Fig. 2

The structure of microaneurysms in DR. Ultrastructurally, there are 4 types of microaneurysms: (a) Type I microaneurysms exhibit intact endothelium and basement membrane without the encirclement of pericytes, and circulating leukocytes is extensively accumulated in the lumen; (b) Type II microaneurysms are characterized by the absence of both endothelial cells and pericytes, thickened basement membrane, as well as a multitude of red blood cells inside the lumen; (c) Type III microaneurysms share similar appearances with Type II microaneurysms, but debris of red blood cells are contained; (d) Type IV microaneurysms are in sclerosed forms with heavily thickened basement membrane and fibrous infiltration into the lumen. Moreover, early in DR, retinal neurons undergo apoptotic cell death, accompanied by a decreased number of astrocytes and activation of microglial cells with amoeboid morphology