I used to work in eeg and eye tracking software (for neuro-motor rehabilitation and control of robotic arms). Using gaze for fine control is very difficult and terribly unnatural due to saccades and general scene scanning. One easy way to demonstrate how difficult it is is to have a cursor appear at the point of gaze. You're vision "chases" the cursor away from your target like it does a floater. Controlling anything directly with gaze is very very hard.