The commonest cause of rubeosis iridis is
**Core Concept**
Rubeosis iridis, also known as neovascularization of the iris, is a condition characterized by the growth of new blood vessels on the surface of the iris, often in response to chronic ischemia or inflammation. This condition can lead to complications such as neovascular glaucoma and vision loss.
**Why the Correct Answer is Right**
The commonest cause of rubeosis iridis is diabetic retinopathy, which involves the growth of new blood vessels in response to chronic hypoxia. This is due to the upregulation of vascular endothelial growth factor (VEGF) and other angiogenic factors, leading to the formation of fragile and leaky new vessels. In diabetic retinopathy, the retinal ischemia triggers a cascade of events that ultimately result in the growth of new vessels on the iris.
**Why Each Wrong Option is Incorrect**
**Option A:** While trauma can cause rubeosis iridis, it is not the most common cause. Traumatic rubeosis is often associated with severe eye injuries and is relatively rare compared to diabetic retinopathy.
**Option B:** Central retinal vein occlusion can cause rubeosis iridis, but it is not the most common cause. This condition is often associated with retinal ischemia and neovascularization, but it is less common than diabetic retinopathy.
**Option C:** Hypertensive retinopathy can cause rubeosis iridis, but it is not the most common cause. This condition is often associated with severe hypertension and retinal ischemia, but it is less common than diabetic retinopathy.
**Clinical Pearl / High-Yield Fact**
In diabetic retinopathy, the growth of new blood vessels on the iris can be a sign of advanced disease and a high risk of vision loss. Early detection and treatment of diabetic retinopathy are crucial to prevent complications such as rubeosis iridis and neovascular glaucoma.
**Correct Answer:** D. Diabetic retinopathy.