An ophthalmic preparation consisting of an aqueous solution, or collyrium, containing a dispersion of BIOSECUR® liposomes of a mixture containing flavonoid- rich citrus extracts, in the form of a liposomal preparation, provides excellent antibacterial protection, in the parameters indicated by the A classification of the Pharmacopoeia XII ed. Preferably, such a collyrium, in borate isotonic buffer, is made viscous to improve its stability and mucoadhesiveness, with the addition of hydroxypropy1-methylcellulose (hypromellose). A method is also described for preparing such a solution for ophthalmic use comprising Biosecur® or a composition based on flavonoid-rich citrus extracts, in liposomal form, wherein the liposomes have a size smaller than 200 nm.