Diabetic Macular Edema

David J. Browning

7.1 Epidemiology and Risk Factors

Diabetic retinopathy is the leading cause of blindness in persons under age 60 in the United States, and diabetic macular edema (DME) is the most common cause of visual loss in those with diabetic retinopa- thy.1–3 Natural history studies of eyes with DME show that 24% will lose at least three lines of vision over a period of 3 years.4 DME is increasing in prevalence throughout the world. In cross-sectional studies, the prevalence of DME in patients with diabetes has been reported to be 1.0–5.7%.5,6 The prevalence of DME in patients with diabetic retinopathy has been reported to be 2.7–11.0%.5,7–9 Suggestive data have been reported that the prevalence of DME relative to proliferative diabetic retinopathy (PDR) may vary by race with rates of DME relatively low in Native Americans relative to the rate of PDR.10 Besides its adverse effects on affected patients, DME is associated with large economic costs. In a Medicare claims study, diagnosis of DME was associated with a 34 and 33% increase in 1- and 3-year direct medical costs after adjustment for demographic variables and baseline comorbid conditions.11

The prevalence of DME depends on the type of diabetes and the duration of the disease. For diabetes occurring in insulin-taking patients under age 30 (generally type 1 diabetics), DME begins to appear after 5 years and the prevalence thereafter increases to 30–40% after 30 years of disease

D.J. Browning (*)

Charlotte Eye Ear Nose & Throat Associates, Charlotte, NC 28210, USA

e-mail: dbrowning@ceenta.com

(Fig. 7.1). For diabetes with onset after age 30 (generally type 2 diabetes), 3–5% of patients manifest DME at the time of diagnosis, presumably because of having undiagnosed diabetes for several years before diagnosis. Thereafter, prevalence increases with a plateau at approximately 30% after 25–30 years. In general, in this older onset group, noninsu- lin-taking diabetics have lower prevalence rates than insulin-taking diabetics (Fig. 7.1). Because of different prevalences according to diabetes type, and evidence that serum cholesterol is associated with retinopathy severity and severity of hard exudates in older onset diabetics using insulin (mostly type 2) but not in younger onset diabetics using insulin (type 1), there is conjecture that the pathophysiology of retinopathy and DME may differ between these categories of diabetes.12,13 In the absence of further explorations of this possibility, in what follows we will discuss DME in both groups as though they have similar bases, understanding that this perspective may need modification as new information becomes available.

In population-based studies, certain systemic factors were associated with diabetic macular edema. In patients under age 30, associated factors were longer duration of diabetes, proteinuria, male sex, negative history of cardiovascular disease, use of diuretics, and higher hemoglobin A1C.9 In patients 30 years of age and older, associated factors were longer duration of diabetes, higher systolic blood pressure, and higher hemoglobin A1C. Proteinuria was an associated risk factor in the insulintaking older onset group, but not for the noninsu- lin-taking group. In type 1 diabetics, high serum lipids have been associated with an increased risk