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The Prevalence of Refractive Errors Among Adults in the United States, Western Europe, and Australia
The Eye Diseases Prevalence Research Group*
Arch Ophthalmol. 2004;122:495-505.
ABSTRACT
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Objective To estimate the prevalence of refractive errors in persons 40 years and older.
Methods Counts of persons with phakic eyes with and without spherical equivalent refractive error in the worse eye of +3 diopters (D) or greater, –1 D or less, and –5 D or less were obtained from population-based eye surveys in strata of gender, race/ethnicity, and 5-year age intervals. Pooled age-, gender-, and race/ethnicity–specific rates for each refractive error were applied to the corresponding stratum-specific US, Western European, and Australian populations (years 2000 and projected 2020).
Results Six studies provided data from 29 281 persons. In the US, Western European, and Australian year 2000 populations 40 years or older, the estimated crude prevalence for hyperopia of +3 D or greater was 9.9%, 11.6%, and 5.8%, respectively (11.8 million, 21.6 million, and 0.47 million persons). For myopia of –1 D or less, the estimated crude prevalence was 25.4%, 26.6%, and 16.4% (30.4 million, 49.6 million, and 1.3 million persons), respectively, of whom 4.5%, 4.6%, and 2.8% (5.3 million, 8.5 million, and 0.23 million persons), respectively, had myopia of –5 D or less. Projected prevalence rates in 2020 were similar.
Conclusions Refractive errors affect approximately one third of persons 40 years or older in the United States and Western Europe, and one fifth of Australians in this age group.
INTRODUCTION
A refractive error may be defined as a state in which the optical system of the nonaccommodating eye fails to bring parallel rays of light to focus on the fovea. Myopia and hyperopia are the states of refractive error in which the optical system of the eye brings parallel rays of light into focus anterior and posterior to the fovea, respectively, resulting in blurred vision. Mild to moderate hyperopia can be overcome by accommodation in youth and early adulthood, with the result that low degrees of hyperopia often are not noticed until the onset of presbyopia in midadulthood. Myopia results in blurred vision at all ages.
Blurred vision from refractive error can be relieved—in most cases—by neutralizing the refractive error with spectacles, contact lenses, or refractive surgery. Nevertheless, the high prevalence of refractive errors and the costs of refractive correction make these conditions a substantial public health and economic problem in many parts of the world. The extent of the problem of refractive error in the United States has not been evaluated, except in select populations, since the 1971-1972 National Health and Nutrition Examination Survey found that 25% of the 12- to 54-year-old US population was myopic.1
The Eye Diseases Prevalence Research Group, an initiative jointly sponsored by the National Eye Institute of the National Institutes of Health (Bethesda, Md) and Prevent Blindness America (Schaumburg, Ill), seeks to estimate the prevalence rates for major eye disorders in older adults by combining data from large, high-quality, population-based eye surveys. Population-based surveys provide the optimal method of estimating the population prevalence of medical conditions. In recent years, several locally representative population-based eye surveys have assessed the prevalence of refractive error in older adults. To estimate the current extent of the problem of refractive error in older adults in the United States, Western Europe, and Australia, the Eye Diseases Prevalence Research Group applied pooled data from these population-based eye surveys to obtain population prevalence estimates for these regions.
METHODS
INCLUSION OF STUDIES
For refractive error, eligible studies were those conducted since 1985 in the United States, Western Europe, and Australia that used a method of refractive error measurement deemed to have an acceptable degree of reproducibility and comparability between studies. Participating studies were the Baltimore Eye Survey in Maryland,2 the Beaver Dam Eye Study in Wisconsin,3 the Proyecto VER (Vision Evaluation and Research) study in Arizona,4 the Rotterdam Study in the Netherlands,5 the Blue Mountains Eye Study in Australia,6 and the Melbourne Visual Impairment Project in Australia7 (Table 1). All eligible studies agreed to participate except the Salisbury Eye Evaluation Project.8 The research activity was conducted in accordance with the principles of the Declaration of Helsinki and was approved by the institutional review board of The Johns Hopkins University School of Medicine, Baltimore.
