**Core Concept**
Optic atrophy refers to the degeneration of the optic nerve, which can result from various causes, including toxic substances that affect the optic nerve directly or indirectly. This condition leads to visual loss and can be irreversible.

**Why the Correct Answer is Right**
The correct answer is related to the toxic effect of a specific substance on the optic nerve. Ethambutol, an antitubercular medication, is known to cause optic neuropathy, which can lead to optic atrophy. This is due to its ability to inhibit the synthesis of myelin in the optic nerve, leading to damage and atrophy.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because arsenic poisoning primarily affects the gastrointestinal system, skin, and nervous system but is not typically associated with optic atrophy.

**Option B:** This option is incorrect because lead poisoning primarily affects the hematopoietic, gastrointestinal, and nervous systems, but it is not characteristically associated with optic atrophy.

**Option C:** This option is incorrect because carbon monoxide poisoning primarily affects the cardiovascular system and nervous system through its binding to hemoglobin, but it is not characteristically associated with optic atrophy.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize that ethambutol-induced optic neuropathy can be reversible if detected early and treated promptly, emphasizing the importance of regular ophthalmological evaluations in patients receiving this medication.

**Correct Answer:** C. Ethambutol