE

To investigate the origins of age-related decreases in axial length in the literature.

METHODS

A literature review was performed, including all articles regarding axial length changes with age. These data were combined with mean body length and education level for the countries of each study to assess their influence in a multivariate analysis. Furthermore, analyses were performed of how optical path length, used by optical biometers to measure axial length, is affected by the known age-related changes in the crystalline lens. The influence of other factors mentioned in the literature was also investigated.

RESULTS

Seventeen cross-sectional studies were found that met the search criteria. The decrease in axial length over time was consistent across most of these studies. However, when plotted as a function of year of birth, mean body length and number of years in school, the data indicated an increase in length. Multivariate analysis confirmed the influence of body length (P = 0.005) and birth year (P = 0.017), but not age (P = 0.50). Meanwhile, the lenticular changes due to aging and cataract formation cause a minor bias in the form of increased axial length measurements. Finally, a gradual thinning of the choroidal arteries was reported to cause an increase in axial length.

CONCLUSION

The age-related decrease in axial length is mainly associated with gradual changes in increased body length and education level, while attenuated by minor biases in measurement procedure and thinning of the choroidal arteries.

High prevalence of myopia in children and their parents in Hong Kong Chinese Population: the Hong Kong Children Eye Study

PURPOSE

To determine the myopia prevalence in Hong Kong Chinese children and their parents.

METHODS

It was a population-based cross-sectional study. A total of 4257 children aged 6-8 years, and 5880 parents were recruited in the Hong Kong Children Eye Study. Cycloplegic autorefraction was measured for children; and non-cycloplegic autorefraction for parents. Parental educational level, children's outdoor time, and near work were collected by validated questionnaires.

RESULTS

In children aged 6-8 years, 25.0% were myopic, and among them, 12.7% for the 6-year-olds, 24.4% for the 7-year-olds and 36.1% for the 8-year-old. About 0.7% of children aged 8 years were high myopia. In all age groups, boys (their myopia rate: 13.9% at 6 years, 26.7% at 7 years, and 38.3% at 8 years) were more myopic than girls (11.3% at 6 years, 22.0% at 7 years, 33.4% at 8 years). Among parents, 72.2% were myopic (mother, 73.2%; father, 70.7%) and 13.5% high myopia (mother, 12.8%; father, 14.5%). It was observed that prevalence decreased with ages and increased with education level.

CONCLUSION

There is a strikingly high prevalence of myopia in Hong Kong children aged 6-8, much higher than that of other regions of China. Of note, the prevalence of children was similar to that in 15 years ago. Furthermore, the myopia prevalence of parents is high, and it had already increased in this cohort. Prevention of childhood myopia is important, likewise for visual complications from high myopia in adults.

Correlation between refractive state, corneal thickness, and keratometry in ametropic patients

PURPOSE

To analyze the correlation between age, gender, refractive error, keratometry, and corneal thickness in a large group of subjects.

METHODS

This study is a retrospective analysis of patients who underwent refractive surgery between January 2000 and February 2015 at Care Vision Refractive Clinic, Tel Aviv, Israel. Patient demographics, subjective refraction, pachymetry, and average keratometry were collected.

RESULTS

Overall, 51,113 eyes of patients averaging 28.8 ± 9.3 years of which 53.9% were males were included. Average keratometry, spherical equivalent and cylindrical error differed significantly between male and female subjects (p < 0.001), while pachymetry did not (p = 0.332). In myopic eyes, correlations between age, pachymetry, average keratometry, spherical equivalent, and cylindrical error were all statistically significant except for the correlation between age and either pachymetry (p = 0.462) or spherical equivalent (p = 0.016). All correlations found were negligible or small (|r|= 0.003 to 0.141). In hyperopic eyes, correlations between age, pachymetry, average keratometry, spherical equivalent, and cylindrical error were all statistically significant except for the correlation between average keratometry and either pachymetry or cylindrical error (p = 0.344 or p = 0.274, respectively). All correlations found were negligible or small, except for a moderate correlation found between age and cylindrical error (r = 0.365).

CONCLUSION

Refractive state, pachymetry, and keratometry of refractive surgery candidates are mostly weakly correlated.

Optical and pharmacological strategies of myopia control

Recent increases in global myopia prevalence rates have raised significant concerns as myopia increases the lifelong risk of various sight-threatening ocular conditions. This growing public health burden has generated significant research interests into understanding both its aetiology and developing effective methods to slow down or stop its development, methods collectively termed 'myopia control'. The growing body of research has demonstrated benefits of various optical and pharmacological treatments resulting in myopia control management increasingly becoming a part of main stream clinical practice. This review will discuss the peer-reviewed literature on the efficacy of various myopia control interventions including multifocal spectacles and contact lenses, orthokeratology and pharmaceutical eye drops, as well as potential future research directions.

Prevalence and risk factors for myopia in older adult east Chinese population

BACKGROUND

To determine the prevalence and associated factors for myopia and high myopia among older population in a rural community in Eastern China.

METHODS

A community-based, cross-sectional survey was conducted in the Weitang town located in Suzhou, an urban metropolis in East China. A total of 5613 Chinese residents aged 60 years and older were invited to complete a questionnaire and participated in a detailed eye examination,including measurements of visual acuity and refractive error using autorefraction and subjective refraction. Myopia and high myopia was defined as SE < -0.5 diopters (D) and < -5.0 D, respectively.

RESULTS

Among the 5613 participating individuals, 4795 (85.4%) complete refraction data of phakic right eye was included for analysis. The age-adjusted prevalence was 21.1% (95% confidence interval [CI], 19.9-22.2) for myopia and 2.5% (95% CI, 2.1-2.9) for high myopia. The prevalence of myopia tended to increase significantly with age(p < 0.001),and women had a higher rate of myopia than men (p < 0.001). According to multivariate logistic regression analysis, adults who were older (odds ration[OR]:1.05; 95% CI:1.04-1.07), spent more time for sleeping at night (OR:1.12;95% CI: 1.06-1.18),or had cataract (OR:1.60;95% CI:1.36-1.88) and family history of myopia (OR:1.47;95% CI:1.23-1.77), are more susceptible to myopia (p < 0.001). People who had older age, family history, cataract and specially longer night-time sleep duration, would have a higher risk of myopia.

