1. Movement 

We are in constant movement, as are our eyes. A normal eye is moving all the time; it can make 3,600 saccadic movements per minute The more relaxed your eyes are, the more they move, and consequently, you can see more clearly. In fact, fewer eye movements is common in people with poor eyesight.

Also, it is important to consider the apparent or opposite movement. This is the perception of movement of static objects when we move our eyes. It is easier to understand if you think of the view from a train window. You perceive  the landscape going by, but you know the only movement is the train (with you inside). There are apparent movements all the time in our life, and developing an awareness of this and your peripheral vision helps to relax your eyes. 

2.  Central fixation or centralization 

Central fixation means we see more clearly in the center of our visual field. This is the fovea centralis. Often, people with poor eyesight try to see all their visual field perfectly clearly at the same time, but that isn’t possible because our vision doesn't work like that. A normal eye is moving all the time depending on its interest, focusing the images in the fovea centralis, so we can see what we are looking at clearly, and we see the surrounding area (peripheral vision) less clearly.  

3. Relaxation

A relaxed mind and body relaxed means relaxed eyes. This is a different kind of relaxation from lying down on the beach or the sofa when we might allow our minds to wander. It's a conscious and active awareness.  

Normal eyes look effortless with no tension. This allows the eyes to move freely from one point of interest to another.

These three principles are intrinsically linked:

• There is no movement without relaxation and central fixation.
• There is no relaxation without movement and central fixation.
• And there is no central fixation without relaxation and movement. 

Also, there are more principles to consider: 

• Memory: Recalling visual memories improves our eyesight.
• Imagination: Imagining visions in detail develops our ability to see more clearly.