**Core Concept**
Giant cell arteritis (GCA) is a large vessel vasculitis that predominantly affects the elderly population. It is characterized by inflammation of the medium to large-sized arteries, including the branches of the external carotid artery. The ocular manifestations of GCA are a significant concern due to the potential for permanent vision loss.

**Why the Correct Answer is Right**
Anterior ischemic optic neuropathy (AION) is the most common ocular complication of GCA. It occurs due to the inflammation of the short posterior ciliary arteries, which supply the optic nerve head. The resulting ischemia leads to optic nerve infarction, resulting in sudden and painless vision loss. The exact mechanism is thought to involve the disruption of blood flow to the optic nerve head, which is particularly vulnerable to ischemia due to its high metabolic demands.

**Why Each Wrong Option is Incorrect**
**Option A:** Papilloedema is the swelling of the optic disc due to increased intracranial pressure, which is not a direct consequence of GCA.

**Option B:** Central retinal artery occlusion (CRAO) is a rare but serious condition that occurs due to the blockage of the central retinal artery. While it can cause sudden vision loss, it is not a specific hallmark of GCA.

**Option D:** Central retinal vein occlusion (CRVO) is a condition that occurs due to the blockage of the central retinal vein, leading to retinal hemorrhages and vision loss. It is not a direct consequence of GCA.

**Clinical Pearl / High-Yield Fact**
AION is often described as "sudden, painless, and unilateral" vision loss in patients with GCA. This classic presentation should prompt a high index of suspicion for GCA in patients presenting with these symptoms.

**✓ Correct Answer: C. AION**