CONCLUSION

Myopia and high myopia among rural old adult population in Eastern China presents common. The current literature unanticipated suggests that there was a positive significant association between prevalence of myopia and night-time sleep duration among adult. Our data provide some evidence of this relationship and highlight the need for larger studies to further investigate this relationship longitudinally and explore mechanism therein.

EPIDEMIC OF PATHOLOGIC MYOPIA: What Can Laboratory Studies and Epidemiology Tell Us?

PURPOSE

To systematically review epidemiologic and laboratory studies on the etiology of high myopia and its links to pathologic myopia.

METHODS

Regular Medline searches have been performed for the past 20 years, using "myopia" as the basic search term. The abstracts of all articles have been scrutinized for relevance, and where necessary, translations of articles in languages other than English were obtained.

RESULTS

Systematic review shows that there is an epidemic of myopia and high myopia in young adults in East and Southeast Asia, with similar but smaller trends in other parts of the world. This suggests an impending epidemic of pathologic myopia. High myopia in young adults in East and Southeast Asia is now predominantly associated with environmental factors, rather than genetic background. Recent clinical trials show that the onset of myopia can be reduced by increasing the time children spend outdoors, and methods to slow the progression of myopia are now available.

CONCLUSION

High myopia is now largely associated with environmental factors that have caused the epidemic of myopia in East and Southeast Asia. An important clinical question is whether the pathologic consequences of acquired high myopia are similar to those associated with classic genetic high myopia. Increased time outdoors can be used to slow the onset of myopia, whereas methods for slowing progression are now available clinically. These approaches should enable the current epidemics of myopia and high myopia to be turned around, preventing an explosion of pathologic myopia.

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.

The epidemics of myopia: Aetiology and prevention

There is an epidemic of myopia in East and Southeast Asia, with the prevalence of myopia in young adults around 80-90%, and an accompanying high prevalence of high myopia in young adults (10-20%). This may foreshadow an increase in low vision and blindness due to pathological myopia. These two epidemics are linked, since the increasingly early onset of myopia, combined with high progression rates, naturally generates an epidemic of high myopia, with high prevalences of "acquired" high myopia appearing around the age of 11-13. The major risk factors identified are intensive education, and limited time outdoors. The localization of the epidemic appears to be due to the high educational pressures and limited time outdoors in the region, rather than to genetically elevated sensitivity to these factors. Causality has been demonstrated in the case of time outdoors through randomized clinical trials in which increased time outdoors in schools has prevented the onset of myopia. In the case of educational pressures, evidence of causality comes from the high prevalence of myopia and high myopia in Jewish boys attending Orthodox schools in Israel compared to their sisters attending religious schools, and boys and girls attending secular schools. Combining increased time outdoors in schools, to slow the onset of myopia, with clinical methods for slowing myopic progression, should lead to the control of this epidemic, which would otherwise pose a major health challenge. Reforms to the organization of school systems to reduce intense early competition for accelerated learning pathways may also be important.

Age-related differences in ocular biometry in adult Korean population

Background

To evaluate the relationship between age, axial length (AL), anterior chamber depth (ACD) and corneal steepness (K) in patients with cataract.

Methods

In this retrospective study, medical records of 800 patients (800 eyes) who were diagnosed with cataract and received preoperative ophthalmologic examination were reviewed. Data including age, gender and ocular biometric data including AL, ACD and K were collected and analyzed using univariate and multivariate analyses.

Results

Univariate analysis showed increased age has significant correlation with shorter AL (P < 0.001), shallower ACD (P < 0.001) and steeper K (P < 0.001). K value has a negative correlation with AL (P < 0.001). In multivariate analysis, increasing age has a significant association with shorter AL (P < 0.001) and ACD (P < 0.001), although the association between age and K was not significant (P = 0.398). Negative correlation between AL and K remained significant in multivariate analysis (P < 0.001).

Conclusion

In patients with cataract, older age had significant association with shorter AL and ACD. AL and K had negative correlation.

The Future of Myopia Control Contact Lenses

The growing incidence of pediatric myopia worldwide has generated strong scientific interest in understanding factors leading to myopia development and progression. Although contact lenses (CLs) are prescribed primarily for refractive correction, there is burgeoning use of particular modalities for slowing progression of myopia following reported success in the literature. Standard soft and rigid CLs have been shown to have minimal or no effect for myopia control. Overall, orthokeratology and soft multifocal CLs have shown the most consistent performance for myopia control with the least side effects. However, their acceptance in both clinical and academic spheres is influenced by data limitations, required off-label usage, and a lack of clear understanding of their mechanisms for myopia control. Myopia development and progression seem to be multifactorial, with a complex interaction between genetics and environment influencing myopigenesis. The optical characteristics of the individual also play a role through variations in relative peripheral refraction, binocular vision function, and inherent higher-order aberrations that have been linked to different refractive states. Contact lenses provide the most viable opportunity to beneficially modify these factors through their close alignment with the eye and consistent wearing time. Contact lenses also have potential to provide a pharmacological delivery device and a possible feedback mechanism for modification of a visual environmental risk. An examination of current patents on myopia control provides a window to the future development of an ideal myopia-controlling CL, which would incorporate the broadest treatment of all currently understood myopigenic factors. This ideal lens must also satisfy safety and comfort aspects, along with overcoming practical issues around U.S. Food and Drug Administration approval, product supply, and availability to target populations. Translating the broad field of myopia research into clinical practice is a multidisciplinary challenge, but an analysis of the current literature provides a framework on how a future solution may take shape.

