A method of preventing or treating an eye condition includes administering a sterile aqueous ophthalmic solution to an eye for the prevention or treatment of dry eye syndrome or dry eye sign and/or dry eye symptom. The sterile aqueous ophthalmic solution includes about 0.05% to about 0.5% (w/w) of N—；(N-acetylcysteinyl-)chitosan or a pharmaceutically acceptable salt thereof in a carrier solution, wherein the N—；(N-acetylcysteinyl-)chitosan has a content of free thiol groups in an amount of from 80 μmol/g polymer to 280 μmol/g polymer.
