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Appendix B
Review of the Prevalence Literature
Myopia prevalence refers to the proportion of individuals in a population who are myopic
at a given time. Two major issues in measuring prevalence concern the ability to correctly
classify individuals as myopic and nonmyopic and the manner in which the observed group
was selected from the population at large. Classification criteria are described in Chapter I,
in the section on interpreting the myopia literature. Chapter 4 contains the working group's
recommendations for classification standards for future studies.
AGE
In most populations, age is the most important determinant of the distribution of
refractive error, at least during the first three decades of life. Prevalence studies necessarily
take a cross-sectional view of the patterns of refraction in relation to age. The characteristics
of this pattern depend on the longitudinal development of refraction within the population,
secular trends in refraction, and selective (survival) factors operating from one age group to
the next. If two of these are known or can be reasonably assumed, and if sampling is valid,
then inferences about the third can usually be maple from cross-sectional data. Age patterns
of myopia prevalence seem to be used in two major areas of inquiry. The first concerns the
progression of myopia and changes of refraction with age. An excellent example of this kind
of interpretation of cross-sectional data is provided by Hirsch (1952) in a study of 9,552
schoolchildren, ages 5 to 14, in the vicinity of Los Angeles, California. In the context of
universal education, one would expect little selection- or refraction-associated attrition in
such a study. There is also little reason to expect a major secular trend over the 10 years
separating the 5-year-olds from the 14-year-olds. This study uses a sophisticated statistical
analysis that addresses the problems of making longitudinal inferences from cross-sectional
data, presenting both means and centiles. The reporting of the percentage of students
having various refractive states by age and by gender also makes possible the estimation of
the prevalence of myopia based on various degrees of refractive error.
Kalogjera (1979) studied 483 children ages 3 to Tin Central Zagreb, Yugoslavia. Ex-
aminations, consisting of skiascopy under cycloplegia, were done in connection with vacci-
nations. Refractive error was reported in 1.00 diopter (D.) intervals. About 3.4 percent of
eyes had a negative refractive error of -1.00 D. or more. There was no apparent trend with
age, but the numbers were small.
Hirsch (1952) found that the percentage of children with a negative refractive error
45
OCR for page 46
46
greater than -1.00 D. increased from 0.6 percent in 5- and ~year-olds to 5.4 percent in
13- and 14-year-olds. The prevalence of any negative refractive error increased from 6.8
percent in ~ and ~year-olds to 23.9 percent in 1~ and 14-year-olds. Kempf et al. (1928)
examined 1,860 Washington, D.C., schoolchildren in 1924. Refractive error was determined
by retinoscopy under cycloplegia. The percentage of right eyes with a negative refractive
error equal to or greater than -0.25 D. rose from 1.4 percent among ~ and 7-year-olds to
9.1 percent among 12- and 13-year-olds and also in those 14 years and older.
In Finland, Laatikainen and Erkkila (1980) studied 411 schoolchildren; 1.9 percent of 7-
and ~year-olds had a negative refractive error equal to or greater than -0.50 D., increasing
to 21.8 percent among 14- and 15-year-olds.
Most studies of older children and young adults show a continued increase in the
prevalence of myopia into the third decade. Johansen (1950) studied Danish students ages
12 to 15 and found an increased prevalence of myopia with increasing age. Goldschmidt
(1968) studied Danish schoolchildren ages 13 to 14 and found that 9.7 percent had either
a previously ascertained myopia, reduced visual acuity, or a school record of use of glasses
accompanied by optimum vision achieved by spherical concave lenses in one or both eyes.
Among military recruits ages 18 to 25, 14.5 percent wore glasses with a negative correction.
The author concluded that about one-third of myopes become myopic after their fourteenth
year. Fledelius (1983) studied patients referred for ophthalmological evaluation of general
disease, excluding referrals for glasses prescriptions. Among nondiabetics, the highest
prevalence occurred in the age group 26 to 35 .
Two surveys conducted by;the U.S. government contain data on older children and
young adults. Angle and Wissmann (1980a) reported on an analysis of data from the
United States Public Health Service Health Exarn~nation Survey, cycle Ill, summarized
Originally by Roberts and Slaby (1974~. They found a slight increase in the prevalence of
myopia with age, from 29.9 percent at 12 to 33.2 percent at 17. Sperduto et al. (1983)
analyzed a subset of the data in the National Health and Nutrition Examination Survey
(NHANES) collected between 1971 and 1972 and reported by Roberts and Roland (19783.
Although Sperduto et al. report little variation with age, the data show an increase in
prevalence of myopia from'24 percent among 12- to 17-year-olds to 27.7 percent among 18-
to 24-year-olds, followed by a drop to 2~25 percent in the older age groups. Whereas the
differences may not be statistically significant, they are consistent with other observed age
patterns.
Adults over age 40 were studied in Israel by Hyams et al. (1977~. The study was done in
conjunction with a glaucoma screening program, and refractive error was determined from
the subjects' own glasses. This methodology was felt to be valid by the authors because of
the availability and use of ocular care. The authors report no change in the prevalence of
myopia from the age of 40 to age 70 and a decrease thereafter.
Many studies that report mean refraction other than prevalence suggest that the
prevalence of myopia reaches a peak at about age 20 to 25, declines slightly to age 45, and
then begins to rise very slightly again (Brown and Kronfeld, 1929; Jackson, 1932; Pendse
and Bhave, 1954; Sorsby et al., 1960~.
