Something i learned the hard way in North Norway might be useful
Obviously its unwise to bury your head inside the sleeping bag while asleep as your breath builds up moisture inside the bag
To begin with i thought a silk balaclava would suffice to keep face warm outside the bag
However, below a certain temp, the worst thing by far is the dread sensation of freezing eyeballs
My tip is to pack a clean unused buff inside your sleeping bag, which you can insulate your eyes with, if need be
The only problem you have left after that is the freezing condensation on the inner tent ceiling, so always pack your bag away before that drip melts onto it in the morning