Ethambutol can cause optic neuritis; which symptom would indicate this side effect?

Ethambutol can cause optic neuritis; which symptom would indicate this side effect?

• A. Headache
• B. Decreased visual acuity
• C. Abdominal pain
• D. Fever

Answer: (B)

Ethambutol can damage the optic nerve, leading to optic neuritis. The key sign of this side effect is a change in vision, specifically decreased visual acuity such as blurred or reduced sharpness of sight. Patients may also notice color vision changes, often trouble distinguishing colors like green or red. The other options don’t reflect optic nerve dysfunction: headache is nonspecific, abdominal pain is unrelated to the optic nerve, and fever signals systemic illness rather than a localized optic toxicity. So the symptom that indicates this side effect is decreased visual acuity. If this occurs, stop ethambutol and evaluate the patient promptly to prevent lasting vision impairment.

Ethambutol can damage the optic nerve, leading to optic neuritis. The key sign of this side effect is a change in vision, specifically decreased visual acuity such as blurred or reduced sharpness of sight. Patients may also notice color vision changes, often trouble distinguishing colors like green or red. The other options don’t reflect optic nerve dysfunction: headache is nonspecific, abdominal pain is unrelated to the optic nerve, and fever signals systemic illness rather than a localized optic toxicity. So the symptom that indicates this side effect is decreased visual acuity. If this occurs, stop ethambutol and evaluate the patient promptly to prevent lasting vision impairment.