I was learning about Computer Vision Syndrome (CVS) and I noticed that it said that one of the symptoms was "neck and shoulder pain". What confuses me is that CVS (or digital eye strain) seem to be a problem experienced by the eyes. However the neck and shoulders don't seem to be muscles very related to the eyes but rather it seems that discomfort in these would be caused by bad posture rather than anything to do with the eyes. If that is the cause how does eye strain causes discomfort in the shoulders or neck or visa versa?
As anecdotal experience (I know its not scientific evidence but it might be the cause of my confusion), whenever I've personally experienced digital eye strain the major discomfort for me has been from the upper part of my eyes or headaches. I think my neck has felt a bit stiff but I find it hard to believe that there is actually some causation between the two, specially because the neck pain is an order of magnitude smaller.
Does someone with more knowledge on this can explain this phenomenon? If the relation between eye strain and neck pain is real it seems that if I were to look down say and bend my neck for a prolonged period of time, that should cause eye strain or if I over use my eyes (by looking at the same thing for long time, say a screen) then my neck should hurt. But it doesn't seem that any information travels from the eye to the neck to the brain (rather more directly to the brain).
So essentially with my mental model of how things work, it seems that neck/shoulders issue are more common accompanied to computer vision syndrome due because people that look at screens a lot might also have bad habits of posture but it doesn't seem there an actual causation of one to the other. Am I right in this?