Which drug is associated with retrobulbar optic neuropathy and blue-yellow color defects?

• A. Digoxin
• B. Ethambutol
• C. Sildenafil
• D. Oral contraceptives

Answer: (A)

Ethambutol is known to cause optic nerve toxicity, producing retrobulbar optic neuropathy with color vision defects. While red-green defects are the classic finding, blue-yellow (tritan) color disturbances can also occur with ethambutol toxicity. The optic neuropathy is dose- and duration-related and often bilateral, with patients noticing decreased visual acuity and difficulty with color discrimination. If identified early, stopping the drug can lead to improvement, though deficits may persist in some cases.

Digoxin can cause visual changes such as yellow vision (xanthopsia) and other disturbances but not typically retrobulbar optic neuropathy. Sildenafil may cause a blue-tinted vision due to retinal PDE6 effects but again not the classic optic neuropathy. Oral contraceptives are not associated with retrobulbar optic neuropathy.