Method, implemented by computational means, for determining a progressive lens for a wearer to whom an astigmatism, a power and an addition (Add) have been prescribed, comprising the steps of: - providing a progressive semifinished eyeglass having an unknown aspherical surface borne by the front surface of the progressive semifinished eyeglass, the progressive semifinished eyeglass having known items of information comprising the index value of said semifinished eyeglass, the base value of said semifinished eyeglass, the addition of said semifinished eyeglass and the progression length of said semifinished eyeglass; and - determining a progressive lens, in which the progressive lens determined has the front surface of the semifinished eyeglass and a back surface having a surface obtained by summation of a complex aspherization layer, defined as a complex model surface characterized at any point by its altitude determined by optimization and obtained by a method for determining an aspherization layer, and of a simple surface such that the value of the power at the reference point is equal to the prescribed power and the value of the astigmatism at the reference point is equal to the prescribed astigmatism; in which the method for determining an aspherization layer comprises the steps of: - choosing a generic surface (S G) having at each point known values of sphere and cylinder, the generic surface being chosen so as to have substantially the same known items of information as the progressive semifinished eyeglass; - creating a target model lens (L C) having: • a front surface being the generic surface (S G), and • a back surface being a first simple surface chosen from a torus or a sphere, the target model lens (L C) defining optical targets for each direction of the gaze on the basis of the astigmatism and/or power prescribed to the wearer; - creating a current model lens (L F), the current model lens (L F) initially being a trial initial model lens (L I) having: • a front surface being the generic surface (S G), and • a back surface being a second simple surface chosen from a torus or a sphere, - optimizing the current model lens (L F) by modulating the back surface to achieve the optical targets of the target model lens (L C) for each direction of the gaze; and - determining the complex aspherization layer corresponding to the back surface of the optimized current model lens from which the back surface of the trial initial model lens is subtracted. - providing a progressive semifinished eyeglass having an unknown aspherical surface borne by the front surface of the progressive semifinished eyeglass, the progressive semifinished eyeglass having known items of information comprising the index value of said semifinished eyeglass, the base value of said semifinished eyeglass, the addition of said semifinished eyeglass and the progression length of said semifinished eyeglass; and - determining a progressive lens, in which the progressive lens determined has the front surface of the semifinished eyeglass and a back surface having a surface obtained by summation of a complex aspherization layer, defined as a complex model surface characterized at any point by its altitude determined by optimization and obtained by a method for determining an aspherization layer, and of a simple surface such that the value of the power at the reference point is equal to the prescribed power and the value of the astigmatism at the reference point is equal to the prescribed astigmatism; in which the method for determining an aspherization layer comprises the steps of: - choosing a generic surface (S G) having at each point known values of sphere and cylinder, the generic surface being chosen so as to have substantially the same known items of information as the progressive semifinished eyeglass; - creating a target model lens (L C) having: • a front surface being the generic surface (S G), and • a back surface being a first simple surface chosen from a torus or a sphere, the target model lens (L C) defining optical targets for each direction of the gaze on the basis of the astigmatism and/or power prescribed to the wearer; - creating a current model lens (L F), the current model lens (L F) initially being a trial initial model lens (L I) having: • a front surface being the generic surface (S G), and • a back surface being a second simple surface chosen from a torus or a sphere, - optimizing the current model lens (L F) by modulating the back surface to achieve the optical targets of the target model lens (L C) for each direction of the gaze; and - determining the complex aspherization layer corresponding to the back surface of the optimized current model lens from which the back surface of the trial initial model lens is subtracted. • a front surface being the generic surface (S G), and • a back surface being a first simple surface chosen from a torus or a sphere, - creating a current model lens (L F), the current model lens (L F) initially being a trial initial model lens (L I) having: • a front surface being the generic surface (S G), and • a back surface being a second simple surface chosen from a torus or a sphere, • a front surface being the generic surface (S G), and • a back surface being a second simple surface chosen from a torus or a sphere, - optimizing the current model lens (L F) by modulating the back surface to achieve the optical targets of the target model lens (L C) for each direction of the gaze; and - determining the complex aspherization layer corresponding to the back surface of the optimized current model lens from which the back surface of the trial initial model lens is subtracted.