**Core Concept**
Methanol toxicity is a well-known cause of visual impairment and blindness. The conversion of methanol to its toxic metabolites is a critical step in understanding the pathophysiology of methanol poisoning.

**Why the Correct Answer is Right**
Methanol is metabolized by alcohol dehydrogenase (ADH) to form formaldehyde, which is then rapidly converted to formic acid by aldehyde dehydrogenase (ALDH). Formic acid is highly toxic and causes damage to the retinal ganglion cells, leading to visual impairment and blindness. The optic nerve head is particularly susceptible to formic acid toxicity, resulting in optic neuropathy.

**Why Each Wrong Option is Incorrect**
* **Option A:** Acetaldehyde - This is a metabolite of ethanol, not methanol, and is not responsible for methanol toxicity.
* **Option B:** Formaldehyde - While formaldehyde is an intermediate in the metabolism of methanol, it is not the primary toxic compound responsible for methanol-induced eye damage.
* **Option D:** Methyl alcohol - This is simply another name for methanol, and does not represent a toxic metabolite.

**Clinical Pearl / High-Yield Fact**
Methanol toxicity can be treated with fomepizole, a competitive inhibitor of alcohol dehydrogenase, which helps to prevent the formation of formic acid. This is a critical intervention in the management of methanol poisoning.

**Correct Answer: C. Formic acid.**