The present invention relates to a sterile aqueous ophthalmic solution comprising 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, for the specific use in the prevention or treatment of dry eye syndrome or dry eye signs and/or symptoms wherein said solution is applied prior to sleep.