|Fourth Cranial Nerve Palsy|
|Specialty|| Ophthalmology |
Fourth cranial nerve palsy, also known as trochlear nerve palsy, is a condition affecting cranial nerve 4 (IV), the trochlear nerve, which is one of the cranial nerves. It causes weakness or paralysis of the superior oblique muscle that it innervates. This condition often causes vertical or near vertical double vision as the weakened muscle prevents the eyes from moving in the same direction together.
Cranial nerves are the nerves that emerge directly from the brain, in contrast to spinal nerves. Ten of the cranial nerves originate in the brainstem. Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck.
The superior oblique muscle, or obliquus oculi superior, is a fusiform muscle originating in the upper, medial side of the orbit which abducts, depresses and internally rotates the eye. It is the only extraocular muscle innervated by the trochlear nerve.
Because the trochlear nerve is the thinnest and has the longest intracranial course of the cranial nerves, it is particularly vulnerable to traumatic injury.
To compensate for the double-vision resulting from the weakness of the superior oblique, patients characteristically tilt their head down and to the side opposite the affected muscle.
When present at birth, it is known as congenital fourth nerve palsy.
Congenital fourth nerve palsy is a condition present at birth characterized by a vertical misalignment of the eyes due to a weakness or paralysis of the superior oblique muscle.
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 brainstem is the posterior part of the brain, continuous with the spinal cord. In the human brain the brainstem includes the midbrain, and the pons and medulla oblongata of the hindbrain. Sometimes the diencephalon, the caudal part of the forebrain, is included.
The oculomotor nerve is the third cranial nerve. It enters the orbit via the superior orbital fissure and innervates extrinsic eye muscles that enable most movements of the eye and that raise the eyelid. The nerve also contains fibers that innervate the intrinsic eye muscles that enable pupillary constriction and accommodation. The oculomotor nerve is derived from the basal plate of the embryonic midbrain. Cranial nerves IV and VI also participate in control of eye movement.
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.
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.
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.
The inferior oblique muscle or obliquus oculi inferior is a thin, narrow muscle placed near the anterior margin of the floor of the orbit. The inferior oblique is an extraocular muscle, and is attached to the maxillary bone (origin) and the posterior, inferior, lateral surface of the eye (insertion). The inferior oblique is innervated by the inferior branch of the oculomotor nerve.
The superior orbital fissure is a foramen in the skull, although strictly it is more of a cleft, lying between the lesser and greater wings of the sphenoid bone.
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.
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.
Hypertropia is a condition of misalignment of the eyes (strabismus), whereby the visual axis of one eye is higher than the fellow fixating eye. Hypotropia is the similar condition, focus being on the eye with the visual axis lower than the fellow fixating eye. Dissociated vertical deviation is a special type of hypertropia leading to slow upward drift of one or rarely both eyes, usually when the patient is inattentive.
The Harada–Ito procedure is an eye muscle operation designed to improve the excyclotorsion experienced by some patients with cranial nerve IV palsy. In this procedure, the superior oblique tendon is split, and the anterior fibers – the fibers most responsible for incyclotorsion – are moved anteriorly and laterally. This selectively stretches and tightens these fibers, enhancing the incyclotorsion power of the superior oblique.
Superior oblique myokymia is a neurological disorder affecting vision and was named by Hoyt and Keane in 1970.
Brown's syndrome is a rare form of strabismus characterized by limited elevation of the affected eye. The disorder may be congenital, or acquired. Brown syndrome is caused by a malfunction of the superior oblique muscle, causing the eye to have difficulty moving up, particularly during adduction. Harold W. Brown first described the disorder in 1950 and initially named it the "superior oblique tendon sheath syndrome".
Oculomotor nerve palsy is an eye condition resulting from damage to the third cranial nerve or a branch thereof. As the name suggests, the oculomotor nerve supplies the majority of the muscles controlling eye movements. Thus, damage to this nerve will result in the affected individual being unable to move their eye normally. In addition, the nerve also supplies the upper eyelid muscle and the muscles responsible for pupil constriction. The limitations of eye movements resulting from the condition are generally so severe that the affected individual is unable to maintain normal alignment of their eyes when looking straight ahead, leading to strabismus and, as a consequence, double vision (diplopia).
Cranial nerve disease is an impaired functioning of one of the twelve cranial nerves. Although it could theoretically be considered a mononeuropathy, it is not considered as such under MeSH.
The Parks–Bielschowsky three-step test, also known as Park's three-step test or Bielschowsky head tilt test, is a method used to isolate the paretic extraocular muscle, particularly superior oblique muscle and trochlear nerve, in acquired vertical double vision. It was originally described by Marshall M. Parks.