With normal vision, both eyes aim at the same spot. The brain then combines the two pictures into a single, three-dimensional image. This three-dimensional image gives us depth perception.
When one eye is out of alignment, two different pictures are sent to the brain. In a young child, the brain learns to ignore the image of the misaligned eye and sees only the image from the straight or better-seeing eye. The child then loses depth perception.
Adults who develop strabismus often have double vision because their brains have already learned to receive images from both eyes and cannot ignore the image from the turned eye. A child generally does not see double.
In some cases, strabismus may result from problems in the brain. Sometimes, a child's brain may not be correctly combining the two images it receives from the eyes. In rare cases, a tumor may affect how the brain processes visual information. Often children experience strabismus as a result of problems that can be easily treated with glasses.