1.What is strabismus? Simply put, strabismus is the deviation of one eye when both eyes are looking straight ahead (inward, outward, upward and downward deviation). 2.Why does strabismus not occur in normal people? The reason why our normal eyes can turn up and down at will is that the muscles attached around the eyeball pull and move. There are six muscles attached to the outer wall of each eye, each responsible for a different direction of movement, and twelve muscles in both eyes, whose movements are coordinated by the brain. The oculomotor center directly controls and innervates the nucleus of each extraocular muscle movement, and the nucleus sends commands to both eyes simultaneously, through each nerve innervating the extraocular muscles, to reach the corresponding muscles of both eyes, which produce different degrees of contraction and relaxation according to the strength of nerve impulses and different commands. This command and movement is never carried out simultaneously by both eyes, and the magnitude of force and rotation of both eyes is exactly the same, which ensures that both eyes rotate in any direction in a uniform pace without strabismus. This is one of them. Another important factor is to have binocular monovision, which means that in daily life, people look at objects with both eyes, and the images of the objects they see are focused by the refractive system of both eyes and fall on the macula of the retina of both eyes, which stimulates the visual cells in the macula to produce nerve impulses, which reach the visual center of the occipital lobe at the back of the brain through the transmission of the optic nerve of both eyes. The visual center is like a highly sophisticated electronic computer, which overlaps and integrates the received binocular objects to form a complete, single object with stereoscopic sensation. This function is called binocular monocularity, also known as fusion function. The binocular monovision function is divided into three levels according to the degree. Level 1: both eyes can see an object at the same time, also known as simultaneous vision function; Level 2: both eyes can not only see an object at the same time, and when the two eyes see the object position change, in a certain range can still be seen as a complete object, that is, the fusion function; Level 3: not only the binocular image can be fused together, but also to distinguish the near and far depth and stereo shape, that is, stereo vision function. Good binocular monocular function is like an adhesive that holds the binocular position firmly together and cannot be separated, thus ensuring that binocular strabismus does not occur. The normal human eyes rely on this binocular monovision function to constrain, adjust, and maintain normal position at all times. If one eye becomes blind due to injury or disease, the affected eye will gradually tilt outward, which is medically known as disuse exotropia. This is the consequence of losing the function of monocular vision in both eyes. 3.Why strabismus is easy to occur in childhood We often see that most of the patients with strabismus are children, and even those adults with strabismus are mostly suffering from the disease in childhood. According to statistics, the incidence of strabismus in children in China is 1% to 2%, which is indeed an alarming figure. The main reasons are as follows: (1) Children, especially infants, have imperfectly developed binocular monocular function and cannot coordinate the balance of extraocular muscles well, so any unstable factors can contribute to the occurrence of strabismus. The binocular monovision function is gradually developed later in life. After birth, infants can only move their legs but cannot walk; although both eyes can turn, they cannot see objects, not to mention the coordinated movement of both eyeballs and the monovision function. The establishment of this function, like the visual function, is applied in the later life practice, more importantly, repeatedly accept the stimulation of external clear objects, gradually developed and matured. Infants are able to meld their vision in general 2 months after birth, and the establishment of precise melding function lasts until after 5 years of age, while the establishment of stereopsis function is the latest, approaching that of adults at 6-7 years of age. During this period, if the infant suffers from high refractive error and refractive aberration, so that the two eyes see objects of unequal size, the difference in clarity is too great, resulting in optical barriers, can not form binocular monocularity, can cause strabismus. In addition, due to the abnormal development of the retinal macula and macular disease and visual conduction pathway disorders, resulting in sensory impairment, can not form binocular monocularity, can also cause strabismus. Also due to some children originally formed binocular monovision instability, at this time any external factors of stimulation, such as fever, shock, minor trauma, can make this instability ability to weaken or lose and cause strabismus. I often hear some parents of children with strabismus complain that my child’s eyes are slanted by fever or fallen from bed ……, in fact, these are causative factors, the real reason is that the monocular function of both eyes is not firmly established, this situation occurs mostly in children with more fragile nerve types. After the eye strabismus, both eyes can’t see together anymore, which hinders the development of binocular monovision, thus aggravating the development of strabismus, thus forming a vicious circle and making strabismus more and more serious. Therefore, the period before the age of 5 when the function of binocular monocularity is not perfect is the period of high incidence of strabismus in children. (2) Strabismus in children caused by congenital developmental abnormalities. This kind of strabismus is mostly caused by abnormal development of the position of the congenital extraocular muscles, imbalance of strength or paralysis of the nerves that govern the muscles. In some cases, the use of forceps during childbirth can cause injury to the baby’s head and face, or the mother can overexert herself during childbirth to the point where the cranial pressure of the fetus rises, resulting in punctate hemorrhage in the brain, which does not affect the general area, but can cause extraocular muscle paralysis if it occurs in the nucleus that directs eye movements. In addition, there are also genetic factors, one of the parents has strabismus, the child also appears strabismus, this is only a small number of cases, this strabismus is mostly present at birth, but because the infant can not look well, the appearance of performance is not obvious, so parents can not be detected in time, generally found in the birth of 6 months of strabismus is mostly caused by congenital factors, this congenital eye strabismus children, do not have the basic conditions to establish binocular vision, the most harmful to the visual function. It is the most harmful to visual function, and it accounts for a small proportion of childhood strabismus. (3) The characteristics of eye development make children prone to strabismus. Because children have small eyes and short eye axes, they are mostly hyperopic, and because children have large corneal and lens refraction, strong ciliary muscle contraction, i.e. strong regulation, such children need to use more regulation to see near objects, and at the same time, both eyes also turn inward with force to produce excessive convergence, which is most likely to cause internal strabismus, which is caused by strong regulation. This kind of internal strabismus is caused by over-regulation, which is called regulatory internal strabismus. (4) Insufficient control of the eye movement center. This kind of strabismus is not a problem of the eye itself, but is caused by the dysfunctional regulation of the command center. The main manifestation is the imbalance between the inward collecting movement of both eyes and the outward abducting movement of both eyes. If there is too much assembly or not enough abduction, or both, it produces an internal oblique; on the contrary, if there is too much abduction and not enough assembly or both, it produces an external oblique. As in a river race, which side is strong, the eye will run toward which force.