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Table 1. Studies Included in Estimates of the Prevalence of Refractive Error
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STANDARDIZATION BETWEEN STUDIES
Refractive error measurement varied only slightly between studies. All studies measured noncycloplegic refractive error. The Baltimore,2 Beaver Dam,3 Proyecto VER,4 and Rotterdam5 studies all used autorefraction followed by subjective refinement. The Blue Mountains study6 and the Melbourne Visual Impairment Project7 scored refractive error as zero if uncorrected visual acuity was 54 letters or more on an Early Treatment Diabetic Retinopathy Study chart, equal to the current spectacles if visual acuity with current correction was 54 letters or more, or equal to an autorefraction with subjective refinement if neither of these criteria were met. These methods of ascertaining refractive status were judged to be comparable for purposes of our outcome definitions (see "Comment" section). In addition to refractive error status, each of the population-based eye surveys provided data on age, gender, and race/ethnicity based on self-report.
Refractive error was categorized on the basis of the consensus of our research group. Hyperopia was defined as a refraction of +3 diopters (D) or more positive, myopia was defined as a refraction of –1 D or more negative, and high myopia was defined as the subset of myopia of –1 D or less with a refraction of –5 D or more negative. For purposes of this report, refractive error results are reported by person, rather than by eye. The eye with the larger absolute value of the measured spherical equivalent refraction was used to categorize each subject's refractive state. Subjects for whom the refraction of the more ametropic eye was between –1 D and +3 D, not inclusive, were considered not to have refractive errors.
Counts of the number of persons with phakic eyes with and without hyperopia of +3 D or more, myopia of –1 D or less, and myopia of –5 D or less, as well as the number of persons with phakic eyes evaluated, were provided by the participating studies (Table 1) in strata of gender, race/ethnicity, and 5-year age bands (40-44 years, 45-49 years, etc, through  80 years). Thus, persons with pseudophakic and aphakic eyes, who made up 3.7% to 8.3% of the populations studied, were not considered in either the numerator or the denominator for refractive error prevalence estimations, because their refraction had been altered at the time of cataract surgery. The 2000 US Census data were used for the US population in that year.9 Year 2000 population data for Western Europe and Australia, as well as the anticipated population of all 3 regions in the year 2020, also were obtained from the US Department of the Census.10 (Western Europe was defined as including Andorra, Austria, Belgium, Denmark, the Faroe Islands, Finland, France, Germany, Gibraltar, Greece, Guernsey, Iceland, Ireland, Italy, Jersey, Liechtenstein, Luxembourg, Malta, the Isle of Man, Monaco, the Netherlands, Norway, Portugal, San Marino, Spain, Sweden, Switzerland, and the United Kingdom.)
AGE-SPECIFIC PREVALENCE ESTIMATES
Age-specific prevalence rates for white, black, and Hispanic men and women were derived from the contributing studies in 2 steps. First, pooled prevalence proportions were estimated for each stratum of age, gender, and race/ethnicity by means of minimum variance linear estimation. Stratum-specific proportions from each study were transformed by means of a log odds transformation; proportion variances were calculated assuming the binomial distribution. The Cochran test for homogeneity was used to evaluate variation between studies for the pooled age- and gender-specific rates. Second, logistic regression models were fitted to the pooled prevalence proportions using the midpoint of each age interval as the independent variable. Models for prevalence estimates for black and Hispanic persons each were based on the data from a single study, Baltimore and Proyecto VER (a study of primarily Mexican-American Hispanics), respectively.4 Population-based data meeting entry criteria on the prevalence of refractive errors in persons not identifying themselves as black, white, or Hispanic were not available. To make national projections, rates for these other racial/ethnic groups were assumed to equal the average of the pooled stratum-specific rates for white, black, and Hispanic persons. Age and race/ethnicity effects in the models were tested by the Wald  2 test statistic. Tests for gender differences, based on the observed data from all contributing studies, were performed separately by race/ethnicity with the Mantel-Haenszel 2 test, controlling for both age and study.
ESTIMATES OF PREVALENCE RATES IN THE UNITED STATES, WESTERN EUROPE, AND AUSTRALIA
The estimated number of cases in the United States in each race/ethnicity, gender, and age category was generated by applying the modeled prevalence rate for each year of age to the US census population for the year 2000 and summing over the age range for each 5-year age category. Projected estimates were derived in the same manner with US Census middle series projections for the year 2020, assuming constant age-, gender-, and race/ethnicity–specific refractive error rates over time. Stratum-specific US prevalence rates were computed by dividing the total number of estimated cases for each stratum by the stratum-specific US population.
Prevalence estimates for Western Europe were based on the modeled age-specific rates for white persons from the Baltimore, Beaver Dam, and Rotterdam studies. Prevalence estimates for Australia were based on the pooled age- and sex-specific rates from the Blue Mountains and Melbourne Visual Impairment Project studies.
