Why is my left eye constantly twitching, like a muscle spasm?

No exaggeration, it WILL NOT STOP, and its getting really annoying. What is causing this, and most importantly how can I get it to stop?! It's CONSTANT!!!!Why is my left eye constantly twitching, like a muscle spasm?
Stress can bring this on. It can last for a few weeks up until a few months. Try to reduce the stress. Yes, this is a muscle spasm and it will stop in time.
Mine did that for a few months and then quit as mysteriously as it arrived. Smoking can cause muscle spasms. I don't smoke so I think my problem was from medication I take.