The visual process of perceiving a single object when both eyes look at it simultaneously is known as binocular vision, also known as binocular monocularity. Binocular vision is governed by a series of extremely delicate, flexible and coordinated physiological functions, in addition to the well-developed tissue structure of the human eye. When both eyes look at an object at the same time, the object falls on the corresponding part of the retina of both eyes, and the stimulus it generates forms a nerve impulse that reaches the brain center along the visual afferent pathway, and the visual center of the cerebral cortex analyzes and organizes these visual signals from both eyes to become a complete, three-dimensional perceptual impression. With binocular vision, human beings can acquire not only the concept of shape, size and color of objects, but also the concept of spatial orientation of objects, and can correctly determine the relative position between themselves and the objective environment. This function plays a very important role in human evolution and physiological development. Binocular vision is superior to monocular vision, not only because it has the effect of superimposing the two eyes, lowering the visual perception threshold, expanding the visual field, and eliminating the physiological blind spot of one eye, but also because it has three-dimensional vision, which makes the subjective visual space more accurately reflect the actual external space. Stereo vision makes hand-eye coordination more accurate. In modern life, whether for work or leisure, having good stereoscopic vision is of great importance. Under normal circumstances, when we look at an object, the visual axis of both eyes must converge, that is, point in the same direction, so that the visual image of both eyes will fall on the central fossa, that is, on the corresponding point of the two eyes, then the object can be seen as a single. In everyday life we do not realize that we are seeing with two eyes, as if the object is seen by one eye. Thus we can see the two eyes as one organ, and we can also represent this organ with an imaginary eye, and call this imaginary eye the central eye (Cyclopcan eyc), which is located right in the center of the forehead. If the two retinas are overlapped so that the two central fossae and the corresponding parts coincide. Then this overlapping retina represents the retina of the hypothetical central eye. The central eye is an important basis for our spatial orientation of vision. The direction of vision is not determined by either the left eye or the right eye, but by taking the central fossa of the central eye as the center of one’s body and projecting the direction line forward as the front of vision. The directional line in front of the central eye is the basis for our judgment of direction. Each pair of corresponding points on the retina of both eyes has a common visual direction, and they are located to the left or right of the visual direction line of the central eye, respectively. In binocular vision, the units on the retinas of both eyes that receive stimuli and produce the same visual direction are the corresponding points of the two retinas. Thus, the central fossa of the two eyes is the corresponding point of the retinas of the two eyes, and the other units in the two retinas with the same visual direction are also corresponding points. The visual direction of the central fossa is the primary visual direction, which varies with the position of the eye, and this direction is directly in front of the vision. The visual directions of all other corresponding points of the retina are referenced to this primary visual direction to determine whether an object is to the left or right of the visual front. Thus we rely on the visual direction of the central eye to determine the spatial location of objects. If stereo vision and depth perception are lost, it is stereo blindness, and many jobs requiring fine vision cannot be involved, such as driving transportation, etc. Some occupations, such as airline pilots and surgeons, require good stereo vision. Simultaneous binocular vision in humans begins 1.5-2 months after birth, and the sensitive period of binocular vision development is 3-5 months after birth, with a peak in binocular vision development at 1-3 years of age, and continues to develop until 6-9 years of age. Therefore, stereo vision health care for toddlers and children plays a key role in ensuring that children can develop normal binocular vision, establish a central eye, and develop sharp stereo visual acuity. It is also important to study the binocular visual function of children for early detection and early treatment of strabismus and amblyopia.