Abstract
Aim:
To provide contemporary longitudinal data on the incidence and progression of diabetic retinopathy (DR) in a multi-ethnic population of whites, African Americans, Chinese and Hispanics in the United States.
Methods:
A prospective, multi-region, multi-ethnic population-based cohort study that included 498 participants with diabetes, aged 45 to 84 years at baseline, from the Multi-Ethnic Study of Atherosclerosis with retinal images obtained twice, on average 8 years apart. Presence and severity of DR were graded from these retinal images according to the modified Airlie House classification system. Main outcome measures were 8-year incidence, progression and improvement of DR, and their associated risk factors.
Results:
Over the 8 years, the cumulative rates were 19.2% for incident DR, 17.3% for DR progression, 23.3% for DR improvement, 2.7% for incident vision-threatening DR, 1.8% for incident proliferative DR, and 2.2% for incident macular edema. In multivariate analysis, significant risk factors associated with incident DR were higher glycosylated hemoglobin (RR 1.28; 95% CI: 1.16, 1.41) and higher systolic blood pressure (RR 1.14; 95% CI: 1.04, 1.25). Significant factors associated with DR progression were higher glycosylated hemoglobin (RR 1.20; 95 CI: 1.00, 1.43) and higher low-density lipoprotein cholesterol (RR 1.01; 95% CI: 1.00, 1.03).
Conclusion:
Over an 8-year period, approximately one in five participants with diabetes developed DR, while almost a quarter of those with DR at baseline showed improvement, possibly reflecting the positive impact of clinical and public health efforts in improving diabetes care in the United States over the last two decades.
Synopsis / Precis:
This prospective multi-ethnic population-based study suggests that about one in five persons with diabetes developed diabetic retinopathy, while almost a quarter showed regression in retinopathy over an 8-year period in the United States.
INTRODUCTION
Over 400 million people have diabetes worldwide, with numbers projected to increase to 650 million by 2040.1 In the United States (U.S.) alone, about 30 million people have diabetes.2 Diabetic retinopathy (DR) therefore remains a global threat to vision and the economy.3,4 However, there are few sources of contemporary population-based longitudinal data on the incidence and progression of DR in the U.S.5
A recent systematic review of all DR incidence studies reports most of the contemporary studies (published after year 2000) were conducted in Asia.5 All incidence studies from the U.S. were published before 2000, except for the Los Angeles Latino Eye Study (LALES).6 Notably, the annual incidence of DR appears to be lower in studies published after 2000.5 Long-term follow-up data from the Wisconsin Epidemiologic Study of Diabetic Retinopathy also corroborate this observation.7,8 The trend of declining DR incidence may reflect earlier detection of diabetes, improved metabolic control, and DR screening programs.9 Moreover, there is a lack of contemporary, longitudinal studies in the U.S. and other developed countries with accessible and high-quality healthcare systems, in which to assess possible race/ethnicity differences in DR incidence.
This study, conducted after 2000, estimates the incidence, progression and improvement of DR in a multi-ethnic population-based U.S. sample.
METHODS
The Multi-Ethnic Study of Atherosclerosis (MESA) is a prospective cohort study of adults, aged 45 to 84 years at baseline (between 2000 and 2002), sampled from 6 communities in the U.S., who were free of clinical cardiovascular disease at entry. Details of the MESA study design and methodology have been described previously.10 We included 498 participants with diabetes at baseline for the current analyses (eFigure, online supplementary material). All participants underwent extensive assessment for atherosclerotic disease and its risk factors during the course of the study.10–12 Diabetes was defined as fasting glucose ≥7.0 mmol/l (≥126 mg/dl), or use of insulin or oral hypoglycemic medication. Written informed consent was obtained from all the participants. The protocol was approved by the institutional review boards at all the participating institutions.
