• We are sorry, but NCBI web applications do not support your browser and may not function properly. More information
Logo of nihpaAbout Author manuscriptsSubmit a manuscriptNIH Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
Arch Ophthalmol. Author manuscript; available in PMC Jun 1, 2011.
Published in final edited form as:
PMCID: PMC2896217
NIHMSID: NIHMS169047

The Prevalence of Age-Related Macular Degeneration and Associated Risk Factors: The Beaver Dam Offspring Study

Abstract

Objective

To determine the prevalence of age-related macular degeneration (AMD) and examine relationships of retinal drusen, retinal pigmentary abnormalities and early AMD to age, sex and other risk factors in 2810 people 21-84 years of age, participating in the Beaver Dam Offspring Study (BOSS).

Methods

The presence and severity of various characteristics of drusen and other lesions typical of AMD were determined by grading digital color fundus images using the Wisconsin Age-Related Maculopathy Grading System.

Results

Early AMD was present in 3.4% of the cohort and varied from 2.4% in those 21-34 years of age to 9.8% in those 65 years of age or older. In a multivariable model (expressed as Odds Ratio [OR]; 95% Confidence Interval [CI]), age (1.22 per 5 years of age; 1.09, 1.36), being male (1.65; 1.01, 2.69), more pack years smoked (1 to 10 vs 0, 1.31; 0.75, 2.29; 11+ vs 0, 1.67; 1.03, 2.73), higher serum HDL cholesterol (per 5 mg/dL 0.91; 0.83, 0.998), and hearing impairment (2.28; 1.41, 3.71) were associated with early AMD. There were no associations of blood pressure level, body mass index, physical activity, history of heavy drinking, white blood cell count, hematocrit, platelet count, serum total cholesterol, or carotid intimal-medial thickness with early AMD.

Conclusion

These data indicate that early AMD is infrequent before age 55 years but increases with age thereafter. Early AMD is related to modifiable risk factors, e.g., smoking and serum HDL cholesterol.

Keywords: age-related macular degeneration, prevalence, risk factors

While there is a growing number of population-based studies that have described the prevalence and severity of age-related macular degeneration (AMD), most have been limited to middle and older aged cohorts.1-6 Accurate estimates of prevalence of AMD in young adults less than 40 years of age are lacking. Such information is important for understanding the relationships of risk factors to AMD across the age spectrum and for identifying factors that might affect this disease earlier in life. The purposes of this report are to describe the prevalence of AMD and its defining lesions and their relation to age, sex and other factors in the large Beaver Dam Offspring Study (BOSS) cohort.

Methods

The Population

Methods used to identify the population and descriptions of it appear in previous reports.7,8 Briefly, participants in the Epidemiology of Hearing Loss Study (EHLS), a population-based study of hearing loss in Beaver Dam residents 48 to 92 years of age who participated in the baseline Beaver Dam Eye Study (BDES) from 1988-90 and who were alive on March 1, 2003, who had previously reported at least one living child were asked for permission to contact their adult children (n=1902 families).1-9 Of the eligible families, 87.9% (n=1671) gave permission to contact their children, 8.9% (n=170) refused, and 3.2% were lost to follow-up (n=61). Of the 4965 offspring identified, 3285 (66.2%) participated in the study, 731 (14.7%) refused, 23 (0.5%) died, and 926 (18.7%) failed to complete an examination or questionnaire in spite of multiple attempts to schedule them. Compared to those who refused, study participants were slightly older (48 vs 46 years, respectively, P<0.001), more likely to be women (54.6% vs 44.4%, P<0.001) and less likely to live out of state (17.7% vs 32.1%, P<0.001). After adjusting for age and gender, there was no statistically significant difference between participants and non-participants in parental history of AMD (Odds Ratio [OR] = 1.12; 95% Confidence Interval [CI] = 0.99, 1.27).

Procedures

During the examination informed consent was obtained. Pertinent parts of the examination visit included an extensive questionnaire, including information on smoking, physical activity and alcohol drinking. Participants were asked to bring all of their medications with them to the examination. A standardized hearing evaluation including pure-tone air- (500-8000 Hz) and bone- (500, 2000 and 4000 Hz) conduction audiometry was administered.9,10 Blood pressure was measured using a Dinamap (Critikon, Inc, Tampa, FL) after a five minute rest period; the average of the second and third readings were used in analyses. Height, weight, and waist circumference were measured. A B-mode carotid artery ultrasound scan (Biosound AU4, Biosound Esaote, Indianapolis, IN) was obtained and graded using modified Atherosclerosis Risk in Communities (ARIC) Study protocols.11-13 Blood was drawn for a complete blood count, glycosylated hemoglobin A1C, and serum total cholesterol and high density lipoprotein (HDL) cholesterol.

