By 'boss-eyed' I meant an outward deviation of one eye to cause what is called an exotropic squint. Like Marty Feldman has. With each eye pointing in different directions the person cannot be seeing a single image if both eyes are working.
When I was a kid we had an usher in our local cinema with this condition. When facing a group of us her eyes would each be pointing at a different person. I never knew if she was talking to me or the person 3 feet to my left. Eventually I learned that she was talking to whoever her right eye pointed at, which made me wonder if the right eye had dominance over the left one.
In my student days, if I looked down a microscope for long periods it would give me a headache if I kept my left eye screwed closed while I used my right. Eventually I learned to see through the microscope even though I had both eyes open. If I concentrated on the image through the microscope my brain somehow ignored the image from the other eye which eventually disappeared. I wonder if something similar is happening with 'boss-eyed' people and the image from one of their eyes is dominant over the other.