Retinal photography and DR grading
A standardized study protocol was followed for fundus photography and retinopathy grading at the second and fifth MESA exams.12–14 Briefly, participants were seated in a darkened room where a 45-degree, 6.3-megapixel digital non-mydriatic camera (Canon, Lake Success, NY) was used to capture 2 photographic fields of each eye, the first centered on the optic disc and the second centered on the fovea. Images were analyzed at the University of Wisconsin-Madison Ocular Epidemiology Reading Center, where DR grading was performed according to standardized protocols and definitions.12–14
Retinopathy was considered to be present if any characteristic lesion as defined by the Early Treatment Diabetic Retinopathy Study severity scale was present: microaneurysms (MA), hemorrhages, cotton wool spots (CWS), intraretinal microvascular abnormalities (IRMA), hard exudates, venous beading, and new vessels. For each eye, retinopathy severity was assigned according to the modified Airlie House Classification system (eTable, online supplementary material).12–14 The diabetic retinopathy (DR) level for a participant at a given exam was derived by concatenating the collapsed retinopathy levels for the two eyes, giving the eye with the higher-level greater weight. This scheme provided a 15-step scale (10/10, 20<20, 20/20, 31<31, 31/31, 41<41, 41/41, 51<51, 51/51, 60<60, 60/60, 65<65, 65/65, 70<70, 70/70). For purposes of classification, if the DR severity could not be graded in an eye, it was considered to have a score equivalent to that in the other eye. The cumulative incidence of any DR was estimated from all persons who had no DR at exam 2 (severity level step 1, i.e., 10/10) and who participated in the follow-up examination and had a severity level at step 2 are higher (e.g., 20<20). For analysis of PDR steps 12 and above (60+) were grouped as one level. Incidence of PDR was estimated from all persons who were free of this complication at exam 2 but had this level of severity at exam 5. For persons with no or only non-proliferative DR at exam 2 (step 9 or less), progression was defined as an increase in the severity of DR by two steps or more at exam 5. Similarly, improvement in DR was defined for persons with levels 20/20 to 51/51 (severity levels at 9 or under) at exam 2 who had a 2-step or more decrease in the severity of DR at exam 5.
Macular edema was defined as hard exudate in the presence of microaneurysm and blot haemorrhage within one-disc diameter from the foveal center, or presence of focal photocoagulation scars in the macular area. Clinically significant macular edema (CSME) was considered present when the macular edema was within 500 μm of the foveal center, or if focal photocoagulation scars were present in the macular area. Vision-threating diabetic retinopathy (VTDR) was defined as the presence of severe NPDR-proliferative retinopathy or CSME. If an eye was ungradable, the scores for the other eye were used to define these outcomes.
Risk Factor Assessment
All participants underwent an extensive assessment for atherosclerotic disease and its risk factors during the course of the study.10 Data for this analysis were based on those collected at the baseline examination. Standardized questionnaires were used to obtain information about medical history, education level, annual household income, cigarette smoking, alcohol consumption, use of hormone replacement therapy, and antihypertensive and antidiabetic medications taken. Smoking was defined as current, former, or never. Duration of diabetes was estimated from the age of first use of diabetic medication. Diabetic medication use was defined to include oral hypoglycemic medications and/or insulin. Diabetes was defined as fasting glucose ≥7.0 mmol/l (≥126 mg/dl) or use of insulin or oral hypoglycemic medication. Resting blood pressure was measured three times with participants in the seated position. The average of the last two measurements was used in analysis. Hypertension was defined as systolic blood pressure ≥140 mmHg, diastolic blood pressure ≥90 mmHg, or current use of antihypertensive medications. Height and weight were measured with participants wearing light clothing and no shoes. Body mass index was calculated as weight in kilograms divided by height in square meters. The waist-hip ratio was defined as the ratio of the waist circumference and the hip circumference, measured in centimeters.