The pattern of marked increases in the prevalence of myopia during childhood largely
reflects longitudinal growth patterns. Interpretations of the various patterns of plateau or
decline after age 30 are discussed below in the section on secular trends. Whatever the
source of the age- related patterns of myopia prevalence, it is clear that age must always be
considered a potential confounder in comparisons of myopia prevalence between populations
or subpopulation groups. This confounding could probably not be controlled by a single
linear term in a regression mode! if the age range of subjects is very wide. By contrast,
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47
populations of schoolchildren, a common source of data on myopia prevalence, may have
sirn~lar numbers of children at all age levels, in which case there would be no confounding
if the age range of the compared groups ~ the same. Controlling for age may also not
control for age-associated phenomena, such as developmental maturation. Thus, differences
between populations in childhood may not necessarily imply differences in the ultimate
prevalence of myopia.
GENDER
The relationship of myopia prevalence with gender appears to be less consistent, less
well documented, and less predictive than that with age.
Peckham et al. (1977) studied 11,179 children in England, Scotland, and Wales. There
was no significant difference between the sexes in the occurrence of reacquired myopia,"
defined as poor distant vision, satisfactory near vision, ant] a deterioration of two lines in
distant visual acuity in children between ages 7 and 11.
In California, Hirsch (1952) found a more negative (myopic) refraction among boys
than among girls ages 5 to 6, shifting to more myopia among girls at age 13 to 14. The age
pattern depends on the parameter of refraction being considered. For example, for myopia
in excess of 1.00 D., the percentage of girls became slightly higher than the percentage of
boys starting at age 7 to 8, markedly higher at 11 to 12, and only slightly higher again at
13 to 14. By contrast, both the mean and median refraction are higher (less myopic) for
girls than for boys until ages 13 to 14. Hirsch attributes this pattern to the earlier onset of
puberty in girls. Kempf et al. (1928) reported a slightly higher proportion of myopes among
boys than among girls for all ages, including 14 and older. Angle and Wissmann (1980a),
in their analysis of data from the 1966-1970 National Health Examination Survey, found a
higher prevalence of myopia among females than males ages 12 to 17. Whether this varied
with age is not stated. Sperduto et al. (1983) reanalyzed data on people ages 12 to 54 from
the 1971-1972 National Health and Nutrition Examination Survey. They reported higher
prevalences in women than men through ages 25 to 34.
Goldschmidt (1968) found a higher prevalence of myopia in girls than in boys among
Danish schoolchildren ages 13 to 14 but cautions that this does not imply that females are in
general more myopic, since these results may reflect differences in maturational development
between boys and girls at that age. Krause et al. (1982) found a higher prevalence of both
myopia and hyperopia in female than in male Finnish schoolchildren, on the basis of a
questionnaire reporting ophthalmologist visits and records of refraction; they also pointed
out the connection with puberty.
Studies of Eskimo and American Indian populations are also inconsistent in their gender
patterns. Alsbirk (1979) reported a higher prevalence of any negative refractive error as well
as a negative refractive error greater than -2.00 D. among men than among women over
age 40; it was statistically significant for any negative refractive error. Myopia prevalence
was somewhat higher for women than for men ages 15 to 39, but this was not statistically
significant. `~7- - I --my - ~ ~ 1 ~ {< ~_~\ ~ , ~ , . ..
more myopia among females, largely during adolescence. Among Belcher Island Eskimos,
however, Woodruff and Samek (1976) report a lower mean refraction for males than for
females. Since the standard deviation of refractive error is similar for males and females in
this study and there are no high refractive errors, the prevalence of myopia is also probably
higher in males, but this comparison may be confounded by age. Since participation rates
for women tend to be higher than for men in these studies, observed gender differences may
also be due to differences in selection.
lace ruII anti cameos My data on Ontario lnd~an populations suggest
· ~.
--cat cat -
OCR for page 48
48
TERRITORY OF HAWAII
DIAGNOSIS
PERCENT
30 25 20 15 10
5 0
30 25 20 15 10 5 0
PERCENT
ALL RACES 100,377
HAWAIIAN 2,758
PART HAWAIIAN 2O,375
PORTUGUESE 6,562
PUERTO RICAN 1,764
SPANISH 193
OTHER CAUCASIAN 5,353
CHINESE 5,621
JAPANESE 41,684
KOREAN 1,036
FRENCH 9,732
OTHERS 5,299
FIGURE B-1 Myopic errors by race. This figure represents eyes; in many individuals both eyes have
the same defect, so the percentage on a case basis would be somewhat more than half of the figures given
here.
Source: Adapted from Crawford and Hammond, 1949.
RACIAL AND ETHNIC PATTERNS
Asians
The original data from prevalence studies in Asian countries are not among the articles
reviewed. Sato (1957) refers to prevalence rates as high as 67 percent among high school
students in Japan. In Hawaii, Crawford and Hammond (1949) screened nearly 100,000
schoolchildren for a defect in vision or ocular balance. The classification of a student as
myopic was based on the subsequently reported refractive error from an ophthalmologist or
optometrist. As indicated by Figure B-1, myopia was found to be most common among the
Chinese students, followed by Japanese and Korean students. Hawaiians, part-Hawa~ians,
and a group designated as "others" had the lowest prevalences of myopia.
