A method for determining target optical functions for a pair of ophthalmic lenses is provided, the method comprising steps of: generating a first target optical function (OFT1) for a first lens of the pair based at least on data relating to a first eye, generating a second target optical function (OFT2) for a second lens of the pair based at least on data relating to the first eye. This method makes it possible to obtain optical functions having improved symmetry. Thus, when using the target optical functions in an optical optimization method, lenses with improved binocular properties can be obtained. The comfort of the wearer of the pair of lenses is thus improved.