RESULTS
Six population-based eye surveys contributed data from a total of 29 281 persons for the pooled analysis. Age- and gender-specific prevalence rates of myopia and hyperopia were found to vary by geographic locale of the study (Figure 1, Figure 2, and Figure 3), with studies from the United States and Rotterdam having similar results, and Australian studies having lower prevalence rates for myopia and hyperopia. Therefore, for purposes of estimation of US and Western European prevalence rates for refractive errors—and for reports of association with age, race/ethnicity, and gender—only data from the Baltimore, Beaver Dam, Proyecto VER, and Rotterdam studies were used. The 20 957 subjects in these studies (14 414 from US populations and 6543 from Western Europe [Rotterdam]) included 2348 black and 4507 Hispanic persons. For estimation of the Australian prevalence of refractive errors, only Blue Mountains and Melbourne Visual Impairment Project data were used, including results from 8324 white subjects.
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Figure 1. Prevalence of hyperopia of +3 diopters or greater in white persons (A) and black and Hispanic persons (B). BES indicates Baltimore Eye Survey, Baltimore, Md; BDES, Beaver Dam Eye Study, Beaver Dam, Wis; BMES, Blue Mountains Eye Study, Sydney, New South Wales, Australia; RS, Rotterdam Study, Rotterdam, the Netherlands; Melbourne VIP, Melbourne Visual Impairment Project, Melbourne, Victoria, Australia; and Projecto VER, Vision Evaluation and Research, Nogales and Tucson, Ariz.
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Figure 2. Prevalence of myopia of –1 diopter or less in white persons (A) and black and Hispanic persons (B). BES indicates Baltimore Eye Survey, Baltimore, Md; BDES, Beaver Dam Eye Study, Beaver Dam, Wis; BMES, Blue Mountains Eye Study, Sydney, New South Wales, Australia; RS, Rotterdam Study, Rotterdam, the Netherlands; Melbourne VIP, Melbourne Visual Impairment Project, Melbourne, Victoria, Australia; and Projecto VER, Vision Evaluation and Research, Nogales and Tucson, Ariz.
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Figure 3. Prevalence of myopia of –5 diopters or less in white persons (A) and black and Hispanic persons (B). BES indicates Baltimore Eye Survey, Baltimore, Md; BDES, Beaver Dam Eye Study, Beaver Dam, Wis; BMES, Blue Mountains Eye Study, Sydney, New South Wales, Australia; RS, Rotterdam Study, Rotterdam, the Netherlands; Melbourne VIP, Melbourne Visual Impairment Project, Melbourne, Victoria, Australia; Projecto VER, Vision Evaluation and Research, Nogales and Tucson, Ariz.
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RELATIONSHIPS OF REFRACTIVE ERROR PREVALENCE RATES TO DEMOGRAPHIC CHARACTERISTICS
Estimates of age-, gender-, and race/ethnicity–specific prevalence rates based on the pooled data from the studies used to estimate the US and Western European prevalence rates of refractive errors are given in Table 2. The prevalence rates for hyperopia, myopia of –1 D or less, and myopia of –5 D or less varied substantially with age and, to a lesser degree, with gender and race/ethnicity (Figure 1, Figure 2, and Figure 3).
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Table 2. Prevalence Rates for Refractive Error by Age, Gender, and Race/Ethnicity
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The prevalence of hyperopia was observed to be progressively higher with increasing age. The linear association of increasing hyperopia prevalence with age was statistically significant (P  .01) in every gender- and race/ethnicity–specific fitted model except that for black men (P = .76), and was highly significant among both white men (P <.001) and white women (P <.001). Among the gender- and race/ethnicity–specific groups other than black men, the prevalence of hyperopia was 4.2- to 7.4-fold higher in the oldest (80 years) with respect to the youngest (40-49 years) age stratum. Among black men, the prevalence of hyperopia was approximately constant for all age groups.