Digital Fundus Photography

Fundus photography using a 45° 8.2 megapixel digital non-mydriatic camera (Canon, Paramus, NJ) was performed through a pharmacologically dilated pupil using a standardized protocol.14 Two photographic fields were taken of each eye; the first centered on the optic disc (Early Treatment Diabetic Retinopathy Study [ETDRS] Field 1) and the second centered on the fovea (ETDRS Field 2).15

Fundus Image Grading

Capture and grading of digital images and quality control have been described in detail elsewhere.14,15 Each image was graded twice (a preliminary and a detail grade) using a modification of the Wisconsin Age-Related Maculopathy Grading System.15,16 For the purposes of this report, participants with gradable retinal images in at least one eye were included in these analyses. 2810 (99.4%) participants had gradable retinal images (right eye [27], left eye [20], and both eyes [2763]), 16 had ungradable images, 20 were examined but refused imaging, and 439 completed only the questionnaire portions of the study. Among the 2810 participants included in these analyses, 3.6% (102/2810) were also participants in the baseline BDES. They were eligible for the BOSS because their parents were also BDES participants.

Comparisons of parental characteristics for families contributing data to this paper and those not included (non-participating or no available gradable images from any offspring) demonstrated no significant differences in parental history of AMD, history of cardiovascular disease (CVD), diabetes, and smoking or heavy drinking status (Table 1). There was a statistically significant difference in the distribution of the highest education level among parents, consistent with the slightly older age of participants.

Table 1
Comparisons of Parental Characteristics of Families Included in Analyses* and Excluded Families in the Beaver Dam Offspring Study

Definitions of Variables

Among the AMD features evaluated were drusen size, type, and area, increased retinal pigment, retinal pigment epithelial (RPE) depigmentation, pure geographic atrophy, and signs of exudative macular degeneration (i.e., subretinal hemorrhage, subretinal fibrous scar, RPE detachment, and/or serous detachment of the sensory retina or laser or photodynamic treatment for neovascular AMD). Hard drusen were small (usually <63 μm in diameter although some may be larger) round pale yellowish-white spots. Soft distinct drusen were defined by size (≥250 μm in diameter) and appearance (sharp margins and a round nodular appearance with a uniform density [color] from center to periphery). Soft indistinct drusen were the same size as soft distinct drusen but had indistinct margins and a softer, less solid appearance. Increased retinal pigment appears as a deposition of granules or clumps of grey or black pigment in or beneath the retina. RPE depigmentation is characterized by faint grayish-yellow or pinkish-yellow areas of varying density and configuration without sharply defined borders. Early AMD was defined by the presence of either soft indistinct drusen or the presence of RPE depigmentation or increased retinal pigment together with any type of drusen in absence of signs of late AMD. Late AMD was defined by the presence of any of the following: geographic atrophy or pigment epithelial detachment, subretinal hemorrhage or visible subretinal new vessels, subretinal fibrous scar or laser treatment scar or history of photodynamic or anti-vascular endothelial growth factor treatment for AMD.

When two eyes of a participant were discrepant for the severity of a lesion, the grade assigned for the participant was that of the more severely involved eye. When drusen or signs of AMD could not be graded in an eye, the participant was assigned a score equivalent to that in the other eye.

Eyes were considered gradable if Field 2 was present and if the grader was able to assess whether drusen were present within the grid in ≥25% of the field. The degree of exact agreement achieved between the graders ranged from 66% to 73% for each of the drusen characteristics and 88% or more for the other AMD characteristics. The Kappa scores were generally in the moderate to substantial agreement categories.16

Current age was defined as the age at the time of the examination. Smoking status was defined as past smoking, current smoking, or never smoking, and pack years smoked was calculated by dividing the number of cigarettes smoked per day by 20 and multiplying by the number of years smoked. For modeling, the median number of pack years among those with >0 pack years was used to categorize participants as no pack years, 1 to <11 pack years, or 11 or more pack years smoked. Heavy alcohol drinking was defined by report of consuming four or more alcoholic beverages daily. Hypertension was defined as systolic blood pressure of ≥140 mmHg or diastolic blood pressure of ≥90 mmHg or currently taking blood pressure medication. Obesity was defined as having a body mass index (BMI) of 30 kg/m2 or higher. Hearing impairment was defined as a pure-tone average of thresholds at 0.5, 1, 2, and 4 kHz greater than 25 dB Hearing Level (HL) in the worse ear. Carotid artery intimal-medial thickness (IMT) was categorized as >1.0 mm or ≤1.0 mm.

