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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/14188668 Epidemiology of Myopia Article in Epidemiologic Reviews · February 1996 DOI: 10.1093/oxfordjournals.epirev.a017924 · Source: PubMed CITATIONS 333 READS 6,945 5 authors, including: Some of the authors of this publication are also working on these related projects: The Singapore Epidemiology of Eye Diseases (SEED) Study View project Seang-Mei Saw National University Health System 568 PUBLICATIONS 19,800 CITATIONS SEE PROFILE All content following this page was uploaded by Seang-Mei Saw on 12 January 2014. The user has requested enhancement of the downloaded file.

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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/14188668

Epidemiology of Myopia

Article  in  Epidemiologic Reviews · February 1996

DOI: 10.1093/oxfordjournals.epirev.a017924 · Source: PubMed

CITATIONS

333

READS

6,945

5 authors, including:

Some of the authors of this publication are also working on these related projects:

The Singapore Epidemiology of Eye Diseases (SEED) Study View project

Seang-Mei Saw

National University Health System

568 PUBLICATIONS   19,800 CITATIONS   

SEE PROFILE

All content following this page was uploaded by Seang-Mei Saw on 12 January 2014.

The user has requested enhancement of the downloaded file.

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Epidemiologic ReviewsCopyright © 1996 by The Johns Hopkins University School of Hygiene and Public HealthAll rights reserved

Vol. 18, No. 2Printed in U.S.A.

Epidemiology of Myopia

Seang-Mei Saw,1 Joanne Katz,2 Oliver D. Schein,3 Sek-Jin Chew,4 and Tat-Keong Chan5

INTRODUCTION

Myopia is the state of refraction in which parallelrays of light are brought to focus in front of the retinaof a resting eye (1). Myopia is measured by the spher-ical power in diopters of the diverging lens needed tofocus light onto the retina, which can be expressed asthe spherical equivalent or refraction in the least my-opic meridian (2, 3). The clinical correlates of myopiainclude blurred distance vision, eye rubbing, andsquinting.

Myopia has been classified as either physiologic orpathologic. Physiologic myopia occurs due to an in-crease in the axial diameter of the eye over that whichis attained by normal growth. Pathologic myopia iscaused by an abnormal lengthening of the eyeball, andis often associated with thinning of the scleral wall (1).Another classification is based on age of onset. Con-genital, or infantile, myopia occurs at birth, with areported prevalence in the full-term newborn varyingfrom 0.0 to 24.2 percent. This variability is due totechnical difficulties in measuring refraction in new-borns (4). School myopia occurs at approximately7-17 years of age and stabilizes by the late teens orearly twenties. Both school and adult-onset myopia aremainly the result of idiopathic causes, while congen-ital myopia is often associated with other abnormali-ties.

Severe myopia may be associated with myopic mac-ular degeneration, cataract, glaucoma, peripheral reti-nal changes (such as lattice degeneration), and retinal

Received for publication January 4,1996, and accepted for pub-lication July 16, 1996.

Abbreviation: NHANES, National Health and Nutrition Examina-tion Survey.

1 Department of Epidemiology, School of Hygiene and PublicHealth, The Johns Hopkins University, Baltimore, MD.

2 Department of International Health, School of Hygiene andPublic Health, The Johns Hopkins University, Baltimore, MD.

3 Dana Center for Preventive Ophthalmology, Wilmer Eye Insti-tute, The Johns Hopkins Hospital, Baltimore, MD.

4 Singapore Eye Research Institute, Singapore National Eye Cen-ter, Singapore.

5 Department of Ophthalmology, National University Hospital,Singapore.

Reprint requests to Dr. Joanne Katz, Department of InternationalHealth, School of Hygiene and Public Health, The Johns HopkinsUniversity, 615 North Wolfe Street, Baltimore, MD 21205.

holes and tears, as well as retinal detachment. Methodsof correction of myopia are not without complications,including corneal infections due to contact lens wearand corneal scarring and persistent corneal haze fromrefractive surgery (5).

The public health and economic impact of myopia,the most common eye condition in the world, is enor-mous. In the United States, the cost of correctingrefractive errors with spectacles or contact lenses isestimated to be 2 billion dollars per year (6). Themilitary spends large amounts of money on pilot train-ing, but pilots may not be able to continue flying ifthey develop myopia. Thus, myopia is a condition withsocial, educational, and economic consequences.

Over the past few decades, there has been an in-crease in the prevalence of myopia in some popula-tions, leading to growing concern among the publicand the scientific community. The Chinese and Japa-nese appear to have had escalations of myopia rates.There is no well established or universally acceptedtreatment for the prevention of myopia onset or pro-gression.

This review will summarize the descriptive epide-miology of myopia, possible risk factors for myopia,and the interventions available to prevent the onset andprogression of myopia. The limitations of the existingresearch will be addressed, as well as suggested direc-tions for further research.

DEFINITION OF MYOPIA IN EPIDEMIOLOGICSTUDIES

Different studies have adopted different definitionsof myopia. The most common definitions are a refrac-tive error greater than 0.25 diopter and a refractiveerror greater than 0.50 diopter. The lack of uniformcriteria has led to difficulties in comparing prevalencerates in different studies. Cross-sectional and cohortstudies use different criteria for defining persons asmyopic. All studies should specify the definition ofmyopia used and the range of refractive error of thesubjects in the study.

The accuracy and reliability of ophthalmologic andrefractive examinations is crucial in epidemiologicstudies. The "gold standard" for measurement of re-

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fractive error in children is cycloplegic refraction (1).Cycloplegia is the act of paralyzing the muscles ofaccommodation in the eye. Usually, cyclopentolatehydrochloride eye drops are instilled, which providescycloplegia lasting for 1 hour. Cycloplegic refractionis especially important in children and infants, as theyhave strong accommodative responses which may leadto "pseudomyopia" (7). However, often cycloplegicrefraction is not used for the diagnosis of myopia inchildren and young adults. Thus, myopia rates may beoverestimated in the determination of refractive errorin these studies.

PREVALENCE AND DEMOGRAPHIC PATTERNS

There is considerable geographic variation in thereported prevalence of myopia (table 1). It is difficultto compare prevalence rates between countries basedon previous studies; the definitions of myopia are notuniform, and refraction may have been performedwithout cycloplegia. Prevalence studies are not allpopulation-based, with some studies being conductedon convenient select groups of individuals with limitedgeneralizability. The prevalence of myopia varies withtime and the age of the study population.

From data gathered on 7,401 persons aged 12-54years in the National Health and Nutrition Examina-tion Survey (NHANES) in 1971 and 1972, the preva-lence of myopia in the United States was estimated tobe 25 percent (8). However, the exact criteria formyopia in this survey were not clearly defined. Thispopulation-based survey did not include cycloplegicrefraction (thereby probably overestimating the rateand degree of myopia), and the nonparticipation ratewas 30 percent. A more recent population-based sur-vey in Beaver Dam, Wisconsin, of 4,926 adults be-tween the ages of 43 and 84 years showed a decreasingprevalence of myopia with age, from 43.0 percent inthe age group 43-54 years to 14.4 percent in subjectsabove the age of 75 years (9). Myopia was defined asmore than 0.5 diopter; however, there was no mentionof whether cycloplegia was used.

In Scandinavia, most of the studies were notpopulation-based (10). Myopia prevalence was re-ported to be 50.3 percent among 133 medical studentsin Norway (11). In Sweden, the prevalence of myopiaamong 2,616 Swedish conscripts aged 20 years was8.9 percent. These studies defined myopia as morethan 0.25 diopter, and no cycloplegia was used. Ap-proximately 20.5 percent of 21,000 Icelanders re-fracted with cycloplegia in 1975 were myopic, definedas more than 0.5 diopter (10).

