My cats eye is twitching?

I have a four month old cat we noticed she keeps twitching her left eye and there's mucuse in it and around it I never noticed the mucuse till around a few days ago untill my sister said something I thought it was something she did when she gets playfull and crazy (really you should she her crazy) but then I seen her twitching and the stuff in her eye when she woke up from a nap (which she's always cuddly after) so if anyone knows what's going on plz tell me I would hate for her to suffer she fits are family so well