An eagerly awaited and controversial clinical trial to 'wind back the clock' on aging cells in the eye and restore them to a more youthful state has officially begun.

The gene-therapy trial aims to treat glaucoma by rejuvenating cells in the optic nerve. Plus, the mystery of how things freeze and encouragement to go out into the sunlight.

The first participant has been treated in a landmark clinical trial of cellular reprogramming, which aims to rejuvenate ageing cells.