**Core Concept**
The degree of diabetic retinopathy is influenced by the duration of diabetes, glycemic control, and the presence of other cardiovascular risk factors. The pathogenesis of diabetic retinopathy involves microvascular damage due to hyperglycemia-induced inflammation, oxidative stress, and endothelial dysfunction.

**Why the Correct Answer is Right**
The correct answer is duration of diabetes with poor glycemic control. The longer the duration of diabetes, the higher the risk of developing diabetic retinopathy. This is because prolonged exposure to high blood glucose levels leads to the activation of various cellular pathways, including the polyol pathway, the hexosamine pathway, and the advanced glycosylation end-product pathway, which ultimately result in microvascular damage and retinal neovascularization.

**Why Each Wrong Option is Incorrect**
**Option A:** Duration of diabetes alone is not the sole determining factor for the degree of diabetic retinopathy. Other factors such as glycemic control, hypertension, and hyperlipidemia also play a crucial role.
**Option B:** Glycemic control is an essential factor in determining the degree of diabetic retinopathy. Poor glycemic control can accelerate the progression of retinopathy, while good control can slow its progression.
**Option C:** Hypertension is a significant risk factor for diabetic retinopathy, but it is not the primary determining factor. Hypertension can worsen the microvascular damage caused by diabetes.

**Clinical Pearl / High-Yield Fact**
The Early Treatment Diabetic Retinopathy Study (ETDRS) classification system is widely used to grade the severity of diabetic retinopathy. The ETDRS system categorizes diabetic retinopathy into five stages: mild nonproliferative diabetic retinopathy (NPDR), moderate NPDR, severe NPDR, proliferative diabetic retinopathy (PDR), and diabetic macular edema.

**Correct Answer:** D. Duration of diabetes with poor glycemic control.