Which drug requires baseline vision testing due to optic neuritis risk?

• A. Isoniazid
• B. Ethambutol
• C. Pyrazinamide
• D. Rifampin

Answer: (B)

The key idea is that optic neuritis risk is a known adverse effect of Ethambutol, so baseline and ongoing vision testing are recommended.

Ethambutol can cause dose-related optic neuropathy, leading to decreased visual acuity and color vision deficits (often red-green). Because this damage can become permanent if it’s not caught early, clinicians perform a baseline ophthalmologic assessment (visual acuity and color vision) before starting therapy and monitor vision during treatment. If any signs of optic neuritis appear, Ethambutol is stopped to prevent further harm.

The other drugs listed are associated with hepatotoxicity, neuropathy, or other issues, but optic neuritis is not a typical or well-established risk with them, so routine baseline vision testing isn’t emphasized for those.