Blood samples were assayed for putative biochemical risk factors, including levels of cholesterols, glycosylated hemoglobin, homocysteine, and C-reactive protein. Analyses were performed at a central site at the Collaborative Studies Clinical Laboratory at Fairview–University Medical Center (Minneapolis, Minnesota, USA). Low-density lipoprotein (LDL) cholesterol was calculated with the Friedewald equation. Carotid artery intima-media thickness was measured using B-mode ultrasound according to a standardized protocol as detailed elsewhere.15
Statistical analysis
Incidence and progression estimates were calculated, with participants having DR at Exam 2 excluded from the estimate of incidence, but only these individuals contributed to analyses of progression and improvement. Comparisons of traditionally associated risk factors, as listed in Table 1, with incident DR outcomes were interrogated by race/ethnic group using chi-square (for categorical variables) and independent sample t-tests (for continuous variables). Univariate Poisson regression models were performed to examine associations, with significant factors associated with DR incidence or progression (p<0.05), along with age, gender and race/ethnicity, being included in a multivariable model. All statistical analyses were performed using STATA statistical software: release 15.0 (StataCorp LP, Texas, USA).
Table 1.
Baseline Characteristics of the MESA Participants with Diabetes
| All | Incident DR | DR Progression | |||||
|---|---|---|---|---|---|---|---|
| Yes | No | Yes | No | ||||
| N=498* | N=70 | N=295 | p | N= 23 | N= 110 | P | |
| Age, years | 63.2 (8.9) | 62.0 (9.4) | 63.8 (8.8) | 0.118 | 58.7 (7.5) | 63.2 (8.8) | 0.026 |
| Gender, female | 247 (49.6) | 38 (54.3) | 144 (48.8) | 0.41 | 9 (39.1) | 56 (50.9) | 0.304 |
| Ethnicity | |||||||
| White | 114 (22.9) | 18 (25.7) | 75 (25.4) | 0.318 | 2 (8.7) | 19 (17.3) | 0.573 |
| Chinese | 57 (11.5) | 11 (15.7) | 35 (11.9) | 2 (8.7) | 9 (8.2) | ||
| African American | 169 (33.9) | 16 (22.9) | 99 (33.6) | 12 (52.2) | 42 (38.2) | ||
| Hispanic | 158 (31.7) | 25 (35.7) | 86 (29.2) | 7 (30.4) | 40 (36.4) | ||
| Education | |||||||
| High school or lower | 214 (43.0) | 35 (50.0) | 122 (41.4) | 0.189 | 10 (43.5) | 47 (42.7) | 0.947 |
| College or higher | 284 (57.0) | 35 (50.0) | 173 (58.6) | 13 (56.5) | 63 (57.3) | ||
| Total household income | |||||||
| <$25,000 | 170 (34.1) | 29 (41.4) | 100 (33.9) | 0.113 | 7 (30.4) | 34 (30.9) | 0.889 |
| $25,000 to $50,000 | 165 (33.1) | 25 (35.7) | 89 (30.2) | 8 (34.8) | 43 (39.1) | ||
| >$50,000 | 163 (32.7) | 16 (22.9) | 106 (35.9) | 8 (34.8) | 33 (30.0) | ||
| Diabetes duration, year | 9.4 (7.9) | 6.5 (3.8) | 7.2 (6.3) | 0.579 | 9.5 (6.0) | 13.7 (9.6) | 0.096 |
| Cigarette smoker, current | 54 (10.9) | 10 (14.3) | 27 (9.2) | 0.208 | 5 (21.7) | 12 (11.0) | 0.163 |
| Body mass index | 31.2 (6.1) | 32.1 (6.6) | 31.0 (6.1) | 0.219 | 31.1 (5.3) | 31.3 (6.0) | 0.887 |
| Hip-to-waist ratio | 1.04 (0.08) | 1.05 (0.07) | 1.05 (0.07) | 0.975 | 1.05 (0.07) | 1.04 (0.09) | 0.697 |