Jews
Two studies comparing Jewish and non-Jewish subpopulations report more myopes
among Jews. Kantor, summarized by Sorsby (1932), compared the prevalence of myopia
among Jews and White Russians (Byelorussians). Among Jews the prevalence of myopia
was 14.75 percent; among White Russians it was 4.93 percent; among the subgroups who
worked as type compositors, the prevalence of myopia was 22.8 percent for Jews and 6.1
OCR for page 49
49
percent for White Russians. The methods for selecting the sample were not specified, nor
were those for estimating myopia. In I`ondon, Sourasky (1928) studied Jewish and non-
Jewish schoolchildren. Among boys ages 8 to 13, visual defects were more common in Jews
than in non-Jews and unrelated to age. He also examined case records and found a higher
proportion classified as myopes among Jews than among non-Jews.
In Israel, Hyams et al. (1977) studied men and women over 40, mostly of eastern
European origin, in communal settlement. The prevalence of any negative error was found
to be 18.4 percent, the prevalence of a negative error greater than -~.00 D. was 11.6
percent. These rates may be underestimates because of the use of subjects' glasses to
determine refractive error. Shapiro et al. (1982a) reported on students ages 18 and 25 at
the Hebrew University in Jerusalem. A negative refractive error of -0.25 D. or more in
at least one eye was found in nearly 13 percent of those who had visited the university
health service. There is, of course, concern that university students who register at the
university health service may not be representative of the general student population and,
furthermore, that prevalence of myopia in university students is likely to be higher than in
the general population.
Taken together, these studies do not seem to provide strong evidence supporting the
belief that myopia prevalence is unusually high among Jews. The values reported are not
noticeably higher than reported values for other Caucasian adult populations, and the
validity of the internal comparisons is uncertain.
Blacks
Two sets of data document a lower prevalence of myopia in blacks than in whites in the
United States: the National Health Examination Survey of youths ages 12 to 17, reanalyzed
by Angle and Wissmann (1980a), and the National Health and Nutrition Exarn~nation
Survey, of which a subset ages 12 to 54 was reanalyzed by Sperduto et al. (1983~.
The two reports from Africa that were reviewed had very different findings. Abiose
et al. (1980) surveyed 5,220 postprimary schoolchildren (ages 12-20) in Kaduna, Nigeria,
to determine the need for ocular care. Of the 5,220 children screened for visual acuity,
visual defects, and any ocular pathology, 886 were referred for further examination, and
744 of these were actually examined. Of the 140 children who were refracted, the records
of 127 were available for analysis, and among those 79 were found to be myopic: these 79
represent less than 2 percent of the original screeners. Even allowing for the possibility of
missing many cases, and despite the absence of a clear criterion for myopia, this finding
represents an unusually low prevalence for students ages 12 to 20. The authors' conclusion
that myopia was common in this population is based on the proportion of myopia among
students refracted.
McLaren (1960) reported on two surveys of related tribes conducted in Tanganyika,
one near Mvumi and the other near Mwanza. One major difference between the two areas
was that, whereas Mwanza had not recently experienced any serious food shortages, the
area around Mvumi had experienced frequent famines, the last of which occurred about
five years before the survey. Thus, the children of Mvumi were survivors of a time of
nutritional deprivation. Refraction was determined by retinoscopy under cycloplegia and
a mean of the four values (two horizontal and two vertical meridians) of the two eyes was
calculated, from which 2.00 D. (1.00 D. for distance and 1.00 D. for cycloplegia) were
subtracted. Estimating from a histogram of the refraction distribution, the proportion of
children with a negative refractive error of -1.50 D. or more appears to be about 7 to 10
percent, somewhat higher among the Mvumi than the Mwanza. This probably corresponds
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50
to myopia greater than -0.25 D. after readjusting for one of the corrections. These data,
though difficult to compare with other studies in the absence of age-specific rates, do not
suggest an extremely low prevalence of myopia in what was then Tanganyika.
~nerican Indians
Three studies of the Americans Indians were reviewed. Jones (1908) reported on 289
Indians ages 14 to 22, from about two dozen different tribes who attended the Hampton
Normal and Agricultural Institute. The criteria for myopia included visual acuity of less
than 20/20 or symptoms accompanied by myopia diagnosed by refraction under cyclople-
gia. Myopia was found in 10 percent and astigmatism in 26 percent of eyes. Wick and
Crane (1976) examined 398 Sioux schoolchildren in Grades 1 through S. Retinoscopy was
performed without cycloplegia, using a cartoon for fixation: 13 percent of the eyes were
found to have a negative refractive error of -0.25 D. or more. In addition, high degrees of
corneal astigmatism are reported. Heard et al. (1976) studied 420 Zuni schoolchildren in
grades K through 12. Mean and median spherical refractive errors for the right eye based
on retinoscopy were reported. The mean spherical refractive error was +0.87 D. in grade K
through 6, and -0.62 D. in grades 7 to 10. There was no mention as to what, if any, means
were used to relax accommodation. Wick and Crane concluded that mean refractive error
is hyperopic compared with a study of Caucasian schoolchildren. However, there was no
discussion of the comparability of these two studies. They also reported an unusually high
degree of astigmatism. Overall, while these studies do not indicate a pattern of either very
high or very low prevalence of myopia, they do suggest the possibility that astigmatism is
unusually common among American Indians.
Australian Aborigines
Taylor (1980) studied visual acuity and the Attribution of refractive errors in 161
Australian aborigines in eight communities and 152 Australians of European origin, 20 to
30 years of age. Approximately 4.8 percent of the aborigines had a negative refractive error
greater than -0.75 D., compared with 13.5 percent of the Europeans; no aborigine had
myopia of greater than -4.00 D. No mention was made of the level of literacy in either of
the two groups; however, visual acuity was determined using an illiterate E chart. It was
specified that the areas sampled had only recently come under European influence and that
traditional values and lifestyles of the aborigines were maintained.
