Signs and Symptoms of Fourth Nerve Palsy

Fourth Nerve Palsy, also known as Superior Oblique Palsy, Limited Eye Movement and Trochlear Nerve Palsy, is a neurological defect that results from dysfunction of the fourth cranial nerve. It is the most frequent isolated cranial nerve palsy. The fourth cranial nerve gives impulses to one of the muscles on the surface of the eye which is called the superior oblique muscle. The main function of the superior oblique muscle is to move the eye downward. The main characteristic of Fourth Nerve Palsy is one eye is slightly higher than the other and this improves or worsens with different head positions.

Fourth Nerve Palsy was mentioned in ophthalmology texts that date back to the mid nineteenth century, but received only brief mention and was hardly recognized. In 1935 it was recognized as the most common cause of vertical diplopia. It can affect just one or both eyes. The weak or paralyzed eye movement causes double vision that disappears when either eye is closed.

Fourth Nerve Palsy can be congenital or acquired and is often idiopathic, meaning that the cause is unknown. It can be the result of other disorders such as Myasthenia gravis, diabetes, meningitis, microvascular disease and any other cause of increased intracranial pressure. Rare causes include aneurysms, tumors and multiple sclerosis. Another cause is closed head trauma. This can cause unilateral or bilateral Fourth Nerve Palsy. Bilateral Fourth Nerve Palsy usually occurs after severe trauma with a period of unconsciousness.

The symptoms, signs and history needed to make a diagnosis include: complaint of diplopia, asthenopia (especially while reading), head tilt, facial asymmetry and trauma. Diplopia means double vision. This can occur vertically, torsional or both. Asthenopia is a condition caused by weak eye muscles and causes the eyes to get tired easily. Symptoms of Asthenopia include eye pain, headache, dim vision, dizziness and nausea. Facial Asymmetry is secondary to the head tilt. The fuller side of the face is opposite of the head tilt.

Treatment is usually conservative because most cases of Fourth Nerve Palsy are idiopathic. A six month to one year waiting period is needed to look for spontaneous improvement. A prism may resolve or improve double vision during this period so that the patient can continue on with daily tasks and activities. Surgery may be required if the double vision gets worse, head tilt causes neck pain and if there is a poor cosmetic appearance. The prognosis of Fourth Nerve Palsy depends on the underlying cause.