How much should a normal person's eyesight be?

The visual acuity of normal eyes is above 1.0. Usually, vision refers to the minimum separable vision of the eyes, not the minimum visible vision. Therefore, the eye chart reflects the minimum visual angle at which the two points of the subject's gaze are separated, that is, the minimum separable visual acuity, or the visual acuity of 1', which can represent the best visual function of the subject.

standard

Many people think that it is normal as long as the vision can reach 1.0 or above. In fact, the vision of 1.0 only shows that some people's vision is normal. Strictly speaking, the standard of normal vision also includes the following:

1. central vision: that is, the vision determined by people looking at the eye chart at ordinary times, including far vision (looking at the eye chart at a distance of 5 meters) and near vision (looking at the eye chart at a distance of 30 centimeters). The performance of hyperopia patients is that hyperopia is better than myopia; Myopia patients are the opposite. Astigmatism patients have poor farsightedness and myopia. When the near and far vision reaches above 0.9, it can be said that the central vision is normal.

2. Peripheral vision: When the eyes look at a certain target, whether the visual range of the non-gaze area is large or small is called peripheral vision, which is often called "canthus". Generally speaking, the peripheral visual range of normal people is quite large, reaching 90 degrees on both sides, 60 degrees above and 75 degrees below. Peripheral vision of patients with myopia and night blindness is poor, and some fundus diseases can also cause peripheral vision decline.

3. Stereo vision: Stereo vision is the highest kind of vision, that is, on the basis of normal vision in the center of both eyes, the distance relationship between objects in space can be felt through the harmony of the two hemispheres of the brain. Some people have normal central vision, but abnormal stereoscopic vision, which is called stereoscopic blindness in medicine.

Although we usually only check the central vision, in medicine, only the central vision, peripheral vision and stereoscopic vision meet the physiological requirements can be regarded as normal vision.

Extended data:

Abnormal vision

1. Myopia

The professional definition is that "distant objects are refracted by the eyeball and focused in front of the retina, rather than forming a clear image on the retina". Myopia is the most common eye disease among children in China, and the high myopia rate in Chinese mainland is much higher than that in other countries and regions. Many eye diseases caused by high myopia are threatening the eyesight and eye health of many children.

2. hyperopia

Nearby objects are refracted by the eyeball and focused on the back of the retina, forming a blurred image on the retina. So hyperopia patients can't see clearly. Myopia in infants is rare. More than 90% of preschool children are hyperopia, most of which are physiological, reflecting the normal development of eyes. 20% ~ 25% hyperopia is pathological, which is the main reason for children's poor eyesight and eye dysplasia.

3. amblyopia

Amblyopia is a disease that seriously affects visual function. It refers to those who have no obvious organic lesions in the eyeball, and their near and far vision is less than 0.8, so they can't drive straight. According to statistics, the number of amblyopia patients has exceeded150,000, which has become a social problem that needs urgent attention.

Protect eyesight

Generally speaking, when human eyes look at things with different distances and brightness, they have certain adjustment ability to make the image irradiated on the retina as clear as possible. However, excessive use of eyes will increase the pressure of extraocular muscles on the eyeball, especially for primary and secondary school students, whose eyeballs are in the development stage and the ball wall is relatively extensive. Excessive use of eyes for a long time is more likely to cause abnormal eyeball development, resulting in refraction of distant light passing through the eyes, and the focus deviates from the retina, resulting in decreased vision. Then, in order to protect your eyesight, you should pay attention to the following points.

1. Rest with your eyes

Pay attention to the habit of using your eyes and rest regularly. The time in front of the computer screen should not be too long. Rest for 5- 10 minutes every 40 minutes, and try to relax your eyes during the interval. Eyes look inward and downward, so when resting, try to look up to the left and up to the right.

When people are resting, they should also exercise their neck and shoulder muscles, because the stiffness and disorder of neck muscles will affect their eyesight. Students should also pay attention to the diet structure, supplement more vitamins A, C and D, and eat more carrots, fruits and seafood.

2. Appropriate light brightness

Poor light brightness (too bright or too dark), especially in the study, work and life with high eye intensity, is the first factor affecting vision. To this end, the state has formulated strict standards for the illumination requirements of different indoor occasions (such as the illumination of reading/writing in the study >; 300Lux), but for ordinary people, this is not so direct to protect their eyesight.

The reason is that ordinary people don't have so much knowledge about the illumination (brightness) of ambient light, and the measurement of illumination requires eye-protection light pens or special lighting equipment. Therefore, it is not easy for ordinary people to judge whether the light is appropriate in their daily study, life and work.

Usually, there are three main situations of poor light:

First, the light of the environment itself is not suitable (such as too bright or too dark);

Second, because the body posture (such as sitting posture or head posture) blocks the light incorrectly, the originally suitable light darkens when it hits the target area;

Third, the light will change (for example, the sunlight in the morning and evening, the natural light on cloudy days or rainy days, and the position or illumination angle of the desk lamp will change). Usually, these situations must be avoided to ensure that the light in the target area is bright and soft, so that the eyes are always relaxed. If you can't judge whether the brightness of the light in the study/workplace is appropriate, you'd better do some tests with an eye-protection photometric pen.

3. Good posture of closing eyes

Close eye posture is another factor that affects the incidence of myopia. Bad habits such as riding in a car, lying in bed and reading at a desk will increase the frequency and range of eye adjustment and should be avoided as far as possible. When using eyes at close range, it is best to rest, sit up straight, and put books about 30cm away from your eyes. If you are watching TV, the distance from the TV is more than 6 times the diagonal of the TV.

4. Shorten the time of using eyes at close range

In addition to pathological factors, most students' vision decline is the decline of eye mediation function. Using eyes at close range for a long time under the condition of poor ambient light is more likely to lead to the decline of eye accommodation function, which in turn leads to the decline of vision, and should be avoided as far as possible. When using eyes at close range, rest every 45 ~ 60 minutes 10 ~ 15 minutes.

References:

Baidu Encyclopedia-Vision (medical terminology)