Risk factors for the development of severe forms of diabetic retinopathy were examined prospectively in a group of 153 patients with long-standing insulin-dependent diabetes mellitus. During a 4-yr follow-up study, 34 individuals progressed to preproliferative and proliferative retinopathy. The risk of progression to severe forms of diabetic retinopathy was determined by the degree of background diabetic retinopathy and several systemic factors. It increased steeply with hemoglobin A1c, declined proportionally with increasing age, and was dramatically different in patients with diastolic blood pressure below versus above 70 mmHg. Although the mechanisms of action of these systemic factors are unclear, the findings emphasize the multifactorial nature of the pathogenesis of severe forms of eye lesions.

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