Bibliography

CHAPTER 30  DIPLOPIA  257

6.Why do aneurysms involve the pupil in oculomotor nerve palsies, whereas infarctions generally do not?

Pupillary parasympathetic fibers travel superficially and dorsomedially in the third nerve as it traverses the subarachnoid space. These fibers are often affected first in a compressive lesion. Ischemic infarction often occurs in the center of the nerve, so the superficial fibers remain unaffected.

7.What is the workup of an isolated pupil-sparing but otherwise complete oculomotor nerve palsy in the vasculopathic age group?

A lesion that compresses the central third-nerve fibers sufficiently to produce a complete paresis should affect the peripheral pupillary fibers sufficiently to produce at least some degree of pupil involvement. If not, the likelihood of an aneurysm or other compressive etiology is extremely low. The patient may be treated for an assumed vaso-occlusive etiology. At a minimum, diagnostic workup includes measuring systemic blood pressure, a lipid panel, and fasting blood glucose and/or hemoglobin A1c. If the patient has symptoms of giant cell arteritis, check for an elevated erythrocyte sedimentation rate, C-reactive protein, and platelet count; administer corticosteroids; and perform a temporal artery biopsy; otherwise, the patient may be seen again in 6 weeks. Some physicians reexamine the patient within 5 days to ensure the pupil remains uninvolved. If no resolution of symptoms occurs over 3 months, neuroimaging with an MRI is generally performed.

8.What are the causes of isolated cranial neuropathies?

Many cranial neuropathies are idiopathic, but the causes of isolated cranial neuropathies are summarized in Table 30-1.

9.How do you test for a trochlear nerve palsy in the presence of an oculomotor nerve palsy?

It is important to specifically test trochlear, abducens, and trigeminal nerve function in a patient with an oculomotor nerve palsy to localize the lesion. Because the third-nerve palsy may prevent adduction, it may be difficult to test fourth-nerve function. When the patient attempts to look down and in with the paretic eye, you will observe intorsion if the trochlear nerve is intact. This can be done by telling the patient to look at his or her nose.

10.Describe the three-step test.

This is a test to determine if a hypertropia is due to superior oblique palsy or other causes (Fig. 30-1). Step 1: Which eye is hyperdeviated? A right hyperdeviation could be caused by palsy of any of the

muscles circled in Fig. 30-1, A. Determine which muscles might cause this.

Step 2: Is the hyperdeviation worse in the right gaze or the left gaze? Isolate these muscles. A right superior oblique palsy reveals worsening of the right hyperdeviation in the left gaze (Fig. 30-1, B).

Step 3: Is the hyperdeviation worse on right head tilt or left head tilt (Fig. 30-1, C)? The muscle isolated in all three steps is the palsied muscle. A right superior oblique palsy reveals increased hyperdeviation upon head tilt to the right. A double Maddox rod can then be used to determine if the trochlear nerve palsy is bilateral. If excyclotorsion is more than 10°, bilateral superior oblique palsies exist.

Table 30-1.  Causes of Isolated Cranial Neuropathies

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11.What is the best procedure to treat unresolved superior oblique palsy? Does one have to memorize Knapp’s Rules?

Knapp published his treatment scheme some years ago, and many surgeons use similar schemes.

It is not necessary to memorize his particular scheme, but the principles should be understood. Generally, there are three possible surgical approaches:

1.Strengthen (tuck) the palsied superior oblique muscle.

2.Weaken (recess or myectomize) the antagonist ipsilateral inferior oblique muscle.

3.Weaken the yoke contralateral inferior rectus muscle.

Typically, the surgeon operates on the muscle or muscles that act in the field of gaze where the diplopia is worst. For example, if the left hyperdeviation in a left superior oblique (LSO) palsy is worse in downgaze, one would consider an LSO tuck or a right inferior rectus recession. The latter procedure may be favored because an adjustable suture technique can be used and there is no chance of producing an iatrogenic Brown’s syndrome.

12.Explain the Harada-Ito procedure.

The Harada-Ito procedure involves anterior and lateral displacement of the anterior portion of the palsied superior oblique muscle. This procedure is used primarily for correction of excyclotorsion but will correct a small degree of hyperdeviation. The amount of incyclotorsion created is variable, but the procedure is generally successful, especially in patients with <10 degrees of preoperative torsion.

13.What else should you know about trochlear nerve palsy?

1.It is the longest and most commonly injured cranial nerve in trauma.

2.It crosses to the contralateral side as it exits the dorsal midbrain.

3.Patients of all ages with trochlear nerve palsy and increased vertical fusional amplitudes do not need further evaluation; they have decompensated “congenital” trochlear nerve palsies.

4.Always consider MG and TED in the evaluation of diplopia, even if the palsy “maps out” to a specific cranial nerve.

14.List the major causes of abduction deficit other than cranial neuropathy.

