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1 From the Department of Preventive Medicine, University at Stony Brook, Stony Brook, New York; 2 Ministry of Health, Barbados, West Indies; 3 the Johns Hopkins University, School of Medicine, Baltimore, Maryland.
Abstract
PURPOSE. To describe the prevalence of refractive errors in a black adult population.
METHODS. The Barbados Eye Study, a population-based study, included 4709 Barbados-born citizens, or 84% of a random sample, 40 to 84 years of age. Myopia and hyperopia were defined as a spherical equivalent <-0.5 diopters and >+0.5 diopters, respectively, based on automated refraction. Analyses included 4036 black participants without history of cataract surgery. Associations with myopia and hyperopia were evaluated in logistic regression analyses.
RESULTS. The prevalence of myopia was 21.9% and was higher in men (25.0%) than in women (19.5%). The prevalence of hyperopia was 46.9% and was higher in women (51.8%) than in men (40.5%). The prevalence of myopia decreased from 17% in persons 40 to 49 years of age to 11% in those 50 to 59 years of age, but increased after 60 years of age. The prevalence of hyperopia increased from 29% at 40 to 49 years of age to 65% at 50 to 59 years of age, and tended to decline thereafter. A higher prevalence of myopia was positively associated (P < 0.05) with lifetime occupations requiring nearwork, nuclear opacities, posterior subcapsular opacities, glaucoma, and ocular hypertension. Factors associated with hyperopia were the same as for myopia, except for occupation, and in the opposite direction.
CONCLUSIONS. High prevalences of myopia and hyperopia were found in this large black adult population. The prevalence of myopia (hyperopia) increased (decreased) after 60 years of age, which is inconsistent with data from other studies. The high prevalence of age-related cataract, glaucoma, and other eye conditions in the Barbados Eye Study population may contribute to the findings.
Refractive errors are the most common eye conditions in the world. Although most errors can be corrected by optical or surgical methods, these treatments have some drawbacks and pose a large economic burden. In the US, an estimated 12.8 billion dollars were spent on the correction of refractive errors in 1990.1 The etiologic mechanisms of refractive errors can be both genetic and environmental.2 3 4 Genetics plays a role in the growth and structure of the eye, as demonstrated in twin and family studies.5 6 7 Close-up work, particularly reading, is generally considered as an environmental factor that may lead to myopia.2 3 4 Furthermore, other eye conditions such as cataract, glaucoma, or ocular hypertension often coexist with refractive errors.8 9 10 11 12 13 The interaction of all these factors and the underlying mechanisms of refractive errors remain unclear.
Prevalence data on the magnitude and distribution of refractive errors
are important for public health care planning. However, limited
population-based data exist on the distribution of refractive errors in
black adults. The National Health and Nutrition Examination Survey
(NHANES; 1971–1972) showed a lower prevalence of myopia for
African–Americans than for whites between the ages of 12 and 54 years
of age.14
More recently, the Baltimore Eye Survey reported
that refractive errors are common among adult inner city residents 
40
years, but African–Americans had less myopia and hyperopia than
whites.15
In addition to race, the distribution of
refractive errors varies by age and gender.14
15
This
report describes the prevalence of refractive errors in a large
predominantly black adult population from the Barbados Eye Study (BES).
An additional aim is to evaluate associations with demographic factors,
while accounting for concomitant ocular conditions.
Methods
The Barbados Eye Study (BES), a population-based study, included 4709 Barbados-born citizens, or 84% of the eligible members of a simple random sample, 40 to 84 years of age. The BES (1987–1992) aimed to determine prevalence and evaluate factors for ocular diseases, and its design and methods have been described elsewhere.16 In brief, the BES protocol included various ophthalmic and other measurements, such as best-corrected visual acuity with a Ferris–Bailey chart, Humphrey perimetry, applanation tonometry, lens grading, and color stereophotography. The study followed the tenets of the Declaration of Helsinki. Non-cycloplegic refractive errors were measured on all participants with the Humphrey Automated Refractor #530. When the refractor could not be used or refraction was unreliable, the participant’s present correction, if any, was determined with a lensometer.
