|Conjugate gaze palsy|
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.
The term gaze is frequently used in physiology to describe coordinated motion of the eyes and neck. The lateral gaze is controlled by the paramedian pontine reticular formation (PPRF). The vertical gaze is controlled by the rostral interstitial nucleus of medial longitudinal fasciculus and the interstitial nucleus of Cajal.
Ophthalmoparesis refers to weakness (-paresis) or paralysis (-plegia) of one or more extraocular muscles which are responsible for eye movements. It is a physical finding in certain neurologic, ophthalmologic, and endocrine disease.
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.
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, or Niemann-Pick Disease, Type C.
The midbrain or mesencephalon is a portion of the central nervous system associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation.
The pons is part of the brainstem, and in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum.
A stroke is a medical condition in which poor blood flow to the brain results in cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both result in parts of the brain not functioning properly. Signs and symptoms of a stroke may include an inability to move or feel on one side of the body, problems understanding or speaking, dizziness, or loss of vision to one side. Signs and symptoms often appear soon after the stroke has occurred. If symptoms last less than one or two hours it is known as a transient ischemic attack (TIA) or mini-stroke. A hemorrhagic stroke may also be associated with a severe headache. The symptoms of a stroke can be permanent. Long-term complications may include pneumonia or loss of bladder control.
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.
The abducens nucleus is the originating nucleus from which the abducens nerve (VI) emerges—a cranial nerve nucleus. This nucleus is located beneath the fourth ventricle in the caudal portion of the pons, medial to the sulcus limitans.
The abducens nerve is a nerve that controls the movement of the lateral rectus muscle in humans, responsible for outward gaze. It is also known as the abducent nerve, the sixth cranial nerve, sixth nerve, or simply CNVI. It is a somatic efferent nerve.
The lateral rectus muscle is a muscle on the lateral side of the eyeball in the orbit. It is one of six extraocular muscles that control the movements of the eye. The lateral rectus muscle is responsible for lateral movement of the eyeball, specifically abduction. Abduction describes the movement of the eye away from the midline, allowing the eyeball to move horizontally in the lateral direction, bringing the pupil away from the midline of the body.
One other type of gaze palsy is a horizontal saccadic palsy. Saccades are very quick involuntary eye movements.The paramedian pontine reticular formation(PPRF), also in the pons is responsible for saccadic movement, relaying signals to the abducens nucleus. Lesions in the PPRF cause what would be saccadic horizontal eye movements to be much slower or in the case of very severe lesions, nonexistent. Horizontal gaze palsies are known to be linked to Progressive Scoliosis. This occurs because pathways controlling saccadic movements are disrupted by the lesion and only a slow movements controlled by a different motor pathways are ineffected.
The paramedian pontine reticular formation, also known as PPRF or paraabducens nucleus, is part of the pontine reticular formation, a brain region without clearly defined borders in the center of the pons. It is involved in the coordination of eye movements, particularly horizontal gaze and saccades.
Scoliosis is a medical condition in which a person's spine has a sideways curve. The curve is usually "S"- or "C"-shaped over three dimensions. In some, the degree of curve is stable, while in others, it increases over time. Mild scoliosis does not typically cause problems, but severe cases can interfere with breathing. Typically, no pain is present.
Lesions in the midbrain can interfere with efferent motor signals before they arrive at the pons. This can also cause slowed horizontal saccadic movements and failure for the eye to reach its target location during saccades. This damage normally happens in the oculomotor nucleus of the midbrainAs in horizontal saccadic palsy, the saccades are stopped or slowed from the disrupted pathway, only in this case the signal is disrupted before it reaches the PPRF.
Efferent nerve fibers refer to axonal projections that exit a particular region; as opposed to afferent projections that arrive at the region. These terms have a slightly different meaning in the context of the peripheral nervous system (PNS) and central nervous system (CNS). The efferent fiber is a long process projecting far from the neuron's body that carries nerve impulses away from the central nervous system toward the peripheral effector organs. A bundle of these fibers is called a motor nerve or an efferent nerve. The opposite direction of neural activity is afferent conduction, which carries impulses by way of the afferent nerve fibers of sensory neurons.
