Conjugate gaze palsies are neurological disorders affecting the ability to move both eyes in the same direction. These palsies can affect gaze in a horizontal, upward, or downward direction. These entities overlap with ophthalmoparesis and ophthalmoplegia. Signs and symptoms Symptoms of conjugate gaze palsies include the impairment of gaze in various directions and different types of movement, depending on the type of gaze palsy. Signs of a person with a gaze palsy may be frequent movement of the head instead of the eyes. For example, a person with a horizontal saccadic palsy may jerk their head around while watching a movie or high action event instead of keeping their head steady and moving their eyes, which usually goes unnoticed. Someone with a nonselective horizontal gaze palsy may slowly rotate their head back and forth while reading a book instead of slowly scanning their eyes across the page. Cause A lesion, which is an abnormality in tissue due to injury or disease, can disrupt the transmission of signals from the brain to the eye. Almost all conjugate gaze palsies originate from a lesion somewhere in the brain stem, usually the midbrain, or pons. These lesions can be caused by stroke, or conditions such as Koerber-Salus-Elschnig syndrome, Progressive supranuclear palsy, Olivopontocerebellar syndrome, Niemann-Pick Disease, Type C, or envenomation such as from a scorpion sting. Mechanism The location of the lesion determines the type of palsy. Nonselective horizontal gaze palsies are caused by lesions in the Abducens nucleus. This is where the cranial nerve VI leaves on its way to the Lateral rectus muscle, which controls eye movement horizontally away from the midline of the body. The cranial nerve VI also has interneurons connecting to the medial rectus, which controls horizontal eye movement towards from the midline of the body. Since the lateral rectus controls movement away from the center of the body, a lesion in the abducens nucleus disrupts the pathways controlling outward movements, not allowing the right eye to move right and the left eye to move left. Nerve VI has the longest subarachnoid distance to its target tissue, making it susceptible to lesions. Lesions anywhere in the abducens nucleus, cranial nerve VI neurons, or interneurons can affect eye movement towards the side of the lesion. Lesions on both sides of the abducens nucleus can cause a total loss of horizontal eye movement. One other type of gaze palsy is a