A method implemented by computer means for calculating an optical system by optimization in the field of ophthalmic lenses so as to take into account a large number of criteria while simplifying the optimization, where the optical system is defined by all its surfaces, an index of material and the position of each surface relatively to each other, the method comprising the steps of: i) providing a set of optical system parameters so as to define a starting optical system, each optical system parameter being set up at a starting value; ii) defining a plurality of criteria (C k) and a target value to be reached for each criterion of the plurality of criteria (C k); iii) associating for each criterion (C k) at least one cost function (CF k); iv) defining a plurality of global cost functions (GCF l,..., GCF ND) by associating to each global cost function (GCF p) at least one cost function (CF k); v) defining a vector of variable parameters (X p) associated to each global cost function (GCF p) by selecting for each vector of variable parameters (X p) at least one optical system parameter; vi) alternatively optimizing the plurality of global cost functions (GCF l,..., GCF ND) by modifying the values of the optical system parameters of the vectors of variable parameters (X l,..., X ND) so as to obtain a intermediate system; vii) repeating step vi) until an equilibrium is reached so as to obtain an optical system, wherein, during step v), the at least one optical system parameter is selected for only one vector of variable parameter (X p), and wherein: - at least one global cost function (GCF p) is defined by associating only one or several cost function(s) (CF k) associated to optical criteria (C k) selected in the list consisting of power in central vision, astigmatism in central vision, high order aberration in central vision, acuity in central vision, power in peripheral vision, astigmatism in peripheral vision, high order aberration in peripheral vision, or a variation of preceding criteria, and/or - at least one global cost function (GCF p) is defined by associating only one or several cost function(s) (CF k) associated to optical criteria (C k) selected in the list consisting of prismatic deviation in central vision, ocular deviation, object visual field in central vision, image visual field in central vision, magnification in central vision, pupil field ray deviation, object visual field in peripheral vision, image visual field in peripheral vision, prismatic deviation in peripheral vision, magnification in peripheral vision, magnification of the eye, temple shift or a variation of preceding criteria, and/or - at least one global cost function (GCF p) is defined by associating only one or several cost function(s) (CF k) associated to a geometrical criteria. i) providing a set of optical system parameters so as to define a starting optical system, each optical system parameter being set up at a starting value; ii) defining a plurality of criteria (C k) and a target value to be reached for each criterion of the plurality of criteria (C k); iii) associating for each criterion (C k) at least one cost function (CF k); iv) defining a plurality of global cost functions (GCF l,..., GCF ND) by associating to each global cost function (GCF p) at least one cost function (CF k); v) defining a vector of variable parameters (X p) associated to each global cost function (GCF p) by selecting for each vector of variable parameters (X p) at least one optical system parameter; vi) alternatively optimizing the plurality of global cost functions (GCF l,..., GCF ND) by modifying the values of the optical system parameters of the vectors of variable parameters (X l,..., X ND) so as to obtain a intermediate system; vii) repeating step vi) until an equilibrium is reached so as to obtain an optical system, - at least one global cost function (GCF p) is defined by associating only one or several cost function(s) (CF k) associated to optical criteria (C k) selected in the list consisting of power in central vision, astigmatism in central vision, high order aberration in central vision, acuity in central vision, power in peripheral vision, astigmatism in peripheral vision, high order aberration in peripheral vision, or a variation of preceding criteria, and/or - at least one global cost function (GCF p) is defined by associating only one or several cost function(s) (CF k) associated to optical criteria (C k) selected in the list consisting of prismatic deviation in central vision, ocular deviation, object visual field in central vision, image visual field in central vision, magnification in central vision, pupil field ray deviation, object visual field in peripheral vision, image visual field in peripheral vision, prismatic deviation in peripheral vision, magnification in peripheral vision, magnification of the eye, temple shift or a variation of preceding criteria, and/or - at least one global cost function (GCF p) is defined by associating only one or several cost function(s) (CF k) associated to a geometrical criteria.