The human eye is often compared to a camera. In fact, its function is simpler than that of a camera. It has neither a shutter nor a film, but is at best a monitor. The information collected is transmitted to the brain in real time, and the information enters the brain and is processed in order to virtually create an external space, and the brain is the key part to reproduce the external space. This is the third eye of man, with it, we see the world is three-dimensional. The monitor is generally only one, it can only pass a plane information into the central control system, presenting a flat image. On this image, the target can only be judged by the surrounding reference points, or the size of the object in contrast, to determine the distance from the monitor. The vast majority of animals, in the evolutionary process, have chosen to have two eyes. Evolution to primates, both eyes are facing directly in front, which is ready to judge the distance in a timely and accurate manner. Humans need to judge and operate more accurately, and the processing of information from both eyes is more demanding. The two eyes of Xu Yuan in the studio ophthalmology have only extremely subtle differences when looking at distant objects. But the brain can then use these differences in the process of information processing to virtually create a space that is as consistent as possible with the real space. The ability to do this is known as sound distant stereopsis. The closer the virtual is to the real, the more accurate the actual judgment will be. The more accurate and rapid the judgment, the less chance of operational error. If the far stereo vision function is not sound enough, only one eye plane imaging can be selected, when the person is driving a high-speed car and finds the target in front of him/her, he/she will not be able to judge the distance directly. Need to combine the reference to make a judgment, and so on to make a judgment is too late. Such a person driving, the chances of problems are much more than normal people. When both eyes look close at the same time, the imaging of the two eyes will look much worse. The left eye sees more from the left side of an object, and the right eye sees more from the right side of the object. But such an image is simultaneously transmitted to the brain, which can also make it virtualize a space that is consistent with the object of gaze. The ability to achieve this function is called near-stereoscopic soundness. In this virtual space, the closer the shape and position to the real, the more accurate the judgment will be, and the better the actual ability to operate. We often see that some people are exceptionally good at fine manipulation, while others have difficulty with training, and it is this prerequisite that is at work. Far stereopsis is not sound enough, you can not drive, at least not as a professional driver. Near stereo vision is not sound enough, you lose the ability to do a lot of fine work. Most people with inadequate stereopsis have both impaired distance and near stereopsis, and some have only distance stereopsis or only inadequate near stereopsis. Why would someone have inadequate stereopsis? It starts with the tertiary visual function of the human eye. The imaging of each eye is transmitted to the brain, and if you let this dynamic image stop, it is like a photograph, just a flat image. With it, it means that the first level of visual function is sound. When both eyes look at an object at the same time, the image transmitted to the brain by both eyes is a flat image, and the ability to fuse the two images into one, even if the two pictures have some partial mutilation, will be fused into one image, and the ability to achieve this function is called sound secondary visual function. Of course this image can still only be on one plane. When two eyes gaze at a picture taken in two different directions, and these two different directions simulate exactly the position of the two eyes taken at the same time. When the two eyes each look at these two different pictures, they can restore the space at the time of being photographed, such as accurately reflecting the prominence and depression in the figure, or accurately determining the distance of two objects without reference, etc., it means that the third level of visual function is sound. Each of these three levels of visual function requires the soundness of the previous level of visual function. The first level of visual function is sound in order to have the second level, and the second level of visual function is also sound in order to have the third pole. A sound third level of visual function is the third eye of a person. Not everyone is born with this third eye. The advanced functions that species evolved are actually formed later in life. What the eye sees after birth is not necessarily the real world. It is only after two weeks of life that what is seen gradually begins to correspond to the physical outside world. at 17 months, there are many children who have been able to achieve planar vision close to that of an adult, with sound first-level visual function. However, for a variety of reasons, most children do not get this far yet. Some do not reach this level until after 6 years of age or even later. It is when visual acuity approaches this level that second level visual function begins to build up gradually. In other words, when the primary visual function is perfected, when the secondary visual function is established. Some children, however, do not reach this level of visual acuity for various reasons. The better the visual acuity, the more opportunities there will be to achieve secondary visual function. A basic requirement is that the difference in visual acuity between the two eyes should not be too great, usually no more than two lines on the standard visual acuity scale. Insufficient visual acuity for various reasons, or too great a difference in visual acuity between the two eyes, will not have the conditions to achieve secondary visual function. If the conditions are not sufficient, the formation of secondary visual function will be affected. Another important factor that affects the formation of secondary visual function is eye position. Both eyes must be able to fixate on an object in order to form two flat images that can be fused. The eyes, for different targets near and far, must have the ability to track accurately. The position of the eye is different from the near target, to the far target. Accurate tracking can only be guaranteed if the range of eye movements required to track near and far targets can be achieved. The ability to track accurately in different directions and at different distances creates good conditions for the fusion of the two images, and this range is called the fusion range. The normal fusion range is from -5° to +25°, and a fusion range of 30° is required to ensure accurate tracking of targets near and far and in all directions. If this range is less than 10°, even the originally formed secondary vision function may be lost. Not only is secondary visual function lost, but strabismus may also develop. Of course, many congenital strabismus or strabismus that develops later in life certainly do not reach this normal range of fusion. Without fusion (secondary visual function), there is no condition to achieve tertiary visual function. So, is there nothing that can be done if there is no congenital formation, or if the stereopsis is lost later in life? There are still solutions. One is prevention, and the other is treatment. First, we should pay attention to the early detection of vision changes, and take early measures against refractive errors, refractive aberrations, impingement, ptosis and other unfavorable factors affecting vision, especially the timely correction of binocular vision inconsistencies (difference of more than 0.2); second, we should pay attention to various eye position abnormalities, and through means of lens adjustment, fusion training, surgical correction, 4D training, etc. Second, pay attention to all kinds of eye position abnormalities and ensure normal eye position and fusion range by means of lens adjustment, fusion training, surgical correction and 4D training. For children who are found to have inadequate stereopsis or no secondary or tertiary visual function, we need to determine the cause and extent of the problem and choose the appropriate treatment method. Generally, secondary visual function begins to establish at the age of two and is not perfected at the age of six, making it difficult to have a chance later. Tertiary visual function is formed later, and the sensitive period can last until the age of nine. Generally before the age of 9, there is still a possibility of soundness as long as the conditions are available. Some have formed binocular simultaneous vision and stereopsis before the age of two, but have lost it again due to later strabismus and masking, etc. The time of loss needs to be judged. Usually it is not more than 3 years, and there is still a chance to get it back. This opportunity is precisely the perfected primary visual function and secondary visual function. As long as normal visual acuity, normal eye position and normal fusion range are ensured within a limited age period, the tertiary visual function can be sound. The third eye, which gives us accurate judgment and fine manipulation; provides us with invisible help to ensure safety, smooth work and pleasant life. For various reasons, the function of this eye has not been taken seriously, and many people have unknowingly lost the opportunity to form normally, prevent loss and redeem by treatment, resulting in lifelong deficiencies and even paying the price of life. With the development of science and human progress, we are increasingly required to make fast and accurate judgment and response to the position and distance of moving objects; we are increasingly required to implement accurate arrangement and operation of fine targets. We believe that, through our efforts, we can make people pay attention to stereopsis, protect stereopsis, and perfect stereopsis. Please take care of our third eye.