Racial differences in AMD
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appear to have similar risks of developing nonexudative and exudative
Age-related macular degeneration (AMD) as whites in the United States,
according to a recent study.
Several large population-based studies have examined differences in
the prevalence of AMD between whites and blacks in the United States
(Table). These studies have consistently demonstrated that AMD affects
whites more than blacks. When examining differences in prevalence of
AMD between other racial minorities and whites, there are conflicting
findings as to whether Latinos have higher or lower rates of AMD
relative to whites. An analysis of data from the National Health and
Nutrition Examination Survey (NHANES) and another from the
Multi-ethnic Study of Atherosclerosis (MESA) study found that Latinos
had lower rates of early and late nonexudative AMD relative to whites.
In contrast, findings from the Colorado-Wisconsin Study of Age-related
Maculopathy showed higher rates of nonexudative AMD in Latinos
compared with whites and the Proyecto VER identified signs of early
AMD in over one quarter of Latinos over 50 years of age. While studies
have assessed rates of AMD among individuals residing in Asian
countries, little is known about the prevalence of AMD among Asian
Americans. Given that Latino and Asian Americans constitute the 2
fastest-growing minorities in the United States,12 representing nearly
20% of the population, it is becoming increasingly important to have
an improved understanding of the epidemiology of AMD for these groups.
Methods & Results
In this retrospective longitudinal cohort study billing records of all
encounters for 2 259 061 beneficiaries aged ≥40 enrolled in a
large, national US managed care network from 2001 through 2007 were
reviewed and the incidence and prevalence of nonexudative and
exudative AMD were determined and stratified by race. Cox regression
analyses determined the hazard of nonexudative and exudative AMD for
each race, with adjustment for confounders.
During the study, 113,234 individuals (5.0%) were diagnosed with
nonexudative and 17,181 (0.76%) with exudative AMD. After adjustment
for confounders, blacks had a significantly reduced hazard of
nonexudative (hazard ratio [HR]=0.75, 95% confidence interval [CI]:
0.71-0.79) and exudative AMD (HR=0.70, 95% CI: 0.59-0.83) at age 60
and a reduced hazard of nonexudative (HR=0.56, 95% CI: 0.52-0.60) and
exudative AMD (HR=0.45, 95% CI: 0.37-0.54) at age 80 relative to
whites. Similar comparisons for Latinos demonstrated an 18% reduced
hazard for nonexudative AMD at age 80 (HR=0.82, 95% CI: 0.76-0.88)
relative to whites. Asian Americans showed a 28% increased hazard for
nonexudative AMD at age 60 (HR=1.28, 95% CI: 1.20-1.36) but a 46%
decreased hazard for exudative AMD at age 80 (HR=0.54, 95% CI:
0.40-0.73).
Discussion & Conclusions
In this large national study, we followed a cohort of individuals of
each of the 4 major races longitudinally over time to assess for
differences among the races in the hazard of developing nonexudative
and exudative AMD. After adjustment for a number of key confounding
factors in the multivariable regression analysis, we identified
several important differences in the rates of developing AMD among the
races. Our analysis confirms the findings of many other studies,
demonstrating significantly lower rates of nonexudative and exudative
AMD at ages 60 and 80 in blacks relative to whites. No differences
were noted in rates of nonexudative AMD between Latinos and whites at
age 60; however, by age 80 the hazard of developing nonexudative AMD
was lower in Latinos relative to whites. In contrast, Latinos
exhibited higher rates of exudative AMD relative to whites at age 60,
though this difference became insignificant by age 80. The only group
found to have an increased hazard of nonexudative AMD relative to
whites were 60-year-old Asian Americans, though by age 80 no
significant differences were noted between these 2 races. Below are
comparisons among the findings from the present analysis with other
published studies in the literature.
Blacks
Several large population-based studies, including the Atherosclerosis
Risk in Communities Study, the MESA study, and the Salisbury Eye
Evaluation Project, have reported decreased risk of early
(nonexudative) AMD among blacks as compared with whites. Other
population-based studies (the Baltimore Eye Survey and NHANES III)
also showed less early AMD in blacks relative to whites, though the
findings of these studies did not reach statistical significance. Our
analysis confirmed the findings of these population-based studies,
demonstrating a 25% decreased hazard of developing nonexudative AMD
for blacks at age 60 (P < .0001) and a 44% decreased hazard of
nonexudative AMD at age 80 (P < .0001) when compared to similar-aged
whites.
