When you say slouched, do you mean slouched over his desk looking forwards, or slouched back down in his seat? The first position would have put his head slightly into extension and, for those with instability, often the chin is well forwards. At one point, following my injury, if my chin was forwards and I rotated my head to my left, it would send my pupils into all kinds of shapes, so from experience I know that there is some connection there, to the eyes, with them being affected.