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

Superior oblique muscle

For the abdominal muscle see: Abdominal external oblique muscleThe 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...

.

Other names for fourth nerve palsy include superior oblique palsy and trochlear nerve

Trochlear nerve

The trochlear nerve is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye....

 palsy.

Pathophysiology

The fourth cranial nerve innervates the superior oblique muscle for each eye. The superior oblique muscle is one of the six extraocular muscles

Extraocular muscles

The extraocular muscles are the six muscles that control the movements of the eye . The actions of the extraocular muscles depend on the position of the eye at the time of muscle contraction.-List of muscles:-Importance:...

 that allow movement of eye. Specifically, the superior oblique muscle primarily intorts the eye (such that the top of the eye rolls toward the nose), with secondary actions of depression (downgaze) and abduction

Abduction (kinesiology)

Abduction, in functional anatomy, is a movement which draws a limb away from the median plane of the body. It is thus opposed to adduction.-Upper limb:* of arm at shoulder ** Supraspinatus** Deltoid* of hand at wrist...

 (looking away from the nose). When this muscle’s function is diminished due to a fourth cranial nerve (CN IV) palsy, the affected eye will extort, deviate upward (hypertropia

Hypertropia

Hypertropia is a condition of misalignment of the eyes , 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....

), and, to a smaller extent, drift inward.

Causes

The cause of congenital fourth nerve palsy is unclear in most cases. Though usually neurogenic in origin, due to a dysgenesis

Dysgenesis

Dysgenesis may refer to:* Dysgenesis , which indicates abnormal organ development during embryonic growth and development* Anterior segment dysgenesis, a failure of the normal development of the tissues of the anterior segment of the eye...

 of the CN IV nucleus or nerve, a clinically similar palsy may result from absence or mechanical dysfunction (e.g., abnormal laxity) of the superior oblique tendon

Tendon

A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...

. Usually unilateral, congenital fourth nerve palsies can also occur bilaterally. Bilateral congenital fourth nerve palsy may be unmasked only after corrective surgery of one eye for what was thought to be a unilateral palsy.

Presentation

Though present from birth, congenital fourth cranial nerve palsy may not become symptomatic until later childhood or adulthood. Young children adopt a compensatory head position in order to compensate for the underacting superior oblique muscle. The characteristic head tilt is usually away from the affected side to reduce the second image. Old photographs may reveal the presence of a consistent head tilt (torticollis

Torticollis

Torticollis, or wryneck, is a stiff neck associated with muscle spasm, classically causing lateral flexion contracture of the cervical spine musculature...

) from an early age. Most patients with congenital CN IV palsy have facial asymmetry due to the chronic head tilt. Other compensatory measures for congenital fourth nerve palsy are development of large vertical fusional amplitudes and lack of subjective symptoms of torsion

Torsion

The word torsion may refer to the following:*In geometry:** Torsion of a curve** Torsion tensor in differential geometry** The closely related concepts of Reidemeister torsion and analytic torsion ** Whitehead torsion*In algebra:** Torsion ** Tor functor* In medicine:** Ovarian...

, even in the presence of great ocular rotation.

Congenital fourth nerve palsy may remain undetected until adulthood, when intermittent diplopia

Diplopia

Diplopia, commonly known as double vision, is the simultaneous perception of two images of a single object that may be displaced horizontally, vertically, or diagonally in relation to each other...

 may arise, due to decompensated ability to overcome the vertical deviation. Reduced vertical fusional reserves result from fatigue (stress, fever, other illnesses) or simply the effects of old age. Diplopia from congenital fourth nerve palsy has occasionally been reported to manifest transiently during pregnancy

Pregnancy

Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

. Congenital fourth nerve palsy may also become evident following cataract

Cataract

A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...

 surgery once binocular vision

Binocular vision

Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...

 is restored after a long period of progressive monocular visual loss and accompanying vergence decompensation

Decompensation

In medicine, decompensation is the functional deterioration of a previously working structure or system. Decompensation may occur due to fatigue, stress, illness, or old age. When a system is "compensated," it is able to function despite stressors or defects. Decompensation describes an inability...

. Other adult patients complain of neck pain, after years of head tilting.

Treatment

Symptomatic congenital fourth cranial nerve palsy can be treated with strabismus surgery, where muscle attachment sites on the globe are modified to realign the eyes. Prism

Prism (optics)

In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...

 lenses set to make minor optical changes in the vertical alignment may be prescribed instead of or after surgery to fine-tune the correction.

See also

• Eye movements