At close range everyone is a pretty good shot, so it is critically important to get the first hit to stop the fight. The pistol presentation must be smooth and the shot must be delivered just as soon as the sights are on the target. Making good use of your visual ability has a lot to do with how fast this center hit is delivered.
Once you determine that an individual is an immediate threat, your eyes should never leave him. It is a horrible mistake to look down at your holster, your gun, or anything else, during your pistol presentation. Not only should your eyes stay on the threat, but they should focus on the exact spot that you intend to deliver your shot to. Imagine a man wearing a shirt with two pockets, with one of his shirt buttons centered between those two pockets. That is as good an aiming point as you will find. Even if he is wearing some other kind of garment, you now know the spot where your shot should go. You can visualize it and focus on it.
We should visualize the vital zone (the upper part of the thoracic cavity) in a three-dimensional manner. So, should the suspect move and turn during his attack, we still know where the vitals are and where we need to deliver a fight-stopping shot. At the completion of our pistol presentation, we bring the pistol to our eyes. We don't take our eyes to the pistol.
Just before we break our shot, our focus goes to the front sight. However, we never stop seeing the threat. As the attacker goes down, we follow him with our eyes and the gun muzzle. Again, we keep our eyes on him until we are certain that he is no longer a threat. At that point, and only at that point, do we look at the area around us to see if there are other threats that need our attention.
Our eyes are wonderful tools and we should let them work for us, especially when we are under a violent criminal attack. Our eyes identify the threat, they focus on the exact spot that we will deliver our shots to, and they continue to evaluate the threat until the encounter is over. It should be part of our defensive plan and it should be part of our defensive practice.