palsies affect gaze of both eyes either toward or away from the midline of the body. Horizontal gaze palsies are generally caused by a lesion in the brain stem and connecting nerves, normally in the pons. Progressive scoliosis Horizontal gaze palsy with progressive scoliosis (HGPPS) is a very rare form of conjugate gaze palsy, appearing only in a few dozen families worldwide. HGPPS prevents horizontal movement of both eyes, causing people with this condition to have to move their head to see moving objects. In addition to the eye movement impairment, HGPPS is coupled with progressive scoliosis, although eye symptoms usually appear before scoliosis. HGPPS is caused by a mutation in the ROBO3 gene, which is important in cross-over of motor and sensory signals, preventing horizontal eye movement. In addition to the mutation, lesions in the midbrain and pons are common. This can also include a complete absence of a formation in the pons, the facial colliculus, which is responsible for some facial movements. The cause of progressive scoliosisin HGPPS and why HGPPS does not affect vertical gaze is unclear. Progressive scoliosis is normally treated with surgery. Vertical gaze palsies Vertical gaze palsies affect movement of one or both eyes either in upward direction, up and down direction, or more rarely only downward direction. Very rarely only movement of one eye in one direction is affected. Vertical gaze palsies are often caused by lesions to the midbrain due to a stroke or a tumor. In the case that only downward gaze is affected, the cause is normally progressive supranuclear palsy. Treatment There is no treatment of conjugate gaze palsy itself, so the disease or condition causing the gaze palsy must be treated, likely by surgery. As stated in the causes section, the gaze palsy may be due to a lesion caused by stroke or a condition. Some of the conditions such as Progressive supra nuclear palsy are not curable, and treatment only includes therapy to regain some tasks, not including gaze control. Other conditions such as Niemann-Pick disease type C have limited drug therapeutic options. Stroke victims with conjugate gaze palsies may be treated with intravenous therapy if the patent presents early enough, or with a surgical procedure for other cases. Prognosis The prognosis of a lesion in the visual neural pathways that causes a conjugate gaze palsy varies greatly. Depending on the nature of the lesion, recovery may happen