"Vision mode" is a difficult new mode that can be applied to all maps, this, whilst it isn't a map or an actual game-mode itself, it is something that makes gameplay more difficult and interesting, fortunately it gives a slight increase to loot drop chances.
There are 3 variations of "Vision mode" with each one of the 3 giving more of a loot bonus than the last, but this comes at the cost of greater difficulty.
Turrets can still work as normal however in each version.
The standard version makes it so that you can't see enemies behind walls or anything like that, the enemy has to be in a relatively realistic field of view around you, it also disables the minimap unless the enemy is in the field of view.
The advanced version is pretty much the same as the standard, however rather than seeing enemies in a field around you, the vision is more like a cone, simular to an actual person's field of view.
The brutal difficulty is just like advanced however rather than just blocking out enemies outside of the field of view, it blocks out EVERYTHING. So it acts even more like a real field of view, with anything outside of your field of view just looking like complete darkness, this can be incredibly hard to deal with in most situations.
In all 3 modes but especially so for Advanced and Brutal they're very difficult to deal with in both wide open and cluttered maps. In wide-open maps you may be able to see more but it gives more areas for zombies to approach from, and in cluttered maps there's a lot of things to block your vision.