Statistical Methods

Confidence intervals for prevalence estimates were calculated using the normal approximation or exact binomial methods as appropriate. Logistic regression was used to estimate age and sex associations with drusen and early AMD outcomes. The following variables were considered in multivariate logistic regression models for early AMD: education status, smoking status, pack years smoked, history of heavy alcohol drinking, systolic blood pressure, diastolic blood pressure, hypertension status, BMI, obesity, diabetes status, history of weekly exercise, hearing impairment, white blood cell count, hematocrit, platelet count, serum total cholesterol, serum HDL cholesterol, and carotid IMT and plaque. First, age- and sex-adjusted models were constructed for each variable. Next, a multivariate model was developed by initially including variables that had P<0.20 in the age- and sex-adjusted models, then sequentially removing variables that were neither statistically significant nor impacted the other covariate estimates by more than 20%. When multiple variables described very similar concepts (e.g., smoking and pack years smoked, systolic/diastolic blood pressure and hypertension) only one variable was selected for inclusion in the multivariate model to reduce problems of collinearity. Once the subset of variables retained in the multivariate model was identified, each of the variables originally excluded from the multivariate model were added one at a time to the model to confirm that none were significant or confounders. Interactions of each variable with age and sex were tested. Because sampling in our study was explicitly in family units and because AMD aggregates in families, we reran the models using generalized estimating equations to account for family relationships and test the robustness of the results to the independence assumption. SAS version 9.1 (SAS Institute Inc., Cary, NC) and Stata 10.1 (College Station, TX) statistical software were used for analyses.

Results

Drusen were present in the macula in 63.3% of the cohort (Table 2). There was an increase in the frequency of drusen with age (OR per 5 years of age 1.16; 95%CI 1.11, 1.21) (Table 2). While controlling for age, the frequency of drusen was similar in males compared to females (OR males vs. females 0.95; 95%CI 0.82, 1.11).

Table 2
Prevalence of Drusen Outcomes by Age and Gender in the Beaver Dam Offspring Study

There was an increase in the frequency of large drusen ≥125 μm in the macula with age (OR per 5 years of age 1.38; 95%CI 1.25, 1.53) (Table 2). Drusen ≥125 μm were found as the largest drusen present in 0.6% of people aged 21-34 years and in 9.2% of those aged 65 years or older. While controlling for age, males had a significantly higher frequency of larger drusen than females (OR 1.90; 95%CI 1.24, 2.92).

Eight percent of the population had at least one soft drusen within the macula (Table 2). There was one person (0.04%) with reticular drusen present. Soft distinct drusen were more frequent than soft indistinct drusen (age-adjusted OR 19.45; 95%CI 2.48, 152.60). The prevalence of soft distinct and indistinct drusen significantly increased with age (OR per 5 years of age 1.42; 95%CI 1.32, 1.54 and OR per 5 years of age 1.53; 95%CI 1.30, 1.79, respectively). While controlling for age, males had a significantly higher frequency of soft distinct and indistinct drusen than females (OR 1.42; 95%CI 1.04, 1.92 and OR 2.70; 95%CI 1.32, 5.54, respectively). There were no interactions of sex and age for soft distinct or indistinct drusen.

The area of the macula covered by drusen in the more severely involved eye increased with age (for drusen area ≥250μm2, OR per 5 years of age 1.42; 95%CI 1.29, 1.56) (Table 3). Adjusting for age, males were more likely to have larger areas of the macula covered by drusen than females (OR 1.67; 95%CI 1.13, 2.47). When only hard small drusen were present in the right eye as the most severe type of drusen, older persons were more likely to have a larger area of the macula covered by drusen than those who were younger (data not shown). Of right eyes with an area 250μm2 or greater covered by drusen, 29% had soft indistinct/reticular, 55% had soft distinct and 16% had hard distinct drusen as the most severe type of drusen present. For left eyes, respective percentages were 28%, 63%, and 9%.

Table 3
Drusen Area Distribution for Worse Eye by Age and Gender in the Beaver Dam Offspring Study

RPE depigmentation was present in 1.8%, increased retinal pigment in 2.7%, and pigmentary abnormalities in 2.9% of the population (Table 4). The frequency of these lesions increased with age (for increased retinal pigment OR per 5 years of age 1.27; 95%CI 1.13, 1.42, and for RPE depigmentation OR per 5 years of age 1.25; 95%CI 1.09, 1.43) (Table 4). While controlling for age, males had a significantly higher frequency of increased retinal pigment and RPE depigmentation than females (OR 2.79; 95%CI 1.70, 4.58 and OR 2.87; 95%CI 1.56, 5.27, respectively). There were no interactions of sex and age for increased retinal pigment or RPE depigmentation.

Table 4
Prevalence of Retinal Pigmentary Abnormalities by Age and Gender in the Beaver Dam Offspring Study

The prevalence of AMD was 3.4% and increased with age in persons 55 years and older (OR per 5 years of age 1.30; 95%CI 1.18, 1.44) (Table 5). While controlling for age, males had a significantly higher frequency of AMD than females (OR 2.39; 95%CI 1.55, 3.69). There was no interaction of sex and age for AMD. No one in the cohort had signs of either pure geographic atrophy or exudative macular degeneration.

Table 5
Prevalence of Early Age-related Macular Degeneration by Age and Gender in the Beaver Dam Offspring Study

While controlling for age and sex, a history of current smoking, greater number of pack years smoked, higher serum HDL cholesterol, and hearing impairment were associated with early AMD (Table 6). There was a borderline association with history of heavy alcohol drinking. There were no statistically significant associations of education status, blood pressure level, hypertension status, body mass index, obesity, diabetes status, physical activity, white blood cell count, hematocrit, platelet count, serum total cholesterol, or carotid IMT or plaque with AMD.

