**Core Concept**
Central retinal venous occlusion (CRVO) and ocular ischemic syndrome due to carotid artery stenosis are two distinct ocular conditions that can present with similar symptoms. Differentiating between these conditions is crucial for proper management and treatment. The key to differentiation lies in understanding the pathophysiology of each condition.

**Why the Correct Answer is Right**
Central retinal venous occlusion (CRVO) typically presents with a sudden onset of vision loss, retinal hemorrhages, and a dilated and tortuous retinal vein. In contrast, ocular ischemic syndrome due to carotid artery stenosis is characterized by a gradual onset of vision loss, retinal ischemia, and neovascularization. The presence of neovascularization is a key distinguishing feature of ocular ischemic syndrome. Neovascularization is the formation of new, fragile blood vessels in response to ischemia, which can lead to severe vision loss and even retinal detachment.

**Why Each Wrong Option is Incorrect**
**Option A:** Fluorescein angiography can be used to differentiate CRVO from ocular ischemic syndrome due to carotid artery stenosis. In CRVO, the fluorescein dye leaks out of the dilated and tortuous retinal veins, whereas in ocular ischemic syndrome, the dye shows up as a characteristic "arteriovenous" pattern due to the presence of neovascularization.

**Option B:** Fundus photography can also be used to differentiate between the two conditions. CRVO typically shows extensive retinal hemorrhages, whereas ocular ischemic syndrome shows retinal ischemia, neovascularization, and sometimes even choroidal neovascularization.

**Option C:** Optical coherence tomography (OCT) can be used to evaluate the retinal thickness and morphology in both conditions. However, OCT is not a reliable method for differentiating CRVO from ocular ischemic syndrome.

**Option D:** Intraocular pressure (IOP) measurements can also be used to differentiate between the two conditions. However, IOP is not a reliable method for differentiating CRVO from ocular ischemic syndrome.

**Clinical Pearl / High-Yield Fact**
One key clinical pearl to remember is that neovascularization is a hallmark of ocular ischemic syndrome due to carotid artery stenosis. The presence of neovascularization on fluorescein angiography or fundus photography is a strong indicator of ocular ischemic syndrome.

**Correct Answer:** D. Intraocular pressure (IOP) measurements are not a reliable method for differentiating CRVO from ocular ischemic syndrome.