T=E TEl:NDS
Evidence about secular time trends of myopia prevalence is of two types: comparisons
of myopia prevalence at two different times and inferences from the age patterns of myopia
prevalence. Actual comparisons over time are limited by differences between studies in
methods of measurement and the selection of study subjects. For example, Ask (1925)
described a drop in the prevalence of myopia in Sweden from 1885 to 1920, which he
attributed to changes in the school curriculum and "hygienic measures." However, there
may also have been a change in the selective nature of the school population during that
time.
Denmark
Table ~1 presents data regarding time trends in Danish schoolchildren ages 12 to 14.
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51
TABLE B-1 Studies of Myopia Prevalence Among Danish Schoolchildren, 1884-1968
Study Year Number Age Criterion Class Prevalcncc
(years) (D.) (%)
B jcrrum 1884 198 13- 14 > - 1.50
Philipsen 1884 210 13-14 >-1.50
Normal school 10.6
Normal school 12.4
(advanced)
Johansen 1950? 12-15 >-0.50 Rural school 8.2
(boys)
Goldschmidt 19629,243 13-14 > -1.50 All streams 6.0
Goldschmidt 19623,226 13-14 > -1.50 Academic stream 8.4
Goldschmidt 1962486 13-14 >-1.50 Grammar school 10.7
In 1962, Goldschmidt (1968) surveyed 9,243 children born in 1948 who were residing in
Copenhagen. The criteria for myopia included a previously ascertained myopia or reduced
visual acuity-or a school record of the use of glasses and, in addition, an examination in
which the optimal visual acuity was achieved by use of spherical concave lenses in one or
both eyes. By these criteria, 9.7 percent of students attending normal schools were found to
be myopic. Goldschmidt compares his results with those of Bjerrum and Philipsen (1884),
who report approximately 11.5 percent myopia among schoolchildren ages 13 and 14 in
1884. This is believed to correspond approx~rnately to a myopia greater than 1.50 D. The
prevalence of myopia of this degree in Goldschmidt's study was 6.2 percent. However,
Goldschmidt felt that Bjerrum and Philipsen may have overestimated the prevalence of
myopia, since 60 percent of their population came Tom `'higher schools," probably resulting
in an overrepresentation of the more academically oriented students. When these data from
the earlier study are compared with the prevalence Goldschmidt found in academic classes
(8.4 percent) and grammar schools (10.7 percent), there is much less discrepancy. Johansen
(1950) studied boys ages 12 to 15 in seven schools outside Copenhagen. He found that
8.2 percent of boys exhibited a negative refractive error greater than or equal to -0.50
D. based on reduced visual acuity in either eye plus an "ordinary eye examination" for
"simple myopia." These results are very close to the 8.5 percent myopia reported in boys
by Goldschmidt.
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52
TABLE B-2 Studies of Myopia Prevalence Among Danish Men, 1882-1983
55 Myopic
Military Recruits
Tscherning (1882)a
Goldschmidt (1968)b
excluding refractive error of -1.5 D. or less
ReferralsC
Fledelius (1983) d: refractive error -0.25 D. or greater
excluding mild myopia
8.3
14.5
9.2
32.6
10.3
aProbably refractive error greater than 1.5 D.
bAges 18-25; negative refractive error based on subjects' own glasses.
CAges 16-25.
dInciudes a high proportion of diabetics.
Table B-2 represents data on young men in Denmark. In 1964, Goldschmidt (1968)
surveyed 3,651 Danish young men ages 18 to 25 who attended the medical board for
conscription. Approximately 14.5 percent had a negative correction based on the refractive
value from subject's own glasses. He compared these data with those reported by Tscherning
(1882), who found a prevalence of myopia of 8.3 percent among rn~litary recruits in 1882,
probably corresponding to a negative refractive error of at least -1.5 D. Upon excluding
negative refractive errors of -1.5 D. or less, the prevalence of myopia among the 1964
recruits was 9.2 percent, and after stratification by occupational category, even this small
difference disappeared.
Fledelius (1983) compared the data from his 16- to 25-year-old age group with those
reported by Tscherning and Goldschmidt. His study population was comprised of referrals
for ophthalmological evaluation of general disease (see methods above) and included females
and a high proportion (20 percent) of diabetics. His reported prevalence of negative
refractive error of greater than or equal to -0.25 D. was 32.6 percent (diabetics and
nondiabetics combined). However, upon removal of lower degrees of myopia (degree not
specified but probably a negative error smaller than -2.00 D.), the reported prevalence was
10.3 percent, a figure quite close to those of Tscherning and Goldschmidt.
United States
Table B-3 summarizes the four sets of data providing information regarding time trends
in prevalence of myopia in the United States:
(1) A survey of Washington, D.C., schoolchildren ages 6 to 14 and over (Kempf et al.,
1928~.
(2) A survey of California schoolchildren ages 5 to 14 (Hirsch, 1952~.
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TABLE B-3 Myopia Prevalence Among Children and Adults in the United States,
1924-1972 (Percentage)
i
Myopic Error (D.)_ _
Throughout Throyghout
U.S.C U.S.a
Washington, D.C.a Californiab 1966-70 1971-72
Age 1924 - 1952 % eyes (right eye)
- > -.25> 1.0 > 1.1 > -.12 D. > -1.O D. > -.12D. > -.] 2D.