In Asia, there is currently a high prevalence ofmyopia, especially among the Chinese and Japanese.As early as the 1930s, Rasmussen (12) estimated aprevalence of myopia of approximately 70 percent inChina; however, the refraction procedures were notclearly described. A total of 4,000 schoolchildren aged6-18 years were refracted with cycloplegia in anisland-wide survey in Taiwan in 1983. There was anincreasing prevalence of myopia with age, from 4percent at age 6 years to 40 percent at age 12 years,more than 70 percent at age 15 years, and more than75 percent at age 18 years (13). Three studies carriedout in Singapore showed varying myopia rates: 24.9percent in 10-year-old Chinese children, 63 percent inuniversity freshmen aged 19 years, and 82 percent inmedical students (14-16). However, the definitions ofmyopia differed. Various surveys in India have foundmyopia prevalences ranging from 6.9 percent to 19.7percent (17, 18). The techniques used for refractionand the definition of myopia used were often notmentioned in the studies conducted in Asia.

In agricultural countries, the prevalence of myopiahas been low. There have been several population-based studies. On the South Pacific island of Vanuatu,788 Melanesian children aged 6-19 years were exam-ined and refracted without cycloplegia. Only 2.9 per-cent were found to be myopic by 0.5 diopter or more(19). In the Solomon Islands, an ophthalmic surveyconducted in 1966 found that only 0.8 percent of thestudy population from the islands of Bougainville andMalaita were myopic by 0.25 diopter or more. No

TABLE 1. Summary of selected studies of myopia prevalence

oounuy

Solomon IslandsVanuatuSweden

Iceland

United StatesNorway

Taiwan

Study(ref. no.)

Verlee (20)Grosvenor(19)Str6mberg (cited by

Fledelius (10))Sveinsson (23)

Sperduto et al. (8)Midelfart et al. (11)

Lin et al. (13)

Population-based?

YesYesNo, conscripts

No, spectacle/MrtCI iftC

YesNo, medical

studentsYes

Samplesize

512788

2,616

21,000

7,401133

4,000

Cycloplegicrefraction?

NoNoNo

Yes

NoNo

Yes

Myopiadefinition

>0.25 diopter>0.5 diopter>0.25 diopter

>0.5 diopter

>0.25 diopter

Age(years)

1-696-19

20

1-89

12-5421-33

6-18

Prevalence(%)

0.82.98.9

21

2550.3

75 at age18 years

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Epidemiology of Myopia 177

cycloplegic refraction was done on the 512 subjects(20).

Myopia not only shows regional variation in prev-alence but also exhibits country-specific differences insecular trends as well. A possible reason for the in-crease in myopia rates in many countries is the in-crease in formal education, with more time being spenton closeup work, in the past few decades. The preva-lence of myopia has increased over the past severaldecades in Singapore and Japan (21, 22). Similarly,the prevalence of myopia in Iceland increased from3.6 percent in 1935 to 20.51 percent in 1975 (23). TheIceland study included the use of cycloplegic refrac-tion and the same myopia definition of more than 0.5diopter over the 50-year period.

Sex and race also affect the distribution of myopia.The 1971 and 1972 NHANES data showed that prev-alence rates were higher in females than in males andhigher in whites than in blacks in the United States (8).Several other studies have found a slightly higherpreponderance of myopia in females (9, 21). Certainethnic groups, such as Asians and Jews, have a higherprevalence of myopia, whereas Africans and AfricanAmericans have a low myopia prevalence rate (8). InHawaii, the prevalence of myopia varies among thedifferent ethnic populations: 17 percent in Chinese, 13percent in Koreans, 12 percent in Japanese, and 12percent in Caucasians (24). In a Taiwanese survey,where the eyes of children in one school were re-fracted under cycloplegia, the prevalence of myopiaamong the purely aboriginal children was 13 percent,compared with 30 percent in the Chinese children(25).

The prevalence of myopia changes considerablywith age. Newborns are usually hyperopic. In subse-quent years, the ocular axis elongates, with thinning ofthe lens and flattening of the cornea, which leads toemmetropia in children by age 8-10 years (22). Whenmyopia occurs, it usually develops between the ages of6 and 14 years. Thereafter, the prevalence of myopiaremains relatively constant between the ages of 12 and54, as reported in the US NHANES data (8). There isa decreasing prevalence of myopia with increasing ageafter age 40 years (9).

To facilitate appropriate comparisons of the preva-lence of myopia across different populations, studiesshould be population-based, have similar definitionsof myopia, refract children under cycloplegia, andreport findings by age. This will allow researchers tocompare prevalence rates across geographic bound-aries. Similarly, studies of secular trends in myopiarates and the sociodemographic characteristics of my-opia should have the same definitions of myopia andshould include refraction by cycloplegia.

Incidence and progression of myopia

There is a lack of adequate data on the incidence ofmyopia from population-based cohort studies. Over a10-year period, the incidence of myopia among Israelipilots was 7.4 percent in 991 pilots with 20/20 visionin each eye upon entry into the profession and 22.5percent in 221 pilots with 20/25 vision in one eye uponentry into the profession (26). The results of this studyare only generalizable to populations of pilots in Is-rael, who are varied ethnically (European, North Af-rican, Asian). This is also a very unusual definition ofmyopia; it is unclear how 20/25 vision relates to re-fractive error.

Longitudinal studies have found that myopia stopsincreasing earlier in females than in males, and thatmean cessation ages range from 14.44 to 15.28 yearsfor females and 15.01 to 16.66 years for males (27).Lin et al. (28), however, showed that even after pu-berty, myopia continues to progress slowly, and theincrease in axial length is the main component inmyopia progression. Both Goss (29) and Chew et al.(30) have reported that a greater amount of myopia atthe initial examination age is associated with a greaterrate of progression. In a study of Finnish schoolchil-dren by Parssinen and Lyyra (31), myopia progressedfaster in girls than in boys, in children with an earlierage of onset of myopia, and in children who had moresevere myopia at initial examination. All of thesestudies have a potential bias in that they examinedpopulations that self-referred for spectacle or contactlens correction of myopia (i.e., perhaps only certaintypes of people seek help when they first start tobecome myopic, while others wait longer before seek-ing correction of their myopia).

RISK FACTORS FOR MYOPIA

Both environmental and genetic factors have beenassociated with the onset and progression of myopia.The use-abuse theory states that closeup work causesmyopia, as seen in the higher prevalence of myopiaamong persons who are more highly educated and arein white collar occupations. The genetic theory, on theother hand, is based on the belief that natural individ-ual variation in eye growth will produce myopia incertain individuals (3). The mechanisms underlyingthe environmental and genetic factors, and the natureof the interaction between the two factors, is notcertain. Educational level, intelligence, certain person-ality traits, and socioeconomic status have all beenassociated with myopia. Premature and low-birth-weight infants have a higher risk of developingmyopia later in life (32-34). The effects of malnutri-tion and height on myopia are poorly substantiated

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(35-37). The strongest evidence for an environmentalcause is the effect of closeup work on the onset andprogression of myopia.

Family history

There is a greater prevalence of myopia in childrenof myopic parents than in children of nonmyopic par-ents (38, 39). Genetic studies of myopia have mainlybeen twin studies, pedigree studies, and studies offamilial correlation. Family studies by Sorsby et al.(40) and Keller (41) demonstrated significant parent-child correlations. However, it is difficult to separatehereditary factors from environmental factors such assimilar work patterns in parents and their children(41). Initial cross-sectional results of the Orinda Lon-gitudinal Study of volunteer schoolchildren showedthat before the onset of myopia, the children of myopicparents had longer eyes, suggesting a possible hered-itary predisposition to myopia. However, early envi-ronmental factors may also have led to longer eyes(42). The role of heredity is postulated to be moresignificant in persons with higher degrees of myopia.In a study of 258 myopic patients, the percentage ofparents with myopia was 15 percent for those withmyopia of less than 1.00 diopter versus 55 percent forpatients with myopia of more than 7.00 diopters (43).

