Eye muscle spasm causes blurry vision

Why do eye muscles spasm causes blurred vision
1 Main problem is that eye cannot refocus to different distances. With myopia oblique eye muscles are spasmodic. With Hyperopia straight rectus muscles are spasmodic. For example, a person was looking at his laptop at the same distance for a long time without changing position, distance to the screen, and without giving rest to his eyes. Eye muscles got super tired and without conscious rest got into a spasm and cannot relax and to refocus to a different distance.
2 problem is eye muscles pump blood, and our eyes require a lot of blood to provide necessary nutrients and to supply the retina.