The postings from Barbara above are right on the mark.. but I have a question about #4. what breed is your cat ? some breeds have a little more eye discharge than others, and sometimes its just a mild allergy that causes those little "Eye Boogers"
its nothing to worry about if the cat is acting normal and healthy.. If it's an URI (Upper Respiratory Infection) or COLD.. the kitty will act sick, not eat or drink much, and needs to be watched carefully for complications. Runny eyes can also be a symptom of internal parasites (Worms) you can take a stool sample to your vet and have it checked . Otherwise, if kitty is acting normal, its just those silly old "Eye Boogers"