Table 6
Age and Sex-Adjusted Logistic Regression Estimates for Outcome Early Age-related Macular Degeneration, Worse Eye in the Beaver Dam Offspring Study

Many of the significant age- and sex-adjusted associations remained significant in multivariate analyses. The final model included age, sex, pack years smoked, serum HDL cholesterol, and hearing impairment (Table 7). When the multivariate model was rerun with never smokers excluded, number of pack years smoked was no longer statistically significant (data not shown). Rerunning the models, using general estimating equation to adjust for familial correlations, resulted in similar statistically significant associations (age, sex, pack years smoked, serum HDL cholesterol, and hearing impairment [data not shown]) with early AMD, except the relation of HDL cholesterol was of marginal statistical significance (OR 0.91; 95%CI 0.83,1.00).

Table 7
Multivariate Logistic Regression Estimates for Age-related Macular Degeneration in the Beaver Dam Offspring Study.*

When using a dichotomous age variable that split age at 55 years, a significant age-hearing impairment interaction for early AMD (P=.03) was present. Among participants younger than 55 years, 8.7% (15/172) with hearing impairment had early AMD while 1.8% (33/1865) without hearing impairment had early AMD. Among those ≥55 years of age, 8.9% (20/224) of those with hearing impairment had early AMD while 4.9% (27/547) without hearing impairment had early AMD. Incorporating this interaction into the multivariate model showed that among persons <55 years of age the OR for early AMD in those with hearing impairment compared to those without was 4.33 (95%CI 2.26, 8.29) while in those ≥55 years the OR was 1.57 (95%CI 0.85, 2.92).

Discussion

The BOSS provides prevalence data on various signs of AMD in a well-defined large cohort of people over a wide age range beginning at age 21 years. Standardized detailed procedures were used for obtaining digital color fundus images of the macula and an objective system was used for grading those images for AMD.14-16 This allowed comparisons of the frequency of specific lesions associated with AMD to population-based studies which used similar grading systems.1-6,16 The main findings of the study include the relatively low prevalence of early AMD especially in those less than 55 years of age, the higher prevalence of early AMD in men, and the association of early AMD with a history of current smoking and amount smoked, serum HDL cholesterol level, and hearing impairment.

The prevalence of AMD in the BOSS cohort was 3.4%. No one in the cohort had signs of late AMD. These low prevalence estimates, compared to previous studies, do not appear to be totally explained by the younger age of the cohort. Using definitions similar to those used in the BDES to define AMD in the BOSS, age-specific prevalences were lower in those in the BOSS compared to the BDES (43-54 years 2.7 vs 8.6%, 55-64 years 5.0 vs 15.6%, and 65-84 years 9.8 vs 29.1%), and the overall direct age-sex adjusted (using the BDES as standard) prevalence rate of AMD was 6.3% compared to 19.1% in the BDES, suggesting that the prevalence of AMD may actually be decreasing over time. However, this finding may also reflect a birth period cohort effect and is consistent with the birth-period cohort effect found for early AMD in the BDES.17,18 In that study, for most age groups, there was a lower 5-year incidence of early AMD in later birth cohorts or periods.18 For example, the 5-year incidence rates of early AMD in people examined when they were 65 to 69 years of age was 14% among those born from 1918 through 1922, 10% among those born from 1923 through 1927, 6% among those born from 1928 through 1932, and 4% among those born from 1933 through 1937. It is thought that persons born at different times or seen in different periods may have differing exposures to factors (e.g., smoking, uncontrolled blood pressure, sedentary lifestyle, intake of multivitamins) and different patterns of care for systemic conditions (e.g., inflammatory or infectious disease) that may affect the incidence of AMD.

A second possible reason for the decreased prevalence of early AMD in the BOSS might be due, in part, to differences resulting from the grading of AMD from digital (BOSS) and film images (BDES). However, this is less likely in that it has been shown that detection of AMD resulting from high-resolution digital images, especially when the pupil is pharmacologically dilated, is comparable with those resulting from film-based images, with moderate to almost perfect agreement between the digital and film-based cameras for detecting AMD and its lesions.14

The BOSS data show that early AMD and specific lesions defining early AMD are infrequent in persons under 55 years of age and increase markedly in people aged 65 years or older. There are few data to compare the frequencies of lesions characterizing early AMD in young adults with rates reported in the BOSS.19-21 In a histopathological study of 182 unpaired postmortem human maculae from patients between 8 and 100 years of age, van der Schaft et al. first found hard drusen beginning at age 34 years and soft drusen at age 54 years.19 In a twin study, at least one small hard drusen was found in the macular area in 18 of 220 (8.2%) of subjects 20 to 46 years of age.20 Only 2 subjects (0.9%) in that study had soft drusen present. In the population-based Colorado-Wisconsin Study of Age-related Maculopathy, the prevalence of AMD among participants aged 20-42 years was 6.0% among non-Hispanic whites and 6.7% among Hispanics in the San Luis Valley.21 The lower prevalence in the BOSS may reflect geographic differences or birth cohort effects because these photographic images were obtained in the 1980s.

