A method for determining optical power of an optical lens to be placed in front of an eye of a person, the method including: a first distance determining during which a first gazing distance is determined, which is the distance between the eye of the person and a first visual stimulus when the person gazes at the first visual stimulus in a given gazing direction with a first level of attention: a second distance determining during which a second gazing distance is determined, which is the distance between the eye of the person and a second visual stimulus when the person gazes at the second visual stimulus in the given gazing direction with a second level of attention different from the first level of attention; and an optical power determining during which the optical power adapted for the person is determined based on the first and second gazing distances.