Well, yes, dark circles may be a sign of diabetes. First, you should know that eye disease caused by diabetes is often indicated initially by seeing dark circles under eyes. Also, you may see the floaters in the eyes. Also, if you have got diabetes, you will have retinopathy, cataracts, and glaucoma. And generally speaking, retinopathy is the most common disease which is related to diabetes. What is more, it can lead to weaker blood vessels and have a high potential for problems later. In this way, it can lead to blurred vision. so dark circles can be normal for this kind of diseases. to treat it, you can eat as many water and vitamin rich vegetables as possible. also, some black oil, even fish oil can be effective to your eyes. Anyway, you can just have a try.