One of the hardest parts of the game of golf is that, when we set up to take a swing, our body needs to line up to the left (for right handed golfers) of our target.  The only time we have a chance to put our eyes along the target line is when we putt.  The advantage is that it allows us to have a better perspective of where we are trying to hit the ball.

Imagine trying to shoot a gun by extending our arms and shooting to the right or left and not aiming by looking down the barrel.  To make sure you are "aiming down the barrel," set up to a ball in your putting stance.  Without moving your head take a second ball, place it under your back eye and let it drop to the ground.  Wherever that ball lands is where your eyes are in relation to the ball you are hitting.  Correct the problem by simply moving your stance farther or closer to the ball.