What is NASA astronaut Peggy Whitson doing to poor French astronaut Thomas Pesquet on the International Space Station?

Pesquet explains:

For International Space Station research Peggy Whitson was measuring the pressure of my eyes (no easy task in weightlessness) for the Fluid Shift experiment. We do a lot of research into our eyes because some astronauts suffer a change in visual acuity during and after spaceflight but fortunately it does not last… at least that is what they told me before launch! ;)

It’s been known for a while that spaceflight affects eyesight so research is being conducted to understand what’s going on.