Determining an optical property of a sample having an illumination of a surface of the sample with the aid of a light beam, so as to form, on the surface of the said sample, an elementary illumination zone, corresponding to the part of the said surface illuminated by the said sample. A detection of N optical signals, backscattered by the sample, each optical signal emanating from the surface of the sample at a distance, termed the backscattering distance, from the said elementary illumination zone, N being an integer greater than or equal to 1, so as to form as many detected signals. A determination of at least one optical property of the sample, by comparison between: a function of each signal thus detected and a plurality of estimations of the said function each estimation being carried out by considering a predetermined value of the said optical property, characterized in that during the said detection step, at least one backscattering distance is less than 200 pm.