Literal and metaphysical aspects apply. In karate power is necessary, along with lots of other variables, to achieve effective karate technique. In the practice of karate the "eyes" become a significant factor.
Literally the eyes are required to "see" and thus "assess" before action is involved. This is practiced in kata by "looking or seeing" before committing to a move such as a parry or strike. The "eyes" provide decisiveness in application of the technique. Before the brain can determine which technique or tactic to take it must perceive the problem.
Next, the "eyes" provide a focus for that same technique. Look with determination and resolve at the target, which is the opponent. Put your eyes dead on their shoulder/head area and lock on with the facial and body language that speaks of determination and resolve. The direction of the gaze, eyes, will also provide additional focus toward the target area. Try it, hit the heavy bag while gazing at it directly then try it again with the eyes down, left, right, up at the sky or what ever and see if things don't go hinkey.
The "eyes" also provide stability to the body. Eyes turning toward the target provide a line of embarkation for the body and the weapon of choice so it starts the physical process that provides power, speed, and such to hit. Eyes must point to the opponent and target, in general, to achieve maximum effectiveness.
If you don't put your eyes on target then you lose focus, that of seeing what is occurring and what effectiveness the weapon, hand or foot, etc., will have on the target. It the eyes lose direction and focus then the ability to protect and defend; utilize good solid technique effectively; will suffer.
The eyes truly must see all sides, all sides of the spatial arena, all sides of the opponent, all sides of the effectiveness of action, and all sides of any situation.