Evaluations in this report were based on automated refractor data,
after excluding participants with a previous history of cataract
surgery. Because of the high correlation between eyes (Pearson’s
r = 0.78) and because of the similarity of results
based on left or right eyes, we report data from right eyes only. For
the purpose of comparison across studies, myopia was defined as having
a spherical equivalent <-0.5 diopter (D), and hyperopia was defined
as having a spherical equivalent >0.5 D. Additional analyses based on
a more stringent definition using cutoff values such as ± 1 D
were also conducted. Distributions of refractive errors by
self-reported race were compared and evaluated in regression analysis,
controlling for age and gender. Age-gender specific distributions of
refractive errors and prevalence of myopia/hyperopia, as well as risk
factor analyses, were limited to black participants. Associations with
myopia/hyperopia were evaluated by logistic regression. Factors
evaluated included age, gender, years of education, lifetime
occupation, lens opacities (by type), and glaucoma status. The lifetime
occupation (based on the question: "what kind of work have you done
for MOST of your life") was categorized as mainly involving nearwork
(including professional, managerial, clerical, and technical or
electrical occupations) or not (including service, agricultural,
forestry, fishing or water-related activities, production work, and
homemaker). The classification of lens status was based on LOCS
II17
gradings at the slit lamp and a score 2 was used to
define nuclear, posterior subcapsular (PSC), and cortical
opacities.18
For this report, individuals with any
glaucoma included those with open-angle glaucoma, which required both
visual field and optic disc criteria for glaucoma damage as described
previously,16
suspected glaucoma, and other types of
glaucoma. Ocular hypertensives included persons with an intraocular
pressure >21 mm Hg or with a history of intraocular pressure–lowering
treatment, but without glaucoma visual field defects or disc
damage.19
Results
Of the 4631 participants who completed the BES visit at the study site, 137 had a previous history of cataract surgery, and another 164 had no data on the Humphrey refractor because of poor visual acuity, media opacities, or other reasons. After excluding these participants, the distribution of refractive errors by self-reported race was based on 4330 right eyes. Table 1 presents demographic information on this study population. Median age was 57 years; and 57% of the participants were female. Over 90% of the population self-reported their race as black and most participants (36%) had a lifetime occupation in the service industry. Although persons excluded from the analysis were older (median age, 73 years), the age and gender distributions of the 4330 participants in this report were similar to the total BES study population (median age, 58 years; 57% female).
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Table 4 presents results from logistic regression analyses, which show differences in prevalence by age, after controlling for gender, indicators of socioeconomic status (such as lifetime occupation and education), and various ocular conditions. Age had a complex relationship with refractive errors. Persons 50 to 59 years of age had a significantly decreased prevalence of myopia compared with persons 40 to 49 years of age (OR = 0.58). This relationship was not seen in the age group 60 to 69 years (OR = 1). Furthermore, there was a nearly twofold increased likelihood of being myopic for persons 70 years of age or older, compared with those 40 to 49 years of age (OR = 1.77).
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Except for occupation, which was not statistically significant, the associations with hyperopia were the same as those found for myopia and as expected, in the opposite direction (Table 4) . In the multivariate analysis, increasing age was associated with a higher prevalence of hyperopia, as shown by the odds ratios over unity. However, in every decade of life after the age of 60 years, the magnitude of the odds ratios decreased as the age advanced. Therefore, although there were positive associations between the prevalence of hyperopia and advancing age, the odds of becoming hyperopic decreased after the age of 60 years. Very similar results were found when the associations were evaluated using cutoff values of ±1D (data not shown).
Discussion
The BES is a large epidemiologic study that investigated major eye
diseases in a predominantly black population with a high participation
rate. The study had a demographic composition similar to the census
population,16
thus supporting the generalizability of the
findings. Refractive errors were very common in the BES adult
population, 40 years of age and older, in which approximately 1 in 4
persons was estimated to be myopic and 1 in 2 persons was hyperopic.
