| ■ What is nearsightedness? ■ | |
| Nearsightedness is in the state where a distant thing cannot be seen clearly, and it can fade and be seen. | |
|
The upper row expresses an ordinary state (stigmatism). |
正常な場合:In the case it looks normally |
|
Nearsightedness has two patterns and the one is that lens (crystalline lens) is in a still thick state compared with stigmatism. As anime shows, refraction becomes strong for a thick lens and the image of the triangle which is far away is made before the retina. On the retina, it becomes the image which faded. |
|
|
The 2nd pattern is the cases where a vitreous body becomes long forward and backward. As anime shows, lens is the same as stigmatism, and the vitreous body is extended forward and backward, that is, an eye axis is in a long state. Therefore, a triangular image does not reach the retina. The image in the retina fades. If we see continue seeing a nearby thing, a lens becomes thick. Therefore, if a long distance is seen after the lens has become thick, seeing the neighborhood, a thing will become hard to see. |
|
|
False nearsightedness will be in such a state. If an eye is rested, it will return to the original state. It seems that however, the muscular group which adjusts a lens remains becoming it tense when the state where a lens was thick continued for the long period of time. It seems that a lens remains thick now. |
|
| In the case of many nearsightedness, that an eye axis of the 2nd pattern is long seems to be a cause. | |
Then, what is it like that an eye axis becomes long? From the first, the length of an eye axis is 17-18 mm for a newborn infant. It is extended rapidly in several months, it is 22.5mm at the age of three, and after that it grows up every 0.1 mm by 14 years old every year , and it is said that it is set to 23-24 mm by an adult. The form of an eyeball is a form like a ping -pong ball. A size is about somewhat smaller than a ping -pong ball and somewhat larger than a ten-yen coin (23mm). In other animals, the eye ball of a rabbit is the same size of a human being, and the ones of a cow and a pig are larger than the ones of a human being. If an eye axis becomes long at 23-24 mm or more, a thing as showed by anime will happen. Why will it become long? This is a difficult question. |
|
 |
|
