Originally Posted by
wonky donky
All that Robin has said, the condition is called "greying out" & the biggest cause is over long aiming.
If your in the aim for longer than 5-8secs then you may well experience a problem, more so as we get older.
Top shooters already have the aiming mark in the near centre of the forsight before they even look through the rearsight thus cutting down on aiming time. They also look away if the aiming process starts to take too long & try again after giving the eyes a short rest by looking at a far object without breaking the position.