•Restricted medial rectus muscle

•Trauma (entrapment, damage)

•Inflammatory pseudotumor or myositis

•Thyroid-related eye disease

•Spasm of the near reflex

•Myasthenia gravis

•Prior strabismus surgery (slipped lateral rectus, highly recessed lateral rectus)

15.How do you treat an unresolved abducens nerve palsy?

1.Weaken the ipsilateral medial rectus with strengthening of the ipsilateral lateral rectus muscle.

2.Vertical transposition procedure.

3.Botulinum toxin (Botox) injections may be used with the above procedures or alone.

16.What else should you know about abducens nerve palsy?

1.It may occur as a nonspecific sign of increased intracranial pressure. It may also occur after lumbar puncture.

2.In the case of bilateral abducens paresis, you must consider tumor, multiple sclerosis, subarachnoid hemorrhage, or infection.

3.In children with bilateral abducens paresis, reconsider strabismus and check for “doll’s eyes.” Doll’s eyes should be incomplete in a paretic disorder.

4.Third-order sympathetic fibers briefly join the abducens nerve in the cavernous sinus. Horner’s syndrome with an abducens nerve palsy localizes to this region.

5.Always consider MG and TED in the evaluation of diplopia, even if the palsy “maps out” to a specific cranial nerve. (Sound familiar?)

17.What are the localizing symptom complexes of nerve palsy?

See Table 30-2.

18.What is internuclear ophthalmoplegia?

The medial longitudinal fasciculus carries nerve fibers from the abducens nucleus on each side to the contralateral medial rectus subnucleus to coordinate horizontal gaze. This area of the brain stem may be damaged by demyelination, ischemia, or tumor. Ipsilateral decreased adduction and contralateral

CHAPTER 30  DIPLOPIA  261

amplitudes of fusion. Patients can fully adduct during conjugate gaze movements, and the deviation is comitant for a given distance. The isolated condition is rarely associated with tumor or other serious pathology. Patients are treated with near-point exercises such as focusing on the end of a pencil while moving from arm’s length toward the face.

23.What is skew deviation?

Skew deviation is a vertical deviation that is caused by a prenuclear disturbance and cannot be isolated to a single extraocular muscle or muscles. It is distinguished from a superior oblique palsy in that it is associated with incyclotorsion, rather than excyclotorsion, as seen in a superior oblique palsy. It is associated with other manifestations of posterior fossa disease.

24.What other supranuclear conditions commonly produce diplopia?

Progressive supranuclear palsy produces a variety of systemic and ocular motility disturbances, including bradykinesia, axial rigidity, and difficulty with vertical eye movements. If diplopia is present, it is typically caused by convergence difficulty. Similarly, patients with parkinsonism, Huntington’s disease, and Parinaud’s dorsal midbrain syndrome may also have diplopia at near owing to convergence difficulty.

25.Explain divergence paresis.

Patients with divergence paresis present with an esodeviation at distance causing diplopia. Patients are able to fuse at near. The esodeviation is comitant, and horizontal versions are normal. This condition tends to be benign and self-limited; however, it may be associated with infection, demyelinating disease, and tumor. A thorough neurologic evaluation should be performed, and consideration should be given to MR imaging, especially if any neurologic signs or symptoms are present.

26.Do vaso-occlusive nerve palsies present with aberrant regeneration?

No. Aberrant regeneration of the third nerve does not occur after a vaso-occlusive (e.g., diabetic) third-nerve palsy. Primary oculomotor aberrant regeneration is highly suggestive of a lesion that is slowly compressing the third nerve, such as an intracavernous meningioma or aneurysm.

27.To what anatomic region does Horner’s syndrome with an abducens nerve palsy localize?

It localizes to the cavernous sinus. Third-order sympathetic fibers briefly join the abducens nerve in the cavernous sinus. Often, however, diseases of the cavernous sinus such as a carotid cavernous fistula or cavernous sinus thrombosis cause cranial nerve III, IV, and VI deficits in addition to proptosis, elevated intraocular pressure, conjunctival hyperemia, and reduced vision.

28.What is the ice test?

The ice test is a noninvasive test for myasthenia gravis. The palpebral fissure is measured before and immediately after a 2-minute application of ice to the ptotic eyelid. Many patients with myasthenia gravis will show an improvement in the ptosis after ice application. The sensitivity of the ice test in patients with complete ptosis decreases considerably.

KEY POINTS: MYASTHENIA GRAVIS

1. Always suspect MG in any patient with diplopia, especially if it is variable and associated with ptosis.

2. Have atropine available for adverse reactions if Tensilon tests are performed.

3. If a patient has classic MG symptoms and signs but negative acetylcholine receptor antibodies, consider checking for anti-MuSK or obtaining electrophysiological studies.

4. Thymomas and hyperthyroidism are common in patients with MG. Patients need a chest MRI and thyroid function tests.

29.Why is a trapdoor orbital fracture important to recognize?

A trapdoor fracture occurs when an orbital wall, most often the floor, breaks and then springs back together, entrapping a herniated extraocular muscle within it. This is more often seen in pediatric