Ethambutol and Retinal Detachment
Retinal detachment is NOT a recognized adverse effect of ethambutol therapy. The primary ocular toxicity associated with ethambutol is retrobulbar optic neuritis, not retinal detachment.
Primary Ocular Toxicity of Ethambutol
Ethambutol causes optic neuritis (retrobulbar neuritis), not retinal detachment. 1 This manifests as:
- Decreased visual acuity affecting one or both eyes 1
- Impaired red-green color discrimination 1, 2
- Blurred vision 3, 2
- Visual field defects (particularly cecocentral scotomas) 3, 2
The mechanism involves toxicity to retinal ganglion cells through an excitotoxic pathway and mitochondrial dysfunction, not retinal structural detachment. 4
Dose-Related Risk Profile
The risk of optic neuritis is dose-dependent:
- At 15 mg/kg/day: Minimal risk (<0.5%) 1, 2
- At 25 mg/kg/day: Risk increases to approximately 3% 2
- Above 30 mg/kg/day: Risk escalates to 18% 1
No difference in visual acuity was found between regimens containing ethambutol at 15 mg/kg and those without the drug. 1
High-Risk Populations for Optic Toxicity
Renal insufficiency dramatically increases toxicity risk regardless of dose due to reduced drug clearance and accumulation. 1, 3, 2 Other risk factors include:
- Treatment duration exceeding 2 months 3, 2
- Daily therapy versus intermittent dosing (6% vs 0% in one study) 3
- Advanced age 3, 2
Monitoring Requirements
Baseline visual assessment is mandatory before initiating ethambutol, including:
Monthly monitoring is required for high-risk patients, including those receiving doses >15 mg/kg, treatment duration >2 months, or any patient with renal insufficiency. 1, 3
Pattern visual evoked potential (VEP) and retinal nerve fiber layer optical coherence tomography (RNFL OCT) can detect subclinical toxicity earlier than standard visual testing. 5
Management of Visual Symptoms
Discontinue ethambutol immediately and permanently at the first sign of any visual disturbance. 1, 3, 2 This includes:
Never rechallenge with ethambutol after visual toxicity occurs, even if vision normalizes. 3 Arrange urgent ophthalmological assessment to evaluate the extent of optic neuritis. 3
Reversibility and Prognosis
Recovery of visual acuity usually occurs within weeks to months after drug discontinuation. 2 However, irreversible vision loss can occur despite careful monitoring and prompt discontinuation. 6 Subclinical changes detected on RNFL OCT and pattern VEP may progress for 6 months after stopping ethambutol before returning to baseline by 12 months. 5
Common Pitfall
Do not confuse optic neuritis with retinal detachment. These are distinct pathologies with different presentations, mechanisms, and management approaches. Ethambutol causes optic nerve toxicity affecting the retinal ganglion cells and optic nerve, not structural separation of the retina from the underlying retinal pigment epithelium that characterizes retinal detachment.