The presence of larger areas of small hard drusen increases the risk of developing soft drusen and pigmentary abnormalities. Over a 15-year follow-up period in the BDES, compared to eyes with approximately 1-3 small hard drusen, large areas of small hard retinal drusen (≥9087 μm2, approximately 8 or more with an average diameter of 40μm), in the absence of larger soft drusen or pigmentary abnormalities at baseline, were associated with a threefold increase in the risk of developing soft indistinct drusen and pigmentary abnormalities, signs of early AMD.22 In the presence of soft drusen at baseline in the BDES, there was marked increase in the odds (OR 13.0) of developing late AMD. The findings from the BOSS indicate about 16% (74/470) of persons under 40 years of age had at least 8 or more small hard drusen based on estimates from total area of the macula involved with drusen, and were at higher risk of developing signs of early AMD over the next 15 years of follow-up. Further follow-up of the cohort will be informative regarding actual risk of developing signs of early AMD in these young to early middle aged adults.

Although we found no significant age-sex interaction for early AMD, when we stratified by age group, we saw stronger associations between gender and early AMD among those aged <55 years (age-adjusted, men vs. women OR 3.68; 95%CI 1.90, 7.11) than we observed among those aged ≥55 years (age-adjusted, men vs. women OR 1.61; 95%CI 0.88, 2.93). The reason for this is not clear. Our findings are consistent with a possible protective effect in younger women that is lost as they near menopause. It may reflect hormonal differences between men and women. We have previously shown that use of hormone replacement therapy in post menopausal women was associated with a lower prevalence of RPE depigmentation compared to those not using hormone replacement therapy.23 In an ancillary study to the Women's Health Initiative, a clinical trial of hormone therapy in 4262 post menopausal women, those randomized to conjugated equine estrogens combined with progestin had a reduced risk of soft drusen (OR 0.83, 95%CI 0.68, 1.00) and of neovascular AMD (OR 0.29; 95%CI 0.09, 0.92) compared to those randomized to placebo.24

A history of cigarette smoking was associated with early AMD in the BOSS, independent of age, sex and other risk factors. This relation was expected because smoking has consistently been found to be associated with AMD in epidemiological studies.25 Smoking is thought to depress antioxidant levels, decrease luteal pigments in the retina, activate the immune system, reduce choroidal blood flow, reduce drug detoxification by the retinal pigment epithelium, and potentiate nicotine angiogenic activities, all of which have been hypothesized to be involved in the pathogenesis of AMD.26-32 The relation between heavy drinking and early AMD was of borderline statistical significance, and this variable was not retained in the multivariable model. A relation of heavy drinking had been reported in the BDES and was attributed to the fact that heavy alcohol intake may reduce antioxidant nutrients, resulting in increased oxidant stress in the retina.33,34 However, only a few studies have found a relation between alcohol consumption and AMD.35 Heavy drinking is often associated with heavier cigarette smoking, so it is possible that a small amount of the smoking effect seen in this study may be attributable to heavy drinking.

Higher serum HDL cholesterol was associated with lower prevalence of early AMD in the BOSS. The protective effect of serum HDL cholesterol in the BOSS, an approximate 10% reduction in the odds per 5 mg/dL increase in HDL while controlling for other factors, was consistent with data from the Blue Mountains Eye Study but not most epidemiological studies.35,36 In the BDES and the Rotterdam Study, high serum HDL cholesterol was associated with higher 5-year incidence of geographic atrophy.37-39 The MESA, the POLA study, and a case control study by Hyman et al. also found a positive relation of HDL cholesterol with AMD.40-42 The reasons for the inconsistencies among studies are not understood. Most studies of early AMD found either a protective association or no association while most studies reporting an adverse association were studying late stage AMD. Differences in the distribution of AMD endpoints (and definitions), gender, age of the cohorts and serum HDL levels may contribute to the lack of consistency across studies. Given the younger age of the BOSS compared to these studies it is likely that this is an important factor in explaining the discrepancies. It is possible that among younger adults (including pre-menopausal women) serum HDL has a protective effect for the development of early lesions that is not detectable at older ages. The opposite (positive) association observed for late AMD in some older cohorts may reflect the effects of early mortality for people with lower serum HDL levels or differences in effects of factors that contribute to the development of early stages of AMD compared to those that contribute to the transition from early AMD to late AMD. Understanding the longitudinal relationships is further complicated by the impact of the changing patterns of medication usage including anti-hypercholesterolemia agents and hormone replacement therapy which have occurred during many of the older studies. Long-term follow-up studies from younger ages are needed to determine the impact of serum HDL level on the development and progression of early AMD.

