The way that our 2 eyes move together in absolute sync, and can move both so smoothly and so quickly is amazing.
These properties aren’t coincidence, there are some very cool design features that make our eyes ‘track’ together like they do.
When we look towards something there are groups of nerve cells in the brain that fire signals to both eyes exactly the same amount. When you look sideways to catch a ball those cells send increased signal to one muscle in each eye, the muscle that will quickly shift the eyeball to the new position. The signal is perfectly balanced and both eyes move the same amount.
Eye muscles are very thin and long. They work like little leashes or control strings coming from well behind your eye. When a muscle tightens the eye rotates in that direction. These muscles are all working all the time, constantly kept in balance with each other.
The tissue around the eyeball and muscles is a bit like a lubricant, which means the eyeball has no resistance to movement. Very small changes in the tension on the muscles or position of where a muscle attaches to the eyeball rotates it. So when an eye surgeon shifts the point of attachment of a muscle by a few millimetres the eye is realigned. Since both eyes always move together by the same amount in any direction this new alignment works for any direction the eyes look in after the surgery.