6
7 2.11.2 0.9
8 10.4 0.9
9 16.4 1.9
10 5.42.4 1.6
11 21.2 4.4
12 29.9
13 9.13.9 3.2 31.5
14 23.9 5.4 31.2 24.0 ,
15 31.9 (
16
17 32.2 ~
18-24 - - 27.7
25-34 24.
aKempf et al. (1928).
bHirsch (1952).
CRoberts and Slaby (1974~; Angle and Wissmann (1980a).
dRoberts and Roland (1978~; Sperduto et aL (1983).
(3) The 196~1970 Health Examination Survey (HES) Cycle Ill of noninstitutionalized
youths ages 12 to 17, reanalyzed by Angle and Wissmann (1980a).
(4) A subset ages 12 through 54 of the 1971-1972 National Health and Nutrition
Examination Survey (NHANES), which was reanalyzed by Sperduto et al (1983~.
Kempf et al. (1928) collected data on 1,860 Washington, D.C. schoolchildren in 1924.
All the children were Caucasian and ranged in age from 6 to over 14 years. The measure
of refractive error was based on retinoscopy under homatropine cycloplegia. In order to
examine whether the requirement of parental permission for the administration of cyclo-
plegia might have resulted in a selection bias, the authors compared the visual acuity of
the children in the study with that of nearly 1,000 children In the same schools whose
parents refused to permit the use of cycloplegia and with the visual acuity of groups of
children tested in South Carolina, Maryland, Delaware, and New York. The distributions
of visual acuity based on the Snellen eye chart were similar for all three groups. The paper
presents extensive, detailed distributions, usually of the right eye alone or the right and left
eye separately, of various measures, including visual acuity with and without cycloplegia,
refractive errors in the vertical and horizontal axes, and astigmatism, using various criteria
for classification. From these, the prevalence of myopia based on various criteria of refrac-
tive error can be estimated. Categories of refraction are designated by a single number at
.
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54
quarter diopter intervals. The prevalence of negative refraction error of -0.25 D. or more
and greater than -1.00 are presented in Table B-3.
Hirsch (1952) examined 9,552 schoolchildren In a number of towns in the vicinity of Los
Angeles, California. The measure of refractive error was by skiametry, with accommodation
"relaxed physiologically" and reported as spherical equivalents. Means, medians, 7th, 25th,
75th, and 93rd percentiles, ranges in diopters for various percentages, and the percentages
of cases having various refractive states are presented for the right eye for males and females
at various ages. The percentage of children with myopia in excess of 1.00 D. is also presented
by age and gender. For the purposes of Table ~3, the rates for males and females were
averaged to obtain overall estimates of myopia prevalence in excess of 1.00 D. and the
prevalence of any negative refractive error.
From 1966 through 1970, 6,768 youths ages 12 to 17 were examined as part of the
Health Examination Survey, Cycle Ill (Roberts and Slaby, 1974~. There was a 90 percent
participation rate among subjects selected as a probability sample of noninstitutionalized
youths. While there were no explicit criteria for myopia, 42 percent of those surveyed had
a visual acuity less than 20/20 in one or both eyes, and 82 percent of these (i.e. 34 percent
of those surveyed) required negative correction or showed "some evidence of myopia." This
suggests an overall prevalence of myopia of 34 percent based on reduced visual acuity plus
any negative correction on either a trial lens or the subject's own lens for either eye. Since
the emphasis of this report is on visual acuity and the adequacy of the current correction, it
is difficult to find basic age-specific prevalence information on myopia. However, these data
were reanalyzed by Angle and Wissmann (19SOa), who reported the age-specific prevalence
of myopia (Table B-3) as a percentage of all eyes, based on a combination of: (1) the
subject's own corrective lens having a negative spherical equivalent, (2) uncorrected visual
acuity less than 20/20 and improved by a negative sphere trial lens, and; (3) no vision
problem not correctable with a lens. It would appear from the description that an eye with
any negative spherical equivalent would be counted as myopic if the individual either wore
corrective lenses or failed the visual screen for one or both eyes, but that many eyes with a
small negative refractive error (up to -0.50 D.) might escape detection.
In 1971-1972, 9,263 people ages 4 to 74 were screened to detect refractive errors and
motility defects (Roberts and Rowland, 1978~. These individuals were from a Location
subsample of the National Health and Nutrition Examination survey; there was a 71.6
percent response rate. There was no classification of Myopia as such. In fact, different
data were collected on different individuab depending on whether they brought corrective
lenses with them, what their corrected or uncorrected visual acuity was, and whether they
were in a subsample designated for retinoscopy. Figure ~2 is a flow chart illustrating the
data collection procedure inferred from the report of this study. It provides a useful guide
to the categorization of subjects by refractive error. Sperduto et al. (1983) published a
reanalysis of 5,282 of these individuals ages 12 to 54, basing their classification of myopia on
the refractive error from the subjects' lenses adjusted according to their visual acuity if their
usual visual acuity was at least 20/40 and improved with pinhole testing, or usual visual
acuity less than 20/40 and negative trial lens or retinoscopic refraction. Fifteen percent of
individuals were not classified; the authors believe that that underestimated the prevalence
of myopia by about 1 percent, but they do not refer to any dioptric criterion.
