A method for determining at least one behavioural, postural or geometric-morphological characteristic of a person wearing spectacles, the method includes the steps of: a) illuminating the wearer's head using an infrared light source (220, 230, 240), b) acquiring an image of the wearer's head using an infrared image sensor (210)； c) in the image, locating reflections from the infrared light surface, reflected by the two lenses of the spectacles； and d) using a computation unit (250) to deduce the required characteristic as a function of the positions of the reflections in the image.
