The distribution of refraction in three isolated communities in Western Newfoundland

Reappraisal of the historical myopia epidemic in native Arctic communities

PURPOSE

This study was developed to explain the extraordinary rise in myopia prevalence beginning after 1950 in Indigenous Arctic communities considering recent findings about the risk factors for school myopia development. Myopia prevalence changed drastically from a historical low of less than 3% to more than 50% in new generations of young adults following the Second World War. At that time, this increase was attributed to concurrent alterations in the environment and way of life which occurred in an aggressive programme of de-culturalization and re-acculturation through residential school programmes that introduced mental, emotional and physical stressors. However, the predominant idea that myopia was genetic in nature won the discussion of the day, and research in the area of environmental changes was dismissed. There may have also been an association between myopia progression and the introduction of extreme mental, emotional and physical stressors at the time.

RECENT FINDINGS

Since 1978, animal models of myopia have demonstrated that myopiagenesis has a strong environmental component. Furthermore, multiple studies in human populations have shown since 2005 how myopia could be produced by a combination of limited exposure to the outdoors and heavy emphasis on academic subjects associated with intense reading habits. This new knowledge was applied in the present study to unravel the causes of the historical myopia epidemics in Inuit communities.

SUMMARY

After reviewing the available published data on myopia prevalence in circumpolar Inuit populations in the 20th century, the most likely causes for the Inuit myopia epidemic were the combination of increased near work (from almost none to daily reading) and the move from a mostly outdoor to a much more indoor way of life, exacerbated by fewer hours of sunshine during waking hours, the lower illuminance in the Arctic and the extreme psychophysical stress due to the conditions in the Residential Schools.

Global variations and time trends in the prevalence of childhood myopia, a systematic review and quantitative meta-analysis: implications for aetiology and early prevention

The aim of this review was to quantify the global variation in childhood myopia prevalence over time taking account of demographic and study design factors. A systematic review identified population-based surveys with estimates of childhood myopia prevalence published by February 2015. Multilevel binomial logistic regression of log odds of myopia was used to examine the association with age, gender, urban versus rural setting and survey year, among populations of different ethnic origins, adjusting for study design factors. 143 published articles (42 countries, 374 349 subjects aged 1–18 years, 74 847 myopia cases) were included. Increase in myopia prevalence with age varied by ethnicity. East Asians showed the highest prevalence, reaching 69% (95% credible intervals (CrI) 61% to 77%) at 15 years of age (86% among Singaporean-Chinese). Blacks in Africa had the lowest prevalence; 5.5% at 15 years (95% CrI 3% to 9%). Time trends in myopia prevalence over the last decade were small in whites, increased by 23% in East Asians, with a weaker increase among South Asians. Children from urban environments have 2.6 times the odds of myopia compared with those from rural environments. In whites and East Asians sex differences emerge at about 9 years of age; by late adolescence girls are twice as likely as boys to be myopic. Marked ethnic differences in age-specific prevalence of myopia exist. Rapid increases in myopia prevalence over time, particularly in East Asians, combined with a universally higher risk of myopia in urban settings, suggest that environmental factors play an important role in myopia development, which may offer scope for prevention.

The cause(s) of myopia and the efforts that have been made to prevent it

In spite of a long history of study, as well as a significant, recent increase in research attention, the cause(s) and the means of preventing or mitigating the progression of myopia in children are still elusive. The high and growing prevalence of myopia, especially in Asian populations, as well as its progressive nature in children and its effect on visual acuity, have contributed to the recent surge in interest. Animal research carried out in the 1970s also helped spark this interest by legitimising the study of environmental influences on the refractive development of the eye. Efforts that include the use of visual training or biofeedback, bifocal and progressive lenses, contact lenses and pharmaceuticals are reviewed. Current research trends that focus on the relationship between genetics and environment, as well as studies, both animal and human, that explore the effect of peripheral refractive error on the refractive development of the central retina are also reviewed.

Temporal constraints on experimental emmetropization in infant monkeys

PURPOSE

To characterize the temporal integration properties of the emmetropization process, the authors investigated the effects of brief daily interruptions of lens wear on the ocular compensation for negative lenses in infant rhesus monkeys.

