In the case of different adjustment, parallel light of the outside world, through the eyes of refractive system occurred bending, just focused on the macular central sunken place, this is what eyes in the face.
The majority of children born to, there is a certain degree of farsightedness, we call it "physiological hyperopia". Along with the development of the body, farsightedness degree less and less, finally formed neither hyperopia, also does not have the nearsightedness, we called emmetropia, normally the standard emmetropia eye axis is 24 mm. The ocular axial length and corneal curvature is the matching relation between guarantee when we see something, just focus on niche in the center of the macular, so the things is clear. As the face of excess, the eye is more and more long, the cornea and eye axis matching balance is broken, look at this time the focus will move in front of the retina, when we put a concave lens in front of the eyes, push the focus away from the front of the retina to the retina, see things clearly and also to reach the purpose of correction. So, in layman's terms, myopia is the inside of the eye "tall", the normal eye axis is 24 mm, each 1 mm long, myopic degree of 300 degrees, hypothesis is 1000 degrees of myopia, the eye eye axis 3 mm, longer than the normal children myopic degree is the highest example of more than 3000 degrees, so that his eye axis than normal eye axis more than 10 mm.