While atherosclerosis of the choroidal circulation and lipid deposition in Bruch's membrane have been thought to increase the risk of AMD, the BOSS data did not show a relation of IMT or serum total cholesterol with early AMD.

Few data are available regarding the relation of hearing loss with AMD in large cohorts.43 The finding in the BOSS of an increase in the odds of having early AMD in those with hearing loss compared to those without, after controlling for age and other risk factors, is consistent with the increased risk of late AMD (OR 3.2) in persons with hearing loss in the BDES. The effect was more pronounced in younger persons in the BOSS cohort (age <55 years) suggesting possible differences in the age-related processes affecting the retinal pigment epithelium and Bruch's membrane that lead to development of signs of early AMD in the eye and changes in the cochlea or the auditory nerve that causes hearing loss. It is possible that this association reflects uncontrolled residual confounding from shared risk factors for these two age-related sensory disorders. Alternatively, given the strong gender difference in hearing loss,9 some of the variability attributable to gender may be reflected in this point estimate.

There are many strengths to this study, including the use of standardized protocols to measure risk factors and AMD endpoints. It is the largest study including younger adults and provides important insights about the onset of AMD. Participation was unrelated to the health (AMD, CVD, or diabetes) of the parent population and unrelated to patterns of parental smoking and drinking. Although less educated families were slightly more likely to be included in these analyses, neither this study nor the BDES have demonstrated an association between education and AMD. Therefore, it is unlikely that the prevalence estimates have been affected by participation bias. While this population is predominately non-Hispanic white, these data provide important estimates of the prevalence of AMD in baby boomers and younger generations not previously studied. Studying the offspring from a population-based cohort is a strong design for evaluating the impact of changing environmental and behavioral exposures in a genetically similar group. The consistency of the reported results when adjusting for familial correlations as well as their consistency with other published studies adds to the evidence that early AMD may be preventable at younger ages.

Any conclusions or explanations regarding associations or lack of them, described herein, must be made with caution for a number of reasons, including the cross-sectional design. In this middle-aged cohort the concomitant low frequency of some risk factors (e.g., maximum IMT >1.0 mm) and of the prevalence of early AMD limits our ability to detect or reject meaningful relationships. Some factors important in the development of late, vision-threatening stages might contribute to the progression of the disease but not to the development of early lesions, and therefore would be missed in this study of early stages of AMD. As in other studies of AMD, there may be misclassification of factors and uncontrolled confounding which might impact the effect size estimates. Direct comparisons with the BDES must be also made with caution in that 3.6% of the BOSS cohort with gradable photographs were also participants in the baseline BDES. However, removing these participants from the BOSS did not change any of the reported associations (Klein R et al., unpublished data).

In summary, the BOSS data provide precise estimates of the prevalence of various signs of AMD (soft drusen, pigmentary abnormalities) over a wide spectrum of ages from the 3rd to the 9th decade of life. They demonstrate that early AMD onset may occur in mid-life. Some modifiable factors (smoking, serum HDL cholesterol) associated with AMD in older cohorts were associated with early AMD in this cohort of middle-aged adults. The higher frequency of AMD in people aged 65 years or older in an aging American population makes this an important public health problem. Further information regarding the natural history of AMD and its risk factors, especially early in life, is important for developing preventive approaches to it.

Acknowledgments

This research was supported by the National Institutes of Health grant AG021917 (KJ Cruickshanks) from the National Institute on Aging and, in part, by the Research to Prevent Blindness (R. Klein and BEK Klein, Senior Scientific Investigator Awards), New York, NY. The National Institute on Aging provided funding for entire study including collection and analyses of data; RPB provided further support for data analyses. Dr. Ronald Klein has full access to the data in the study and takes full responsibility for the integrity and the accuracy of the data.

Footnotes

Financial Disclosure: Dr. Ronald Klein has served as a consultant to Pfizer and Genentech. None of the other authors have any financial or proprietary interests pertaining to this manuscript.

Author contributions: Conception and design (RK, KC, BK), acquisition of data (RK, KC, SN), analysis and interpretation of data (RK, KC, SN, EK, FJN, GH, JP), drafting of the manuscript (RK, FJN, EK), critical revision of the manuscript for important intellectual content (KC, SN, GH, JP, BK), statistical expertise (KC, SN, EK, FJN, GH), obtaining funding (KC), administrative/technical/material support (SN, BK).

