The timing of strabismus surgery is a question that families ask a lot, and it is also an important thing because the timing of surgery directly affects the final outcome of treatment. This starts with the development of binocular vision in humans. Under normal circumstances, both eyes are able to look at the same visual marker, and the retina of each eye presents a similar object image. The process by which the brain fuses two images from two eyes is what we call binocular vision. The perception of three-dimensionality is stereopsis. Binocular vision is not innate, it is developed in the environment of life. However, it is important to know that binocular vision cells begin to develop in infancy, and if they do not have a chance to develop within 4-5 months, they will not develop again in later life. Dr. David H. Hubel was awarded the Nobel Prize in Physiology for the discovery of binocular vision cells in the primate brain. His work pioneered the modern treatment of congenital cataracts and infantile strabismus What is internal strabismus? Internal strabismus is a condition in which one eye is looking at a visual marker directly in front of it, while the other eye is turned inward nasally and cannot look at that marker at the same time. In most cases, the eye is free to move, and if you block the eye that is looking at the target, the other eye (the eye that was inwardly squinted) will turn outward to the direction of the target. The original eye becomes inwardly slanted. How does internal strabismus affect visual development? If an internal strabismus occurs, especially in infants and young children, both eyes cannot look at one visual mark at the same time. In layman’s terms, the oblique eye does not see the same object as the orthogonal eye, and the brain suppresses the image information received by the oblique eye. There would be no binocular vision or stereopsis as mentioned earlier. More importantly, this monocular inhibition prevents the development of binocular vision cells in the brain. If not treated early and in a timely manner, binocular vision can be permanently lost. After a certain age, even if the eye position is corrected, the brain will not have binocular vision and stereopsis. Therefore, early treatment of internal strabismus is essential to stimulate binocular vision and stereopsis development. Treatment of internal strabismus The principle of treating internal strabismus is to correct the eye position early so that both eyes have a chance to work together, thus establishing binocular vision and stereopsis. In children with hyperopia with internal strabismus, all of the hyperopia needs to be corrected, so that in some cases, the internal strabismus can disappear completely and binocular vision and stereopsis can be regained by continuing to wear glasses; in other cases, the internal strabismus only improves after wearing glasses, but some degree of internal strabismus remains, or wearing glasses does not help improve the internal strabismus, so surgery is necessary to correct the internal strabismus. In some cases, the surgery may be followed by a lens. Surgery to correct strabismus is safe and effective, and some parents, especially grandparents and great-grandparents, often have concerns about the surgery or the risks of anesthesia. In fact, modern anesthesia and surgical techniques are quite advanced, and my hospital performs about 3,000 strabismus surgeries each year, and I have been here for more than 10 years. However, the timing of surgery for internal strabismus is controversial. Dr. Kenneth Wright, a pioneer in this field, has shown that the longer one waits, the worse the outcome of binocular vision. His series of patients underwent surgical correction within 6 months of age, and quite a few at 3 months of age, and 80% of those operated on early achieved binocular vision and advanced stereopsis.