METHODS

Eighteen monkeys wore -3 D lenses binocularly starting from approximately 3 weeks of age. Six of these monkeys wore the lenses continuously. For the other animals, the -3 D lenses were removed for four 15-minute periods each day. During these periods, the monkeys viewed through either zero-power lenses (n = 6) or +4.5 D lenses (n = 6). Three monkeys reared with binocular plano lenses and 16 monkeys reared normally served as controls. Refractive development was assessed by cycloplegic retinoscopy and A-scan ultrasonography.

RESULTS

As expected, the group of animals that wore the -3 D lenses continuously exhibited clear evidence of compensating axial myopia. These predictable myopic changes were mostly eliminated by the brief, daily periods of viewing through plano lenses. Interestingly, brief periods of viewing through +4.5 D lenses produced weaker protective effects.

CONCLUSIONS

Brief periods of unrestricted vision can prevent the axial myopia normally produced by long daily periods of imposed hyperopic defocus. Thus, the temporal integration properties of the emmetropization process normally reduce the likelihood that transient periods of hyperopic defocus will cause myopia.

Homeostasis of eye growth and the question of myopia

As with other organs, the eye's growth is regulated by homeostatic control mechanisms. Unlike other organs, the eye relies on vision as a principal input to guide growth. In this review, we consider several implications of this visual guidance. First, we compare the regulation of eye growth to that of other organs. Second, we ask how the visual system derives signals that distinguish the blur of an eye too large from one too small. Third, we ask what cascade of chemical signals constitutes this growth control system. Finally, if the match between the length and optics of the eye is under homeostatic control, why do children so commonly develop myopia, and why does the myopia not limit itself? Long-neglected studies may provide an answer to this last question.

Ocular and visual defects amongst people with intellectual disabilities participating in Special Olympics

PURPOSE

To analyse data from vision screening of people with intellectual disabilities from the UK participating in Special Olympics during the National Summer Games in Cardiff 2001, in order to determine visual status and access to eye care.

METHODS

Athletes were invited to take part in vision screening, according to Special Olympics protocols.

RESULTS

Testability rates were high. Findings confirmed the high prevalence of eye and vision defects reported in other studies of people with intellectual disabilities. In particular, visual acuity was below normal for most athletes. Significant improvement to acuity could be achieved with spectacles although correction after full refraction did not always provide normal vision. Over 40% of athletes undergoing full refraction had below normal corrected acuity.

CONCLUSIONS

Athletes with intellectual disabilities were no more likely to access eye care and have adequate spectacle correction than other people with intellectual disabilities. Optometrists and carers need to be aware of the high prevalence of defects and the importance of regular eye examinations in people with intellectual disabilities.

Refractive errors and axial length among Alaskan Eskimos

An epidemiological study of the prevalence of refractive errors was made of the Eskimo population of the Norton Sound and Bering Straits region of Alaska. It was possible to determine the subjective refraction in 83.7% of 1673 persons examined: 44.9% were emmetropic, 44.7% myopic and 10.4% hyperopic. Myopia was found more often in women (48.3%) than in men (41.3%), while emmetropia was found more often in men (49.3%) than in women (40.3%). Nine,four percent of the men were hyperopic and 11.4% of the women. The prevalence of myopia increased with age, with a maximum of 67.2% in the age group between 30 and 40 years. Subsequently, the number of myopes decreased rapidly. Little hyperopia was seen before the age of 50 years, it then increased rapidly, up to 71.5% for persons above the age of 80 years. Emmetropia, on the other hand, decreased with age. Ultrasound examination showed that an increasing axial length was associated with more myopia.

Nearwork, school achievement and myopia

Data from 723 families tested for ocular refraction, measures of cognitive ability and school achievement, and measures of school-related nearwork activity were analysed, to examine the association of nearwork and intellectual ability with the development of myopia. The basis of the tests was detection of heterogeneity of standardized regression coefficients, derived from the regression of spherical refraction on age, between scaled nearwork or achievement measures. The results did not provide any evidence in support of the hypothesis that nearwork influences myopia but did confirm a relationship between school grades and myopia.

