Which factor mediates the hallmark of proliferative diabetic retinopathy?

The hallmark of proliferative diabetic retinopathy is the presence of neovascularization, which is the formation of new, often abnormal blood vessels in the retina. This process is primarily mediated by vascular endothelial growth factor (VEGF). In response to hypoxia (reduced oxygen supply) in the retinal tissue, VEGF is released, stimulating the growth of new blood vessels in an attempt to restore blood supply to the affected areas. However, these new vessels are fragile and can easily rupture, leading to serious complications such as bleeding and vision loss.

While insulin resistance, intraocular pressure, and high blood sugar levels are important factors in the broader context of diabetic complications, they do not directly mediate the specific process of neovascularization associated with proliferative diabetic retinopathy. Insulin resistance contributes to the development of type 2 diabetes and its complications, intraocular pressure is more relevant to glaucoma, and high blood sugar levels cause general damage to retinal cells but are not directly responsible for the formation of new blood vessels. Thus, VEGF is the key mediator in this particular condition, making it the correct answer.