Ethnic differences in the clinical and laboratory associations with retinopathy in adult onset diabetes: studies in patients of African, European and Indian origins.

OBJECTIVE: To evaluate the prevalence of diabetic retinopathy (DR) and its associations in adult onset diabetic patients of African, European and Indian origins.
DESIGN: The prevalence of retinopathy was determined by 60 degrees retinal photography in 507 consecutive out-patients. Clinical and laboratory associations were evaluated.
SETTING: Diabetes clinic in a large community hospital. MAIN OUTCOME MEASURES: The associations between clinical and laboratory measurements with retinopathy.
RESULTS: African patients (A) had shorter duration of diabetes (P < 0.001), higher HbA1 levels (P < 0.01) compared to those of Europeans (E) and Indian (I) extraction. A also had lower C-peptide levels (median 0.57 nmol L-1; vs. E. 0.81 nmol L-1 and I, 0.93 nmol L-1) (P < 0.001). The prevalences of retinopathy at diagnosis (21-25%) and overall were similar (A 37%, E 41%, I 37%). Severe DR was more frequent in the Africans (52%, P < 0.0001) and Indians (41%, P = 0.03) compared to the Europeans (26%). In Africans DR was significantly associated only with duration of diabetes (P < 0.0001) and macro-albuminuria (P = 0.01); in I it was also associated with systolic BP (P = 0.03); in E also with lower C-peptide levels (P = 0.0002), worse glycaemic control and greater use of insulin (P < 0.0001). In patients with DR insulin was used less frequently in A (35%) than in E patients (62%) (P = 0.001).
CONCLUSIONS: In South Africa, the African population with adult onset diabetes has the highest prevalence of severe retinopathy, probably the result of very poor glycaemic control attributable to more severe insulinopenia and infrequent insulin treatment. Visual loss from diabetic retinopathy is likely to be considerable in Africans.