on an eye tracking system is described application_number US 35647499 A description fig1 is a schematic diagram showing one preferred embodiment of an eye tracking system 100 in accordance with the present invention the eye tracking system 100 includes a position detection device 20 control electronics 50 and a scanner 60 to track the eye movement during a photo refractive surgery the tracking system 100 incorporates with a reference 10 affixed on the eye 11 the position detection device 20 projects an infrared illumination beam 4 on the reference 10 detects the position of the reference 10 and thus detects any displacement of the subject 39 s eye 11 using the positioning signal 26 from the output of the position detection device 20 the control electronics 50 controls the scanner 60 to steer a surgical laser beam 62 to follow the movement of the subject 39 s eye 11 the reference 10 is a retro reflective disk with a diameter of a few millimeters the reference disk 10 should be attached onto the cornea of the eye 11 and located near and outside the surgical area practically the reference disk 10 can be attached onto the cornea simply by moisture the reference disk 10 has a retro reflective surface to enhance significantly the backward scattering of an illumination beam the position detection device 20 consists of an infrared light source 21 a beam splitter.