Methods for optimizing postural prism to be added to a pair of ophthalmic multifocal lenses (lenses) adapted to a wearer and to slow down myopia progression are described. The method includes an initial pair of lenses in a providing step S1. In a postural prism adding step S2, a same postural prism is added to each lens. In a gazing step S3, the wearer gazes at a first distance target through the lenses with the added postural prism. A gazing direction determining step S4 determines the wearer's gazing direction during S3. Steps S2 to S4 may be repeated while changing the added postural prism, wherein the added postural prism is smaller than or equal to a maximum prism value. Steps S2 to S4 may be repeated to determine the smallest added postural prism for which the wearer's gazing direction in step S4 passes through the first vision zone.