While several studies describe reduced rates of exudative AMD among
blacks relative to whites, only 2 studies have been able to show a
statistically significant difference between the 2 races. All of the
existing population-based studies that have attempted to compare rates
of exudative AMD between blacks and whites have been limited by small
numbers of blacks with exudative AMD (ranging from only 0 to 7
individuals in each study). As many of these studies have
acknowledged, they were under-powered to detect a true difference in
the rate of exudative AMD between the 2 races. The present analysis
had adequate numbers of blacks (366 persons) and whites (12,857
persons) with exudative AMD to make comparisons among the groups. Our
results corroborate the findings of a study by Javitt and associates,
who performed a similar analysis by using Medicare claims data and
showed significantly lower rates of exudative AMD in blacks relative
to whites.
Latinos
The prevalence of nonexudative AMD in Latinos (3.81%) in our study was
similar to that reported in the MESA study (4.0%), but considerably
lower than 3 other population-based studies (7.0%-27.9%). The majority
of participants in the latter 3 studies were of Mexican-American
ancestry. According to the US Census Bureau, one-third of all Latinos
residing in the United States originated from Latin American countries
other than Mexico. Therefore, the rates of AMD generated from these 3
population-based studies may not be fully reflective of all Latinos
residing in the United States.
In this study we found that Latinos at age 60 had a similar hazard of
developing nonexudative AMD relative to whites, but had an 18%
decreased hazard by age 80 (P < .0001). Three previous studies that
compared early AMD in whites vs Latinos found no significant
differences between these groups, but did not stratify the results by
age, making direct comparisons difficult. Our analyses also
demonstrated that Latinos had a significantly increased hazard for
exudative AMD at age 60 relative to whites (P < .0001), which is
contrary to what has been previously reported, though at age 80 this
hazard was no longer significantly different for Latinos compared to
whites (P = .17).
Asian Americans
While several papers have reported the prevalence of AMD among Asians
residing in China, Japan, and other Asian countries, we are aware of
only 1 population-based study that examined rates of AMD among Asian
Americans (specifically, Chinese Americans) residing in the United
States. In the present analysis, Asian Americans had a 28% increased
hazard for developing nonexudative AMD at age 60, but this difference
was no longer significant at age 80 relative to whites. Similar
hazards were found when comparing 60-year-old Asian Americans to
whites for exudative AMD, but the hazard was found to be significantly
decreased for 80-year-old Asian Americans. Our findings differ from
those of the MESA study, which showed a similar rate of early AMD for
Chinese Americans compared to whites (OR: 0.74, CI: 0.48-1.15) but a
significantly higher risk for exudative AMD (age- and sex-adjusted OR:
4.30, CI: 1.30-14.27).10 Reasons for these differences may include
study design, particularly the fact that our analysis included Asians
of many ethnicities, not just of Chinese ancestry, which was the
predominant Asian ethnicity represented in MESA.
Recently, Kawasaki and associates performed a meta-analysis of data
from 4 large population-based studies conducted in Asia along with
Chinese Americans from the MESA study. These researchers found that
Asians aged 40 to 79 had a prevalence rate of 6.8% for early AMD and
0.56% for late AMD. Despite major differences in study design between
these population-based studies included in the meta-analysis and the
methods we used, the prevalence estimates for early and late AMD are
remarkably similar among the 2 studies.
Implications
One factor that may account for some of the differences in risk of
exudative AMD among the races is tobacco use, a known risk factor for
exudative AMD. A recent study by the Kaiser Family Foundation compared
smoking rates among races within the United States and showed that
both Latinos and Asians were less likely to smoke than whites. It is
possible that the higher hazards of exudative AMD observed among
whites in this study relative to other races may be attributable, in
part, to greater tobacco use in persons of this race. A similar
finding has been observed in the Hisayama and Funagata studies. When
comparing rates of exudative AMD in Japanese male and female subjects,
these studies report higher exudative AMD rates among male subjects,
which may be attributable to greater tobacco use among Japanese males.
Unfortunately, our data source does not contain information on
smoking, so we were not able to explore how tobacco use may affect our
study findings.
The proportion of the US population who are Latino or Asian American
is expected to rise to 33% by 2050, and will number over 135 million
people. Understanding rates of AMD in these groups is imperative, so
that clinicians can have better insight into who is most at risk for
developing this disease and health policymakers can use this
information to help guide decisions pertaining to healthcare resource
allocation.
In summary, racial minorities, including Latinos and Asian Americans,
do not appear to have similar risks of developing nonexudative and
exudative AMD as whites. Additional studies using other sources should
be conducted to determine the generalizability of this study's
findings to other groups.
Am J Ophthalmol. 2011 Aug;152(2):273-282.e3
http://www.ncbi.nlm.nih.gov/pubmed/21696700
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