Ethambutol causes retrobulbar optic neuropathy.

• A. Ethambutol
• B. Digoxin
• C. Sildenafil
• D. Pseudotumor cerebri

Answer: (A)

Ethambutol is the anti-tuberculosis drug most classically linked to optic nerve toxicity, specifically a retrobulbar optic neuropathy. This means the damage occurs behind the eye, so the optic disc may look normal early on even as vision worsens. Patients typically notice reduced visual acuity and color vision deficits, especially red–green desaturation. The effect is dose-related and more likely with higher daily doses or in those with impaired renal function. The key management step is to stop ethambutol promptly; vision often improves after cessation but can be permanent if the drug is continued too long. In contrast, the other options aren’t characteristically associated with retrobulbar optic neuropathy in this context—digoxin can cause visual disturbances like yellow vision, sildenafil can cause transient color changes, and pseudotumor cerebri presents with papilledema from raised intracranial pressure rather than a drug-induced retrobulbar neuropathy.