Reciprocally, the prevalence of myopia of –1 D or less tended to be substantially lower for older than younger age groups, as demonstrated in every gender- and race/ethnicity–specific model. However the association of myopia and age was not linear, in that all gender- and race/ethnicity–specific groups (except black men) demonstrated an increase in myopia among the oldest age groups. Among black men, who had very low rates of myopia in the oldest age groups, the prevalence of myopia was 8.0-fold higher in the youngest (40-49 years) with respect to the oldest (80 years) age stratum. In other gender- and race/ethnicity–specific groups, the youngest age groups had a 1.3- to 2.7-fold higher prevalence of myopia of –1 D or less than the oldest age groups, whereas the youngest age groups had a 1.7- to 3.1-fold higher prevalence of myopia of –1 D or less than the age group with the lowest myopia prevalence. Quadratic models that allowed for decreasing myopia prevalence with age and also allowed for an increase in prevalence in the oldest age strata were supported by the data for white women (P <.001), white men (P <.001), black women (P <.001), and Hispanic women (P = .03). For Hispanic men (P = .06), the quadratic model was less well supported. For black men, the pattern of decreasing myopia prevalence with age was strongly linear (P = .001), with almost no improvement in model fit by adding a quadratic term. For most gender- and race/ethnicity–specific groups, the inflection point in the quadratic curve appeared to lie close to age 70 years.
Similarly, myopia of –5 D or less was strongly associated with age among white persons (P = .007) and Hispanic persons (P = .008), in a nearly linear pattern, with the highest prevalence in the youngest strata. Among white and Hispanic persons, the prevalence of myopia of –5 D or less was 2-fold and 3.3-fold higher, respectively, in the youngest with respect to the oldest stratum. However, no clear association between age and myopia of –5 D or less was evident among black persons (P = .71).
The general patterns of higher prevalence rates of hyperopia and lower prevalence rates of myopia with increasing age were consistent across all studies.
Overall, women were found to have a higher prevalence of hyperopia (odds ratio [OR], 1.28; P <.001) than men, after adjusting for age and race/ethnicity. However, the overall age- and race/ethnicity–adjusted prevalence of myopia of –1 D or less was similar in men and women (OR, 1.01; P = .89). The age-adjusted prevalence of myopia of –5 D or less tended to be higher in women than men (OR, 1.16; P = .07). Although the latter association was nonsignificant in the pooled data set from the US-European studies, in the pooled data set from the Australian studies white women had significantly higher age-adjusted rates of myopia of –5 D or less than men (OR, 1.61; P = .002).
Adjusting for age and gender, white persons had significantly higher prevalence rates for hyperopia (OR, 1.22; P <.001), myopia of –1 D or less (OR, 1.25; P <.001), and myopia of –5 D or less (OR, 1.41; P <.001) than did Hispanic persons. Hispanic persons in turn had significantly higher age- and gender-adjusted prevalence rates of hyperopia (OR, 1.69; P <.001) and myopia of –1 D or less (OR, 1.52; P = .001) than did black persons. For myopia of –5 D or less, the age- and gender-adjusted prevalence was higher among Hispanic persons than among black persons, but the difference was not statistically significant (OR, 1.32; P = .09). The age- and gender-adjusted prevalence rates of hyperopia (OR, 2.50; P <.001), myopia of –1 D or less (OR, 2.43; P <.001), and myopia of –5 D or less (OR, 2.52; P <.001) all were substantially higher among white persons than black persons.
PREVALENCE RATES FOR REFRACTIVE ERRORS IN THE UNITED STATES, WESTERN EUROPE, AND AUSTRALIA
The estimated overall prevalence rates for refractive errors in the US population 40 years or older in the year 2000 are given in Table 3, Table 4, and Table 5. The estimated prevalence of hyperopia was 9.9% (95% confidence interval, 9.7%-10.1%), and the estimated prevalence of myopia of –1 D or less was 25.4% (95% confidence interval, 24.5%-26.4%). The estimated prevalence of myopia of –5 D or less was 4.5% (95% confidence interval, 4.2%-4.7%). Thus, persons with high myopia, according to this definition, made up 17.4% of all persons with myopia. These prevalence rates correspond to a burden of 11.8 million persons with hyperopia and 30.4 million persons with myopia of –1 D or less (5.3 million of whom have myopia –5 D) in the year 2000 US population 40 years or older. A total of 42.2 million persons (35.3%) in this age group are estimated to have either hyperopia or myopia, according to our definitions. Applying age-, gender-, and race/ethnicity–specific rates to the anticipated population structure of the United States in the year 2020, the projected prevalence rates for hyperopia, myopia of –1 D or less, and myopia of –5 D or less are 10.8% (16.6 million persons), 22.5% (34.7 million persons), and 4.0% (6.2 million persons), respectively.
