It could be a drug side effect. If you are feeling okay, you might see an optometrist. But then they would numb your eyes with Atropine, and your MG might get worse!
Read this.
http://www.rxlist.com/voltaren-drug.htm
You should stop the drug if you have vision problems!!! Talk to your pharmacist and doctor again.
Can you take Tylenol?
NSAIDs might not make MG worse, but that doesn't mean the side effects can't be serious.
And taking them WITH Prednisone can be a problem. It's not only a single drug, but how that drug interacts with anything else you are taking (or eating) that can adversely affect you.
I think you need to discuss this with a doctor pronto. I hope you can get some relief from the knee pain!
Annie