@mdstevens0612 ...a change in focus in the dominant eye. Therefore, they wear an occluder over the non-aiming eye instead to reduce distraction without the need to close that eye. However, not everyone needs that. One can train to just ignore the input from the other eye. Or if you don't see very well with it anyway, you can more easily focus on the dominant eye and thus don't need to block the other (that's the case for me).