A computer-implemented method for determining an optical system, comprising at least an ophthalmic lens, intended to equip a person on the basis of the adaptability of the person to a visual modification of his environment, the method comprising: - a person visual behaviour parameter providing step (S2), during which a person visual behaviour parameter indicative of the visual behaviour of the person relative to a given state of the environment is provided; - a reference value providing step (S4), during which a first value of the person visual behaviour parameter corresponding to a reference state of the environment is provided; - a visual modification providing step (S6), during which a visual modification of the reference state of the environment is provided so as to define a modified state of the environment; - an evaluating step(S12), during which an index representative of the adaptability of the person is evaluated based on the first value of the person visual behaviour parameter and on a second value of the person visual behaviour parameter associated with the modified state of the environment; and - a determining step (S8), during which an optical parameter of the optical system is determined based on the evaluation of the index representative of the adaptability - a visual display device providing step (S20), during which a visual display device is provided and arranged so as to display a dynamic visual pattern to the person, and - a display step (S22), during which the dynamic visual pattern is displayed on the visual display device to the person at least during the modified state, characterized in that in a step S24 of the visual modification step S6 the dynamic visual pattern displayed by the visual display device to the person comprises a varying blur parameter and/or a varying defocus and/or a varying field of view parameter. - a person visual behaviour parameter providing step (S2), during which a person visual behaviour parameter indicative of the visual behaviour of the person relative to a given state of the environment is provided; - a reference value providing step (S4), during which a first value of the person visual behaviour parameter corresponding to a reference state of the environment is provided; - a visual modification providing step (S6), during which a visual modification of the reference state of the environment is provided so as to define a modified state of the environment; - an evaluating step(S12), during which an index representative of the adaptability of the person is evaluated based on the first value of the person visual behaviour parameter and on a second value of the person visual behaviour parameter associated with the modified state of the environment; and - a determining step (S8), during which an optical parameter of the optical system is determined based on the evaluation of the index representative of the adaptability - a visual display device providing step (S20), during which a visual display device is provided and arranged so as to display a dynamic visual pattern to the person, and - a display step (S22), during which the dynamic visual pattern is displayed on the visual display device to the person at least during the modified state, <EOS>