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Table 3. Estimated Prevalence of Hyperopia of +3.0 Diopters or Greater in the United States, by Age, Gender, and Race
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Table 4. Estimated Prevalence of Myopia of –1.0 Diopter or Less in the United States, by Age, Gender, and Race
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Table 5. Estimated Prevalence of Myopia of –5.0 Diopters or Less in the United States, by Age, Gender, and Race
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In the Western European population for the year 2000, an estimated 11.6% of persons 40 years and older had hyperopia (21.6 million persons), 26.6% had myopia of –1 D or less (49.6 million persons), and 17.1% of the latter group (4.6% of the general population, 8.5 million persons) had myopia of –5 D or less. In the year 2020, projected prevalence rates for hyperopia, myopia of –1 D or less, and myopia of –5 D or less are 12.8% (27.8 million persons), 26.5% (57.4 million persons), and 4.6% (10.0 million persons), respectively.
In Australia, which had lower age-specific prevalence rates for refractive errors and has a younger general population age structure than Western Europe and the United States, the estimated population prevalence rates for hyperopia, myopia of –1 D or less, and myopia of –5 D or less among the year 2000 population 40 years and older were 5.8% (471 000 persons), 16.4% (1.3 million persons), and 2.8% (231 000 persons), respectively. In the year 2020, projected prevalence rates are 6.4% (721 000 persons), 15.7% (1.8 million persons), and 2.6% (292 000 persons), respectively.
COMMENT
Pooled data from the participating population-based eye studies, conducted in persons 40 years or older, indicate that the crude prevalence of myopia is the highest of any eye disorder in this age group, affecting about 1 in 4 persons in the United States and Western Europe, and about 1 in 6 Australians. Approximately 1 of 6 persons with myopia—1 of every 24 persons in the general US and Western European population 40 years or older—has myopia of –5 D or less and may be at risk of pathologic complications of high myopia. Even with our conservative definition of hyperopia, its estimated prevalence is substantial, affecting about 1 in 10 persons in this age group. Prevalence rates would be higher if a definition including lower degrees of hyperopia were used. Refractive errors, in aggregate, affect approximately 1 in 3 older adults in the United States and Western Europe, and about 1 in 5 older Australians.
Because refractive error typically can be neutralized with spectacles, contact lenses, or refractive surgery, persons with refractive error who access treatment generally are not disabled. However, population-based studies have demonstrated that refractive errors often are not adequately corrected in the general population; rather, they generally are the leading cause of mild visual impairment observed in population-based studies in developed nations.4, 6, 8, 11-13 In addition, vision loss uncorrectable by refraction may occur as a complication of treatments for refractive error. Bacterial keratitis, the primary vision-threatening complication of contact lens use, has been estimated to occur at a rate of 1 case per 2500 person-years of daily-wear contact lens use, and 1 case per 500 person-years of extended-wear contact lens use.14 Vision loss due to complications of refractive surgery also is uncommon but appears to be more frequent than with contact lens use.15-17 Also, persons with a high degree of myopia appear to have higher risk of associated ocular diseases that may lead to vision loss, including peripheral retinal lesions that may predispose to retinal detachment,18-19 glaucoma,20 cataract,21-22 and myopic degeneration23 (sometimes complicated by choroidal neovascularization24). In the Rotterdam study, 6% of visual impairment was attributed to myopic degeneration, which was 1 of the 2 leading causes of visual impairment in persons younger than 75 years.25 Our data suggest that a large number of persons are in this at-risk category. Thus, while the per-case risk of loss of best-corrected visual acuity in persons with refractive error is less than that of the other eye conditions studied by our group, the high prevalence of refractive errors suggests that the absolute number of persons losing vision as a result of complications of contact lens use, refractive surgery, or high myopia–associated ocular diseases is substantial.
Similarly, while the per-person costs of using spectacles and contact lenses are modest (by developed-country standards), in aggregate these costs are substantial. An estimated $12.8 billion (1990 US dollars) was spent to correct refractive errors of Americans in 1990.26 Refractive surgery incurs a higher up-front cost than spectacles or contact lenses, but these costs may be recovered to a large extent over the years,26 provided that subsequent shifts in refractive state that require refractive correction are unusual—an assumption that may not be warranted (discussed later).
