Visual fatigue is the main factor that triggers myopia and causes myopia to deepen. Visual fatigue not only affects vision, but is also a cause of other related diseases, especially those of the nervous system. Therefore, it is very important to understand the causes of visual fatigue and control it. Visual fatigue, also known as eyestrain, is a symptom of eye strain and nervous tension caused by excessive eye use or other causes. Its symptoms include: sore eyes, dry eyes, eye pain, drowsiness, blurred vision and reduced visual acuity. In severe cases, headache and nausea, numbness of the limbs, back pain, and fatigue. In the past, we did not pay much attention to the problem of visual fatigue, thinking that visual fatigue is just a state of fatigue, which can be relieved by relaxing emotionally, taking more rest and using less eyes. In fact, with the increase of study pressure, employment pressure and competition pressure, the problem of visual fatigue has become more and more prominent and harmful, and many people in modern society are often in a subhealthy state related to visual fatigue. The pressure of learning, employment and competition forces people to learn and learn again from childhood, and the lack of rest, sleep and eye overload all contribute to eye fatigue, which causes mental tension, anxiety and irritability, depression, and a subhealthy state of mind and body. The neurological factors caused by visual fatigue make many people mentally unstable. Visual fatigue is different from muscular fatigue. To give a simple example, a person muscle fatigue as long as a break, if reading a book for a long time fatigue want to sleep, because the central nervous inhibition caused by visual fatigue makes people feel paralyzed, despite sitting still and not giving physical strength. This typical visual fatigue is commonly known as injury to the mind. One of the main causes of visual fatigue is excessive eye use, especially excessive eye use at close range. There are four states of human eye use: ① a person at rest looking at a stationary object; ② a person at rest looking at a moving object; ③ a person in motion looking at a stationary object; ④ a person in motion looking at a moving object. The most likely cause of visual fatigue is the first state, which is also the main factor that induces myopia and myopia increase. There are various causes of visual fatigue. In addition to prolonged eye overload. There is an important relationship with the continuous tension of the inner and outer muscles of the eye. The eye muscles of the human eye are: 1) 6 extraocular muscles in charge of eye rotation: 1) upper rectus, 2) lower rectus, 3) inner rectus, 4) outer rectus, 5) upper oblique, 6) lower oblique; 2) inner muscles in charge of pupil opening and closing: iris sphincter and dilator; 3) inner muscles in charge of lens adjustment: ciliary muscle; 4) orbicularis oculi and levator muscle in charge of eyelid opening and closing; inner and outer eye muscles of the eye are like other muscles of the human body. The contraction of the inner and outer eye muscles, like other muscles in the body, can cause tension, fatigue, soreness, and numbness, resulting in sluggish blood flow, bruising, and nervous tension. Three of the 12 pairs of central nerves are associated with the ophthalmic nerve. The causes of eye strain due to eye muscle fatigue are: light, too much light causes strong pupil constriction. If the contraction is strong and continuous, the sphincter of the iris becomes fatigued, causing central nervous tension and resulting in visual fatigue. In addition, strong light contains a lot of harmful rays that can damage the retina of the human eye, especially arc light, which can damage the cornea and lens and cause keratitis and cataracts. In the hot summer, strong sunlight can not open the eyes, the pupil will be strongly contracted to inhibit the central nervous system, coupled with high temperatures, people are prone to heat stroke. If the light is too weak then the illumination of the retina is not enough, the contrast of the object decreases, the visual effort, the optic nerve is tense, or move closer to the object to improve vision with the pupil contraction of the optic near reflex triad, but it will increase the regulation of the lens and increase the fatigue of the ciliary muscle, causing visual fatigue. If there is strabismus or cryptopia, it will increase the tension of the external eye muscles. The eye position of the human eye at rest is on the temporal side facing upward, i.e., the resting eye position, so opening the eye requires the use of the internal rectus muscle of the external eye, and lack of sleep will increase the use of the internal rectus muscle for a long time. If the person has a malpositioned eye or a large cryptopia, more of the external eye muscles will be used. Some adolescents who have external cepheid strabismus or inadequate accommodation and who try to wear progressive multifocal lenses to control the growth of myopia often fail to control the increase in myopia and instead make it increase faster. The balance of the triplet is more severely disrupted in near vision, requiring more internal rectus muscle strength, and therefore causing eye fatigue. The human eye needs to align the visual axis to the object, if too much use of the external eye muscles to obtain binocular vision, it will easily cause eye fatigue. If the external eye muscles are still unable to form normal binocular vision after the force of the external eye muscles, they will give up binocular vision or form a non-normal correspondence between binocular vision, and vision will decline. The most common type is strabismic amblyopia. Refractive error should be corrected, if not, it will easily cause eyestrain. In particular, the balance of the optic-near reflex triad is disrupted, and the coordination between regulation and assembly cannot be properly maintained, which is more likely to cause eye fatigue. If you squint your small eyes are more prone to eye fatigue, because squinting the small eyes when the eyelid muscle tension and fatigue, although you can temporarily improve vision, but can not last. Everyone can do an experiment on their own: squinting at something for a few minutes will cause eye fatigue. This is the result of tension in the eyelid lift and orbicularis muscle. The refractive correction is incorrect, the correction of the spherical lens is insufficient or overcorrected so that the light from 5 meters away enters the eye and the focus is not at the retinal macula, the retina cannot form a clear image, the vision is blurred, you need to force to see clearly or squint to see clearly, it will cause eye fatigue. In particular, overcorrection of myopia causes an increase in lens accommodation, resulting in a deepening of myopia. This has been confirmed in de-focusing experiments on animals. Astigmatism is most common in optometry. Astigmatism is supposed to be present in everyone and can be found in everyone to a greater or lesser extent by corneal topography in clinical practice. Only about 30% of people have astigmatism that is small enough to affect vision, called physiological astigmatism, and as long as astigmatism affects vision it should be completely corrected. The symptoms of astigmatism are double vision, clear in some directions and blurred in others, distortion or distortion of vision, fatigue from long hours of looking, blurred vision, loss of vision, and in some cases, migraine near the temples. Low degree astigmatism can improve vision by different adjustment of the lens in all directions to relieve the degree of total astigmatism. However, the increase in accommodation can cause visual fatigue. High astigmatism is different, no more effort will result in clear vision and the brain will instruct to give up the adjustment, when the retinal macula is not stimulated by the focus of light leading to amblyopia. Astigmatism correction has two parameters: astigmatism and astigmatism axis. If these two parameters are not correct, no focal point can be formed on the retina, which will easily cause visual fatigue. Therefore, the correction of astigmatism is very important. In clinical practice, we often encounter patients who think they have migraines or suspect brain tumors, but after various tests, the cause cannot be found. After refractive examination, the patient was found to have refractive error and the symptoms disappeared after prescription of glasses. After understanding the causes of visual fatigue, we can make targeted measures to reduce visual fatigue, that is, to reduce the conditions of excessive eye use and eye muscle tension: 1, pay attention to eye hygiene, do not use the eyes for a long time, close; 2, pay attention to eye posture do not lie down to read, correct writing posture; 3, pay attention to the intensity of light when reading and writing; 4, ensure sufficient sleep time; 5, balanced intake of nutrition 6, exercise regularly to enhance physical fitness; 7, correct optometry, timely maintenance of glasses, to ensure that the glasses are clear and transparent; 8, regular review of the use of the prescription lenses to ensure the correct position of the lens and the eye; 9, often to the wilderness to breathe fresh air, relax, reduce all kinds of stress; 10, when the eyes feel red, swollen and painful should be promptly checked.