| Physical activity, hours/week | 72.2 (73.4) | 76.8 (77.4) | 69.6 (75.4) | 0.478 | 90.7 (65.7) | 72.3 (67.1) | 0.231 |
| Hypertension | 312 (63.8) | 39 (55.7) | 181 (63.3) | 0.243 | 12 (52.2) | 80 (72.7) | 0.052 |
| Anti-hypertensive medications | |||||||
| Diuretics | 107 (22.4) | 20 (29.0) | 57 (20.4) | 0.125 | 8 (34.8) | 22 (20.6) | 0.142 |
| Angiotensin 2 antagonist | 46 (9.6) | 5 (7.2) | 18 (6.5) | 0.812 | 4 (17.4) | 19 (17.8) | 0.967 |
| ACE inhibitor | 163 (34.1) | 19 (27.5) | 90 (32.3) | 0.449 | 9 (39.1) | 45 (42.1) | 0.796 |
| Systolic blood pressure, mmHg | 128.7 (21.4) | 131.6 (19.7) | 126.3 (19.1) | 0.040 | 123.7 (19.2) | 134.0 (26.9) | 0.082 |
| Diastolic blood pressure, mmHg | 70.9 (10.1) | 71.9 (8.8) | 70.8 (10.2) | 0.403 | 71.6 (9.4) | 70.6 (10.8) | 0.669 |
| Insulin use | 42 (8.8) | 5 (7.2) | 11 (3.9) | 0.241 | 4 (17.4) | 22 (20.6) | 0.73 |
| HbA1c, % | 7.3 (1.7) | 7.9 (2.0) | 6.9 (1.2) | <0.001 | 9.3 (2.7) | 7.6 (1.7) | <0.001 |
| Total cholesterol, mmol/L | 181.0 (35.6) | 183.6 (39.4) | 180.4 (34.9) | 0.493 | 193.5 (38.2) | 178.6 (34.3) | 0.071 |
| HDL cholesterol, mmol/L | 46.9 (12.5) | 46.1 (13.8) | 46.5 (11.5) | 0.816 | 44.9 (10.4) | 48.9 (14.5) | 0.224 |
| LDL cholesterol, mmol/L | 103.5 (31.0) | 101.7 (30.0) | 103.3 (31.9) | 0.709 | 122.9 (34.5) | 101.7 (27.6) | 0.002 |
| Statin use | 177 (37.0) | 21 (30.4) | 105 (37.6) | 0.265 | 8 (34.8) | 43 (40.2) | 0.63 |
| Homocysteine | 9.2 (3.2) | 8.4 (2.4) | 9.5 (3.5) | 0.021 | 9.3 (3.3) | 8.8 (2.6) | 0.393 |
| C-reactive protein | 4.6 (5.8) | 4.6 (4.6) | 4.6 (6.1) | 0.977 | 5.2 (8.8) | 4.5 (4.7) | 0.591 |
| Proteinuria | 116 (23.5) | 17 (24.6) | 57 (19.5) | 0.344 | 6 (26.1) | 36 (32.7) | 0.533 |
| Internal carotid IMT, mm | 1.14 (0.63) | 1.05 (0.51) | 1.13 (0.64) | 0.376 | 1.15 (0.56) | 1.25 (0.66) | 0.511 |
| Z-score maximum IMT | 0.18 (0.96) | 0.08 (0.96) | 0.15 (0.95) | 0.591 | 0.15 (0.88) | 0.32 (0.99) | 0.452 |
DR = diabetic retinopathy; MESA = Multi-Ethnic Study of Atherosclerosis; HbA1c = glycosylated hemoglobin; HDL = high-density lipid; LDL = low-density lipid; IMT = intima-media thickness; ACE = angiotensin converting enzyme
Data for a given column are expressed as numbers (percentages) for categorical variables or means (standard deviations) for continuous variables; p values calculated based on simple chi-square or Wilcox test (categorical), or independent sample t-tests, comparing characteristics between participants with and without incident DR or DR progression.
Of these, 133 participants had DR at baseline eye examination (i.e., were not at risk of incident DR at follow-up eye examination)
RESULTS
Table 1 summarizes baseline characteristics for the 498 participants with diabetes. Compared to participants without incident DR, those with incident DR had higher levels of systolic blood pressure and glycosylated hemoglobin, and lower levels of homocysteine. Compared to those without DR progression, participants whose DR progressed were younger, and had higher levels of glycosylated haemoglobin and LDL cholesterol.