Our results demonstrate a strong association of refractive error with age, wherein older persons tended to have higher rates of hyperopia and lower rates of myopia. It has been debated whether this pattern of association is due to changes in the optical system with age, or differences in the environment experienced during life by persons born during different calendar-year periods (cohort effects). Graphic analysis of cross-sectional data from 3 US eye surveys suggested that the observed pattern is more consistent with age effects than cohort effects.27 However, the Beaver Dam Eye Study, which has provided the only available report of longitudinal changes in refractive error with age during a 10-year period in a population-based sample,28 found that both aging and cohort effects on refractive error appeared to be important in determining changes in age-specific prevalence of refractive error over time. Cohort effects were demonstrated by substantial changes in mean refractive error between birth intervals, nearly –0.5 D per 5-year birth interval from 1918 through 1942, suggesting that environmental factors changed in a manner that promoted myopia for persons born during this period in rural Wisconsin. Further longitudinal data are needed to evaluate whether similar cohort effects occurred in other populations during this period and subsequently. Aging effects also were demonstrated in the Beaver Dam study, in that participants aged 43 to 59 years at enrollment had an average 10-year change in refraction of +0.54 D, those initially aged 70 years and older had an average 10-year change in refraction of –0.41 D, and those aged 60 to 69 years at enrollment had little change. A similar pattern has been observed in 5-year longitudinal data from the Blue Mountains Eye Study.29 These patterns are in close agreement with the pattern observed in our pooled cross-sectional myopia data, in which the prevalence of myopia of –1 D or less declined with age to a nadir near the age of 70 years, after which an increase in the prevalence of myopia of –1 D or less was observed.
A hyperopic shift of this magnitude in the population's average refractive error during middle age would seem to have considerable importance in evaluating the appropriate use of and goals for refractive surgery in myopic adults. Potential explanations for a hyperopic shift in measured refractive error during middle age include loss of accommodative tone with progressive presbyopia, and/or actual biometric changes (decreasing axial length and/or increasing corneal power) during this period of aging. These theories could be addressed, at least partially, by performing cycloplegic refractions and biometry in future longitudinal population-based eye studies. Under the accommodative tone theory, studies using cycloplegic refraction would be expected to find a hyperopic shift of the refractive error distribution with respect to our results (based on noncycloplegic refraction) in younger age groups, with higher rates of hyperopia and lower rates of myopia.
The theory that nuclear sclerosis contributes to a myopic refractive shift in the elderly is well supported by longitudinal data.28-29 However, actual biometric changes with age also could have contributed to a myopic change in age-specific prevalence in elderly adults. It is worth noting that if elderly persons with nuclear sclerosis–induced myopia in the participating studies were more likely to undergo cataract surgery than other study participants before participating in the surveys—resulting in censoring from the pooled analysis—the myopic shift in the elderly may be even greater than is reported herein.
Other important observations of our study were that hyperopia, but not myopia (except perhaps high degrees of myopia), was more common in women than men, and that race/ethnicity–specific differences in the prevalence of refractive errors appear to exist. It is interesting to note that both hyperopic and myopic refractive errors occurred more frequently among white persons than Hispanic persons, and among Hispanic persons than black persons. Although only one study, the Baltimore Eye Survey, evaluated more than one racial group simultaneously, the pattern we observed in our pooled analysis was observed within that study. Thus, the observed differences between racial/ethnic groups appear to exist in the variability aspect of the refractive error distribution, suggesting that the Hispanic and especially black racial/ethnic groups, on average, may more frequently have successful emmetropization during life than the white group. Research evaluating the genetic and/or environmental factors underlying these differences between racial/ethnic groups is needed. Western European, US, and Australian data were sparse regarding Asian persons, a group thought to have a different pattern of refractive error prevalence than the racial/ethnic groups studied herein,30-31 with too few persons studied to make population prevalence estimates. Research assessing the prevalence of refractive errors in Asian persons living in the United States, Western Europe, and Australia is needed.
We interpreted differences between the US and Western European studies with respect to the Australian studies as reflecting regional differences in the prevalence of refractive errors. An alternative explanation of the observed differences is the possibility that the populations included in the estimation process for the United States and Western Europe and/or the 2 Australian studies were nonrepresentative to a substantial degree. However, because the studies were all population based and showed agreement with each other within these geographic groupings, this possibility seems unlikely. Another alternative explanation is that because the Australian studies did not perform autorefraction on participants who saw well with their current refraction, they underascertained refractive errors. However, it is difficult to believe that a substantial number of participants with hyperopia of +3 D or greater and/or myopia of –1 D or less would have had normal visual acuity on rigorous testing, as done in these studies. Therefore, our results suggest that a real difference exists in the prevalence of refractive errors between Australia and the United States–Western Europe. Further research as to what environmental differences might underlie regional differences in the age-, gender-, and race/ethnicity–specific prevalence of refractive errors potentially could provide important information regarding the etiology of refractive error and means of prevention.
