**Core Concept**
Amaurosis fugax is a transient, painless loss of vision in one eye, often described as a curtain or shade descending over the eye. It is a symptom of a potential underlying vascular or cardiac condition.

**Why the Correct Answer is Right**
Amaurosis fugax is typically caused by occlusion of the ophthalmic artery or its branches, which supply blood to the eye. The ophthalmic artery is a branch of the internal carotid artery. The occlusion can be due to atherosclerosis, emboli, or vasculitis, leading to temporary ischemia of the retina. This results in a transient loss of vision, often resolving spontaneously.

**Why Each Wrong Option is Incorrect**
**Option A:** The middle cerebral artery is not directly involved in the pathogenesis of amaurosis fugax.
**Option B:** The posterior communicating artery is not the primary cause of amaurosis fugax; it is more commonly associated with aneurysms and third nerve palsy.
**Option C:** The vertebral arteries are involved in the posterior circulation of the brain, not directly related to the pathogenesis of amaurosis fugax.

**Clinical Pearl / High-Yield Fact**
Amaurosis fugax is a "red flag" symptom that warrants further investigation for underlying vascular or cardiac disease, particularly atherosclerosis or atrial fibrillation.

**Correct Answer: C. The ophthalmic artery.**