A comparison between the Washington, D.C., schooIchildrenin 1924 at ages 12 to over
14 (Kempf et al., 1928) with the 1952 California schoolchildren at ages 11 to 14 (Hirsch,
1952) shows a higher prevalence of myopia (3.2 versus about 5 percent) greater than 1 D.
in the latter. This difference is statistically significant at the 5 percent level based on a
chi-square test under the assumption that Hirsch's age categories contain approximately
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l
55
Wears glasses or contact lenses
full or part time by history
-
yes (52%)
-
-
brought glasses or contacts- no (59.3%)
yes (40.7%)
lensometer (90% in ages 6-74)
(45% ages 4 & 5)
+
visual acuity assessment, <20/50
corrected
>20/50
no further information
(correction from glasses
accepted)
FIGURE B-2 NHANES data collection procedure.
Source: Adapted from Roberts and Rowland, 1978.
no (48%)
visual acuity assessment,
uncorrected
<20/50
-
-
-
>20/50
no further
information
nutritional detailed examines
examines (1 9%)
(81%)
refraction with trial
lens, spherical with
0.5 dineriments
retinoscopy
.
to determine best VA and
characteristics of the lens
required
J
equal numbers (these are not given in his paper). A comparison based on a criterion of
myopia of greater than or equal to 1.00 D. would lead to an underestimation of the difference
between them. Other problems of comparability between these two studies include:
(1) Relaxation of accommodation: Kempf used cycloplegia, while Hirsch used convex
lenses to relax accommodation.
(2) Summary of meridians: Hirsch reports spherical equivalents; Kempf et al. classified
compound astigmatism according to the spherical correction (i.e., the axis with
the smaller correction) and simple astigmatism according to the abnormal axis
and excluded cases of mixed astigmatism from the analysis. These differences
would yield a lower percentage of myopes in the Kempf et al. study compared to
that of Hirsch.
(3) Reported categories of refractive error: Kempf et al. reported refractive error as
0.00, -0.25, -0.50, etc.; the actual cutoff point for each category is unclear. Hirsch
reported categories as a range 1 D. wide (e.g., ~1, 1-2, 2-3~. Although one of the
tables and the text indicate that the Tower value was not actually included in each
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56
category, prevalence estimates from Kempf et al. including -1.00 D. are included
in Table B-3 to provide for a more ~conservative" comparison.
(4) Population: the D.C. schoolchildren were all Caucasian, while the racial de-
mographics of the California schoolchildren were not stated. In extracting and
summarizing Hirsch's data, overall age-specific prevalences were taken to be the
mean of the age- and gender-specific prevalences, whereas the estimates from
Kempf et al.'s studies were based on the actual numbers of males and females in
each age category. However, in no age category did either gender comprise less
than 46 percent or more than 54 percent of the population. No other demographic
characteristics of the population of either study are specified.
- an--r ---
Comparison of Kempf et al.'s myopia greater than or equal to -0.25 D. with Hirsch's
prevalence for all myopia (9 versus 24 percent) suggests the possibility of an even larger
increase in low-order myopia at all ages, but the comparability of classification criteria is
even less secure. Myopia greater than -1.00 D. in younger children appears to be about the
same in both studies.
Due to the vagueness in the estimation of myopia prevalence from the national surveys,
these data are difficult to interpret. An underestimation of myopia prevalence by 1 percent
by Sperduto et al. (1983) does not explain the difference between his estimate of 24 percent
of right eyes in 1971-1972 and Angle and Wissmann's estimate of 29.9 to 33.2 percent of
eyes in 1966 1970. Furthermore, in their article on myopia and corrective lenses, Angle and
Wissmann (1980a) state, "Cycle Ill of the Health Examination Survey showed that 23.6%
of eyes free of a problem that cannot be corrected by lenses have a corrective lens with a
negative spherical equivalent correction for myopia." Whether these discrepancies are due
to criteria of classification, methods of classification, the use of a subset of the data, or
some other factor is not clear. It is unlikely that there was a drop in myopia prevalence of
5 percent between the late 1960s and the early 1970s.
If the 24 percent estimate is to be believed, the data suggest that the U.S. myopia
prevalence among 12- to 17-year-olds in 1970 wan similar to-that observed by Hirsch in
California in 1952.
Japan
Sato (1957) references a number of studies that suggested a major increase in the
prevalence of myopia in Japan between about 1911 and 1937, a reported drop in the
prevalence of myopia during World War II, and then a subsequent increase.
Canada
Of particular interest are the data on changes in myopia prevalence with the introduction
of schools to previously isolated communities. Although not fully documented by surveys,
it has been generally accepted that, until recently, myopia was rare among Eskimos in
Canada. Surveys in East Greenland (referenced by Alsbirk, 1979) and the Belcher Islands
(Woodruff and Samek, 1976) indicate that myopia prevalence remains low among Eskimos
in areas that are isolated and with no universal public education. The results of surveys
among Canadian Eskimos and American Indians are described as showing an epidemic of
myopia in the younger population.
Boniuk (1973) examined 951 northwestern Ontario Indians at Sioux Lookout in 1970
1971. The project was service-related and selection was by self-referral, although most
school-age children were examined routinely. The highest proportion of the population
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s7
examined was 50 percent in Big Trout Lake and Fort Hope. Of those examined 53 percent
were between the ages of 4 and 19. Moderate myopia, defined as -~.00 to -5.00 D. spheres
based on retinoscopy under cycloplegia, was the most prevalent refractive error, peaking to
over 50 percent in the second and third decade and then falling off markedly. The unusually
high myopia prevalence reported in this study may be in part due to the use of positive
cylinder. In this form the spherical component will, by convention, be -more negative when
expressed as a sphere combined with a positive cylinder (Woodruff and Samek, 1977~.