References

1. Klein R, Klein BE, Linton KL. Prevalence of age-related maculopathy: The Beaver Dam Eye Study. Ophthalmology. 1992;99(6):933–943. [PubMed]
2. Vingerling JR, Dielemans I, Hofman A, et al. The prevalence of age-related maculopathy in the Rotterdam Study. Ophthalmology. 1995;102(2):205–210. [PubMed]
3. Mitchell P, Smith W, Attebo K, Wang JJ. Prevalence of age-related maculopathy in Australia: The Blue Mountains Eye Study. Ophthalmology. 1995;102(10):1450–1460. [PubMed]
4. Klein R, Klein BE, Jensen SC, Mares-Perlman JA, Cruickshanks KJ, Palta M. Age-related maculopathy in a multiracial United States population: the National Health and Nutrition Examination Survey III. Ophthalmology. 1999;106(6):1056–1065. [PubMed]
5. Varma R, Fraser-Bell S, Tan S, Klein R, Azen SP. Prevalence of age-related macular degeneration in Latinos: the Los Angeles Latino eye study. Ophthalmology. 2004;111(7):1288–1297. [PubMed]
6. Munoz B, Klein R, Rodriguez J, Snyder R, West SK. Prevalence of age-related macular degeneration in a population-based sample of Hispanic people in Arizona: Proyecto VER. Arch Ophthalmol. 2005;123(11):1575–1580. [PubMed]
7. Cruickshanks KJ, Schubert CR, Snyder DJ, Bartoshuk LM, Huang GH, Klein BEK, Klein R, Nieto FJ, Pankow JS, Tweed TS, Krantz EM. Measuring taste impairment in epidemiologic studies: The Beaver Dam Offspring Study. Annals of the New York Academy of Sciences. 2009 In Press. [PMC free article] [PubMed]
8. Cruickshanks KJ. Population-based epidemiologic studies of aging: the contributions of a Wisconsin community. Wis Med J. 2009 In Press. [PMC free article] [PubMed]
9. Cruickshanks KJ, Wiley TL, Tweed TS, et al. Prevalence of hearing loss in older adults in Beaver Dam, Wisconsin: The Epidemiology of Hearing Loss Study. Am J Epidemiol. 1998;148(9):879–886. [PubMed]
10. Cruickshanks KJ, Tweed TS, Wiley TL, et al. The 5-year incidence and progression of hearing loss: the epidemiology of hearing loss study. Arch Otolaryngol Head Neck Surg. 2003;129(10):1041–1046. [PubMed]
11. The ARIC Study Group. High-resolution B-mode ultrasound scanning methods in the Atherosclerosis Risk in Communities Study (ARIC) J Neuroimaging. 1991;1(2):68–73. [PubMed]
12. The ARIC Study Group. High-resolution B-mode ultrasound reading methods in the Atherosclerosis Risk in Communities (ARIC) cohort. J Neuroimaging. 1991;1(4):168–172. [PubMed]
13. Carlsson CM, Nondahl DM, Klein BE, et al. Increased atherogenic lipoproteins are associated with cognitive impairment: effects of statins and subclinical atherosclerosis. Alzheimer Dis Assoc Disord. 2009;23(1):11–17. [PMC free article] [PubMed]
14. Klein R, Meuer SM, Moss SE, Klein BE, Neider MW, Reinke J. Detection of age-related macular degeneration using a nonmydriatic digital camera and a standard film fundus camera. Arch Ophthalmol. 2004;122(11):1642–1646. [PubMed]
15. Klein R, Davis MD, Magli YL, Segal P, Klein BE, Hubbard L. The Wisconsin age-related maculopathy grading system. Ophthalmology. 1991;98(7):1128–1134. [PubMed]
16. Klein R, Klein BE, Knudtson MD, et al. Prevalence of age-related macular degeneration in 4 racial/ethnic groups in the multi-ethnic study of atherosclerosis. Ophthalmology. 2006;113(3):373–380. [PubMed]
17. Huang GH, Klein R, Klein BE, Tomany SC. Birth cohort effect on prevalence of age-related maculopathy in the Beaver Dam Eye Study. Am J Epidemiol. 2003;157(8):721–729. [PubMed]
18. Klein R, Knudtson MD, Lee KE, Gangnon RE, Klein BE. Age-period-cohort effect on the incidence of age-related macular degeneration: the Beaver Dam Eye Study. Ophthalmology. 2008;115(9):1460–1467. [PMC free article] [PubMed]
19. van der Schaft TL, Mooy CM, de Bruijn WC, Oron FG, Mulder PG, de Jong PT. Histologic features of the early stages of age-related macular degeneration: A statistical analysis. Ophthalmology. 1992;99(2):278–286. [PubMed]
20. Munch IC, Sander B, Kessel L, et al. Heredity of small hard drusen in twins aged 20-46 years. Invest Ophthalmol Vis Sci. 2007;48(2):833–838. [PubMed]
21. Cruickshanks KJ, Hamman RF, Klein R, Nondahl DM, Shetterly SM. The prevalence of age-related maculopathy by geographic region and ethnicity. The Colorado-Wisconsin Study of Age-Related Maculopathy. Arch Ophthalmol. 1997;115(2):242–250. [PubMed]
22. Klein R, Klein BE, Knudtson MD, Meuer SM, Swift M, Gangnon RE. Fifteen-year cumulative incidence of age-related macular degeneration: the Beaver Dam Eye Study. Ophthalmology. 2007;114(2):253–262. [PubMed]
