Toxic amblyopia can be caused by
**Core Concept**
Toxic amblyopia, also known as toxic optic neuropathy, is a rare condition characterized by progressive vision loss due to exposure to certain toxic substances. This condition is often associated with the use of medications, heavy metal poisoning, or other toxic exposures.
**Why the Correct Answer is Right**
Toxic amblyopia typically occurs when a toxic substance damages the optic nerve, leading to vision loss. The most common causes of toxic amblyopia include isoniazid, ethambutol, and chloramphenicol, which are often used in the treatment of tuberculosis. These medications can cause damage to the optic nerve by inhibiting the synthesis of folate or by directly damaging the optic nerve cells.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a known cause of toxic amblyopia. While certain medications can cause vision loss, this option is too vague to be a correct answer.
**Option B:** This option is incorrect because it is not a known cause of toxic amblyopia. Vitamin B12 deficiency can cause optic neuropathy, but it is not typically classified as a toxic cause.
**Option C:** This option is incorrect because it is not a known cause of toxic amblyopia. Heavy metal poisoning can cause a range of neurological symptoms, but it is not typically associated with toxic amblyopia.
**Clinical Pearl / High-Yield Fact**
Isoniazid is a common medication used to treat tuberculosis, but it can also cause toxic amblyopia in some patients. To minimize the risk of this side effect, patients taking isoniazid should be monitored regularly for vision changes and should receive pyridoxine supplementation to prevent folate deficiency.
**Correct Answer: C. Heavy metal poisoning**