Your son needs to be examined by a paediatric ophthalmologist. If he has a cylindrical power as suggested, then he should be given glasses to correct that power and allow him to see clearly. Apart from this he may need to be evaluated for squint or nystagmus or any muscle imbalance, which may be contributing to it. It is important to get a complete eye examination done by an expert ophthalmologist to make sure his problem is diagnosed and treated correctly; else permanent changes in neck/ posture may occur. A vision assessment and refraction under dilation is also necessary. Please get these tests done.