A CCD camera is supported by a guide rail in such a manner that the camera is be reciprocally movable in the direction toward an opening of a left main unit. When a motor is rotated, the rotation is transmitted to a rack via gears, thereby moving the CCD camera. ...http://www.google.com/patents/US5822033?utm_source=gb-gplus-sharePatent US5822033 - Diagnostic apparatus for measuring pupil size and/or iris area of an eyeball 
