An optical instrument includes: a collimation element (30) having a focal distance; a point light source (25-27) with a wavelength of between 700 and 1000 nm and a diameter less than or equal to a fiftieth of the focal distance, placed at a first focus of the collimation element, so that the light becomes a beam (20) of collimated light; a backscatterer (12); a support for receiving an ophthalmic lens (14), with the collimation element, support and backscatterer being placed so that the beam of collimated light encounters the lens location (15) where micro-etching is present; an image analyzing element (32) and an image capture element (31) linked to the analyzing element and including an objective lens (35) placed at a second focus of the collimation element, which objective lens is developed to provide the analyzing element with images of the backscatterer in order to identify and locate the micro-etching.