These subjects will be randomized equally to 3 groups: acarbose, rosiglitazone and pioglitazone. The investigators will follow up for 6 months to investigate the short-term effects and 5 years to evaluate the long-term outcomes. The primary study end point of short-term study will be the macular thickness changes measured by optical coherence tomography, the changes in the level of urinary albumin-to-creatinine ratio, circulating metabolic parameters and adipocytokines during thiozolidinediones treatment. Secondary end point will be fasting blood glucose, A1C levels, development of clinically significant macular edema, serum creatinine change in patients with no history of diabetic retinopathy and nephropathy at baseline.