Hello, the pink eye that you are describing is a condition known as Conjunctivitis. Conjunctivitis is the inflammation of conjunctiva. The conjunctiva is generally transparent but in inflammation it appears pink or reddish. It can result due to infection bacterial or viral, allergies, chemicals, fumes, and dry eye. Viral conjunctivitis is caused by adenovirus. It usually presents with redness of the eye, itching, watering of the eyes, swelling associated with thick discharge. Staphyloccus, Hemophilus influenza type B, and gonorrhea cause bacterial conjunctivitis. Here it presents with swelling, redness of the eye, pseudoptosis, this usually and lasts for 7-10 days. However the other causes of red eye are presence of foreign body, glaucoma, and injury to the eye. I would suggest you to consult your ophthalmologist for a complete evaluation of the eye .In regard to your question on the instructions on the leaflet, usually the medications come with an expiry date and can be used up to 6 months to a year depending on that particular medication. In your case, this medication is mainly used for bacterial conjunctivitis and should be discarded within a month as the preservatives in the drops can only protect up to 4 weeks after opening it. So don't use the old one and it would be best to consult the doctor. Thank you.