The method includes the steps of: a) illuminating the pupil of an eye of a subject by a light source of a portable electronic device, the light source being formed by a lighted area displayed on a screen of the portable electronic device; b) acquiring a picture of the pupil of the eye of the subject by an image-capture apparatus of the portable electronic device, the picture including an image of the reflection of the light source on the retina of the eye; and c) determining a refraction feature of the eye taking into account at least a geometrical feature, a positional feature or an intensity distribution of the image of the reflection. An associated portable electronic device is also described.