**Core Concept**
The sudden painless loss of vision in one eye, without any history of trauma, suggests an ocular or central nervous system cause. This presentation is often associated with conditions that affect the optic nerve or the retina.

**Why the Correct Answer is Right**
The absence of fundal glow (also known as the "red reflex") on examination, along with the history of sudden painless loss of vision, points towards a diagnosis of central retinal artery occlusion (CRAO). CRAO occurs when there is a blockage of the central retinal artery, which supplies blood to the retina. This blockage leads to ischemia and subsequent infarction of the retina, resulting in sudden painless loss of vision. The normal anterior segment examination and absence of fundal glow make CRAO the most likely cause.

**Why Each Wrong Option is Incorrect**
**Option A:** Optic neuritis typically presents with pain on eye movement, redness, and swelling of the optic disc, which are not features in this case.
**Option B:** Retinal detachment would typically present with flashes of light, floaters, and a sudden increase in floaters, which are not mentioned in the scenario.
**Option C:** Macular degeneration is a chronic condition and would not typically cause sudden painless loss of vision.

**Clinical Pearl / High-Yield Fact**
In a patient presenting with sudden painless loss of vision, remember to check for the absence of fundal glow, which is a key feature of central retinal artery occlusion.

**Correct Answer:** C.