Incidence rates were 19.2% for DR, 17.3% for DR progression, 23.3% for DR improvement, 2.7% for vision-threatening DR, 1.8% for proliferative DR, and 2.2% for clinically significant macular edema (Table 2). Although Hispanics were most likely to develop vision-threatening DR (5.3%), followed by African Americans (1.8%), Chinese (1.8%) and whites (0.9%) (Figure 1), these differences were not statistically significant (p = 0.116). Risk factors significantly associated with incident DR were higher glycosylated hemoglobin and higher systolic blood pressure (Table 3). Risk factors significantly associated with DR progression were higher glycosylated haemoglobin and low-density-lipoprotein cholesterol.
Table 2.
Eight-year Incidence and Progression of Diabetic Retinopathy in the MESA
| Incident DR | DR Progression | DR Improvement | Incident VTDR | Incident PDR | Incident CSME | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| No. at Risk | Incidence (%) | No. at Risk | Incidence (%) | No. at Risk | Incidence (%) | No. at Risk | Incidence (%) | No. at Risk (%) | Incidence (%) | No. at Risk | Incidence (%) | |
| Total | 365 | 70 (19.2) | 133 | 23 (17.3) | 133 | 31 (23.3) | 482 | 13 (2.7) | 491 | 9 (1.8) | 465 | 10 (2.2) |
| White | 93 | 18 (19.4) | 21 | 2 (9.5) | 21 | 3 (14.3) | 112 | 1 (0.9) | 113 | 1 (0.9) | 106 | 1 (0.9) |
| African | ||||||||||||
| American | 115 | 16 (13.9) | 54 | 12 (22.2) | 54 | 15 (27.8) | 164 | 3 (1.8) | 167 | 3 (1.8) | 154 | 2 (1.3) |
| Hispanic | 111 | 25 (22.5) | 47 | 7 (14.9) | 47 | 10 (21.3) | 151 | 8 (5.3) | 156 | 4 (2.6) | 149 | 6 (4.0) |
| Chinese | 46 | 11 (23.9) | 11 | 2 (18.2) | 11 | 3 (27.3) | 55 | 1 (1.8) | 55 | 1 (1.8) | 56 | 1 (1.8) |
| p-value | 0.318 | 0.573 | 0.623 | 0.116 | 0.794 | 0.285 | ||||||
DR = diabetic retinopathy; VTDR = vision-threatening diabetic retinopathy; PDR = proliferative diabetic retinopathy; CSME = clinically significant macular edema; DR progression / improvement was defined as a two-step or more change (+/−) in the DR severity scale as described in e-Table 1.
Figure 1.
Incidence and Progression of Diabetic Retinopathy by Ethnic Groups in the MESA. DR = diabetic retinopathy; VTDR = vision-threatening diabetic retinopathy; DR progression / improvement was defined as a two-step or more change (+/−) in the DR severity scale as described in e-Table (online supplementary material).
Table 3.