The fibers of the oculomotor nerve arise from a nucleus in the midbrain, which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. From this nucleus the fibers pass forward through the tegmentum, the red nucleus, and the medial part of the substantia nigra, forming a series of curves with a lateral convexity, and emerge from the oculomotor sulcus on the medial side of the cerebral peduncle.
One-and-a-half syndrome is associated with damage to the paramedian pontine reticular formation and the medial longitudinal fasciculus.These combined damages cause both a complete gaze impairment on the ipsilateral side and a "half" gaze impairment on the contralateral side. As seen in horizontal saccadic palsy, the impairment of the contralateral side gaze is caused by the disrupted pathways coming from the PPRF, while the "half" impairment is from the signal passing through the medial longitudinal fascicles not being able to reach its target. One-and-a-Half syndrome is normally associated with horizontal gaze.
Although more rare than horizontal, one-and-a-half syndrome from damage to the paramedian pontine reticular formation and the medial longitudinal fasciculus can be shown to affect vertical gaze. This can cause impairment of vertical gaze, allowing only one eye to move vertically.
A patient may be diagnosed with a conjugate gaze palsy by a physician performing a number of tests to examine the patient's eye movement abilities. In most cases, the gaze palsy can simply be seen by inability to move both eyes in one direction. However, sometimes a patient exhibits an abduction nystagmus in both eyes, indicating evidence of a conjugate gaze palsy.A nystagmus is a back and forth "jerk" of the eye when attempting to hold a gaze in one direction.
Conjugate gaze palsies can be classified into palsies affecting horizontal gaze and vertical gaze.
Horizontal gaze 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.
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 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, although by definition this is not a conjugate gaze palsy, because by definition conjugate gaze palsies affect movement of both eyes. 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.
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.
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 rapidly or recovery may never progress. For example, optic neuritis, which is caused by inflammation, may heal in just weeks, while patients with an ischemic optic neuropathy may never recover.
A saccade is a quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction. In contrast, in smooth pursuit movements, the eyes move smoothly instead of in jumps. The phenomenon can be associated with a shift in frequency of an emitted signal or a movement of a body part or device. Controlled cortically by the frontal eye fields (FEF), or subcortically by the superior colliculus, saccades serve as a mechanism for fixation, rapid eye movement, and the fast phase of optokinetic nystagmus. The word appears to have been coined in the 1880s by French ophthalmologist Émile Javal, who used a mirror on one side of a page to observe eye movement in silent reading, and found that it involves a succession of discontinuous individual movements.
The trochlear nerve, also called the fourth cranial nerve or CN IV, is a motor nerve that innervates only a single muscle: the superior oblique muscle of the eye, which operates through the pulley-like trochlea.
The vestibulo-ocular reflex (VOR) is a reflex, where activation of the vestibular system of the inner ear causes eye movement. This reflex functions to stabilize images on the retinas during head movement by producing eye movements in the direction opposite to head movement, thus preserving the image on the center of the visual field(s). For example, when the head moves to the right, the eyes move to the left, and vice versa. Since slight head movement is present all the time, VOR is necessary for stabilizing vision: patients whose VOR is impaired find it difficult to read using print, because they cannot stabilize the eyes during small head tremors, and also because damage to the VOR can cause vestibular nystagmus.
The medial longitudinal fasciculus (MLF) is one of a pair of crossed over tracts, on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem and are made up of both ascending and descending fibers that arise from a number of sources and terminate in different areas. The MLF is the main central connection for the oculomotor nerve, trochlear nerve, and abducens nerve. The vertical gaze center is at the rostral interstitial nucleus (riMLF).
