There may be an interaction between the effect of gender and the type of diabetes. In type 1 diabetes, being female has been associated with higher prevalence of retinopathy; however, men had a higher prevalence of more severe retinopathy.23,45 Similarly, for younger onset diabetes, the 10-year incidence rate of improvement was higher and rate of progression was lower for females than for males.10 There was no gender difference in 10-year incidence rates of any DR, improvement in DR severity, or progression in DR severity for older onset diabetics taking insulin. Females had a higher 10-year incidence rate of improvement of retinopathy in the older onset, not taking insulin group, but gender did not influence incidence rates for any DR or progression of DR.10 The WESDR 25-year analysis in this same cohort demonstrated that being male was significantly associated with progression of retinopathy with a hazard ratio of 1.30 (95% CI 1.11–1.54, p = 0.0002). Being male was also associated with less improvement in diabetic retinopathy.

3.13 Age at Onset of Diabetes

Diabetic retinopathy is associated with age at onset of diabetes.36,45,46 In WESDR, the presence of any

retinopathy, proliferative retinopathy, and macular edema were most frequently encountered in younger onset individuals diagnosed prior to 30 years of age, while they were least frequently

encountered in older onset individuals diagnosed after 30 years of age who did not require insulin.45,46

Other studies support the conclusion that earlier age of onset of type 2 diabetes is a risk factor for increased prevalence and severity of DR independent of other traditional risk factors.71

3.14Socioeconomic Status and Educational Level

The reported influence of socioeconomic status on prevalence, incidence, and severity of diabetic retinopathy has been inconsistent. Associations

between lower socioeconomic status and worse retinopathy have been reported.72–74 Other studies have not found such associations.75,26 Lower educa-

tion has been associated with higher prevalence of DR and lower prevalence of DR.36,65

3.15 Family History of Diabetes

No association of family history of diabetes with

presence of diabetic retinopathy has been reported across multiple studies.26,32,61

3.16 Changes Over Time

Trends over time in diabetic retinopathy endpoints are shown in Table 3.11. Based on Medicare claims data, in elderly persons with diabetes over the period 1994–2004, there are lower rates of prevalence and incidence of NPDR, PDR, and DME within 1

year after diagnosis and during 6 years of follow-up more recently.76 In type 1 diabetics in WESDR, the same trend has been noted in incidence of PDR (Table 3.11).59Analogous trends have been noted

in other studies from Europe and the United States.57,77 It is possible that these data reflect

improvements in primary care of diabetes mellitus over time. Independent population-based studies have not reported decreased rates of blindness due

to diabetes during a time when the rates of PDR and DME have been declining.78,79 The discordance

may reflect a lag phase between improvement in management and decline in some but not all ocular late complications.78

3.17Epidemiology of Diabetic Macular Edema (DME)

In WESDR, the prevalence rates of DME in younger onset, older onset taking insulin, and

older onset not taking insulin groups were 6, 12, and 4%, respectively.45,46 The 4-, 10-, and 25-year

incidence rates of DME are shown in Table 3.12. Persons taking insulin have higher rates than those not taking insulin. The association between insulin use and higher incidence of DME may reflect the increased severity of diabetes in insulin users rather than a causal relationship between insulin use and DME. The annual incidence rates of DME show a decrease in the most recent period compared to earlier periods. In WESDR, for the periods from 1990–1992 to 1994–1996 and from 1994–1996 to

2005–2007, the annual rates of incidence were 2.3 and 0.9%, respectively.80 Similarly, in Denmark, the 20-year cumulative incidence of DME in type 1 diabetics decreased from 18.6% in a cohort diagnosed from 1965 to 1969 to 7.4% for the cohort diagnosed from 1979 to 1984, presumably reflecting better glycemic control in the latter era.81 The annual incidence of DME in studies in which annual examinations were performed is higher, presumably because some eyes develop and then resolve DME and are not counted in study designs such as WESDR without annual examinations. For example, the annual incidence of DME in type 1 diabetics examined annually with diabetes of duration from 10 to 20 years is 6.7%, approximately three times the rate calculated from WESDR data from a similar era.13

Studies consistently report that DME depends on duration of diabetes.80,8,16,20,82 Prevalence rates

of DME vary in younger onset diabetics from 0% in patients whose duration of diabetes is less than 5 years to 29% in patients whose duration of diabetes is 20 or more years.83 In older onset diabetics, the prevalence varies from 3% in patients whose duration of diabetes is less than 5 years to 28% in patients whose duration of diabetes is 20 or more years. Incidence rates also depend on duration of diabetes. Figures 3.4 and 3.5 show the parabolic relationship of 10-year incidence of DME to duration of diabetes in younger onset and older onset diabetes. In younger onset diabetes, the 10-year incidence of DME on average rises from 7% in a newly diagnosed patient to 27% in a patient who has had diabetes for 12 years and thereafter drops.

Fig. 3.4 The peak 10-year incidence of DME in younger onset diabetes as assessed from the fitted curve would be at approximately 12 years duration. Data from Klein et al.82

10 Year Incidence of DME in Younger Onset Dlabetics by Duration

Duration (Years)

Fig. 3.5 The peak 10-year incidence of DME in older onset diabetes as assessed from the fitted curve would be at approximately 10 years

duration. Data from Klein et al.82

10 Year Incidence of DME in Older Onset Diabetes by Duration

Duration (Years)

In older onset diabetes, the 10-year incidence of DME on average rises from 12% in a newly diagnosed patient to 25% in a patient who has had diabetes for 10 years and thereafter begins to drop.

Prevalence rates of DME reported for various populations and ethnic groups studied according to diabetes type are shown in Table 3.13. According

to the Multiethnic Study of Atherosclerosis (MESA), the prevalence of DME was higher in blacks (11.1%), Hispanics (10.7%), and Chinese (8.9%) than whites (2.7%).84 In the Atherosclerosis Risk in Communities Study, DME was also more prevalent in blacks than whites.14 However, race may not be an independent risk factor. When

adjusted for other baseline variables, ethnicity was not associated with prevalence of vision-threatening retinopathy (primarily DME).84 The 9-year incidence rate of DME for blacks in the Barbados Eye Study was 8.7%, lower than the 10-year incidence rate of 13.9% reported for the older onset, not taking insulin group in the predominantly white WESDR from an earlier era.85

Age at diagnosis influenced incidence of DME in WESDR (Fig. 3.6). The relation of 10-year incidence of DME and age at baseline examination was nonlinear with a peak value at approximately

30 years in younger onset diabetics and at approximately 50 years in older onset diabetics. This relationship did not hold when 25-year incidence of DME was examined with adjustment for other baseline variables.80

With control of other baseline variables gender, occupation, income, marital status, educational level, and health insurance status have not been associated

with the 25-year incidence of DME in younger onset diabetics.80,84 The 10-year incidence of DME in both

younger onset and older onset diabetics was not associated with gender in WESDR.82