A method for determining at least one optical design parameter for a progressive ophthalmic lens intended to be fitted in a frame of a wearer, depending on the wearer's visual behaviour, includes: a) placing the wearer in a situation in which he carries out a visual task at a first working distance; b) during this task, determining at least two gaze directions of the wearer at this first working distance in a frame of reference of the wearer's head; c) determining a relative position of a surface related to the frame or to an ophthalmic lens intended to be fitted in the frame; d) determining for each gaze direction at the first working distance the intersection between this gaze direction and the surface so as to establish a map of these points of intersection on this surface; and e) deducing the sought-after optical design parameter from this map.