An Analysis of Morphometric Qualities of Bulbus Oculi in Cataract Patients: A Comparative Biometric Study

Cataract is considered to be the primary reason for curable blindness that is caused by progressive loss of lens transparency and affects millions of people around the world. This study aims to analyze the changes in morphometric qualities of bulbus oculi (BO) as well as its morphometric measurements such as anterior chamber depth (ACD), lens thickness (LT), vitreous length (VL), axial length (AL), etc. depending on age and gender in cataract patients through comparison with healthy eyes. 200 eyes with cataract were separately analyzed in five different categories of ages for males and females at the ages of 40-89. Biometric measurements of a total of 128 eyes (64 males and 64 females) were used as the control group. The study revealed a strong negative relation between age and ACD and a strong positive relation between age and LT in males and females for healthy eyes and eyes with cataract (P < 0.05). No significant relation was found for VL and AL in either gender (P > 0.05). A significant decrease was observed in ACD with aging while a positive correlation with age was detected in LT. We believe that the data obtained from this study will serve as a guide for BO interventions, diagnose and treatment stages and training of physician assistants. Anat Rec, 299:1308-1312, 2016. © 2016 Wiley Periodicals, Inc.

High myopia-partial reduction ortho-k: a 2-year randomized study

PURPOSE

To investigate if the combination of partial reduction (PR) orthokeratology (ortho-k) and spectacles for residual refractive errors in the daytime was effective to slow myopic progression in high myopic children.

METHODS

High myopic children (aged 8 to 11 years) with spherical equivalent refraction at least -5.75 diopters (D) and myopia -5.00 D or more myopic were recruited and randomly assigned into PR ortho-k and control groups. Subjects in the PR ortho-k group were fitted with custom made four-zone ortho-k lenses with target reduction of 4.00 D for both eyes, and the residual refractive errors were corrected with single-vision spectacles for clear vision in the daytime. Control subjects were fully corrected with single-vision spectacles. Axial length of each eye of all subjects was measured with the IOLMaster at 6-month intervals by a masked examiner. This study was registered at www.clinicaltrial.gov with the identifier NCT00977236.

RESULTS

Fifty-two subjects were recruited and randomized to the PR ortho-k and control groups. Twelve PR ortho-k and 16 control subjects completed the study. Compared with the residual refractive errors at the 1-month visit (after stabilization of ortho-k treatment), the median increase in noncycloplegic residual myopia at the 24-month visit was 0.13 D. In the control group, the median increase in myopia was 1.00 D at the end of the study. The mean ± SD increases in axial length were 0.19 ± 0.21 mm in the PR ortho-k group and 0.51 ± 0.32 mm in the control group (95% confidence interval, -0.55 to -0.12; unpaired t test, p = 0.005).

CONCLUSIONS

This single-masked randomized study showed that PR ortho-k effectively slowed myopic progression in high myopes. Axial length elongation was 63% slower in PR ortho-k-treated children compared with children wearing spectacles.

Myopia and international educational performance

PURPOSE

To analyse the relationship between myopia, educational performance and engagement in after-school tutorial classes.

METHODS

Educational performance data and data on engagement in after-school tutorial classes were taken from the results of the Organisation for Economic Cooperation and Development (OECD) Program in Secondary Assessment (PISA) reports for 2009, which tested educational outcomes in representative samples of 15 year-old school children from 65 jurisdictions. High prevalence of myopia (>70%) and low prevalence of myopia (<40%) locations were identified by systematic literature search.

RESULTS

Six locations with a high prevalence of myopia were identified from among the participants in PISA 2009 - Shanghai-China, Hong Kong-China, Taiwan, Singapore, Japan and South Korea. All were ranked in the top quartile on educational performance. Other participants in the top educational performance quartile were identified as locations with a low prevalence of myopia, including Australia and Finland. The locations with a high prevalence of myopia combined high educational performance and high engagement in after-school tutorials, whereas the locations with a low prevalence of myopia combined high educational performance with little engagement in tutorials.

DISCUSSION

These results show that it is possible to achieve high educational outcomes without extensive engagement in after-school tutorials, and that the combination of high educational outcomes with extensive use of tutorials is associated with high prevalence rates of myopia. We suggest that extensive use of after-school tutorials may be a marker of educational environments which impose high educational loads. Further quantification of educational loads to include after- school educational activities, such as homework, tutorials and other after-school classes, as well as formal school classes, is desirable. Policy initiatives to decrease these loads may contribute to the prevention of myopia, perhaps, at least in part, by enabling children to spend more time outdoors.

Increases in the prevalence of reduced visual acuity and myopia in Chinese children in Guangzhou over the past 20 years

BACKGROUND/AIMS

To estimate the prevalence of myopia based on reduced unaided visual acuity (VA) in Chinese school children over the past 20 years.

METHODS

Guangzhou school health authorities have measured VA on Grade 1-12 students from 1988 to 2007 annually, using a LogMAR tumbling E chart. VA is reported as Snellen categories: normal (VA ≥ 6/6), mildly reduced (6/9 < VA <6/6), moderately reduced (6/18 < VA ≤ 6/9), and severely reduced VA (VA ≤ 6/18).

RESULTS

In 1988, over 80% of children in Grade 1 (age 6 years) and about 30% in Grade 12 (age 17 years) had normal unaided VA. By 2007, this dropped to only 60% in Grade 1 and about 10% in Grade 12. Conversely, the prevalence of moderately and severely reduced unaided VA increased from 6.2% in Grade 1 and 62.5% in Grade 12 in 1988 to 14.5% in Grade 1 and 84.11% in Grade 12 in 2007. This rate was unchanged from 2003 to 2007 at both the Grade 1 and Grade 12 levels.

CONCLUSIONS

In Guangzhou, the prevalence of reduced unaided VA has increased markedly in the past 20 years, but has stabilized in the past few years. This increase may result from environmental changes, such as increased schooling intensity and urbanization.

Characteristics of astigmatism as a function of age in a Hong Kong clinical population

PURPOSE

To characterize astigmatism as a function of age in a Hong Kong clinical population.

