A method of determining a refractive power value characterising an ophthalmic lens for correction of an individual's eye ametropia includes: obtaining first data representative of a refraction value and second data representative of a position of the individual's head with respect to a refraction apparatus when the refraction value was determined; determining the refractive power value as a function of the first data and of a relative position, derived the second data, of the refraction apparatus with respect to a centre of rotation of the eye when the refraction value was determined. A corresponding electronic device is also proposed.