Refractive errors in a Finnish rural population

Refractive errors in 611 persons living in a rural area were examined. Males numbered 281 and females 330. The age range was from 6 to 85 years. In 73 (11.9%) persons the refraction was myopic (SER less than or equal to 0.5 D) and in 173 (28.3%) hyperopic (SER greater than or equal to + 2 D). Myopia was most frequently detected in persons aged 21-30 years (22.6%), and the proportion of myopia decreased towards both extremes of age. In all age groups females were more myopic than males. In persons aged 21-60 years the most educated proved to have more myopia and less hyperopia than those with less education. In 158 (25.9%) of the eyes, astigmatism was detectable. The degree of astigmatism changed little with advancing age and was independent of sex. In myopic eyes the range of astigmatic error was wider than in hyperopic eyes. The axis of + cylinders was in hyperopic eyes mostly horizontal and in myopic eyes vertical. Anisometropia of 1.25-2.0 D was detected in 24 (4.0%) persons and in 19 (3.1%) persons it was over 2 D.

The importance of ophthalmic diseases in the economy and national health care system

The incidence of eye diseases in Finland and the use of glasses has not been much investigated. During 1979-80 an inquiry was made in which a questionnaire was sent by mail to 12 000 people. 1500 volunteers from Estern, Western and Southern Finland were invited to a clinical eye examination. The incidence of eye diseases was low. A little over 2% of the respondents needed continuous ophthalmic treatment. The mean visual acuity was normal in 80% with glasses. About half of the patients examined wore glasses, slightly more females than males.

Sex differences in refraction errors up to the age of 15

A health inquiry concerning vision and corrective lenses at the age of 14 was carried out in a northern Finland series about 12,000 children followed up since birth. Data were obtained from more than 99% of cases. 34% of the girls and 18% of the boys had corrective lenses. 55% of the study population were living in the province of Oulu, and the ophthalmological records of these children were analysed (N 1939). The ophthalmological records covered 67% of the children with lenses in the province of Oulu. 71% of the girls with lenses, and 66% of the boys had these for myopia, both myopia and hyperopia were less common among the boys, but the cases were more pronounced. The children with lenses were on average taller and heavier and the myopic children had a better mean ability at school.

Nearwork and familial resemblances in ocular refraction: a population study in Newfoundland

There is considerable epidemiological evidence that the nearwork associated with formal education can cause myopia. The potential for nearwork and education, as aspects of common familial environment, to inflate resemblances among nuclear family members in ocular refraction, was therefore investigated in a sample of 957 persons aged 5 years and over, comprising approximately 80% of the population above that age in three communities on the west coast of Newfoundland. Refraction was evaluated using standard optometric methods, nearwork measured in hours/day as reported by each subject, education measured as last completed school grade in years. The effects of nearwork and education on refraction resemblances were evaluated by adjusting refraction for age and sex, then comparing correlations or regressions among relatives before and after further linear regression adjustment of refraction for nearwork and education. Reductions in sib-sib correlations and offspring-parent regressions were achieved in this way, suggesting that these environmental factors inflate familial resemblances in refraction. Patterns of resemblances among relatives after adjustment suggest that the effects of nearwork and education on refraction resemblances were not completely removed by the linear regression adjustment used.

Refraction, nearwork and education. A population study in Newfoundland

There is little information directly relating ocular refraction and nearwork habits in representative human populations. Ocular refraction (diopters), nearwork (hours per day), and education (years) were therefore measured for 957 persons comprising 80% of the population aged 5 years and above of 3 communities in western Newfoundland. Refraction was moderately, consistently and significantly correlated with nearwork from ages 5 to 60, and remained so after adjustments for the association of refraction and nearwork levels with age, sex and education. Multiple regression coefficients relating refraction to nearwork decreased from -0.43 D/h at ages 5-14 years to -0.22 D/h at ages 60 years and up. The magnitude of this association, and its consistency and persistence over a wide age range, suggest that large amounts of nearwork in childhood may contribute to the prevalence of clinical myopia.