METHODS

All records from new clinical patients at a university optometry clinic in the year 2007 were used for the study. Only data from subjects with corrected visual acuity ≥6/9 in both eyes and with completed subjective refraction were analyzed. The subjects were divided into seven age groups by decade (i.e., 3 to 10 years, 11 to 20 years, …, >60 years). Refractive errors were decomposed into spherical-equivalent refractive error (M), J0, and J45 astigmatic components for analyses. Internal astigmatism was calculated by subtracting corneal astigmatism from refractive astigmatism (RA).

RESULTS

Of the 2759 cases that fulfilled our selection criteria, 58.9% had myopia (M ≥-0.75 D) and 28.4% had RA (Cyl ≥ 1.00 D). The prevalence of RA increased from 17.8% in the 3 to 10 years age group to 38.1% in the 21 to 30 years age group. It then dipped to 25.8% in 41 to 50 years age group but increased again to 41.8% in the >60 years age group. Among the astigmats, almost all 3- to 10-year-old children (92.6%) had with-the-rule (WTR) astigmatism, but a majority of the elderly (>60 years) had against-the-rule (ATR) astigmatism (79.7%). For a subset of subjects who had both subjective refraction and keratometric readings (n = 883), RA was more strongly correlated with corneal (r = 0.35 to 0.74) than with internal astigmatism (r = 0.01 to 0.35). More importantly, the magnitudes of both refractive and corneal J0 were consistent with synchronized decrements (-0.15 and -0.14 D per 10 years, respectively) after the age of 30 years, indicating that the shift toward more ATR astigmatism was related to corneal change.

CONCLUSIONS

In this Hong Kong Chinese clinical population, the prevalence rates of both myopia and astigmatism increased during the first three decades and shared a similar trend before the age of 50 years. The manifest astigmatism was mainly corneal in nature, bilaterally mirror symmetric in axis, and shifted from predominantly WTR to ATR with age.

The increased prevalence of myopia in Finland

PURPOSE

To study change in the prevalence of myopia in Finland during the 20th century.

METHODS

A review of the literature on the prevalence of myopia in Finland.

RESULTS

During the 20th century, the prevalence of myopia among 7- to 8-year-old schoolchildren did not increase in Finland and varied between 0.5% and 1.9%. Among 14- to 15-year-old school children, myopia doubled to about 21%. Among adults born during the first three decades of the 20th century, the prevalence of myopia was <10%, whereas among those born during the second half of the 20th century, the prevalence rose to 21-30%. The change in mean refraction was towards myopia.

CONCLUSIONS

During the course of the 20th century, myopia among teenagers and adults in Finland significantly increased and the mean change in refraction was towards myopia. Increased education is proposed as the main reason behind these changes.

Age, gender, corneal diameter, corneal curvature and central corneal thickness in Nigerians with normal intra ocular pressure

Purpose

To investigate the relationship between age, gender, corneal diameter, central corneal curvature, central corneal thickness (CCT) and intraocular pressure in Nigerians with normal intraocular pressure.

Methods

One hundred and thirty eyes from 130 subjects (mean age = 47.8 ± 16.8 years) including 77 males and 53 females were recruited. CCT was measured by ultrasound pachymetry, intraocular pressure was determined by non-contact tonometry, horizontal and vertical corneal diameters were measured with a ruler and central corneal curvature was measured by keratometry.

Results

The mean values obtained were as follows: CCT = 548.97 ± 34.28 μm, IOP = 15.61 ± 2.69 mmHg, average corneal curvature (AVK) = 42.98 ± 1.19 D, horizontal corneal diameter (HVID) = 11.39 ± 0.69 mm and vertical corneal diameter (VVID) = 10.51 ± 0.50 mm. There was a significant effect of age on CCT (r = −0.35, p < 0.001). A 10-year-increase in age was associated with a 7.0 μm decrease in CCT. Males had significantly wider HVID than females (p = 0.03). Subjects in older age groups have narrower HVID and VVID. Corneal curvature, corneal diameter and gender did not significantly affect CCT.

Conclusion

CCT of normotensive Nigerian adults decreases with increasing age. There was no correlation between CCT and IOP in normotensive subjects. CCT was not significantly influenced by gender, corneal curvature and corneal diameter.

Refractive errors in students from Middle Eastern backgrounds living and undertaking schooling in Australia

BACKGROUND

  Environmental factors associated with schooling systems in various countries have been implicated in the rising prevalence of myopia, making the comparison of prevalence of refractive errors in migrant populations of interest. This study aims to determine the prevalence of refractive errors in children of Middle Eastern descent, raised and living in urban Australia but actively maintaining strong ties to their ethnic culture, and to compare them with those in the Middle East where myopia prevalence is generally low.

METHODS

  A total of 354 out of a possible 384 late primary/early secondary schoolchildren attending a private school attracting children of Middle Eastern background in Melbourne were assessed for refractive error and visual acuity. A Shin Nippon open-field NVision-K5001 autorefractor was used to carry out non-cycloplegic autorefraction while viewing a distant target. For statistical analyses students were divided into three age groups: 10-11 years (n = 93); 12-13 years (n = 158); and 14-15 years (n = 102).

RESULTS

  All children were bilingual and classified as of Middle Eastern (96.3 per cent) or Egyptian (3.7 per cent) origin. Ages ranged from 10 to 15 years, with a mean of 13.17 ± 0.8 (SEM) years. Mean spherical equivalent refraction (SER) for the right eye was +0.09 ± 0.07 D (SEM) with a range from -7.77 D to +5.85 D. The prevalence of myopia, defined as a spherical equivalent refraction 0.50 D or more of myopia, was 14.7 per cent. The prevalence of hyperopia, defined as a spherical equivalent refraction of +0.75 D or greater, was 16.4 per cent, while hyperopia of +1.50 D or greater was 5.4 per cent. A significant difference in SER was seen as a function of age; however, no significant gender difference was seen.

