Ethambutol
- Medication used to treat mycobacterial diseases, including tuberculosis
- Most common ophthalmic side effect: bilateral optic neuropathy
- Optic neuropathy develops in 2% to 5% treated with more than 15mg/kg/day, and in up to 25% treated with more than 25mg/kg/day
- Slowly progressive visual loss in both eyes, appearing within 3 months of starting medication
- Reduced visual acuity in both eyes
- Central scotomas on visual field testing
- Reduced color vision
- Ophthalmoscopy normal at first, later disclosing mildly pale optic discs at their temporal portions
- May be mistaken for cataract or uncorrected refractive error
- Other optic neuropathies
- Refer patient for baseline eye examination
- Repeat ophthalmic examinations every 3 months while patient being treated
- Avoid daily doses of greater than 15mg/kg especially in those with impaired kidney function
- Discontinue medication promptly if optic neuropathy discovered
- Visual loss irreversible and may worsen after medication discontinued, so...
- Early detection critical to preserve vision
- Delayed diagnosis common because visual loss symmetrical, very slowly progressive, and painless