Risk Factors for DR Incidence and Progression in the MESA
| DR Incidence | DR Progression | |||
|---|---|---|---|---|
| Risk Factors | RR (95% CI)* | RR (95% CI)† | RR (95% CI)* | RR (95% CI)† |
| Age, per year | 0.98 (0.96 – 1.01) | 0.99 (0.97 – 1.02) | 0.95 (0.91 – 0.99) | 0.99 (0.94 – 1.04) |
| Gender, female | 1.19 (0.78 – 1.82) | 1.05 (0.67 – 1.63) | 0.67 (0.31 – 1.45) | 0.44 (0.17 – 1.09) |
| Ethnicity | ||||
| White | Reference | Reference | Reference | Reference |
| Chinese | 1.24 (0.64 – 2.40) | 1.21 (0.63 – 2.34) | 1.91 (0.31 – 11.85) | 1.13 (0.23 – 5.51) |
| African American | 0.72 (0.39 – 1.33) | 0.56 (0.30 – 1.07) | 2.33 (0.57 – 9.60) | 1.86 (0.49 – 7.11) |
| Hispanic | 1.16 (0.68 – 2.00) | 0.91 (0.52 – 1.57) | 1.56 (0.35 – 6.94) | 1.11 (0.25 – 5.03) |
| Diabetes duration, per year | 0.98 (0.94 – 1.03) | 0.94 (0.88 – 1.00) | ||
| Education | ||||
| College or higher | Reference | Reference | ||
| High school or lower | 1.32 (0.87 – 2.02) | 1.03 (0.48 – 2.18) | ||
| Total household income | ||||
| >$50,000 | Reference | Reference | ||
| $25,000 to $50,000 | 1.67 (0.94 – 2.97) | 0.80 (0.33 – 1.96) | ||
| <$25,000 | 1.71 (0.98 – 3.00) | 0.88 (0.35 – 2.20) | ||
| Cigarette smoker, current | 1.47 (0.82 – 2.62) | 1.88 (0.80 – 4.41) | ||
| Body mass index, per unit | 1.02 (0.99 – 1.05) | 1.00 (0.94 – 1.06) | ||
| Hip-to-waist ratio, per 0.1 unit | 1.00 (0.74 – 1.33) | 1.09 (0.75 – 1.58) | ||
| Physical activity, per hour/week | 1.00 (1.00 – 1.00) | 1.00 (1.00 – 1.01) | ||
| Hypertension | 0.78 (0.51 – 1.18) | 0.49 (0.23 – 1.01) | ||
| Hypertension medications | ||||
| Diuretics | 1.44 (0.91 – 2.26) | 1.78 (0.83 – 3.79) | ||
| Angiotensin 2 antagonists | 1.10 (0.49 – 2.47) | 0.98 (0.37 – 2.62) | ||
| ACE inhibitor | 0.83 (0.52 – 1.34) | 0.90 (0.42 – 1.94) | ||
| Systolic blood pressure, per 10 mmHg | 1.11 (1.01 – 1.22) | 1.14 (1.04 – 1.25) | 0.85 (0.72 – 1.01) | |
| Diastolic blood pressure, per 10 mmHg | 1.09 (0.90 – 1.32) | 1.08 (0.79 – 1.46) | ||
| Insulin use | 1.62 (0.76 – 3.47) | 0.84 (0.31 – 2.27) | ||
| HbA1c, per % | 1.32 (1.19 – 1.45) | 1.28 (1.16 – 1.41) | 1.29 (1.13 – 1.47) | 1.20 (1.00 – 1.43) |
| Total cholesterol, per mmol/L | 1.00 (1.00 – 1.01) | 1.01 (1.00 – 1.02) | ||
| HDL cholesterol, per mmol/L | 1.00 (0.98 – 1.02) | 0.98 (0.95 – 1.01) | ||
| LDL cholesterol, per mmol/L | 1.00 (0.99 – 1.01) | 1.02 (1.01 – 1.03) | 1.01 (1.00 – 1.03) | |
| Statin use | 0.77 (0.48 – 1.23) | 0.83 (0.38 – 1.81) | ||
| Homocysteine | 0.91 (0.84 – 0.98) | 0.93 (0.85 – 1.00) | 1.05 (0.94 – 1.18) | |
| C-reactive protein | 1.00 (0.97 – 1.03) | 1.02 (0.95 – 1.09) | ||
| Proteinuria | 1.27 (0.78 – 2.06) | 0.76 (0.32 – 1.81) | ||
| Internal carotid IMT, mm | 0.85 (0.60 – 1.19) | 0.79 (0.41 – 1.52) | ||
| Z-score maximum IMT | 0.94 (0.74 – 1.19) | 0.85 (0.57 – 1.26) | ||
DR = diabetic retinopathy; MESA = Multi-Ethnic Study of Atherosclerosis; HbA1c = glycosylated hemoglobin; HDL = high-density lipid; LDL = low-density lipid; IMT = intima-media thickness; ACE = angiotensin converting enzyme
Univariate unadjusted relative Risk (RR) and 95% confidence interval (CI);
Multivariate adjusted RR (95% CI)
Systolic blood pressure and hypertension were evaluated in separate multivariable models due to high collinearity.
