Does using Oxygen help night vision?
 

I seem to remember from my training days that night vision is impaired by flying at higher cabin altitudes.
As a result I sometimes don the mask and breathe 100 % oxygen for a minute or two shortly before starting the approach at the end of a long night flight. (I also figure this might help with fatigue as well)

Can anyone offer opinions as to wether this practice really helps, and if so, how long might the effect last?

In olden days...unpressurised and when all the instruments were lit with red light...if you inhaled some oxygen at altitude all the lights would get suddenly brighter.

...as the cones came back on line.