- 1.
What is diplopia?
Diplopia is a condition in which the patient perceives two images of a single object. Diplopia may be monocular or binocular, constant or intermittent. Check if the double vision resolves with each eye closed. If it does not, the patient has monocular diplopia. If it does, the patient has binocular diplopia.
- 2.
List the causes of monocular diplopia.
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Refractive error: astigmatism is the most common cause of monocular diplopia
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Chalazion or other eyelid tumor producing irregular astigmatism
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Keratopathy: dry eyes, keratoconus, irregular astigmatism (use a retinoscope to see scissoring reflex)
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Iris atrophy, polycoria, large nonreactive pupil
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Cataract, subluxated lens, intraocular lens decentration, capsular opacity
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Retinal disease may produce metamorphopsia or aniseikonia; also consider a psychogenic etiology
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- 3.
What are the causes of binocular diplopia?
Causes of binocular diplopia may be grouped into three general categories:
- 1.
Neuropathic: The pathology may be supranuclear, nuclear, or infranuclear. Specific neuropathic causes include traumatic, vaso-occlusive infarction, compression, inflammation, infection, demyelination, degeneration, decompensated phorias, spasm of the near reflex, and neuromyotonia.
- 2.
Myopathic: The pathology is within the extraocular muscles. Causes include inflammatory pseudotumor or myositis and thyroid-related eye disease (TED).
- 3.
Neuromuscular junction disorders. The major etiology in this category is myasthenia gravis (MG).
- 1.
- 4.
What is the most important sign to check for in a third-nerve (oculomotor) palsy?
Check for the presence of a dilated, poorly reactive, or nonreactive pupil. A pupil-involving oculomotor palsy is an emergency. An aneurysm must be ruled out. One should be suspicious in a patient with mild anisocoria if the larger pupil is ipsilateral to the side of oculomotor nerve dysfunction. Note that diabetic patients without an aneurysm may nonetheless have pupil-involving third nerve palsy.
- 1.
A pupil-sparing palsy is probably vasculopathic in adults. In children, obtain a magnetic resonance image or angiograph to rule out tumor and aneurysm.
- 2.
To test for trochlear nerve palsy in a patient with an oculomotor palsy, have the patient look down and in to check for intorsion.
- 3.
Primary oculomotor aberrant regeneration suggests a compressive lesion.
- 4.
Sixth-nerve palsy may be a false-localizing sign of elevated intracranial pressure.
- 5.
Always rule out trapdoor, “white-eyed” muscle entrapment in a pediatric facial trauma patient with otherwise seemingly normal-looking eyes.
- 5.
What is the workup of a pupil-involving third-nerve palsy?
In adults, perform magnetic resonance imaging/angiography (MRI/A) or spiral computed tomography (CT) angiography. If the results are consistent with an aneurysm or even if the results are negative, consider performing angiography after discussion with neuroradiology and neurosurgery. In children, perform MRI/A regardless of the state of the pupil. If the results are negative, children usually do not need an angiogram.
- 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 .
Table 30-1
Causes of Isolated Cranial Neuropathies
Cranial Neuropathy
Cause
III (pupil-sparing)
Adults: infarction, trauma, giant cell arteritis (GCA), tumor; rarely, an aneurysm.
Children: congenital, trauma, tumor, aneurysm, migraine
III (pupil-involving)
Usually posterior communicating artery aneurysm (rarely, basilar artery)
IV
Adults: trauma, infarction, congenital, GCA
Children: congenital, trauma
VI
Adults: infarction, tumor, trauma, multiple sclerosis, Wernicke’s encephalopathy, sarcoidosis, GCA, herpes zoster, Lyme disease, increased intracranial pressure as in pseudotumor cerebri
Children: trauma, tumor, post-viral infection
- 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 ).
Figure 30-1
The three-step test to determine if hypertropia is a result of superior oblique palsy or other causes. A. Step 1. B. Step 2. C. Step 3. (See question [CR] for explanations.)
(From American Academy of Ophthalmology: Pediatric ophthalmology and strabismus, Section 8. San Francisco, American Academy of Ophthalmology, 1992-1993.)
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.
- 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.
- 1.
- 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?
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It is the longest and most commonly injured cranial nerve in trauma.
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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.
- 1.
- 14.
List the major causes of abduction deficit other than cranial neuropathy.
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Restricted medial rectus muscle
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Trauma (entrapment, damage)
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Inflammatory pseudotumor or myositis
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Thyroid-related eye disease
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Spasm of the near reflex
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Myasthenia gravis
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Prior strabismus surgery (slipped lateral rectus, highly recessed lateral rectus)
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- 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.
- 1.
- 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?)
- 1.
- 17.
What are the localizing symptom complexes of nerve palsy?
See Table 30-2 .