23. Gao F, Wahba G, Klein R, Klein BEK. Smoothing spline ANOVA for multivariate Bernoulli observations, with application to ophthalmology data. J Am Stat Assoc. 2001;96(453):127–160.
24. Haan MN, Klein R, Klein BE, et al. Hormone therapy and age-related macular degeneration: the Women's Health Initiative Sight Exam Study. Arch Ophthalmol. 2006;124(7):988–992. [PubMed]
25. Thornton J, Edwards R, Mitchell P, Harrison RA, Buchan I, Kelly SP. Smoking and age-related macular degeneration: a review of association. Eye. 2005;19(9):935–944. [PubMed]
26. Pryor WA, Hales BJ, Premovic PI, Church DF. The radicals in cigarette tar: their nature and suggested physiological implications. Science. 1983;220(4595):425–427. [PubMed]
27. Stryker WS, Kaplan LA, Stein EA, Stampfer MJ, Sober A, Willett WC. The relation of diet, cigarette smoking, and alcohol consumption to plasma beta-carotene and alpha-tocopherol levels. Am J Epidemiol. 1988;127(2):283–296. [PubMed]
28. Bettman JW, Fellows V, Chao P. The effect of cigarette smoking on the intraocular circulation. AMA Arch Ophthalmol. 1958;59(4):481–488. [PubMed]
29. Friedman E. Choroidal blood flow. Pressure-flow relationships. Arch Ophthalmol. 1970;83(1):95–99. [PubMed]
30. Hammond BR, Jr, Wooten BR, Snodderly DM. Cigarette smoking and retinal carotenoids: implications for age-related macular degeneration. Vision Res. 1996;36(18):3003–3009. [PubMed]
31. Beatty S, Koh H, Phil M, Henson D, Boulton M. The role of oxidative stress in the pathogenesis of age-related macular degeneration. Surv Ophthalmol. 2000;45(2):115–134. [PubMed]
32. Suner IJ, Espinosa-Heidmann DG, Marin-Castano ME, Hernandez EP, Pereira-Simon S, Cousins SW. Nicotine increases size and severity of experimental choroidal neovascularization. Invest Ophthalmol Vis Sci. 2004;45(1):311–317. [PubMed]
33. Klein R, Klein BE, Tomany SC, Moss SE. Ten-year incidence of age-related maculopathy and smoking and drinking: the Beaver Dam Eye Study. Am J Epidemiol. 2002;156(7):589–598. [PubMed]
34. Knudtson MD, Klein R, Klein BE. Alcohol consumption and the 15-year cumulative incidence of age-related macular degeneration. Am J Ophthalmol. 2007;143(6):1026–1029. [PMC free article] [PubMed]
35. Klein R. Epidemiology of age-related macular degeneration. In: Penfold PL, Provis JM, editors. Macular Degeneration. New York, NY: Springer-Verlag; 2005. pp. 79–101.
36. Tan JS, Mitchell P, Smith W, Wang JJ. Cardiovascular risk factors and the long-term incidence of age-related macular degeneration: the Blue Mountains Eye Study. Ophthalmology. 2007;114(6):1143–1150. [PubMed]
37. Klein R, Klein BE, Franke T. The relationship of cardiovascular disease and its risk factors to age-related maculopathy. The Beaver Dam Eye Study. Ophthalmology. 1993;100(3):406–414. [PubMed]
38. Klein R, Klein BE, Jensen SC. The relation of cardiovascular disease and its risk factors to the 5-year incidence of age-related maculopathy: the Beaver Dam Eye Study. Ophthalmology. 1997;104(11):1804–1812. [PubMed]
39. van Leeuwen R, Klaver CC, Vingerling JR, et al. Cholesterol and age-related macular degeneration: is there a link? Am J Ophthalmol. 2004;137(4):750–752. [PubMed]
40. Hyman L, Schachat AP, He Q, Leske MC. Hypertension, cardiovascular disease, and age-related macular degeneration. Age-Related Macular Degeneration Risk Factors Study Group. Arch Ophthalmol. 2000;118(3):351–358. [PubMed]
41. Delcourt C, Michel F, Colvez A, Lacroux A, Delage M, Vernet MH. Associations of cardiovascular disease and its risk factors with age-related macular degeneration: the POLA study. Ophthalmic Epidemiol. 2001;8(4):237–249. [PubMed]
42. Klein R, Knudtson MD, Klein BE, Wong TY, Cotch MF, Barr RG. Emphysema, airflow limitation and early age-related macular degeneration. Arch Ophthalmol. 2009 In press. [PMC free article] [PubMed]
43. Klein R, Cruickshanks KJ, Klein BE, Nondahl DM, Wiley T. Is age-related maculopathy related to hearing loss? Arch Ophthalmol. 1998;116(3):360–365. [PubMed]
PubReader format: click here to try

Formats:

Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...

Links

  • MedGen
    MedGen
    Related information in MedGen
  • PubMed
    PubMed
    PubMed citations for these articles

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...