I have very wide set eyes, meaning there's a greater distance between my eyes than the average person. I find that while my eyes do 'track' in synchrony when I look in all directions, they do tend to look ever so slightly 'wonky' when I look left or right in the extreme like in the picture below
I find this happens because the distance between my eyes is so great that the eye furthest away from what I'm looking at (so using the above picture as an example, mary's left eye) that eye must overcome the curve of my face in order to get a view of what I'm looking at, sometimes this requires that eye to point at a slightly different angle to get the same view as the other eye
I hope that makes sense!