Several potential limitations of our study should be considered in interpreting these results. First, we have assumed that the study populations of the contributing studies are representative of the general populations to which we have applied their results. Clearly, results from our locally representative studies cannot be generalized to the US population with as much confidence as results from a nationally representative study, if such a study were available. In particular, only results from white persons were used for Western European and Australian prevalence calculations, which may have inadequately represented the prevalence rates in other racial/ethnic groups in these regions.
Second, our data do not address the prevalence of refractive errors for some groups of interest. For children and younger adults, no recent data were available. As noted previously, the National Health and Nutrition Examination Survey in 1971-1972 found that persons aged 12 to 54 years had high rates of myopia1; therefore the lack of data on this group is an important gap in our knowledge of the prevalence of refractive errors. Population-based studies of younger Americans are needed to allow such estimates to be made. In addition, data for black and Hispanic persons were obtained from single studies. Because the particular populations studied may not have given an average representation of the broader black and Hispanic populations, our prevalence estimates for these groups may be less reliable than are the estimates for white persons, which are based on pooled data from multiple population-based studies. Because no data were available regarding the prevalence rates for refractive errors in racial/ethnic groups other than white, black, and Hispanic persons, we had to rely on arbitrary methods to estimate the prevalence of refractive errors in these groups for US estimates and projections. Further research evaluating the prevalence of eye diseases in these groups would be of interest, particularly among persons of Chinese and Indian descent, who, respectively, have been reported to have remarkably high30 and low31 rates of refractive errors in population-based studies in Asia. Findings of no increased risk of myopia among Asians in the Melbourne Visual Impairment Project7 suggest that results from Asian persons living in Asia may not be generalizable to a non-Asian setting.
Third, data are reported according to categories determined by consensus of the Eye Diseases Prevalence Research Group. Categories that were more inclusive (eg, –0.50 D or more negative, +1 D or more positive) would have resulted in even higher estimated prevalence rates. We elected to choose these categories to take a conservative approach in reporting the prevalence of refractive errors. However, this conservative approach may have underestimated the number of persons in the populations who would benefit from refractive correction, particularly among older persons with lesser degrees of hyperopia than +3 D. Similarly, our use of the threshold of –5 D for "high" myopia probably led to higher prevalence estimates than the other commonly used threshold of –6 D would have. Sensitivity analyses of how prevalence rates would have differed with different outcome definitions were not possible, because the contributing studies only provided data regarding the cutoffs agreed on by the study group in advance of the pooled analysis.
Finally, future projections of the prevalence rates for refractive errors are difficult to make because longitudinal information from population-based cohort studies is limited to 10-year results from the Beaver Dam study, and lesser degrees of follow-up from other studies. Our future projections are probably the least reliable estimates produced by this study, because cohort effects may alter prevalence rates in years to come in ways that we cannot predict. Use of these future projections for policy decision making should take their uncertainty into account. However, because changes in the prevalence of myopia and hyperopia are not driven by age to the same extent as the prevalence of age-related eye diseases, the dramatic changes in prevalence expected with population aging for cataract, age-related macular degeneration, and glaucoma are not as likely to occur for refractive errors in aggregate.
A relative strength of this study, with respect to most pooled analyses, is that the outcomes of interest were ascertained by highly comparable, reliable methods. All studies included in the estimation of US and Western European prevalence rates used autorefraction followed by subject refinement to measure refractive error. Direct provision of data according to our specifications by each contributing study team allowed use of identical cutoffs for the diagnoses of hyperopia and myopia.
In summary, refractive errors of a magnitude expected to require refractive correction are estimated to be present in one third of the population 40 years or older in the United States and Western Europe, and one fifth of this population in Australia. The prevalence of refractive errors is strongly related to age and varies with gender and race/ethnicity. More research is needed in the United States, Western Europe, and Australia regarding the prevalence rates for refractive errors in younger age groups and in minority populations such as persons of Asian origin to more accurately estimate the extent of the problem in these groups. Also, further research regarding changes in the refraction of individuals over time seems warranted, to evaluate whether refractive surgery is really likely to provide a long-term solution to the problem of refractive error, a concept that seems uncertain on the basis of our results and those of studies with longitudinal follow-up of individuals.28-29 Although the morbidity (if refractive correction is available and is used) and cost associated with refractive errors are lower on a per-case basis than for some other ocular disorders, the aggregate morbidity and cost are substantial enough that these conditions should be considered a priority subject for health policy decision making and research.
