The biggest feature of human eyes is the ability to recognize details, which is often expressed by the resolution of viewing angle, called vision. The standard of expressing vision is the opening angle of the smallest character that human eyes can recognize, and the vision of normal people is above 1.0;
Generally speaking, vision refers to the minimum separable vision of the eyes, not the minimum visible vision, so the eye chart reflects the minimum visual angle separated by the two points of the subject's gaze at the target, that is, the minimum separable vision.
Vision is divided into central vision and peripheral vision. Central vision reflects the function of macular fovea, which is the ability of human eyes to identify the shape and size of external objects. Peripheral vision is also called peripheral vision.
Extended data:
When human eyes look at things with different distances and brightness, they have certain adjustment ability to make the images on the retina as clear as possible. However, excessive use of eyes will increase the pressure of extraocular muscles on the eyeball;
Especially the eyeballs of primary and middle school students are in the development stage, and the walls of the eyeballs are relatively extensive. Excessive use of eyes for a long time is more likely to cause abnormal eyeball development, which leads to the deviation of the focus of distant light from the retina after refraction of eyes, resulting in decreased vision. There is a decline in vision (such as myopia).
References:
Baidu encyclopedia-vision