Morgan and Munro (1973) examined 2,833 Eskimos and 844 Indians in the Yukon and
Northwest Territories. These data were collected as part of a survey of selected settlements
to determine eye care needs. Moderate myopia was defined as a refractive error of -1.00 to
-5.00 D. based on retinoscopy under cycloplegia. The Eskimos and Indians were found to
have similar patterns of myopia, peaking to a prevalence of about 30 percent at ages 15 to
20 and then dropping precipitously to under 10 percent at about age 30.
Woodruff and Samek (1977) examined 4,018 Cree Indians of northern Ontario (approx-
imately 60 percent of the total population) in 1970 and 1971 as part of a program providing
vision screening and care. Nearly all children in any school or community were included,
whereas adults were more likely to have been self-selected. Refractive error was based on
subjective and retinoscopic refraction expressed as the equivalent spherical refractive state
(sphere plus 1/2 cylinder) for each eye; 47 eyes with a negative error greater than -7.00 D.
were excluded. Internal inconsistencies in the reported total numbers and proportions make
it difficult to summarize the results of the study; however, the general pattern is one of
highest rates of myopia occurring among adolescents and young adults, with a considerable
reduction after age 30. The reduction is almost certainly a result of reviewing cross-sectional
data and does not reflect longitudinal changes but rather a change in the prevalence over
different generations. The authors present figures comparing the percentage of myopic per-
sons by age with Morgan's Sioux Lookout data. The peak prevalence for myopia from their
data appears to be under 15 percent occurring between ages 10 and 14, a considerably lower
and earlier peak than that shown by Morgan. The authors interpret this difference to reflect
the fact that their sample is less selected than that of Morgan. The criteria for myopia for
this figure are not stated, however, and a percentile table of spherical equivalent refractive
states indicates a much higher prevalence of myopia: the prevalence of a negative refractive
error greater than -1.00 D. was over 50 percent in the 17- to 2~year-old age group, falling
below 25 percent after age 30 and below 15 percent after age 35.
This pattern, of a peak in myopia prevalence followed by a rapid decline, is what one
might expect to see with a secular trend of increasing myopia. However, it could also be an
artifact of sampling, and it is of concern to note that the pattern is less striking in studies
with higher participation rates.
. ~
RichIer and Bear (1980a) refracted 971 persons representing about 80 percent of the
population of three isolated communities in western Newfoundland in 1974. The population
was all Caucasian and there was no formal compulsory education in the area prior to
1949. Retinoscopy was performed with fogging to relax accommodation and then redefined
subjectively to determine the maximum convex or minimum concave correction required
for distant acuity of 20/20. Data for the right eye were presented. Myopia was defined
as any negative refraction (i.e. myopia of any amount). The proportion of myopes peaked
at ages 15 to 19 at 63.9 percent. By age 40 it had fallen below 20 percent and by 50 to
about 10 percent. The authors compared the age curves for the prevalence of myopia in
populations with the recent introduction of public education to those in which there had
been public education for a long time, the latter showing a much more gradual decrease in
myopia prevalence with age (Figure ~3~.
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-
o
~ 60
LL
~ 40
100 _
80 _
20
_
n
0 10 20
58
Newfoundland
Alaska
At ~Ontario
,~/ ~United States
- an' / \\ ~Greenland
30 40 50 60 70 80
AGE IN YEARS
FIGURE B-3 Changes with age in proportion of subjects who are myopic in a comparison of five studies.
Source: Adapted from Richler and Bear, 1980.
Apart from secular trends and sampling bias, possible explanations for these findings
are differential attrition among myopes and spontaneous regression of myopia. There is
little evidence to support either of these possibilities.
ACTIVITIES
An association of myopia prevalence with certain activities including reading, is sug-
gested by its association with some occupations, with education, and with reading measures.
Reading
Angle and Wissmann (1980a) used grade in school, reading test scores, and reported
time spent reading magazines, books, and newspapers in a typical day as measures of near
work and reading. All three were positively associated with myopia prevalence. Further-
more, the authors estimated refractive status for each individual and regressed myopia on
the social variables of age, sex, race, income, and region. Upon adding the measures of
near work to each regression equation, the regression coefficient for each social variable was
reduced. The authors concluded that at least some of the social patterns of myopia variabil-
ity can be explained by the measures of near work. This study has been criticized because
refractive error was not measured directly but approximated from other measures, and be-
cause there was no control for other confounding, especially by age and ethnic background,
when assessing the impact of the near-work variables (Taylor, 1982~.
Near Work
When Richier and Bear (1980a) measured the refractive status of 971 people in three
communities of Newfoundland, they also obtained data on near work, measured as hours
per day spent at tasks requiring focusing of the eyes at a distance of 20 inches or less, as
reported by the subject, and education measured in years at last completed grade. Results
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s9
were presented separately for five age strata. Refraction and near work were significantly
negatively correlated (indicating a positive correlation between near work and myopia)
for all age strata except age 60 and over. These correlations remained significant after
controlling for age, sex, and education.
