Can a Damaged facial muscle be fixed?

I have a damaged outer eye muscle from 1 year ago when myself and a freind were messing and I received a hard slap while I was laughing that caused my left outer eye muscle to droop slightly. It has made it hard to maintain a smile and over the last year it appears to have gotten weaker. I have tried facial exercises to try strengthen it but as it is damaged i'm not sure this is a good idea. Has anybody had this problem before?