Different modes of Mendelian inheritance, includ-ing autosomal dominant, autosomal recessive, andsex-linked, have been suggested by different authors(44, 45). In a study conducted in Hawaii of 185 fam-ilies with both parents of Japanese ancestry and of 192families with both parents of European ancestry, seg-regation analysis was performed (46). The resultsshowed that there was little evidence for a Mendelianmode of genetic inheritance.

Past twin studies have not defined the mode ofinheritance but have provided evidence to support theheritability of myopia. Accurate classification of zy-gosity and the comparison of monozygotic and dizy-gotic twin populations of similar characteristics areimportant considerations in the design of twin studies(47). Similar results have been obtained from twinstudies conducted in the United Kingdom, Finland,Taiwan, and Shanghai, where there were higher con-cordance rates of myopia in monozygotic twins than indizygotic twins (48-51). In a study of Chinese twinpairs (52), there was a higher concordance rate ofmyopia (92.2 percent) for monozygotic twins withconcordant close-work habits (differences of less than1 hour per day spent studying and reading) than formonozygotic twins (79.3 percent) with discordantclose-work habits. The authors concluded that therewas significant additive interaction between zygosityand close-work habits.

The exact mode of inheritance and possible geneticmarkers for myopia have not been identified. Not allobservations, such as the increase in myopia preva-lence in Taiwan, Singapore, and Hong Kong, can beexplained solely by genetic causes. There may be aninteraction between genetic and environmental factorswherein some individuals have a genetic predisposi-tion such that they are more susceptible to environ-mental influences causing myopia. More conclusiveand well-designed studies of family pedigrees of indi-viduals with high myopia that use genetic markersassociated with myopia must be conducted. The mark-ers for collagen metabolism, intelligence, and retinalneurotransmitters could provide clues to the locationof possible myopia genes.

Education and intelligence

Several cross-sectional studies in Denmark, Israel,the United States, and Finland have shown a higherprevalence of myopia among individuals with highereducational levels (53-56). Other studies have shownan association between myopia and intelligence andsocioeconomic status (57-60).

Refractive error and intelligence have been com-pared in various studies, with inconsistent results. Pos-itive associations were found in Ohio and in Auckland,New Zealand, when the California Test of MentalMaturity and the Otis Self-Administered Test, respec-tively, were used to evaluate intelligence (59, 60).However, no relation was found when the Stanford-Binet Test was used in Ohio or when the Raven MatrixTest was used in Auckland (59, 60).

Ashton (61), in Hawaii, measured the effects of bothcloseup work and intelligence on the onset of myopia.Although no association between myopia and closeupwork was found, a relation between school achieve-ment and myopia was noted. The results of this studymay have been affected by the crude measure ofcloseup work (number of books and magazines readper month), refraction without the use of cycloplegia,and the cross-sectional nature of the study.

Questions about the validity of intelligence testingand the omission of information on other confoundingfactors, such as closeup work, socioeconomic status,and educational level, limit conclusions from previousstudies of intelligence and myopia (57-60). Hirsch(59) noted that intelligence test scores could be influ-enced by the amount of reading a child does or that amore intelligent child might read more and thus be-come more myopic. Educational level and intelligenceare strongly related to amount of closeup work and areprobably not independent risk factors but surrogatesfor closeup work.

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Closeup work

Closeup work encompasses tasks of high accommo-dative demand, such as reading, writing, computerwork, and close television viewing. It has been sug-gested that the side-to-side movement of the eyesduring reading has a different effect on myopia thandoes close work without similar eye movement, suchas sewing (31). The incidence of myopia increases atthe time children start attending school, and this sug-gests that closeup work may be a cause of the devel-opment of myopia (62). The increase in myopia prev-alence observed in Hong Kong, Taiwan, Japan, andSingapore over the past few decades suggests an en-vironmental risk factor, since the gene pool has notchanged. There has been an increase in educationalattainment over the past several decades, with an ac-companying increase in myopia incidence, in coun-tries such as the United States (63). However, theseobservations have generally been ecologic rather thanepidemiologic. An increased prevalence of myopia isobserved in certain occupations, such as microscopy,sewing, and carpet weaving, that require a largeamount of time spent in closeup work (64). However,it is difficult to separate cause from effect; the study ofpersons in select occupational groups who spend largeamounts of time on close work may be part of aselection process whereby individuals with myopiamay prefer these occupations. Further evidence for theclose-work hypothesis is the higher prevalence of my-opia among college graduates, with a higher numberof new cases in the college years, compared with otheradults in the same age group (65). In 1964, Sato (66)noted a higher incidence of myopia among US grad-uates after they studied Chinese in universities.

In the native populations of the Arctic regions ofAlaska and Canada there has been a notable increasein myopia in the younger generation. There is littleparent-child correlation in refractive error, but asibling-sibling correlation now exists. The prevalenceof myopia was much higher in young persons com-pared with older individuals among Alaskan Eskimos,Canadian Inuit, members of a Labrador community,Yupik Eskimos, and American Indians in Ontario (67-71). The increase in myopia incidence in Arctic re-gions has coincided with the establishment of compul-sory schooling after World War II and with an increasein exposure to closeup work. Intermarriage withwhites could also be contributing to a genetic changein the predisposition to myopia. However, a homoge-nous change in refractive error in different populationssuggests that intermarriage is unlikely to be contrib-uting substantially to the rising incidence of myopiaand, more importantly, Caucasians do not have veryhigh rates of myopia. Thus, closeup work has been

implicated as a risk factor for the onset of myopia (8).The mechanisms for myopia onset and progressionmay be similar, and the association between closeupwork and myopia progression can provide evidencefor the causation of myopia onset.

Cross-sectional prevalence studies

Cross-sectional studies conducted in Newfoundlandand Hong Kong have found positive associations be-tween closeup work and the prevalence of myopia(72-74). The odds ratio for myopia in subjects whoattended school in the Hong Kong study was 1.7 (95percent confidence interval 1.0-3.0). However, refrac-tion was measured without cycloplegia in these stud-ies. The measures of closeup work were crude andwere obtained from questions on the amount of read-ing and writing done. The effects of different types ofcloseup work, such as reading or watching television,and variations in levels over time were not assessed.Moreover, the studies did not account for variations inthe amount of closeup work by age, or the distancesused for various tasks.

An interesting study was conducted in Israel inwhich orthodox schoolboys of identical ethnic back-ground had a myopia prevalence of 81.3 percent, ascompared with 27.4 percent among boys from generalschools (myopia was defined as more than 0.50 diop-ter; cycloplegic refraction could not be performed onall subjects) (75). The authors of this study attributedthis increased myopia in orthodox males to theirunique study habits, and to the fact that the printedletters in the commentaries studied may be as small as1 mm in height. In addition, there was a large differ-ence in the amount of time spent reading and writingat school. The girls in the orthodox schools had ratesof myopia comparable to those of girls in the non-orthodox schools. Again, the big difference was in theamount of closeup work, which was much less forgirls than for boys in the orthodox schools. However,individual estimates of the amount of closeup workwere not obtained.

Cohort studies

Parssinen et al. (76) reported a faster rate of pro-gression of myopia among children who spent agreater amount of time on closeup work. Refractiveerror was measured annually with cycloplegia. Aquestionnaire was designed to determine the amountof time spent on closeup work to the nearest half hour,with information obtained on closeup work done onboth weekends and school days, as well as details onreading distance.