In supplementary analyses (data not shown), we observed no significant difference between age or gender groups for the incidence of DR outcomes. None of the factors examined in Table 3 was significantly associated with DR improvement.
DISCUSSION
In this multi-ethnic population-based cohort study, we provide contemporary U.S. estimates on the incidence and progression of DR. We found that over an 8-year period, approximately one of every five participants with diabetes developed incident DR, whereas 23% of participants with DR showed improvement in disease severity. The incidence for vision-threatening DR was 2.7%, despite the potential for prompt treatment to prevent this complication. Higher blood pressure and poorer glycemic control, both treatable, were associated with increased risk of incident DR. Respectively, each percent higher glycosylated hemoglobin and each 10 mmHg higher systolic blood pressure was associated with 28% and 14% increased risk of developing DR over 8 years.
Directly comparable studies with contemporary data on the incidence and progression of DR in countries with high income economies are lacking. Of the 14 population-based studies with incidence data on DR, only 8 were conducted after year 2000.5 Sample sizes of these studies ranged from 117 to 775 participants. None of these studies was conducted in the U.S., except for the LALES which focused on Hispanics (Mexican-Americans) only. In the LALES, the 4-year incidence of DR was 34% and progression of DR was 39%.6 These are much higher estimates than observed in MESA. Although our data showed that Hispanics were most likely to develop vision-threatening DR, their 8-year DR incidence was 22.5% and DR progression was 14.9%. These differences may reflect differences in study populations and/or methodologies. The MESA population was free of clinically overt cardiovascular disease at baseline and may therefore be healthier than that of the LALES, as reflected by younger age (mean age of 55 years vs. 63 years in the LALES), fewer participants with long duration of diabetes (21% vs. 47% >10 years) and better glycemic control (mean HbA1c of 6.4% vs. 8.5%). Moreover, MESA used 2-field non-stereoscopic retinal imaging to assess DR, whereas the LALES used 7-field stereoscopic retinal imaging. This could also partly explain the differences in the results. Nevertheless, it has been shown that 2-field retinal imaging performs generally well against 7-field imaging in the assessment of DR.16
Strengths of our study include its multi-ethnic, population-based sample, prospective design, standardized photographic assessment of DR by trained graders in a central grading center with a low number of ungradable photographs, and standardized assessment of risk factors. However, our sample size was relatively small, and the low incidence rates limited the precision of the risk estimates and power to assess some of the less common risk factors. It also limited our ability to perform more indepth analyses for the less common but more severe forms of DR.
In summary, our study provides contemporary population-based data on the incidence and progression of DR in the U.S.. Our data suggest that compared to estimates reported in older studies, the incidence and progression of DR have decreased substantially, consistent with earlier detection of diabetes and improved clinical management which has occurred over the last two decades. The suggestion of disparities in outcomes and the association of DR progression with treatable risk factors indicate further opportunity for improvement.
Supplementary Material
Acknowledgments:
The authors would like to thank the investigators, the staff, and the participants of the MESA study for their valuable contributions. A full list of participating MESA investigators and institutions can be found at http://www.mesa-nhlbi.org. The views expressed in this manuscript are those of the authors and do not necessarily represent the views of the National Heart, Lung, and Blood Institute; the National Eye Institute; the National Institutes of Health; or the U.S. Department of Health and Human Services.
Funding:
This research was supported by contracts N01-HC-95159, N01-HC-95160, N01-HC-95161, N01-HC-95162, N01-HC-95163, N01-HC-95164, N01-HC-95165, N01-HC-95166, N01-HC-95167, N01-HC-95168, and N01-HC-95169 from the National Heart, Lung, and Blood Institute at the National Institutes of Health. Support for the retinal component at the fifth MESA follow-up examination was provided by Intramural Research Award ZIAEY000403 by the National Eye Institute, National Institutes of Health.
Footnotes
Competing interests: none.
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