Eye movement includes the voluntary or involuntary movement of the eyes, helping in acquiring, fixating and tracking visual stimuli. A special type of eye movement, rapid eye movement, occurs during REM sleep.
Internuclear ophthalmoplegia (INO) is a disorder of conjugate lateral gaze in which the affected eye shows impairment of adduction. When an attempt is made to gaze contralaterally, the affected eye adducts minimally, if at all. The contralateral eye abducts, however with nystagmus. Additionally, the divergence of the eyes leads to horizontal diplopia. That is, if the right eye is affected the patient will "see double" when looking to the left, seeing two images side-by-side. Convergence is generally preserved.
Parinaud's syndrome, is an inability to move the eyes up and down. It is caused by compression of the vertical gaze center at the rostral interstitial nucleus of medial longitudinal fasciculus (riMLF). The eyes lose the ability to move upward and down.
Opsoclonus refers to uncontrolled eye movement. Opsoclonus consists of rapid, involuntary, multivectorial, unpredictable, conjugate fast eye movements without intersaccadic intervals. It is also referred to as saccadomania or reflexive saccade. The movements of opsoclonus may have a very small amplitude, appearing as tiny deviations from primary position.
Sixth nerve palsy, or abducens nerve palsy, is a disorder associated with dysfunction of cranial nerve VI, which is responsible for causing contraction of the lateral rectus muscle to abduct the eye. The inability of an eye to turn outward and results in a convergent strabismus or esotropia of which the primary symptom is diplopia in which the two images appear side-by-side. Thus the diplopia is horizontal and worse in the distance. Diplopia is also increased on looking to the affected side and is partly caused by overaction if the medial rectus on the unaffected side as it tries to provide the extra innervation to the affected lateral rectus. These two muscles are synergists or "yoke muscles" as both attempt to move the eye over to the left or right. The condition is commonly unilateral but can also occur bilaterally.
The one and a half syndrome is a rare weakness in eye movement affecting both eyes, in which one cannot move laterally at all, and the other can move in only one lateral direction. More formally, it is characterized by "a conjugate horizontal gaze palsy in one direction and an internuclear ophthalmoplegia in the other". The most common manifestation of this unusual syndrome is limitation of horizontal eye movement to adduction of one eye with no horizontal movement of the other eye. Nystagmus is also present when the eye on the opposite side of the lesion is abducted. Convergence is classically spared as cranial nerve III and its nucleus is spared bilaterally.
The frontal eye fields (FEF) are a region located in the frontal cortex, more specifically in Brodmann area 8 or BA8, of the primate brain. In humans, it can be more accurately said to lie in a region around the intersection of the middle frontal gyrus with the precentral gyrus, consisting of a frontal and parietal portion. The FEF is responsible for saccadic eye movements for the purpose of visual field perception and awareness, as well as for voluntary eye movement. The FEF communicates with extraocular muscles indirectly via the paramedian pontine reticular formation. Destruction of the FEF causes deviation of the eyes to the ipsilateral side.
A gaze palsy is the paresis of conjugate eye movements.
Conjugate eye movement refers to motor coordination of the eyes that allows for bilateral fixation on a single object. A conjugate eye movement is a movement of both eyes in the same direction to maintain binocular gaze. This is in contrast to vergence eye movement, where binocular gaze is maintained by moving eyes in opposite directions, such as going “cross eyed” to view an object moving towards the face. Conjugate eye movements can be in any direction, and can accompany both saccadic eye movements and smooth pursuit eye movements.
Perihypoglossal nuclei, called also perihypoglossal complex or perihypoglossal nuclear complex or satellite nuclei is a group of neurons in the floor of the fourth ventricle, in close proximity to the nucleus of the hypoglossal nerve in the gray substance of the medulla oblongata, all of which contain cells with characteristics suggestive of reticular connections.
In neuroanatomy, corticomesencephalic tract is a descending nerve tract that originates in the frontal eye field and terminate in the midbrain. Its fibers mediate conjugate eye movement.