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Occupational studies

Rapid industrialization and modernization has led tomany workers' spending more time on closeup workwith video display terminals and to children's usingvideo display terminals for computer-aided instructionand video games, as well as increased televisionwatching (77). Studies of persons in occupations in-volving long hours of closeup work, such as textileworkers and visual display unit workers, show that theprevalence of myopia is higher in these occupations(78, 79). These studies often compare groups of peoplewith different educational levels and socioeconomicstatus; such comparisons are difficult.

There is a growing belief that both genetic andenvironmental factors, such as closeup work, play apart in the onset of myopia. Refraction is possibly aproduct of both genetic and environmental factors,with the environment modifying the genetically deter-mined development of the eye.

Biologic theories for closeup work

The growing eye of a child is sensitive to visual cuesthat could determine axial length and whether the eyegrows in the direction of myopia or hyperopia (80).There are several theories which attribute closeupwork to the increase in axial length that causes myo-pia. One of the most widely held theories is the ac-commodation theory, wherein there is an increase inpressure in the posterior part of the eye during accom-modation which is poorly resisted by the sclera, re-sulting in increased ocular length (63). Although in-traocular pressure plays a role in normal eye growthduring development, there has been no documentedincrease in intraocular pressure in myopic eyes. None-theless, defective accommodation may cause retinalimage defocus, which is increasingly regarded as a keyfactor in myopia development (81).

Animal research showed that monkeys whose visionwas restricted to a distance of 18 inches (46 cm) bydrapes became myopic, and cage-reared animals had ahigher prevalence of myopia than their wild counter-parts (82). This supports the association of closeupwork with increased accommodation and myopia. Ex-periments by Raviola and Wiesel (83) showed thatmonkeys with unilaterally surgically closed eyelidswho were reared in lighted environments developedaxial myopia in the closed eye and none in the other,open eye. This could be due to visual form depriva-tion, as animals with sutured lids who are reared in thedark do not become myopic. Another theory (84)postulates that the printed page provides an impover-ished stimulus for nonfoveal retinal neurons, whichhave large receptive fields. Posterior poles of chicks

show a greater role in myopia development than equa-torial areas. Recent studies have shown strong evi-dence that objects viewed nearby may cause the eye toelongate further than it does during normal growth tomaximize the sharpness of images on the retina. Thisgrowing eye thus elongates and becomes myopic (85).In a study by Hung et al. (86) in Houston, Texas,refractive errors such as myopia were induced in mon-keys by lenses. There was resultant compensating eyegrowth that reduced the effect of refractive errorsproduced by the spectacle lenses. This experimentsupports the hypothesis that lens wearing affects thegrowth of the eye and that myopia progression may behastened by focusing on close objects when wearingminus lenses, but this has not been demonstrated inhumans. Further research is needed to bridge the gapbetween animal models and human eye physiology.

Other risk factors

Other risk factors that have been explored as possi-bly contributing to myopia onset and progression in-clude prematurity, low birth weight, height, personal-ity, and malnutrition. There is strong evidence for alink between prematurity and low birth weight andmyopia, but unconvincing evidence for any associa-tion between myopia and height, personality, or mal-nutrition.

Past studies have reported a greater prevalence ofmyopia later in life in premature infants as comparedwith full-term infants (32-34). Myopia is especiallycommon in premature infants with retinopathy of pre-maturity, which is caused by excessive exposure tooxygen during the first few weeks of life (1).

Eye size may be linked to body stature, with tallerindividuals having longer axial lengths. Several stud-ies have shown that myopic individuals are taller thannonmyopic individuals (35, 87). However, this differ-ence is often explained by a difference in socioeco-nomic status. A Finnish case-control study by Teikari(35) showed that myopic persons were significantlytaller than nonmyopic persons. However, refractivestatus was not directly examined, and height informa-tion was obtained indirectly from a questionnaire.

There have been several studies which investigatedthe association between personality and myopia. Earlystudies showed that myopic individuals may be moreintroverted, reflective, self-confident, dominant, andsedentary than nonmyopic individuals (57, 58), whileother studies, such as a cross-sectional study byBullimore et al. (88), did not find any associationbetween personality and myopia. These personalityattributes of myopic individuals may be associatedwith other risk factors such as intelligence and largeamounts of time spent on closeup work.

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There is no evidence that specific vitamin deficien-cies are associated with myopia (57). The evidence fornutritional causes for the onset of myopia has beenunconvincing, as past studies showing an associationhave had methodological limitations. Studies in Afri-can tribal people and Lebanese Arab infants showedthat malnourished individuals had higher myopia rates(36, 37). However, only limited conclusions may bemade, as the cross-sectional studies do not allow directanalysis of the temporal nature of the relation andthere may be more proximal causes of myopia that areassociated with nutrition that have not been examined.In addition, there is a question as to why there wouldbe an increase in myopia in Singapore, Taiwan, Japan,etc., at a time when people's diets were improving (interms of calories and protein content). If there is anyassociation, the attributable risk is probably verysmall.

NEEDS FOR FURTHER EPIDEMIOLOGICRESEARCH

Currently, there is no conclusive evidence for any ofthe myopia risk factors postulated above. Most of theobserved associations have come from cross-sectionalstudies. There are very few cohort studies that have asufficient sample size, accurate measurement of riskfactors, adjustment for possible confounding factors,and measurement of the different refractive compo-nents in myopia development, which include refrac-tion by cycloplegia, axial length, and corneal curva-ture. There is a need for further well-designedepidemiologic studies to provide us with informationon risk factors for myopia onset and progression.

From our assessment of the available literature, wemust make inferences about the relative importance ofthe different risk factors in order to set directions forfurther epidemiologic research. It appears that there isan hereditary component of myopia, as seen in themany familial correlation, twin, and pedigree studiesthat have been conducted. However, the exact mode ofinteraction between genetic and environmental factors,the relative contribution of genetic factors as opposedto environmental factors, and the nature of the geneticmarkers is unknown. Time trends showing increasedmyopia rates in many countries point to an environ-mental cause for myopia. The most important environ-mental risk factor for myopia appears to be closeupwork, for which several cross-sectional and cohortstudies have shown an association. Other risk factors,such as intelligence, academic achievement, socioeco-nomic status, and educational level, are possible sur-rogates for closeup work. Myopia also varies with age,sex, race, and gestational age at birth. All of the abovefactors are potential confounders and should be mea-

sured and appropriately adjusted for in studies exam-ining the association between myopia and closeupwork. There is no consistent evidence for height, per-sonality, or malnutrition as risk factors for myopia.

INTERVENTIONS

Visual corrective aids, such as spectacles and con-tact lenses, are established methods of correcting thedefective distant vision arising from myopia. How-ever, to date, there has not been any convincing orwidely accepted method of preventing the onset ofmyopia or retarding the progression of myopia inhumans.

A variety of different methods to reduce the onsetand progression of myopia have been described. Thesemethods include visual training, biofeedback training,the use of bifocal spectacles, contact lenses, the instil-lation of atropine eyedrops, the instillation of beta-blocker eyedrops, lowering of the intraocular pressure,and surgery (89). Unfortunately, most of the resultspublished have had limited validity. Some of the earlyintervention trials did not have a control group forcomparison. Many clinical trials did not include ran-domization, thus allowing for selection bias by theinvestigators and participants. Furthermore, the treat-ment groups were not comparable with regard to mea-sured confounding factors. The sample size and lengthof follow-up were often insufficient. In addition, largenumbers of dropouts were common, and a differencein myopia progression among subjects lost tofollow-up may have led to biased conclusions. Mask-ing of subjects is almost impossible, and it is difficultto mask the technicians who refract the subjects withregard to intervention status. The trials discussed hereare limited to those that utilized controls, as shown intable 2.

