With hypotony, pressure within the eyeball becomes dangerously low, leading it to cave in on itself.
It can happen if there is poor production of the natural jelly-like fluid inside the eye, following trauma or inflammation, for example.
Sometimes it's a side effect of eye surgery or certain medications. Without treatment people can go blind.
Before now, doctors have tried using steroids and silicone oil to plump up the eye. But this can be toxic over long periods and doesn't restore much vision.
Even when the cells at the back of the eye used for sight are working, the silicone oil is difficult to see through, causing blurry vision.
The experts from Moorfields decided to try a different approach with something they already had in their cupboard - a low-cost, transparent, water-based gel called hydroxypropyl methylcellulose or HPCM.
It's already used in some types of eye surgery.
But rather than using it as a one-off, the Moorfield's team decided to inject it into the main part of the eye as a new type of therapy.