the eye with respect to a predetermined position based on the relative positions of the spots with respect to the image of the pupil on the detector the simulator also comprises a measurement diaphragm dia situated between the lens l 2 and the beam splitter c 1 and centered on the optical axis z of the different optical elements situated on the optical path of the illumination beam fe the diffusion beam fd and the secondary beam fc the measurement beam fc and diffusion beam fd are substantially focussed at the centre of the measurement diaphragm dia and the illumination aperture apt is off centre with respect to the optical axis z so that only the measurement and diffusion beams are intercepted by the measurement means ma all the other stray light fluxes being deflected away from the measurement means ma the measurement diaphragm makes it possible in particular to filter all the stray light fluxes reflected by the cornea of the eye and any other dioptre situated between the cornea and the diaphragm dia the modulation means md the measurement means ma the emission means si of the measurement light beam fc and all the optical means situated on the path of the secondary beam between the emission means si and the measurement means ma the light source vf and all the optical means situated on the path of the main beam between the source vf and the beam splitter lm 1 the means of emission src of the illumination beam fe and all the optical means situated on the path of the illumination beam between the emission means src and the beam splitter lm 1 are integral and mounted on.