CONCLUSIONS

  This is the first study to report the prevalence of refractive errors for second-generation Australian schoolchildren coming from a predominantly Lebanese Middle Eastern Arabic background, who endeavour to maintain their ethnic ties. The relatively low prevalence of myopia is similar to that found for other metropolitan Australian school children but higher than that reported in the Middle East. These results suggest that lifestyle and educational practices may be a significant influence in the progression of myopic refractive errors.

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

PURPOSE

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

DESIGN

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

PARTICIPANTS

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

METHODS

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

MAIN OUTCOME MEASURES

Axial length distribution.

RESULTS

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

CONCLUSIONS

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

Relationship of 10-year change in refraction to nuclear cataract and axial length findings from an older population

PURPOSE

To examine 10-year changes and other influences on spherical equivalent refraction (SER) in older persons.

DESIGN

Prospective population-based study.

PARTICIPANTS

Three thousand six hundred fifty-four Blue Mountains Eye Study participants 49 or older at baseline (1992-1994) were observed after 5 years (2335; 75% of survivors) and 10 years (1952; 76% of survivors).

METHODS

At each visit, subjective refraction was performed using modified Early Treatment Diabetic Retinopathy Study protocols. Spherical equivalent refraction was calculated as sphere + half cylinder power. Axial length was measured only at the 10-year examinations, using an IOL Master. Right phakic eyes with best-corrected visual acuity > 20/40 (n = 1340) at baseline and 10-year examinations were included.

MAIN OUTCOME MEASURES

Temporal refractive change.

RESULTS

Over the decade, a hyperopic shift was observed among persons <65 years old, and a myopic shift was associated with increasing age among older subjects, with gender-adjusted mean SER changes of 0.40, 0.33, -0.02, and -0.65 diopters (D) in persons with baseline ages 49 to 54, 55 to 64, 65 to 74 and > or = 75, respectively. Apart from age, myopic refractive change was strongly associated with baseline nuclear cataract; mean changes of -0.96 and 0.26 D were observed in eyes with and without nuclear cataract, respectively (P<0.001). A birth cohort effect on refraction was also observed. After adjusting for age and nuclear cataract, baseline refractive status (P = 0.58), education (P = 0.34), and diabetes (P = 0.16) were not associated with changing SER. A 10% increase in against-the-rule astigmatism was observed over the 10-year period. Axial length showed an age-related reduction in 10-year cross-sectional data, from a mean of 23.61 mm (95% confidence interval [CI], 23.50-23.73) in 59- to 64-year-olds to a mean of 23.15 mm (95% CI, 22.83-23.47) in > or = 85-year-olds. After adjusting for age, education, and nuclear cataract, axial length measured 10 years later was not associated with change in SER (P = 0.34).

CONCLUSIONS

This longitudinal study confirms a hyperopic shift in persons younger than 65 and a myopic shift for older ages. Although underlying causes for this age-related hyperopic shift are unknown, it does not appear related to axial length. The myopic shift, however, is most likely caused by increasing nuclear cataract.

Myopia Prevalence in Chinese-Canadian Children in an Optometric Practice

PURPOSE

The high prevalence of myopia in Chinese children living in urban East Asian countries such as Hong Kong, Taiwan, and China has been well documented. However, it is not clear whether the prevalence of myopia would be similarly high for this group of children if they were living in a Western country. This study aims to determine the prevalence and progression of myopia in ethnic Chinese children living in Canada.

METHODS

Right eye refraction data of Chinese-Canadian children aged 6 to 12 years were collated from the 2003 clinical records of an optometric practice in Mississauga, Ontario, Canada. Myopia was defined as a spherical equivalent refraction (SER) equal or less than -0.50 D. The prevalence of myopia and refractive error distribution in children of different ages and the magnitude of refractive error shifts over the preceding 8 years were determined. Data were adjusted for potential biases in the clinic sample. A questionnaire was administered to 300 Chinese and 300 Caucasian children randomly selected from the clinic records to study lifestyle issues that may impact on myopia development.

RESULTS

Optometric records of 1468 children were analyzed (729 boys and 739 girls). The clinic bias adjusted prevalence of myopia increased from 22.4% at age 6 to 64.1% at age 12 and concurrently the portion of the children that were emmetropic (refraction between -0.25 and +0.75 D) decreased (68.6% at 6 years to 27.2% at 12 years). The highest incidence of myopia for both girls ( approximately 35%) and boys ( approximately 25%) occurred at 9 and 10 years of age. The average annual refractive shift for all children was -0.52+/-0.42 D and -0.90+/-0.40 D for just myopic children. The questionnaire revealed that these Chinese-Canadian children spent a greater amount of time performing near work and less time outdoors than did Caucasian-Canadian children.

CONCLUSIONS

Ethnic Chinese children living in Canada develop myopia comparable in prevalence and magnitude to those living in urban East Asian countries. Recent migration of the children and their families to Canada does not appear to lower their myopia risk.

Macular pigment and ocular biometry

This study is designed to investigate the relationship between macular pigment optical density (MPOD) and ocular biometric parameters. The following details were recorded for 180 healthy subjects: demographic profile; best-corrected visual acuity; refractive status; ocular biometric parameters [axial length (AL), anterior chamber depth (ACD), lens thickness (LT) and vitreous chamber depth (VCD)]; ocular dominance; MPOD; serum lutein (L) and zeaxanthin (Z). The mean MPOD (+/-SD) was 0.307 (0.155) and 0.305 (0.149) in the right and left eyes, respectively. No demonstrable relationship was observed between MPOD and AL, ACD or VCD [AL: r=0.091, p=0.225; ACD: r=0.091, p=0.227; VCD: r=0.146, p=0.051]. There was a significant and inverse relationship between LT and MPOD (r=-0.204; p=0.008), which was attenuated to non-significance after correction for age and height (r=-0.058; p=0.466). This study fails to identify an association between MPOD and ocular biometric parameters. This is an important negative finding, which allows investigators to study MP, and its relationship with potentially important variables, without the need to correct for ocular biometric parameters.

