Final answer:
Vision changes like seeing a green halo around lights can be a symptom of digoxin toxicity, a medication used for heart conditions.
Step-by-step explanation:
The medication that may cause a client to see a green halo around lights when experiencing toxicity is digoxin. Digoxin is used in the treatment of heart conditions such as atrial fibrillation and heart failure. Green vision or seeing green halos around lights, known as xanthopsia, is a classic symptom of digoxin toxicity. It's important for healthcare providers to be aware of this potential side effect when monitoring patients on this medication. This visual disturbance occurs because digoxin alters the visual pigment in the retina, which can cause this unusual side effect.