Is ethambutol-induced blurring of vision painful or painless?

Ethambutol-Induced Blurring of Vision is Typically Painless

Ethambutol-induced blurring of vision is typically painless and presents as optic neuritis or retrobulbar neuritis without pain. 1, 2 This visual disturbance is a serious adverse effect that can potentially lead to irreversible blindness if not promptly addressed.

Clinical Presentation of Ethambutol-Induced Visual Disturbances

Ethambutol-induced optic neuritis typically presents with:

• Painless blurred vision
• Decreased visual acuity
• Central scotomas (blind spots in central vision)
• Impaired red-green color discrimination
• Peripheral visual field defects
• Bilateral or unilateral visual changes 1, 3, 2

The absence of pain is a key distinguishing feature of ethambutol-induced optic neuritis compared to some other causes of optic neuritis, which can be painful.

Risk Factors for Developing Ethambutol Ocular Toxicity

The risk of developing ethambutol-related ocular toxicity increases with:

• Higher doses (particularly >25 mg/kg/day)
• Longer duration of treatment (risk is greater with NTM treatment than TB treatment due to longer therapy)
• Renal impairment (reduced clearance leads to drug accumulation)
• Older age 1, 3

In a retrospective analysis, ethambutol-related ocular toxicity was diagnosed in 6% of patients receiving daily therapy (25 mg/kg for the first 2 months followed by 15 mg/kg for the remainder of treatment) compared with 0% in patients prescribed intermittent therapy (ethambutol 25 mg/kg 3× per week). 1

Monitoring and Early Detection

Because visual symptoms often occur before measurable changes can be identified:

• Baseline visual acuity and color vision testing should be performed before starting ethambutol
• Regular monitoring of visual acuity and color discrimination should be conducted throughout treatment
• Monthly testing is recommended for patients on doses >15 mg/kg/day
• Patients should be educated about potential visual side effects and instructed to self-report any changes in vision immediately 1, 3

Management of Ethambutol-Induced Visual Changes

If visual changes occur:

1. Ethambutol should be discontinued immediately
2. Comprehensive ophthalmological evaluation should be arranged promptly
3. Alternative anti-mycobacterial medications should be considered
4. Visual recovery typically occurs over weeks to months after drug discontinuation, but permanent visual impairment can occur in some cases 1, 3, 2

Important Caveat

While most cases of ethambutol-induced visual disturbances improve after discontinuation of the medication, some patients may experience permanent visual impairment, particularly if the drug is not stopped promptly after symptoms develop or in elderly patients 4, 5, 6. This highlights the importance of early recognition and immediate discontinuation of ethambutol when visual symptoms occur.