Based on self-reported race, a definition supported by results of blood
group distribution and pigmentation gradings,20
differences were observed in the distributions of refractive errors
between black and white groups (Fig. 1)
. Black participants had less
deviations from emmetropia than white participants, after adjusting for
age and gender. Although such comparisons were based on small numbers
of participants in the white and mixed racial groups (and should be
interpreted cautiously), the result was consistent with data reported
in the Baltimore Eye Survey.15
Despite the lower
prevalence of myopia found in the black than in the white participants
of the NHANES12
and the Baltimore Eye
Survey,15
myopia was nonetheless fairly common in the
black participants of these two studies, 13% and over 25%,
respectively. In contrast, one survey of the prevalence of refractive
errors conducted in Malawi reported that only 2.5% of participants had
an error of 
-0.5 D.21
It was interesting to note that the prevalence of myopia in the
black BES participants 60 years increased with advancing age (Table 2)
. In addition, the prevalence of hyperopia peaked in the age group of
50 to 59 years but started to decline thereafter (Table 2)
. These
results are inconsistent with data from other studies. The NHANES
(1971–1972),14
although based on a younger population
(12–54 years of age) than the BES, showed little variation in the
overall prevalence of myopia with age. However, prevalence increased
with age in persons with less than 2 D of myopia, whereas prevalence
decreased with age in persons with 2 D or more of myopia. In the
Melbourne Visual Impairment Project, the proportion of participants
(40 years of age) with myopia decreased significantly with age when
gender was controlled for.22
Figure 3
depicts the prevalence of myopia by age in the BES and in two other
population-based studies. The Beaver Dam Eye Study,23
a
population-based study in predominantly white participants 43 to 84
years of age, reported that the prevalence of myopia decreased from
43% at 43 to 54 years of age to 14.4% at 75 years of age or older. In
that study, the prevalence of hyperopia increased from 22% in those 43
to 54 years of age to 68.5% in those 75 years of age or older. The
Baltimore Eye Survey15
also found that myopia prevalence
declined with age and that hyperopia prevalence increased with age in
black and white persons. Different definitions were used in these
studies. In the NHANES,14
myopia was defined as any
negative spherical equivalent, which was calculated from the current
correction for eyes with visual acuity 20/40 or better, and from
retinoscopy or spherical equivalent refraction for eyes with visual
acuity worse than 20/40. The Beaver Dam Eye Study,23
also
using the Humphrey 530 refractor as in our study, defined myopia and
hyperopia as refractive errors <-0.5 D and >0.5 D, respectively. The
study included subjects without cataract surgery and those who had a
best-corrected visual acuity better than 20/40 in at least one eye. The
same cutoff points for myopia and hyperopia were used in the Baltimore
Eye Survey,15
in which a subjective automated refraction
was performed, although this survey did not include a visual acuity
criterion. However, these differences in methods and definitions do not
seem to account for the discrepant findings with our study. For
example, the age patterns observed in the BES persisted even after
excluding participants with visual acuity 20/40 or worse, with myopia
prevalence descending from 16% at 40 to 49 years of age, to 9% at 50
to 59 years of age, and then increasing to 12%, 23%, and 35%,
respectively, for each age group after 60 years of age. Furthermore,
the age patterns of myopia and hyperopia found in BES remained similar
when –2 D and 2 D were used as cutoff points (data not shown). The
same age patterns were also found after changing the definition of
myopia (hyperopia) from <-0.5 D (>0.5 D) to a spherical equivalent
<-1.0 D (>1.0 D), with overall prevalences of 15.8% and 29.6% for
myopia and hyperopia, respectively. Multivariate analyses based on the
study definition yielded the same age patterns, after controlling for
possible confounding factors such as education, occupation, and various
ocular conditions (Table 4)
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Reports on the relationship between gender and refractive errors have not been uniform. In the BES, male gender was associated with a higher prevalence of myopia. Similarly, in a prevalence study of refractive errors of an adult rural population in Israel,24 mild myopia was more common in males than in females. On the contrary, both NHANES14 and the Beaver Dam Eye Study23 reported that myopia is more prevalent in women than in men. Gender was not associated with myopia in the Baltimore Eye Survey.15 The increased hyperopia prevalence in women, as seen in BES, is consistent with data from the Baltimore Eye Survey15 and a prevalence study carried out in Israel.24 No gender differences in hyperopia were seen in the Beaver Dam Eye Study.
Several studies have found a positive link between refractive errors and higher education,14 15 23 supporting the possible role of nearwork factors on the pathogenesis of myopia. Although length of education was not associated with refractive errors in BES, a borderline association was found between education >9 years and myopia (OR = 1.21, P = 0.053). Lifetime occupations that usually require close-up tasks were associated with a higher prevalence of myopia (Table 4) . Overall, 33% of the myopes and 31% of the nonmyopes had nearwork-related occupations. Most of the difference occurred in service-related occupations, which were reported by 33% of the myopes and 39% of the nonmyopes. Although the categorization of occupation in our analyses does not lead to a clear separation of nearwork versus nonnearwork, persons with nearwork-related occupations, as defined, were more likely to be myopic than those who performed less close-up work. These results are consistent with the use-abuse theory2 3 that postulates that myopia is triggered by close-up work, as usually performed by those with higher education and those in white collar occupations. One explanation is the elongation of axial length during accommodation in nearwork.3 4 Alternatively, visual demands from close-up work may cause dysfunction of the accommodation mechanism, which may result in retinal image defocus and lead to myopia.3 25 The magnitude of the odds ratio found in BES, however, was very modest (close to 1), and our results do not necessarily indicate a cause and effect relationship.
