**3. Vitreous biomarkers in proliferative diabetic retinopathy**

A biomarker is an objective measurement that is evaluated as an indicator for some complex processes happening in our body [16]. Biomarkers are usually measured to determine the diagnosis and prognosis of some treatments [17]. There are several biomarkers that can be found in diabetic retinopathy patients including biomarkers of oxidative stress, hypoxiainducible factors, angiogenic factors, pro-inflammatory cytokines, chemokines, cell adhesion molecules, and CD200. The value of these biomarkers tells us their possible role in the progression of diabetic retinopathy [5, 6, 18–21] (**Figure 2**).
