An embodiment of the present invention is an apparatus to determine position of an eye that includes: (a) two off-axis, radiation emitter-photodetector pairs, wherein an emitter of a pair is disposed to transmit radiation toward the eye and a photodetector of the pair is disposed to receive radiation...http://www.google.com.tw/patents/US6220706?utm_source=gb-gplus-share專利 US6220706 - Method and apparatus for determining position of an eye