Bifocal spectacles

Bifocal spectacles have been postulated to slow theprogression of myopia by reducing accommodativedemand. Clinical trials on the effects of bifocals areoften not randomized, and there is no conclusive evi-dence for the effect of bifocals in the slowing ofmyopia progression (90). In 1975, Oakley and Young(91) conducted a clinical trial which assigned bifocalsto volunteers and spectacles to subjects who refused towear bifocals. The study population of 156 NativeAmericans and 441 Caucasians aged 6-21 years wasfollowed for 2-4 years, and an average of three cy-cloplegic refractions were performed. The resultsshowed a significant difference in the rate of progres-sion of myopia of -0.04 diopter in the bifocal groupcompared with —0.51 diopter in the control group. No

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TABLE 2. Clinical trials

Study(ref. no.)

Oakley and Young (91)

Goss and Grosvenor(92)

Grosvenor et al. (93)

Parssinen et al. (76)

Stone (94)

Andreo (95)

Grosvenor et al. (97)

Perrigin et al. (98)

Bedrossian (99)

Kaoetal. (102)

Hosaka (104)

Jensen (105)

of interventions to decrease the rate of progression of myopia

Intervention

Bifocal lenses

Bifocal lenses

Bifocal lenses

Bifocal lenses

Contact lenses

Hydrophilic contactlenses

Gas-permeable contactlenses

Silicone-acrylate contactlenses

1% atropine eyedrops

1 % atropine ointment

Labetalol and timololeyedrops

0.25% timolol maleate

Result

Significant difference in annual rate ofmyopia progression of -0.12 diopterin the bifocal group compared with-0.38 diopter in the control group

No significant difference in myopiaprogression between different groups

No significant difference in myopiaprogression between different groups

No significant difference in myopiaprogression between different groups

Significant difference of annual myopiaprogression of 0.1 diopter in contactlens wearers compared with 0.36diopter in spectacle wearers

No significant difference in myopiaprogression in different groups

Significant difference in annual myopiaprogression of 0.14 diopter in thecontact lens group versus 0.40diopter in the spectacle group

Significant difference in annual myopiaprogression of 0.16 diopter in thecontact lens group compared with0.51 diopter in the spectacles group

No myopia progression in 74% ofatropine treated eyes versus 4%of untreated fellow eyes

Significant difference in myopiaprogression of 0.17 diopter in theatropine group compared with 0.75diopter in the control group

Significant difference in myopiaprogression between eyes treatedwith labetalol and placebo but nodifference for eyes treated with timololand placebo

No statistically significant difference inmyopia progression

Limitations

No randomization; investigatorsmeasuring outcome notmasked

No randomization; refractiveoutcomes from medicalrecords

Large number of dropouts

No randomization; refractionmeasured without cycloplegia

No randomization

No randomization

No randomization; large numberof dropouts

Fellow eye used as control

No randomization

No randomization; small samplesize

Small sample size

masking was done, and this could have led to inves-tigator bias wherein favorable refractive measure-ments were made in the bifocal group. An analysis ofthree studies by Grosvenor et al., Roberts and Banford,and Goss showed decreased rates of progression ofmyopia in patients with convergent strabismus whowore bifocals, but no difference in rates in patientswith no strabismus or divergent strabismus who worebifocals (92). The Grosvenor and Goss (90) bifocalstudy of 112 myopic patients from three optometrypractices in the central United States showed no sta-tistically significant difference in the rate of progres-sion of myopia of —0.44 diopter per year for wearersof single-vision spectacles and —0.37 diopter per yearfor wearers of bifocals. The treatment assignment wasnot randomized, and refractive measurements were

elicited from past medical records. A randomized clin-ical trial (93) in Houston, Texas, placed subjects intothree groups consisting of children wearing single-vision lenses, +1.00 diopter added bifocals, or +2.00diopters added bifocals based on a table of randomnumbers. The mean increase of myopia in the 124participants was —0.34 diopter per year for the single-vision subjects, —0.36 diopter per year for the +1.00diopter added bifocal subjects, and —0.34 diopter peryear for the +2.00 diopters added bifocal subjects.The differences in the rates were not statistically sig-nificant. There was a large number of dropouts, withonly 124 of the 207 subjects remaining in the studyafter 3 years. In Finland, a randomized clinical trial inwhich children aged 8-13 years were assigned to theuse of bifocal lenses, continuous use of single-vision

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spectacles, or use of single-vision spectacles only fordistant vision showed no significant difference be-tween rates of progression in the three groups (76).

Contact lenses

Rigid contact lenses have been used in several clin-ical trials, as it is postulated that these lenses retardmyopia progression by causing corneal flattening. Oneof the first studies to assess' the possible effects ofcontact lenses on the rate of progression of myopiawas conducted by Stone in the London RefractionHospital, where 120 children were followed for 5years (94). However, the subjects were not random-ized into contact lens and spectacle groups, and myo-pia was measured with noncycloplegic refraction. Theincrease in myopia among the contact lens wearerswas 0.10 diopter per year as compared with 0.36diopter per year for the spectacle wearers. Andreo (95)studied a small sample of 56 patients who were wear-ing spectacles or hydrophilic contact lenses over aperiod of approximately 12 months, and the resultsshowed no statistically significant difference in therates of progression between the two groups. As withStone's study, the subjects were not randomized to thetwo different groups. A study by Grosvenor et al. (96)used gas-permeable contact lenses in 100 myopic chil-dren and compared them with another nonrandomizedage-matched group of spectacle-wearers. They foundan increase in myopia of 0.14 diopter in the contactlens group compared with 0.40 diopter in the spectaclegroup in this nonrandomized study. Grosvenor et al.noted that upon discontinuation of contact lens wear,myopia progression increased. However, the reductionin myopia progression was not accounted for entirelyby corneal flattening as measured by the keratometer.The researchers concluded that the keratometer did notprovide an accurate assessment of corneal flatteningfrom contact lens wear (97). However, another Hous-ton study (98) fitted 100 children with silicone-acry-late contact lenses and made comparisons with 20spectacle-wearing children matched by age and initialamount of myopia over a 3-year period. The myopia ofthe contact lenses wearers progressed at a statisticallysignificantly slower rate of 0.16 diopter per year, com-pared with 0.51 diopter per year in the spectacle wear-ers. However, there was a large dropout rate, with only56 of the original 100 children fitted with contactlenses remaining in the study at the end of 3 years, andthere was no randomization of treatment assignments.

Atropine eyedrops

Another putative method of myopia control is thedaily instillation of a long-acting cycloplegic agent

such as atropine to decrease ocular accommodation.Several past clinical trials did not randomize subjects,and dropout rates were high. The findings were oftenequivocal and inconclusive (99-101). Bedrossian'sstudy (99) involving 75 subjects aged 7-13 years usedthe other eye as a control. Bedrossian found that 112of the 150 atropine-treated eyes had no change or adecrease in myopia, whereas in the control eyes, onlyfour had no change or a decrease in myopia. Kao et al.(102) studied the effect of 1 percent atropine ointmenton the progression of myopia in Taiwanese schoolchil-dren with myopia of more than —0.5 diopter. A totalof 40 schoolchildren received 1 percent atropine oph-thalmic ointment in both eyes every night for theduration of 1 year; 40 similarly myopic schoolchildrenwearing spectacles but not receiving atropine treat-ment served as controls. The authors found that 51.3percent of the treated group showed no progression ofmyopia, and only 10 percent showed progression ofgreater than 0.5 diopter. By contrast, in the controlgroup, 12.5 percent showed no myopia progressionand 62.5 percent showed progression of greater than0.5 diopter.