Optical models for human myopic eyes

Data from the author's investigations and other studies are used to construct refractive dependent models. These models include a gradient index lens and aspheric corneal, lens and retinal surfaces. Elements that alter with refraction are anterior corneal radius, vitreous length and retinal shape (vertex radius of curvature and asphericity) and decentration. Two versions of the models are produced, one with centred and symmetrical optical elements, and one with tilts of the lens and decentrations and tilts of the retina. The centred model predicts increase in spherical aberration in myopia. It predicts the relative change in mean sphere in the periphery between the horizontal and vertical meridians that has been observed in a recent experimental study. It overestimates peripheral astigmatism by about 50%. The decentred version has limited success in predicting changes in peripheral refraction of average eyes.

Myopia as a latent phenotype of a pleiotropic gene positively selected for facilitating neurocognitive development, and the effects of environmental factors in its expression

Myopia has become an almost pandemic problem in many populations. There are compelling evidence to suggest that myopia is a hereditary condition. However, myopia would constitute a definite selection disadvantage during most stages of human evolution, which is incompatible with its moderate to high prevalence in most modern populations. The rapid upsurge of myopia over just a few decades also implies that its inheritance does not follow any of the usual patterns, and environmental factors may have an important role in precipitating its occurrence in those who are genetically predisposed. Previous studies showed that myopes were, on average, more intelligent than non-myopes, and this association had been attributed to a biological link between eye growth and brain development. We propose a pleiotropic genetic model to explain the atypical epidemiologic and inheritance pattern of myopia and its relationship with neurocognitive development. This pleiotropic gene was positively selected for its facilitation of human intelligence. The myopic component is a latent phenotype; myopia will not be expressed unless some novel external factors are encountered (i.e. a "quirk" phenomenon). Therefore, the myopic component was selectively neutral in our ancestral environment. The net gain in Darwinian fitness enables the pleiotropic gene to attain a high frequency in the human population, as reflected by our current prevalence of myopia.

Accommodation functions: co-dependency and relationship to refractive error

We assessed the extent to which different accommodative functions are correlated and whether accommodative functions predict the refractive error or the progression of myopia over a 12 month period in 64 young adults (30 myopes and 34 non-myopes). The functions were: amplitude of accommodation; monocular and binocular accommodative facility (6 m and 40 cm); monocular and binocular accommodative response to target distance; AC/A and CA/C ratios, tonic accommodation (dark focus and pinhole), accommodative hysteresis, and nearwork-induced transient myopia. Within groups of related accommodative functions (such as facility measures or open-loop measures) measurements on individuals were generally significantly correlated, however correlations between functions from different groups were generally not significant. Although accommodative amplitude and pinhole (open loop) accommodation were significantly different in myopes than in non-myopes, these functions were unrelated to myopia progression. Facility of accommodation and accommodative lag was independent predictors of myopia progression.

Refractive status of indigenous people in the northwestern Amazon region of Brazil

PURPOSE

The purpose of this study was to investigate the refractive status of the illiterate indigenous people of the upper Rio Negro region of the Amazon rain forest in northwestern Brazil.

METHODS

From an overall sample of 486 people, 259 indigenous people and 78 Brazilians between 12 and 59 years of age with no compromising optical opacities were refracted with cycloplegic retinoscopy. Subjects were categorized as indigenous if they had at least three generations of indigenous ancestry with no folklore suggesting other ancestors.

RESULTS

Myopia was rare among the indigenous population. Only 2.7% of eyes showed myopia of -1.00 D or more and 1.6% (four people) had bilateral myopia of -1.00 D or more. Half of this small group were the only educated indigenous people examined. The prevalence of astigmatism and anisometropia equal to or >1.00 D was 15.5% and 8.2%, respectively. Most of the astigmatism in the indigenous people had an against-the-rule axis. Age was not associated with the refractive errors of the indigenous people. Brazilians from the small city in which the study was performed had higher rates of myopia (6.4% of eyes and 5.1% of subjects bilaterally). Older preeducation adults also had a very low prevalence of myopia (3.2% of eyes and 2.0% of subjects), whereas the younger, slightly educated Brazilians had a higher prevalence of myopia (11.3% of eyes and 9.7% of subjects).

CONCLUSION

The low prevalence of myopia in the illiterate indigenous people is consistent with other studies and suggests that myopia is related to literacy. The generational change among the local mixed race Brazilians further supports this conclusion. The relatively high rates of astigmatism and anisometropia in the indigenous people were unusual for a predominantly emmetropic sample.

How genetic is school myopia?

Myopia is of diverse aetiology. A small proportion of myopia is clearly familial, generally early in onset and of high level, with defined chromosomal localisations and in some cases, causal genetic mutations. However, in economically developed societies, most myopia appears during childhood, particularly during the school years. The chromosomal localisations characterised so far for high familial myopia do not seem to be relevant to school myopia. Family correlations in refractive error and axial length are consistent with a genetic contribution to variations in school myopia, but potentially confound shared genes and shared environments. High heritability values are obtained from twin studies, but rest on contestable assumptions, and require further critical analysis, particularly in view of the low heritability values obtained from parent-offspring correlations where there has been rapid environmental change between generations. Since heritability is a population-specific parameter, the values obtained on twins cannot be extrapolated to define the genetic contribution to variation in the general population. In addition, high heritability sets no limit to the potential for environmentally induced change. There is in fact strong evidence for rapid, environmentally induced change in the prevalence of myopia, associated with increased education and urbanisation. These environmental impacts have been found in all major branches of the human family, defined in modern molecular terms, with the exception of the Pacific Islanders, where the evidence is too limited to draw conclusions. The idea that populations of East Asian origin have an intrinsically higher prevalence of myopia is not supported by the very low prevalence reported for them in rural areas, and by the high prevalence of myopia reported for Indians in Singapore. A propensity to develop myopia in "myopigenic" environments thus appears to be a common human characteristic. Overall, while there may be a small genetic contribution to school myopia, detectable under conditions of low environmental variation, environmental change appears to be the major factor increasing the prevalence of myopia around the world. There is, moreover, little evidence to support the idea that individuals or populations differ in their susceptibility to environmental risk factors.

