Strabismics have problems keeping their heads straight. I have talked about this before, and so has Lynda. We are forever tilting our heads.
I think it has something to do with how we internalize our midline. If you ask someone where the midline of their body is located, they will draw a line down the middle of their body, from nose to belly button. Both strabismics and non-strabismics know objectively where their physical midline is located. But in everyday life, strabismics tend to operate from where they subjectively feel like their midline is.
It's my theory that your subjective midline is determined by the center of your visual field. Normal-eyed people have a unified visual field, and the center of that visual field conveniently lines up with the center of the body.
Strabismics only use one eye, and the center of that visual field becomes their subjective midline. Unfortunately, their subjective midline doesn't line up with their actual midline. The strabismic operates from what feels like his midline, and the result is head tilting and weird posturing. A stabismic may appear as if he has angled himself oddly to look at you, but he has really only centered you in his visual field.
This may also explain why I am duck-footed. I'm an alternating strabismic, and my feet have pointed outward toward my two alternating midlines.
As Dr. Getz explains in Strabismus and Amblyopia, "The problem of strabismus is not strictly an ocular or eye muscle control problem. Most strabismics are strabismics from head to toe."