Macular edema reflects generalized vascular hyperpermeability in type 2 diabetic patients with retinopathy

Diabetic maculopathy (DMa) is the most prevalent sight-threatening type of retinopathy in type 2 diabetes and a leading cause of visual loss in the western world. The disease is characterized by hyperpermeability of retinal blood vessels and subsequent formation of hard exudates and macular edema, the degree of which can be estimated by measurement of retinal thickness. We examined associations between retinal thickness as evaluated by optical coherence tomography scanning (OCT), glomerular leakage as evaluated by urinary albumin excretion rate (UAE), and general vascular leakage as evaluated by the transcapillary escape rate of albumin (TER(alb)) in type 2 diabetic patients with and without DMa.

In 20 type 2 diabetic patients with DMa and 20 type 2 diabetic patients without retinopathy matched for age, sex, and duration of diabetes, we performed OCT, fundus photography, fluorescein angiography, and 24-h ambulatory blood pressure measurement. UAE was determined by radioimmunoassay. TER(alb) was determined as the initial disappearance of intravenously injected (125)I-labeled human serum albumin.

Patients with diabetic maculopathy had higher HbA(1c) (8.5 +/- 1.5 vs. 7.4 +/- 1.2%, P < 0.05) and higher total cholesterol (5.8 +/- 0.7 vs. 5.2 +/- 0.9 mmol/l, P < 0.05) than patients without retinopathy. UAE was higher in the DMa group than in the group with no retinopathy (9.3 x// 3.1 vs. 3.9 x// 1.9 micro g/min, P < 0.01). There was no difference in TER(alb) between the two groups (6.0 +/- 1.6 vs. 6.6 +/- 1.5%, NS). In the group with DMa, OCT, TER(alb), and UAE correlated significantly (OCT versus TER(alb): r = 0.55, P < 0.05; OCT versus UAE: r = 0.58, P < 0.01; UAE versus TER(alb): r = 0.81, P < 0.01). Conversely, there were no correlations between these three parameters in the group without retinopathy.

Macular edema seems to reflect a generalized vascular leakage in type 2 diabetic patients.