AUTHOR INFORMATION
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Corresponding author and reprints: John H. Kempen, MD, PhD, 550 N Broadway, Suite 700, Baltimore, MD 21205 (e-mail: jkempen{at}jhmi.edu).
Submitted for publication May 12, 2003; final revision received November 19, 2003; accepted November 19, 2003.
From the Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, Md (Drs Kempen, Tielsch, Congdon, and Friedman and Ms Broman); Departments of Epidemiology (Drs Kempen and Tielsch) and International Health (Drs Tielsch, Congdon, and Friedman), The Johns Hopkins University Bloomberg School of Public Health, Baltimore; Department of Ophthalmology, University of Sydney, Sydney, New South Wales (Dr Mitchell); Centre for Vision Research, Westmead Hospital, Westmead, New South Wales (Dr Mitchell); Department of Ophthalmology and Visual Sciences, University of Wisconsin Medical School, Madison (Ms Lee); Centre for Eye Research Australia, University of Melbourne, Melbourne, Victoria (Dr Taylor); Departments of Epidemiology and Biostatistics, Erasmus Medical Center, Rotterdam, the Netherlands (Dr Ikram), and School of Public Health and Health Services, George Washington University Medical Center, Washington, DC (Ms O'Colmain); and Macro International, Inc, Calverton, Md (Ms O'Colmain).
This study was supported by contract NO1-EY-8-2108 from the National Eye Institute, Bethesda, Md. Additional support was provided by grant EY00386 (Dr Kempen) from the National Eye Institute.
Data from the 2000 US Census is in the public domain. The research group gratefully acknowledges the work of the many contributors to create these data.
| Members of the Eye Diseases Prevalence Research Group
The members of the Eye Diseases Prevalence Research Group are as follows:
Participating Studies
Baltimore Eye Survey, Baltimore, Md: James M. Tielsch, Alfred Sommer, Joanne Katz, Harry A. Quigley. Beaver Dam Eye Study, Beaver Dam, Wis: Barbara E. K. Klein, Ronald Klein, Scot E. Moss, Kristine E. Lee, Sandra C. Tomany. Blue Mountains Eye Study, Sydney, New South Wales, Australia: Paul Mitchell, Jie Jin Wang, Elena Rochtchina, Wayne Smith, Robert G. Cumming, Karin Attebo, Jai Panchapakesan, Suriya Foran. Melbourne Visual Impairment Project, Melbourne, Victoria, Australia: Hugh R. Taylor, Cathy McCarty, Bickol Mukesh, LeAnn M. Weih, Patricia M. Livingston, Mylan Van Newkirk, Cara L. Fu, Peter Dimitrov, Matthew Wensor, Yury Stanislavsky. Proyecto VER (Vision Evaluation Research), Nogales and Tucson, Ariz: Sheila K. West, Jorge Rodriguez (deceased), Aimee Broman, Beatriz Muñoz, Robert Snyder, Ronald Klein, Harry A. Quigley. Rotterdam Study, Rotterdam, the Netherlands: Paulus T. V. M. de Jong, Johannes R. Vingerling, Roger C. W. Wolfs, Caroline C. W. Klaver, Albert Hofman, Redmer van Leeuwen, M. Kamran Ikram, Simone de Voogd.
Resource Centers
Coordinating Center: John H. Kempen, Nathan G. Congdon, David S. Friedman, Benita J. O'Colmain; National Eye Institute: Frederick L. Ferris III.
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*The Writing Group members for the Eye Diseases Prevalence Research Group who had complete access to the raw data needed for this report and who bear authorship responsibility for this report are John H. Kempen, MD, PhD (Chairperson); Paul Mitchell, MD, PhD; Kristine E. Lee, MS; James M. Tielsch, PhD; Aimee T. Broman, MA; Hugh R. Taylor, MD; M. Kamran Ikram, MSc, MD; Nathan G. Congdon, MD, MPH; Benita J. O'Colmain, MPH; and David S. Friedman, MD, MPH. The Writing Group for this article has no relevant financial interest in this article.
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