Poor Tracking With Right Eye, Does Not Respond To Stimuli, Born With Torticollis, Being Treated For It Successfully. Causes For Eye Lagging ?

Question: our son is 11.5 month old. at 6 months, we noticed that his right eye had a tendency to lag behind. in other words, it tracked objects more slowly than his left eye, particularly when he is looking down at an object and then looks up. our pediatrician referred us to an eye doctor, whom we visited with at 6 months. at that time, we were told everything looks fine. today we went back for a follow up visit and the eye doctor said he did not see the right eye lagging that we described. however, he expressed surprise that our son did not respond as expected to the stimuli he used to conduct various tests (bright lights, animated videos, talking dolls, etc...) and said he was a bit behind his peers in that category. we were told to comeback in six months, but to call if we notice the right eye lagging before then. we are now very concerned and want to know if there is a bigger issue going on here as our son was born with moderate torticollis. he continues to have physical therapy and for the most part, the tilting has corrected itself and it is barely noticeable. the eye doctor thinks torticollis has nothing to do with the eye lagging, but we are not so sure.