Occupation
The prevalence of myopia is not uniform over occupational groups. Kantor, for example
"summarized by Sorsby, 1932), reported a higher prevalence of myopia in type compositors
than noncompositors, both among Jews and White Russians. Goldschmidt (1968) alludes
to many studies in Europe illustrating associations with categories of occupation, which
are based on education and quantity of close work. His data on military conscripts and
those of Tscherning (1882), when classified according to occupation, revealed a prevalence
of myopia that varied from a low of under 3 percent in category six intended to include
men who use their eyes least for close work (e.g., farm laborers, seamen, unskilled and
semiskilled workers) to a high of over 30 percent in category one, which was comprised
mainly of students. Goldschmidt (1968) also describes reports of specific occupations in
which workers have a high probability of having myopia. For example, women employed
in finding and repairing weaving faults in a clothing mill, textile workers, and compositors
have all been found to have a high frequency of myopia, which tends to increase with the
numbers of years spent in the trade. This increase in myopia prevalence could be due to the
effect of the work, but it could also be explained by increasing loss of nonmyopes from the
trade with increased age.
Kinney et al. (1979) summarized three studies concerning the association of the occupa-
tion of submariners with the development of myopia. This possible association is interesting
but unconfirmed. Provines et al. (1983) found that navigators were more likely to become
myopic than pilots. Since these studies concern the development of myopia in visually
selected groups, they do not address myopia prevalence.
ACADEMIC ABILITY
In addition to Angle and Wissmann (1980a), several other authors, including Krause
et al. (1982) in Finland and Peckham et al. (1977) in England, Scotland, and Wales, have
reported associations between myopia and academic ability. Academic ability, however mea-
sured, is probably related to both intelligence and time spent reading. Dalton (1943) studied
nearly 6,000 California schoolchildren and found no difference in academic achievements
between children with sufficiently defective vision to notify their parents and a random
sample of children with normal vision. Since reduced visual acuity alone is an inadequate
indicator of myopia, the results of the study are essentially uninformative.
Rosner and Belkin (1987) recently conducted a nationwide survey in Israel noting the
refractive error and intelligence scores among 157,748 males age 17-19 years. This repre-
sents a largely unselected study population since all Jewish males age 17-19 undergo medical
examination to check fitness for military service. Refractive error was measured only for
those who had less than 20/25 vision in either eye (assuming this criterion screened for my-
opia). They found that both "years of schooling" and "intelligence" weighed anDroximatelY
equally in their significant positive correlation with myopia.
.. ..
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60
OTHER CHARACTERISTICS
Socioeconomic Status
Angle and Wissmann (1980a) and Sperduto et al. (1983) both report an association
between myopia prevalence and income in the United States. Krause et al. (1982) report an
association with myopia with social classes in Finland. Peckham et al. (1977) report that the
prevalence of mvonia in 11-Years-olds was higher for children in "nc~n-man,~al familiar" than
~v _ __ be_ ~
in "manual families." In addition, they report a higher prevalence in small families than
in large families, higher in the first child compared with subsequent children, and higher in
children whose parents showed an interest in school progress compared with children whose
parents were not interested.
Urb~n/Rural Residence
Jain et al. (1983) and Paritsis et al. (1983) report a higher prevalence of myopia among
urban residents. Angle and Wissmann (1980a) report no relation between the prevalence of
myopia and the degree of urbanization of the place of residence.
Height and Weight
Several investigators (Johansen, 1950; Pendse and Bhave, 1951; Krause et al., 1982)
report an association of greater myopia prevalence or negative refractive error with height
and weight in children. It has been suggested that, as with gender differences, this is due to
an association of both variables with clevelopmental maturity. Goldschmidt (1968) studied
the relationship of' myopia and height among 3,511 conscripts. He found that the myopes
were significantly taller than nonmyopes in the group as a whole, but that there was no
significant difference within occupational category.
Low B~rthwei~ht
FIedelius (1980) examined a subset of members of two cohorts, one of premature infants
with low birthweight and one of full-term infants, who had reached age 18. An effort was
made to identify all individuals who had become myopic by using school records. The 18-
year incidence of myopia was 17.6 percent for the low-birthweight group and 13.1 percent
for the full-term group. The author regards these as minimum incidences, because some
individuals with myopia may not have been recorded in school medical records. The higher
incidence in the Tow-birthweight group appeared to be due to 16 cases designated as having
"myopia of prematurity." When these 16 cases were excluded, the proportion of myopia in
the two groups was quite similar.
Genetic Factors
In an analysis of family variations in refractive error and optical components of the
eye, Alsbirk (1979) found an apparent Tower inheritability for refractive error than for axial
length, corneal curvature, or chamber depth. Siblings showed a greater similarity with
respect to refractive error than did parents and children. ~:~ ~u`^v.~ ~.~ -~" "~
The authors proposed that the
influence of a common familial environment best explained these findings, although genetic
factors are theoretically also possible.
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Goldschmidt (1968) provides an extensive review of the literature on genetics in myopia
as well as his own investigation. He concludes that genetic factors are important in the
etiology of myopia, but that there are several types of myopia with different genetic patterns.
Basu and dindal (1983) studied myopia among the Dawoodi Bohras of India, a highly
inbred group. They examined members of 92 families, in each of which at least one member
had myopia. Myopia was found to be associated with consanguinity and low birth order.
In addition to the absence of specification of selection criteria or definition of myopia, ages
were not specified, and it is therefore uncertain whether the compared groups had similar
age distribution.
Geographic Correlates
Daubs (1984) used data collected from 1967 to 1970 in 16 U.S. states of the mode!
reporting area to look for correlates of the incidence of malignant myopia. This study is
analogous to early dental caries research and, like dental caries, malignant myopia was
found to be inversely related to annual hours of sunshine, distance to the seacoast, and
fluoride and calcium levels. The author also mentions his clinical impression that myopic
patients have more dental defects.
Representative terms from entire chapter:
myopia prevalence
