(See also Overview of the Cranial Nerves Overview of the Cranial Nerves Twelve pairs of nerves—the cranial nerves—lead directly from the brain to various parts of the head, neck, and trunk. Some of the cranial nerves are involved in the special senses (such as seeing... read more .)
Palsy refers to paralysis, which can range from partial to complete.
Conjugate gaze palsies affect horizontal gaze (looking to the side) most often. Upward gaze is affected less often, and downward gaze is affected even less often. People may notice that they cannot look in certain directions.
There are no specific treatments for conjugate gaze palsies, but the cause is treated if possible.
Horizontal gaze palsy
The most common cause of horizontal gaze palsy is damage to the brain stem Brain stem The brain’s functions are both mysterious and remarkable, relying on billions of nerve cells and the internal communication between them. All thoughts, beliefs, memories, behaviors, and moods... read more 
, (the lower part of the brain) often by a stroke Ischemic Stroke An ischemic stroke is death of an area of brain tissue (cerebral infarction) resulting from an inadequate supply of blood and oxygen to the brain due to blockage of an artery. Ischemic stroke... read more 
. Often, the palsy is severe. That is, moving the eyes past the midline to the opposite side is very difficult. People with milder cases may have problems looking at one thing for very long. They may also have nystagmus. (Nystagmus is involuntary, repetitive fluttering movements of an eye in one direction, then slow drifting of the eye in the other direction.)
Palsies can also be caused by damage to the front part of the cerebrum, usually by a stroke. The resulting palsy may not be as severe as that caused by damage to the brain stem, and symptoms often lessen with time.
Vertical gaze palsy
Vertical gaze decreases gradually with age, but vertical gaze palsy is more severe than age-related changes. Usually, upward gaze is affected.
The most common cause of vertical gaze palsy is damage to the top part of the brain stem (midbrain), usually by a stroke or tumor.
In upward vertical gaze palsies, the pupils may be dilated. When people with this palsy look up, they have nystagmus. That is, their eye rapidly moves upward, then slowly drifts downward.
Parinaud syndrome is an upward vertical gaze palsy. It usually results from a pineal tumor Pineal Tumors Types of brain tumors (see also table Some Tumors That Originate in or Near the Brain) can vary in their characteristics, such as their location, the people they affect most often, and the symptoms... read more pressing on the area of the brain that controls vertical gaze or from a stroke. People with Parinaud syndrome tend to look down. Their eyelids are pulled back, and the pupils are dilated. They may also have nystagmus.
If downward gaze but not upward gaze is impaired, the cause is usually progressive supranuclear palsy Progressive Supranuclear Palsy (PSP) Progressive supranuclear palsy is characterized by slow movements, muscle stiffness (rigidity), problems moving the eyes, and a tendency to fall backward. Progressive supranuclear palsy progresses... read more .
