In order for the eyes to work properly together as a team, both eyes must be focused on the exact same target. This is the ideal situation when these visual signals get sent back to the brain where the image gets processed as a clear picture. Think about the eyes as if each one is a camera that takes a picture and sends it back to the brain to get processed, or as if the brain is where the film gets developed. If both images from each camera are going to get processed together, we need both cameras, or eyes, to be focused on the exact same spot.
There is a condition called convergence insufficiency which occurs when both eyes are supposed to come together to focus on a near target but the eyes are not coming together enough. For example, if someone with convergence insufficiency is trying to read a book, they won’t receive the most clear image possible because one eye might be pointing exactly on the target in the book, but the other eye might be pointing more outwards.
Using the camera metaphor, in convergence insufficiency, the cameras are not broken. There still is an image being received from the right camera and another image being received from the left camera. However, when these images go to the brain for processing, they do not perfectly overlap to cause the ideal clear picture and instead there is a misalignment between the images.
Convergence insufficiency is a condition when the eyes are not working together properly as a team. It’s when one or both eyes are not properly moving inwards when trying to focus on a near object. This makes it hard to focus or read and can lead to blurry or double vision. It can also cause headaches or eye strain.