1. A system for selectively disabling a surgical instrument operating in a surgical site of a region of interest of a living subject, wherein the surgical instrument has a distal end portion and is operable by a surgeon during a surgery, comprising: (a) an eye-tracking device operatively coupled with the surgical instrument for intra-operatively tracking the visual line of sight of the surgeon and a location of the distal end portion of the surgical instrument in the region of interest of the living subject, respectively; and (b) a controller operatively coupled with the surgical instrument and the eye-tracking device, respectively, and configured to perform during the surgery the steps of: (i) determining an angle between a visual path connecting a predetermined point of the eye-tracking device and the distal end portion of the surgical instrument in the region of interest of the living subject and the line of sight of the surgeon; and (ii) generating a signal to disable the surgical instrument when the angle is within a predetermined angle, but not outside of a boundary of the surgical site of the region of interest.