Without knowing more, I would say your client has this condition: Strabismus (Crossed or turned eye) Overview Strabismus is a problem caused by one or more improperly functioning eye muscles, resulting in a misalignment of the eyes. Normally, each eye focuses on the same spot but sends aStrabismus - eye muscle imbalance slightly different message to the brain. The brain superimposes the two images, giving vision depth and dimension. Here's an easy way to see how the eyes work together: hold your finger at arm's length. While looking at your finger, close one eye, then the other. Notice how your finger changes position. Even though the images are slightly different, the brain interprets them as one. Each eye has six muscles that work in unison to control movements. The brain controls the eye muscles, which keep the eyes properly aligned. It is critical that the muscles function together for the brain to interpret the image from each eye as a single one. Strabismus must be detected early in children because they are so adaptable. If a child sees double, his or her brain quickly learns to suppress or block out one of the images to maintain single vision. In a very short time, the brain permanently suppresses vision from the turned eye, causing a weak or amblyopic eye. Children may also develop a head tilt or turn to compensate for the problem and eliminate the double image. Unlike children, adults with a newly acquired strabismus problem typically see double. There are many causes of strabismus. It can be inherited, or it may be caused by trauma, certain diseases, and sometimes eye surgery. Signs and Symptoms Adults are much more likely to be bothered by symptoms from strabismus than young children. It is unusual for a child to complain of double vision. Children should undergo vision screening exams to detect problems early. The younger the child is when strabismus is detected and treated, the better the chance of normal vision. The following are common signs and symptoms: *Turned or crossed eye *Head tilt or turn *Squinting *Double vision (in some cases) http://www.stlukeseye.com/Conditions/Strabismus.asp

not sure, maybe he needs to go see his eye doctor and get it checked out

Also, see the related condition Amblyopia, or "lazy eye." I have this, when not focusing on something, one eye will wander off to the side. With either condition, the brain compensates for the loss of visual fidelity, so I usually do not notice it.