Abstract: Disclosed is a method for determining an optical system intended to equip a subject, the method including the steps of: —determining an index of sensitivity indicating, when the subject is placed in an environment including surfaces and/or borders forming globally a geometry of this environment; and landmarks associated with specific locations within the environment, how the subject relies on the global geometry and/or on the local landmarks of the environment to navigate within the environment; and —determining the optical system based on this index of sensitivity. The invention also relates to an ophthalmic lens and to an ophthalmic filter determined by such method.