Prevalence of myopia in local and international schools in Hong Kong

PURPOSE

This study aims to investigate genetic and environmental influences on physiological myopia by studying the difference in myopia prevalence between local schools and international schools in Hong Kong.

METHODS

Vision screening was carried out in local and international schools for students 13 to 15 years old. Types of refractive error were identified by visual acuity measurement, the presence of spectacles, a simple refraction, and the use of plus and minus ophthalmic lenses.

RESULTS

Three local schools and six international schools participated in the study. Two hundred eighty-nine students were from the local schools, and 789 students were from the international schools. Prevalence of myopia at the local schools ranged from 85 to 88%, whereas it ranged from 60 to 66% in the international schools. Students in the international schools were subdivided into Chinese origin, white, mixed Chinese, and Asian. Prevalence of myopia was highest in the Chinese group (82.8%) and lowest in the white group (40.5%). There was no age or gender difference in the prevalence of myopia.

CONCLUSIONS

Hong Kong Chinese students had a higher prevalence of myopia regardless of whether they studied in local or international schools when compared with other ethnic groups, such as whites. This further supports a genetic input into myopia development.

Axial length and age at cataract surgery

PURPOSE

To examine the relationship between the axial length of the eye and age at surgery for cataract.

SETTING

Postgraduate teaching hospital.

METHODS

A retrospective review of a consecutive series of 1776 patients older than 40 years was performed. The patient's age at first-eye surgery, axial length, and preoperative and postoperative best corrected visual acuities were recorded. Linear regression analysis was performed using the age at time of cataract surgery as the dependent variable.

RESULTS

Data were available for 1576 of 1670 eyes eligible for inclusion. There was strong evidence of a weak association between a decrease in age at surgery with an increase in axial length (P<.001). The mean patient age at surgery was 74 years for eyes with an axial length less than 25.0 mm, 67 years for eyes with an axial length between 25.0 mm and 30.0 mm, and 61 years for eyes with axial length greater than 30.0 mm.

CONCLUSION

An increase in the axial length of the eye was associated with a lower mean age at time of cataract surgery.

Ocular anisometropia and laterality

PURPOSE

To study the difference in refraction between right and left eyes (anisometropia) in different age groups, look for evidence of eye laterality (more refractive error in one eye) and compare the size of anisometropia in the myopic and emmetropic ranges.

METHODS

The study was based on children in Hong Kong (examined at the age of 6 years and again at the age of 8.5 years) and their parents (aged 26-60 years).

RESULTS

In all age groups the difference between right and left eyes in sphere and cylinder was modest, in most cases < or = 0.25 D. In both children and their parents a tendency towards spherical right eye laterality was found in the myopic individuals (p < 0.05). This was not the case with the cylinder. In the 8.5-year-old children and in their parents, the numerical size of spherical anisometropia increased with myopia (p < 0.05 and p < 0.01, respectively). Cylindrical anisometropia did not exhibit such an increase.

CONCLUSION

In Hong Kong children and their parents we found a tendency towards more spherical myopia in right eyes (laterality) in myopic cases. The numerical size of spherical anisometropia also increased in myopia in these groups. Cylindrical anisometropia appeared to be independent of spherical ametropia. In most cases right/left differences in both sphere and cylinder were small and our findings justify the use of data from one eye only in publications on refraction.

Age, gender, biometry, refractive error, and the anterior chamber angle among Alaskan Eskimos

BACKGROUND

The prevalence of angle-closure glaucoma (ACG) is greater for Eskimos/Inuit than it is for any other ethnic group in the world. Although it has been suggested that this prevalence may be due to a population tendency toward shallower anterior chamber angles, available evidence for other populations such as Chinese with high rates of ACG has not consistently demonstrated such a tendency.

METHODS

A reticule, slit-lamp, and standard Goldmann one-mirror goniolens were used to make measurements in the anterior chamber (AC) angle according to a previously reported protocol for biometric gonioscopy (BG) (Ophthalmology 1999;106:2161-7). Measurements were made in all four quadrants of one eye among 133 phakic Alaskan Eskimos aged 40 years and older. Automatic refraction, dilated examination of the anterior segment and optic nerve, and A-scan measurements of AC depth, lens thickness, and axial length were also carried out for all subjects.

RESULTS

Both central and peripheral AC measurements for the Eskimo subjects were significantly lower than those previously reported by us for Chinese, blacks, and whites under the identical protocol. Eskimos also seemed to have somewhat more hyperopia. There were no differences in biometric measurements between men and women in this Eskimo population. Angle measurements by BG seemed to decline more rapidly over life among Eskimos and Chinese than blacks or whites. Although there was a significant apparent decrease in AC depth, increase in lens thickness, and increase in hyperopia with age among Eskimos, all of these trends seemed to reverse in the seventh decade and beyond.

CONCLUSIONS

Eskimos do seem to have shallower ACs than do other racial groups. Measurements of the AC angle seem to decline more rapidly over life among Eskimos than among blacks or whites, a phenomenon also observed by us among Chinese, another group with high ACG prevalence. This apparent more rapid decline may be due to a cohort effect with higher prevalence of myopia and resulting wider angles among younger Eskimos and Chinese.

The effect of myopic axial elongation and posture on the pulsatile ocular blood flow in young normal subjects

PURPOSE

This study investigated the effect of myopic axial elongation on pulsatile ocular blood flow (POBF) in young normal subjects. A regression equation was derived to quantify the effect. The effect of posture in POBF for eyes with different axial lengths was studied to determine if axial myopia, with different ocular volumes, would result in a change in POBF with various postures.

