If you're up for a bit of practical experimentation, give this a go. Hold your finger out in front of your face, fix your gaze on the tip and then shake your head from side to side, or nodding up and down. Without you having to think about it, your eyes stay locked on their target by precisely matching the movements of your head. But for some people, maintaining a steady gaze like that is impossible because their eyes rhythmically drift off. Luckily a British team of doctors and eye surgeons have come up with a solution based on an implantable pair of magnets. Chris Smith spoke to Parashkev Nachev from UCL...