The case where the focus connects it from the retina forward is said, and the child of the near-sightedness has increased with the near-sightedness compared with old times at the present age. Being given as the reason enthuses about the television, video games, and the personal computer, etc. for as much as one hour and as many as two hours.
Of children, because the crystalline lens is soft, the focus is matched to the long way well while even shortly changing the thickness of the crystalline lens. However, the television is seen for a long time in a short distance or is read without separating the book by 30 centimeters or more in a dark place, and the crystalline lens comes not to return easily to former thickness by losing flexibility. The unbalance is caused in the refraction of light when such a state continues, and the distance in which the focus is connected shortens gradually. It will be able to be said that it is in the environment that becomes a near-sightedness easily recently though there is a part of the inheritance in the near-sightedness, too.
It is important to put the rest of ten minutes by seeing the distance to relax eyes when it keeps seeing the nearby one for 30 minutes to prevent this. However, it is necessary to note it because it becomes easy to become a near-sightedness if it is repeated to put a strain in eyes even if one rest every 30 minutes is put every day.
It is effective in the prevention also such as taking a good meal of the nutritional balance, doing a moderate movement outside to others, and applying the custom of seeing the distance of the near-sightedness.