The author, a medical doctor discusses the relationship between spinal health and blood supply to the head. From the paper (p.310) " I hold the opinion, based on two decades of dedication to the intricacies of the 'Cervical Syndrome' and from a person al experience of 6,000 spinal manipulations done under anesthesia, that concentric narrowing of the visual fields indicates that the child has inferior brain function, which is a serious detriment in both the child's internal and external environment."
R. Frank Gorman. J Manipulative Physiol Ther. 1995 (Jun);18 (5): 308-314