You have the first part right, you would put the center focus on the eye, depress the shutter release halfway and after the lens auto focuses (while keeping the button pressed halfway) you can move the frame to position the subject (your lab) to, let's say, the one third line in the lower left of the frame. Once the subject is where you want it complete the shutter release by pushing it the rest of the way. It is a quick way to focus on what you want then put the focused subject where you want in the frame.