Intraocular pressure reduction using beta-blocking agents

Intraocular pressure could be an important mediatorof scleral stress, causing axial elongation of the eye-ball and resultant myopia (103). On the basis of thishypothesis, pharmacologic agents which lower the in-traocular pressure may have an effect in retarding theprogression of myopia. Hosaka (104) conducted asmall study in which 20 Japanese children aged 6-14years were treated with 0.25 percent timolol maleate (abeta-blocker) twice daily, another 50 subjects weretreated with 0.5 percent or 0.25 percent labetalol eye-drops (another beta-blocker) twice daily, and othersubjects were treated with placebo. With a shortfollow-up period of only 2-5 months, Hosaka found astatistically significant difference in the progression ofmyopia between the labetalol-treated eyes and the eyestreated with placebo, whereas no such difference wasfound in timolol maleate-treated eyes and placebo-treated eyes. Jensen (105), in a preliminary reportpublished in 1988, studied the effect of timolol mal-eate in the control of myopia in 9- to 12-year-oldschoolchildren in Denmark. A total of 159 schoolchil-dren were randomly allocated to one of three groups:a control group, a group with bifocal spectacles, and agroup with 0.25 percent timolol eyedrops instilledtwice daily. Timolol maleate was found not to haveany statistically significant effect in slowing the pro-gression of myopia in these schoolchildren (106).Thus, it can be inferred that there has been no conclu-

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sive evidence that beta-blocking agents help to retardmyopia progression.

The available interventions are limited by their sideeffects, and there has been inconclusive evidence frompresent intervention studies. Atropine instillation mayoccasionally result in side effects such as atropinedermatitis, allergic reactions to atropine, and chronicpupillary dilation leading to cataract, and it has beenreported that the myopia tends to resume at a fasterrate once the eyedrops are withdrawn (107). Further-more, the compliance rate is low, as the individual hasto instill eyedrops daily over long periods of time andis unable to read without bifocals if the drops areinstilled in both eyes. Beta-blocking agents need to beinstilled in the eye daily, with possible side effects anda low compliance rate. The results of clinical trialsusing beta-blocking agents have not been conclusive.Bifocals do not cause much discomfort for wearers.However, the randomized trials of bifocals have notshowed any slowing of myopia progression. Therewas some slowing of myopia progression with the useof contact lenses, but the trials were not randomized.Future research should be directed at interventionssuch as the use of rigid gas-permeable contact lenses,with the emphasis on well-designed randomized clin-ical trials with adequate sample sizes and accuraterefractive measurements.

CONCLUSIONS

Myopia is an ocular condition with a high preva-lence in many parts of the world. The relative contri-bution of genetic and environmental factors to thedevelopment and progression of myopia is not fullyunderstood (108). There are several questions thatremain unanswered. To what extent does closeup workcontribute to the increased prevalence of myopia inJapan, Taiwan, Hong Kong, Singapore, and the UnitedStates? Is the difference in myopia prevalence in dif-ferent ethnic groups due primarily to genetic factors orto environmental influences? How much of myopia isgenetically determined, and how do environmentalfactors alter the onset and progression of myopia? Iscloseup work an equal risk factor for both the onsetand the progression of myopia? Is the age of onset ofmyopia important? Are there different risk factors forhigh and low myopia?

Recent studies have shown that a family history ofmyopia and closeup work are the two strongest riskfactors. The relation between closeup work and ge-netic factors, as well as the interaction between thesetwo variables, should be further studied. It has beensuggested that in populations with little exposure tocloseup work, genetic factors play an important part in

the development of myopia, while in populationswhere closeup work is common, there is a high prev-alence of myopia and genetic factors do not have alarge influence (52).

Over the past few decades, epidemiologic studieshave been mainly cross-sectional in nature, with poordocumentation of the temporal relation between riskfactors and myopia. Confounding variables were notexamined, refraction was measured without cyclople-gia, and the different components of refraction, such asaxial length and corneal curvature, were not measureddirectly. The definition of myopia has varied widely,sample sizes have been insufficient, and longitudinalfollow-up has been poor. Well-designed concurrentcohort studies with accurate instruments for measuringcloseup work, other risk factors, and refractive out-comes will provide us with further insights into theenvironmental causes of myopia. Closeup work isdifficult to quantify, and much more study is needed toobtain precise estimates of amounts and types ofcloseup work and the environmental conditions underwhich closeup work is done. Future studies may ex-amine the effects of reading English and Chinesecharacters, as well as the direction of eye movements,whether vertical or right-to-left. Tools for closeupwork assessment, mainly questionnaires and diaries,may be administered repeatedly over different timeperiods in order to document seasonal variations incloseup activities that result from factors such asschool examinations or vacations. In children withactive accommodation reflexes, refraction with cyclo-plegia is essential. The availability of instruments forbiometric measurements of the eye will enable us tobetter understand mechanisms of myopia onset andprogression.

Twin and familial correlation studies have sup-ported the hypothesis of a genetic component of my-opia causation. However, the exact mode of inheri-tance is uncertain, and marker studies have been few.Further research should be directed at linkage-analysisstudies and the identification of myopia gene markers.

A better understanding of the risk factors for myopiawould enable better public health interventions, suchas health education efforts, to advise the public aboutthe types and circumstances under which closeup workcould accelerate myopia onset and progression. Cohortstudies examining the effects of changes in lighting,types of closeup work, distance from reading material,or type sizes could provide a basis for specific closeupwork interventions in the future. Potential interven-tions for the prevention of the onset and progression ofmyopia should be subjected to rigorously performedrandomized clinical trials.

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REFERENCES

1. Curtin BJ. The myopias: basic science and clinical manage-ment. Philadelphia, PA: Harper and Row, 1985.

2. Curtin B. Topics to be considered when establishing stan-dards for clinical myopia studies. Acta Ophthalmol Suppl1988;185:61-2.

3. Angle J, Wissmann DA. The epidemiology of myopia. Am JEpidemiol 1980;ll 1:220-8.

4. Goldschmidt E. Refraction in the newborn. Acta Ophthalmol(Copenh) 1969;47:570-8.

5. Ruben M, Khoo CY. Contact lenses: medical aspects.Singapore: PG Publishers, 1989.

6. National Advisory Eye Council (US). Vision research: anational plan, 1983-1987. US Department of Health andHuman Services, Public Health Service, National Institutesof Health, 1983. (NIH publication no. 83-2469).

7. Mutti DO, Zadnik K, Egashira S, et al. The effect of cyclo-plegia on measurement of the ocular components. InvestOphthalmol Vis Sci 1994;35:515-27.

8. Sperduto RD, Seigel D, Roberts J, et al. Prevalence ofmyopia in the United States. Arch Ophthalmol 1983; 101:405-7.

9. Wang Q, Klein BE, Klein R, et al. Refractive status in theBeaver Dam Eye Study. Invest Ophthalmol Vis Sci 1994;35:4344-7.

10. Fledelius H. Myopia prevalence in Scandinavia: a survey,with emphasis on factors of relevance for epidemiologicalstudies in general. Acta Ophthalmol Suppl 1988; 185:44-50.

11. Midelfart A, Aamo B, Sjohaug KA, et al. Myopia amongmedical students in Norway. Acta Ophthalmol (Copenh)1992;70:317-22.

12. Rasmussen OD. Incidence of myopia in China. Br J Oph-thalmol 1936,20:350-60.

13. Lin LL, Chen CJ, Hung PT, et al. Nation-wide survey ofmyopia among schoolchildren in Taiwan, 1986. Acta Oph-thalmol Suppl 1988;185:29-33.

