I recommend you call your physician for an immediate appointment. Medication could cause this side-effect but high blood pressure could be the culprit. High blood pressure can affect your vision. If you have no sight in one eye and it comes back again it could be a sign something more serious is going on so it should be checked out immediately. "Black lines" in one eye could mean that your medication needs adjustment. If it is like a shade that goes down on your eye it could mean a TIA or mini-stroke. Especially after heart surgery, it is imperative to keep your physician notified of these types of difficulties.

Cleo Hutton