METHODS

Seventy-nine normal subjects (38 males and 41 females) with different refractive errors were recruited. The mean age of the subjects was 22 years, and only the right eye was used for analysis. The axial length (AL) was measured, followed by Perkins intraocular pressure (IOP) and POBF with an OBF tonometer (OBF Labs [UK] Ltd) in a sitting posture. An "erected arm" blood pressure (BP) was measured with an automatic sphygmomanometer for the calculation of ocular perfusion pressure (OPP), using the formula: mean BP IOP, where the mean BP was calculated as one third of the systolic blood pressure plus two thirds of the diastolic blood pressure. The measurements of IOP, POBF, and BP were repeated in a supine posture.

RESULTS

The POBF was negatively correlated with AL (r = -0.57, p < 0.01). The regression line was in the form of POBF (microl/min) = -78.5 x AL (mm) + 2655.7. There was a significant reduction (17%) in POBF in a supine posture (p < 0.01). The reduction was not significantly correlated with AL. The pulse amplitude also demonstrated a 10% reduction from postural variation (p < 0.01). The OPP increased significantly (33%) in the supine posture (p < 0.01).

CONCLUSIONS

The POBF was significantly influenced by AL. Therefore, AL should be measured in determining the POBF, especially in young myopic subjects. The amount of postural variation in POBF was similar to previous studies with young subjects and was not affected by AL.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Uncorrected binocular distance visual impairment in U.S. Hispanic children and adolescents

PURPOSE

To assess and compare uncorrected binocular distance visual impairment rates in U.S. Hispanic children and adolescents.

METHODS

Data from the Hispanic Health and Nutrition Examination Survey, 1982-1984, were analyzed for 6-19 year-old Cuban-Americans (n = 317), Mexican-Americans (n = 2519), and Puerto Ricans (n = 988). Visual acuity was assessed using Sloan Letters or Landolt Rings.

RESULTS

Prevalence rates of uncorrected binocular distance visual impairment (20/30 or worse) were 15.5%, 14.9%, and 23.6% for Cuban-Americans, Mexican-Americans, and Puerto Ricans, respectively. After adjusting for age and gender, the differences between Puerto Ricans and both Cuban-Americans and Mexican-Americans were significant (p < 0.05). Children 6-12 years of age had lower visual impairment rates than 13-19 year-old adolescents. Girls had higher age-adjusted visual impairment rates than boys; these gender differences were statistically significant among Mexican-Americans (OR = 1.6, 95% CI = 1.1, 2.2) and Puerto Ricans (OR = 1.7, 95% CI = 1.2, 2.4).

CONCLUSIONS

Among Hispanics, Puerto Rican children and adolescents have the highest prevalence rate of uncorrected binocular distance visual impairment; older age and female gender are associated with higher rates of uncorrected visual impairment.

Temporal variations in myopia progression in Singaporean children within an academic year

PURPOSE

Excessive nearwork is believed to be associated with myopia development and progression. To investigate this further, we studied refractive error changes and their correlation with nearwork in a cohort of grade school children in Singapore.

METHODS

Cycloplegic autorefraction was performed 5 times over 10 months on 168 children aged 7, 9, and 12 years who were further divided into myopic and nonmyopic subgroups based in their initial refractive errors. Information about nearwork was obtained through diaries filled out over 24 h at the commencement of the study.

RESULTS

Myopia progression was high (overall mean: -0.87 D per year) and largely linear throughout the year, but significantly higher rates were seen after the final school examinations in 7-year-old myopes and nonmyopes. Overall, myopic groups exhibited higher progression rates than nonmyopic groups, although 33.6% of subjects from the latter groups had become myopic by the end of the study. Nearwork scores derived from the diaries were generally not well correlated with overall myopia progression.

CONCLUSIONS

The tendency for myopia progression rates to increase after the final school examinations in 7-year-olds is interpreted as a delayed effect of the intense nearwork associated with preparing for them. The timing of nearwork-diary data collection at the beginning of the study could be responsible for the poor correlation between these data and overall myopia progression rates.

Ocular components values and their intercorrelations in Saudi Arabians

There are no previous studies on the dimensions of ocular components and their intercorrelations in adult Saudi Arabians. In this study ocular components were measured by ultrasonography and keratometry in 152 adult Saudis. Their ages ranged from 16 to 50 years. The males had significantly longer anterior chamber depth (ACD), vitreous chamber depth (VCD), axial length (AL) and axial length/corneal radius ratio (AL/CR) than females. However, females had non-significantly steeper corneas than males. The AL/CR ratio had the highest correlation with refractive error. Corneal radius of curvature was positively correlated with VCD and AL. Lens thickness was negatively correlated with the VCD, AL and AL/CR ratio. Myopes had significantly deeper ACD, VCD, and higher AL/CR ratio than nonmyopes. Myopes had significantly thinner lenses than hyperopes. The average values of the optical components and their intercorrelations are similar to reported values obtained from subjects of other races but with comparable refractive errors.

Corneal shape in hyperopia

Background: A trend towards decreased peripheral corneal flattening with increasing myopia has recently been demonstrated. The present study was conducted to determine whether corneal asphericity also varies significantly with hyperopic refractive error. Methods: Thirty-five eyes with spherical equivalent refractive error ranging from -0.37 D to +6.00 D were examined. A conicoid equation was fitted to videokeratoscopic (Topographic Modeling System) data and corneal asphericity and apical radius of curvature values were calculated for each subject. Axial length measurements were made using a hand-held biometric ruler. Keratometry was also performed on each eye. Results: The relationship between corneal asphericity (Q) and spherical equivalent refractive error was not statistically significant (p = 0.7419). In addition, no association could be demonstrated between Q and corneal radius of curvature or between Q and axial length. Corneal radius of curvature was positively correlated with axial length (r = 0.367, p = 0.0298). Axial length was found to decrease as hyperopic refractive error increased (r = 0.753, p = 0.0001). Conclusions: For hyperopic eyes, corneal asphericity does not appear to be significantly correlated with refractive error, a finding that is at variance with previous data for myopic eyes showing an association between these two variables. The results suggest that there may be differences between hyperopic and myopic eyes with regard to the anterior segment changes that occur during refractive error development.