Fennel. Fennel can also be used to treat the problem of pink eye. An individual can boil some fennel seeds in water. Washing eyes with this water (strained) after it has cooled down 2 to 3 times on a daily basis can help in reducing the pain, redness and inflammation.ennel. Fennel can also be used to treat the problem of pink eye. An individual can boil some fennel seeds in water. Washing eyes with this water (strained) after it has cooled down 2 to 3 times on a daily basis can help in reducing the pain, redness and inflammation.