Abstract: The technical field is that of instruments for medical examination of ducts in the body by visual examination using an illuminating device, and also making it possible, where appropriate, to act surgically in said ducts. The invention provides an instrument intended mainly for locating veins and simultaneously removing them, the elongate central body of the instrument having at least one optical fiber connected at one end to a light source; according to the invention, said instrument is such that said optical fiber is a fiber that diffuses light laterally and radially relative to its axis XX', and it is provided at its distal end that is not connected to the light source with a transparent head having an outside diameter greater than that of said central body.