hello concerned parent.i have gone through the history of your son and let me put your mind at ease that it would be nothing to cause a significant worry it can be said as an indicator of stress and strain on both the eyes and his brain due to continuous watching he does during a day. i would recommend you,to get his vision and blood pressure checked and a blood routine to assess his hemoglobin levels .i am assuming he has a balanced weight for his height and age. most common cause of a similar symptom presenting at the clinic is usually a case of short sightedness or long sightedness ,which i think is the case here and can be easily corrected with glasses or a case of balance disorder with respect to ear structures associated pathology . in short ,please do the following,keep him well hydrated(dehydration can cause dizziness and blurring of vision),do a vision test,bloodpressure and hemoglobin assessment,ask him to do exercises for his eye muscles and take breaks in between watching if possible i would recommend vertin 8mg twice daily for 3 days,and a multivitamin daily for two weeks. i hope i have given you enough detail and have clarified your doubts.good day