14. Ling SL, Chen AJ, Rajan U, et al. Myopia in ten year oldchildren—a case-control study. Singapore Med J 1987;28:288-92.

15. Chow YC, Dhillon B, Chew PT, et al. Refractive errors inSingapore medical students. Singapore Med J 1990;31:472-3.

16. Law NM, Chew SJ, Ritch R, et al. Survey of refraction in aChinese population shows that myopia severity can be pre-dicted from its age of onset. (Abstract). Invest OphthalmolVis Sci 1992;33:709.

17. Jain IS, Jain S, Mohan K. The epidemiology of highmyopia—changing trends. Indian J Ophthalmol 1983;31:723-8.

18. Mohan M, Pakrasi S, Zutshi R. Myopia in India. Acta Oph-thalmol Suppl 1988;185:19-23.

19. Grosvenor T. Myopia in Melanesian school children inVanuatu. Acta Ophthalmol Suppl 1988;185:24-8.

20. Verlee DL. Ophthalmic survey in the Solomon Islands. Am JOphthalmol 1968;66:304-19.

21. Rajan U, Tan FT, Chan TK, et al. Increasing prevalenceof myopia in Singapore school children. In: Chew SJ,Weintraub J, eds. Proceedings of the Fifth International Con-ference on Myopia, Toronto, Ontario, Canada, June 22-24,1994. New York, NY: Myopia International Research Foun-dation, 1995:41-6.

22. Hosaka A. The growth of the eye and its components: Jap-anese studies. Acta Ophthalmol Suppl 1988; 185:65-8.

23. Sveinsson K. The refraction of Icelanders. Acta Ophthalmol(Copenh) 1982;60:779-87.

24. Crawford HE, Hamman GC. Racial analysis of ocular defor-mities in schools of Hawaii. Hawaii Med J 1949,9:90-3.

25. Lin LL, Hung PT, Ko LS, et al. Study of myopia amongaboriginal school children in Taiwan. Acta OphthalmolSuppl 1988; 185:34-6.

26. Froom P, Biger Y, Erel J, et al. The incidence of myopia in

the Israel Air Force rated population: a 10-year prospectivestudy. Aviat Space Environ Med !992;63:299-301.

27. Goss DA, Winkler RL. Progression of myopia in youth: ageof cessation. Am J Optom Physiol Opt 1983;60:651-8.

28. Lin LK, Shih YF, Lee YC, et al. Changes of the ocularrefraction and its components among the medicalstudents—5 years' longitudinal study. (Abstract). InvestOphthalmol Vis Sci 1995;36:S947.

29. Goss DA. Variables related to the rate of childhood myopiaprogression. Optom Vis Sci 1990;67:631-6.

30. Chew SJ, Ritch R, Leong YK, et al. The age of onset ofmyopia is a predictor of adult myopia severity. In: ShimizuK, ed. Current aspects of ophthalmology: proceedings of theXIII Congress of the Asia-Pacific Academy of Ophthalmol-ogy, Kyoto, Japan, May 12-17, 1991. Amsterdam, TheNetherlands: Elsevier Science Publishers BV, 1992:680-5.

31. Parssinen O, Lyyra AL. Myopia and myopic progressionamong schoolchildren: a three-year follow-up study. InvestOphthalmol Vis Sci 1993;34:2794-802.

32. Graham MV, Gray OP. Refraction of premature babies' eyes.BrMed J 1963; 1:1452-4.

33. Quinn GE, Dobson V, Repka MX, et al. Development ofmyopia in infants with birth weights less than 1251 grams.The Cryotherapy for Retinopathy of Prematurity CooperativeGroup. Ophthalmology 1992;99:329-40.

34. Lue CL, Hansen RM, Reisner DS, et al. The course ofmyopia in children with mild retinopathy of prematurity.Vision Res 1995;35:1329-35.

35. Teikari JM. Myopia and stature. Acta Ophthalmol (Copenh)1987;65:673-6.

36. McLaren DS. Nutrition and eye disease in East Africa:experience in Lake and Central Provinces, Tanganyika. JTrop Med Hyg 1960;63:101-22.

37. Halasa AH, McLaren DS. The refractive state of malnour-ished children. Arch Ophthalmol 1964;71:827-31.

38. Krause UH, Rantakallio PT, Koiranen MJ, et al. The devel-opment of myopia up to the age of twenty and a comparisonof refraction in parents and children. Arctic Med Res 1993;52:161-5.

39. Hui J, Peck L, Howland HC. Correlations between familialrefractive error and children's non-cycloplegic refractions.Vision Res 1995,35:1353-8.

40. Sorsby A, Leary GA, Fraser GR. Family studies on ocularrefraction and its components. J Med Genet 1966;3:269-73.

41. Keller JT. A comparison of the refractive status of myopicchildren and their parents. Am J Optom Arch Am AcadOptom 1973;50:206-ll.

42. Zadnik K, Satariano WA, Mutt DO, et al. The effect ofparental history of myopia on children's eye size. JAMA1994;271:1323-7.

43. Hirsch MJ, Ditmars DL. Refraction of young myopes andtheir parents—a reanalysis. Am J Optom Arch Am AcadOptom 1969;46:30-2.

44. Bartsocas CS, Kastrantas AD. X-linked form of myopia.Hum Hered 1981 ;31:199-200.

45. Karlsson JL. Evidence of recessive inheritance of myopia.Clin Genet 1975;7:197-202.

46. Ashton GC. Segregation analysis of ocular refraction andmyopia. Hum Hered 1985,35:232-9.

47. Schwartz JT. Twin studies in ophthalmology: hereditary andenvironmental determinants of eye disease. Am J Ophthal-mol 1968;66:323-7.

48. Sorsby A, Fraser GR. Statistical note on the components ofocular refraction in twins. J Med Genet 1964; 1:47-9.

49. Teikari JM, O'Donnell JJ, Kaprio J, et al. Impact of heredityin myopia. Hum Hered 1991 ;41:151—6.

50. Lin LL, Chen CJ. Twin study on myopia. Acta Genet MedGemellol (Roma) 1987;36:535-4O.

51. Hu DN. Twin study on myopia. Chin Med J (Engl) 1981;94:51-5.

52. Chen CJ, Cohen BH, Diamond EL. Genetic and environmen-tal effects on the development of myopia in Chinese twin

Epidemiol Rev Vol. 18, No. 2, 1996

by guest on July 14, 2011epirev.oxfordjournals.org

Dow

nloaded from

Page 13: Epidemiology of Myopia - ResearchGate · Epidemiology of Myopia ... INTRODUCTION Myopia is the state of refraction in which parallel ... 3 Dana Center for Preventive Ophthalmology,

186 Saw et al.

children. Ophthalmic Paediatr Genet 1985;6:353-9.53. Teasdale TW, Goldschmidt E. Myopia and its relationship to

education, intelligence and height: preliminary results froman on-going study of Danish draftees. Acta OphthalmolSuppl 1988; 185:41-3.

54. Rosner M, Belkin M. Intelligence, education, and myopia inmales. Arch Ophthalmol 1987,105:1508-11.

55. Angle J, Wissmann DA. Age, reading, and myopia. Am JOptom Physiol Opt 1978;55:302-8.

56. Parssinen TO. Relation between refraction, education, occu-pation, and age among 26- and 46-year-old Finns. Am JOptom Physiol Opt 1987;64:136-143.

57. Baldwin WR. A review of statistical studies of relationsbetween myopia and ethnic, behavioral, and physiologicalcharacteristics. Am J Optom Physiol Opt 1981 ;58:516—27.

58. Young FA, Singer RM, Foster D. The psychological differ-entiation of male myopes and nonmyopes. Am J OptomPhysiol Opt 1975;52:679-86.