Cataract often associates with myopia,12 13 especially nuclear cataract. Lens changes were highly prevalent (42%) in the black participants of BES, with cortical opacities (34%) being most common, followed by nuclear (19%) and PSC (4%) opacities.18 After controlling for other types of opacities, nuclear opacities were highly associated with a higher prevalence of myopia, as expected, and a lower prevalence of hyperopia (Table 4) . To a lesser degree, PSC opacities were also related to a higher (lower) prevalence of myopia (hyperopia). Modest associations of refractive errors and cortical opacities were seen, which were opposite to those of nuclear and PSC opacities (Table 4) . These association patterns can possibly be explained by the different anatomic location and rigidity of the various opacity types.
A high prevalence of open-angle glaucoma (7%) was found in the BES black population.16 The prevalence rose to 11.4%16 after including any type of glaucoma or suspected glaucoma. An additional 13% of the black participants had ocular hypertension.19 Our results confirm the associations between refractive errors and glaucoma or ocular hypertension, as reported by various studies. Perkins and Phelps9 found that myopia occurred more frequently in patients with primary open glaucoma, ocular hypertension, and low-tension glaucoma than in a normal population of similar age and also that myopes with ocular hypertension had a higher risk of developing visual field defects than emmetopes or hypermetropes.9 Seddon et al.10 found a higher prevalence of glaucoma among eyes with myopia than those with hyperopia and emmetropia. Chisholm et al.11 found that the absence of hyperopia was a strong prognostic indicator for the development of visual field defects in patients with suspected glaucoma. Although some studies10 26 found an association between intraocular pressure and refractive status, others did not.27 28 29
Conclusions
Myopia and hyperopia were common in the black population of BES, although black participants had less negative and positive deviations from emmetropia than white participants. The prevalence of myopia was higher in men and increased after 60 years of age. The prevalence of hyperopia was higher in women and decreased after 60 years of age. This age pattern is a new finding, which had not been reported in other population studies, and may be related to the high prevalence of age-related cataract, glaucoma, and other eye conditions in this population. Future studies in similar populations are needed to confirm these findings.
Appendix 1
The Barbados Eye Study Group
Principal Investigator.
M. Cristina Leske, MD, MPH.
Coordinating Center.
University at Stony Brook, Stony Brook, NY: M. C. Leske, MD, MPH;
Leslie Hyman, PhD; Edward P. McManmon, MPH; Ho Cheung, MS; Suh-Yuh Wu,
MA; Vito Squicciarini, MS; Kangjinn Peng, MA; Barbara Springhorn;
Kasthuri Sarma.
Data Collection Center.
Ministry of Health, Bridgetown, Barbados, West Indies: A. M. S. Connell, FRCS, FRCOphth; Coreen Barrow; Doreen Boyce; Audley Byer;
Yolande Babb; Anne Bradshaw; Jillia Bird, MS, OD (1989–1991); Valda
Griffith (1988–1991); Hermes Nurse (1991–1992); Judith Hall
(1991–1992); Carol Selleck (1991–1992).
Fundus Photography Reading Center.
The Johns Hopkins University, Baltimore, MD: Andrew P. Schachat, MD;
Judith A. Alexander; Noreen B. Javornik, MS; Cheryl J. Hiner; Deborah
A. Phillips; Reva Ward; George Whitehead; Terry W. George.
Acknowledgements
The authors thank the Barbados Eye Study participants and the Ministry of Health, Barbados, West Indies, for their role in the study.
Footnotes
4 The Barbados Eye Study Group is shown in the Appendix. 
Supported by Grants EYO7625 and EYO7617 from the National Eye Institute, National Institutes of Health, Bethesda, Maryland.
Submitted for publication April 9, 1998; revised March 30, 1999; accepted April 28, 1999.
Proprietary interest category: N.
Corresponding author: Suh–Yuh Wu, University at Stony Brook, Department of Preventive Medicine, HSC, L3, Room 109, Stony Brook, NY 11794-8036. E-mail: swu@uhmc.sunysb.edu
References
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