Internal strabismus occurring within 6 months of age is mostly “congenital internal strabismus” and is usually not combined with obvious refractive abnormalities, and there is no amblyopia if the strabismus occurs alternately in both eyes. Monocular strabismus can be combined with amblyopia. Due to the crossed visual field of both eyes, there can be pseudo-extension limitation. Congenital internal strabismus can be combined with hypotropia, vertical detached strabismus, and nystagmus. The clinical manifestations of congenital internal strabismus include: onset within the first 6 months of life; no obvious refractive abnormalities; monocular strabismus may be combined with amblyopia; large strabismus; pseudo-extension restriction, which can be ruled out by doll’s head test; can be combined with hypotropia, DVD, nystagmus, etc. Diagnostic points of congenital internal strabismus: based on medical history; visual acuity examination focuses on characterization to determine whether there is monocular amblyopia and the ability to gaze; ciliary muscle paralysis agent dilated pupil examination; fundus examination to exclude congenital abnormalities; ocular movement examination to determine whether combined with hypotropia, DVD, nystagmus, etc. Treatment plan for congenital internal strabismus: exclude monocular amblyopia, if there is monocular amblyopia, it should be treated until the visual balance of both eyes; congenital internal strabismus should be treated surgically, and the timing of surgery is 24 months of age; the combination of hypotropia and DVD should be considered accordingly in the design of surgery; after surgery, the 10△ micro-intraocular strabismus should be preserved to facilitate the establishment of peripheral fusion and coarse stereopsis. Discussion on the treatment of congenital internal strabismus: Most domestic and foreign experts in pediatric ophthalmology believe that for congenital internal strabismus, the best age for surgery can be started at 6 months, and the correction of internal strabismus before 2 years of age can lead to a certain degree of binocularity and stereopsis; the correction of eye position is completed before 2 years of age, and fusion function may be formed; after 4 years of age, fusion function is rarely formed. Since infancy is the most sensitive period for visual development and the plasticity of visual function is large, early correction of eye position allows normal use of the strabismic eye and facilitates the cure of amblyopia. Early surgery can also lead to the development of binocular vision after surgery. On the contrary, if surgery is not performed early, the abnormal reflexes may become more and more serious, affecting not only the development of visual acuity, but also the formation of stereo vision. Parents of children with strabismus will suffer more psychological burden. Because of the special characteristics of children’s visual development, large-angle congenital strabismus that occurs early should be operated as early as possible when it is determined that there are no adjustment factors. However, in reality, we perform much less early surgery for children with strabismus than we should. One of the reasons why early surgery cannot be performed is that the success rate of a single operation is very low, putting increased pressure on the surgeon to perform the procedure. Difficulties in patient examination, anesthesia cooperation, and management of combined vertical muscle paralysis. Professor He Yushi, former president of Tianjin Eye Hospital, the originator of modern strabismus treatment in China, pointed out that children 2-3 years old are the “dead center” of strabismus examination, and any functional examination through subjective examination is difficult to perform. The existing methods of measuring strabismus are actually rarely suitable for children of younger ages or for patients with low intelligence. In some children aged 1-2 years, visualization is often the only examination that can be performed. Some patients with strabismus who are mentally retarded are also difficult to measure strabismus with conventional methods. For all these reasons, early surgery for congenital internal strabismus (up to 2 years of age) is not yet commonly performed nationwide. Some hospitals that perform early surgery for congenital internal strabismus emphasize that the surgery should be completed before the age of 2 years, but it often takes multiple surgeries to complete.