59. Hirsch MJ. The relationship between refractive state of theeye and intelligence test scores. Am J Optom Arch Am AcadOptom 1959;36:12-21.

60. Grosvenor T. Refractive state, intelligence and refractiveerrors. Am J Optom Arch Am Acad Optom 1963;40:257-64.

61. Ashton GC. Nearwork, school achievement and myopia.J Biosoc Sci 1985; 17:223-33.

62. Whitmore WG. Congenital and developmental myopia. Eye1992;6:361-5.

63. Goldschmidt E. The importance of heredity and environmentin the etiology of low myopia. Acta Ophthalmol (Copenh)1981;59:759-62.

64. Adams DW, McBrien NA. Prevalence of myopia and myopicprogression in a population of clinical microscopists. OptomVis Sci 1992;69:467-73.

65. Dunphy EB, Stoll MR, King SH. Myopia among Americanmale graduate students. Am J Ophthalmol 1968;65:518-21.

66. Sato T. The cause and prevention of school myopia. Tokyo,Japan: Excerpta Medica, 1993:106-7.

67. Young FA, Leary GA, Baldwin WR, et al. The transmissionof refractive errors within Eskimo families. Am J OptomArch Am Acad Optom 1969:46:676-85.

68. Johnson GJ. Myopia in arctic regions: a survey. Acta Oph-thalmol Suppl 1988; 185:13-18.

69. Johnson GJ, Matthews A, Perkins ES. Survey of ophthalmicconditions in a Labrador community. I. Refractive errors.Br J Ophthalmol 1979;63:440-8.

70. Alward WL, Bender TR, Demske JA, et al. High prevalenceof myopia among young adult Yupik Eskimos. Can J Oph-thalmol 1985;20:241-5.

71. Boniuk V. Refractive problems in native peoples (the SiouxLookout Project). Can J Ophthalmol 1973,8:229-33.

72. Richler A, Bear JC. Refraction, nearwork and education: apopulation study in Newfoundland. Acta Ophthalmol(Copenh) 1980;58:468-78.

73. Bear JC, Richler A, Burke G. Nearwork and familial resem-blances in ocular refraction: a population study in Newfound-land. Clin Genet 1981; 19:462-72.

74. Wong L, Coggon D, Cruddas M, et al. Education, reading,and familial tendency as risk factors for myopia in HongKong fishermen. J Epidemiol Community Health 1993;47:50-3.

75. Zylbermann R, Landau D, Berson D. The influence of studyhabits on myopia in Jewish teenagers. J Pediatr OphthalmolStabismus 1993;30:319-22.

76. Parssinen O, Hemminke E, Klemetti A. Effect of spectacleuse and accommodation on myopic progression: final resultsof a three-year randomised clinical trial among schoolchil-dren. Br J Ophthalmol 1989,73:547-51.

77. Tokoro T. Effect of visual display terminal (VDT) work onmyopia progression. Acta Ophthalmol Suppl 1988;185:172-4.

78. Nyman KG. Occupational near-work myopia. Acta Ophthal-mol Suppl 1988; 185:167-71.

79. Simensen B, Thorud LO. Adult-onset myopia and occupa-tion. Acta Ophthalmol (Copenh) 1994;72:469-71.

80. Wallman J. Nature and nurture of myopia. (News). Nature1994,371:201-2.

81. Gwiazda J, Thorn F, Bauer J, et al. Myopic children showinsufficient accommodative response to blur. Invest Ophthal-mol Vis Sci 1993;34:690-4.

82. Young FA. The effect of restricted visual space on theprimate eye. Am J Ophthalmol 1961 ;52:799-806.

83. Raviola E, Wiesel TN. Effect of dark-rearing on experimen-tal myopia in monkeys. Invest Ophthalmol Vis Sci 1978; 17:485-8.

84. Wallman J, Gottlieb MD, Rajaram V, et al. Local retinalregions control local eye growth and myopia. Science 1987;237:73-7.

85. Wallman J, McFadden S. Monkey eyes grow into focus.Nature Med 1995; 1:737-9.

86. Hung LF, Crawford MLJ, Smith EL. Spectacle lenses altereye growth and the refractive status of young monkeys.Nature Med 1995;f:761-5.

87. Johansen EV. Simple myopia in schoolboys in relation tobody height and weight. Acta Ophthalmol 1949;28:355-61.

88. Bullimore M, Conway R, Nakash A. Myopia in optometrystudents: family history, age of onset and personality. Oph-thalmic Physiol Opt 1989;9:284-8.

89. Grosvenor T. Myopia: what can we do about it clinically?Optom Vis Sci 1989;66:415-19.

90. Grosvenor T, Goss DA. The role of bifocal and contactlenses in myopia control. Acta Ophthalmol Suppl 1988; 185:162-6.

91. Oakley KH, Young FA. Bifocal control of myopia. Am JOptom Physiol Optics 1975,52:758-64.

92. Goss DA, Grosvenor T. Rates of childhood myopia progres-sion with bifocals as a function of near point phoria: consis-tency of three studies. Optom Vis Sci 1990;67:637-40.

93. Grosvenor T, Perrigin DM, Perrigin J, et al. Houston MyopiaControl Study: a randomized clinical trial. Part II. Finalreport by the patient care team. Am J Optom Physiol Optl987;64:482-98.

94. Stone J. The possible influence of contact lenses on myopia.Br J Physiol Opt 1976;31:89-114.

95. Andreo LK. Long-term effects of hydrophilic contact lenseson myopia. Ann Ophthalmol 1990;22:224-7.

96. Grosvenor T, Perrigin J, Perrigin DM, et al. The use ofsilicone-acrylate contact lenses for the control of myopia:results after two years of lens wear. Optom Vis Sci 1989;66:41-7.

97. Grosvenor T, Perrigin DM, Perrigin J, et al. Rigid gas-permeable contact lenses for myopia control: effectsof discontinuation of lens wear. Optom Vis Sci 1991 ;68:385-9.

98. Perrigin J, Perrigin DM, Quintero S, et al. Silicone-acylatecontact lenses for myopia control: 3-year results. Optom VisSci 1990;67:764-9.

99. Bedrossian RH. The effect of atropine on myopia. AnnOphthalmol 1971 ;3:891-7.

100. Gimbel HV. The control of myopia with atropine. Can JOphthalmol 1973;8:527-32.

101. Dyer JA. Role of cycloplegics in progressive myopia. Oph-thalmology 1979,86:692-4.

102. Kao SC, Lu HY. Liu JH. Atropine effect on school myopia:a preliminary report. Acta Ophthalmol (Suppl) 1988;185:132-3.

103. Pruett RC. Progressive myopia and intraocular pressure:what is the linkage? A literature review. Acta Ophthalmol(Suppl) 1988; 185:117-27.

104. Hosaka A. Myopia prevention and therapy: the role of phar-maceutical agents. Japanese studies. Acta Ophthalmol(Suppl) 1988;185:130-l.

105. Jensen H. Timolol maleate in the control of myopia: apreliminary report. Acta Ophthalmol (Suppl) 1988; 185:128-9.

Epidemiol Rev Vol. 18, No. 2, 1996

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106. Jensen H. Myopia progression in young school children: a of myopia with atropine and bifocals: a long-term prospec-prospective study of myopia progression and the effect of a tive study. Ophthalmology 1984;91:1373-9.trial with bifocal lenses and beta blocker eye drops. Acta 108. Mutti DO, Zadnik K, Adams AJ. Myopia: the nature versusOphthalmol (Suppl) 1991 ;200:1-79. nurture debate goes on. Invest Ophthalmol Vis Sci 1996;37:

107. Brodstein RS, Brodstein DE, Olson RJ, et al. The treatment 952-7.

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