1. A device for determining at least one characteristic for optimizing the wear position of a pair of spectacles on the face of a wearer, said optimizing characteristic being a geometrico-morphological, postural or behavioral characteristic, the device comprising: at least one infrared light source configured to illuminate at least part of the head of said individual; an infrared image sensor configured to acquire an image of at least part of the head of said individual illuminated by the infrared light source; and a processing unit programmed to execute the following steps: locate, on said image, largest reflections of the infrared light source reflected by two lenses of the pair of spectacles and at least one corneal reflection of the infrared light source reflected by one of the two eyes of the wearer, and deduce said geometrico-morphological, postural or behavioral characteristic depending on: the distances separating an observable axis from the centers of the two largest reflections, and the position of said corneal reflection in said image.