Ethambutol and the optic nerve
- Drugs and toxicity
Ethambutol, a tuberculosis drug, can damage both optic nerves. Checking vision and colours during treatment and stopping early can save sight.
See it in 3D: Optic nerve · Optic chiasm
What it is
Ethambutol is part of first-line tuberculosis treatment. It can cause a toxic optic neuropathy affecting both eyes, usually after the first months of treatment and more often with higher doses or kidney failure. Patients notice blurred central vision and loss of colour discrimination. Early detection and stopping the drug give the best chance of recovery, which is not always complete.
What to know
- Symptoms: painless, bilateral blurring of central vision; difficulty telling red from green.
- Signs: reduced acuity, central or centrocaecal scotomas, the disc may be normal at first.
- Risk factors: higher dose, kidney failure (the drug accumulates), older age, long treatment.
- Recovery after stopping is possible but slow and sometimes incomplete.
Toxicity and risks
- Patients should be told to report any change in vision at once.
- Children who cannot report vision changes need special care with this drug.
- Isoniazid can also, rarely, cause optic neuropathy.
Next step / Initial management
- Before starting: baseline visual acuity and colour vision in each eye.
- During treatment: ask about vision at every visit and repeat acuity and colour vision periodically, following the tuberculosis programme.
- Visual symptoms or a drop in acuity or colour vision: stop ethambutol in agreement with the treating team and refer to ophthalmology.
- Adjust the dose to kidney function.
Test yourself
Think of the answer, then tap the question to see it.
What are the typical symptoms of ethambutol optic neuropathy?
Painless blurring of central vision in both eyes and difficulty distinguishing red from green.
Which condition increases the risk of ethambutol toxicity?
Kidney failure, because the drug accumulates.
What must be done before starting ethambutol?
Record baseline visual acuity and colour vision in each eye.
Connections
See it in 3D2
The structures of Durgical's 3D anatomy where it is found.
In Pharmacology1
Educational content; not a clinical guideline and no substitute for assessment by a health professional. For sudden visual loss, severe eye pain, a chemical burn or an eye injury, go to an emergency department at once.
Sources: Ethambutol (StatPearls Publishing (NCBI Bookshelf), 2024); Color Vision (StatPearls Publishing (NCBI Bookshelf), 2022).
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Representative model, for educational purposes only.