Over a long period of time, the stress and strain
on the visual system causes Vertical Heterophoria Syndrome (
VHS). VHS can cause headaches, usually in the front of the face or in the temples. VHS can also cause a feeling of being disoriented, lightheaded or dizzy. As the muscles strain, they become fatigued, causing the image seen by one eye to not continuously overlap the image seen by the other eye. In other words, fusion is no longer continuously maintained.