What to do with my gerbil, think it is dying?

I have had my gerbil for about 4 years now which is already above their life expectancy but do not know what to do with it. Recently it has gotten very weak and walks slowly and very shakily when i take it out, if i dont take it out it will just stay in its nest. Its eyes i think have glazed over with something sticky i think and i am not even sure if it can close them. I am really scared and i do not know what to do.