History
Obtain a detailed history concerning the following characteristics of the diplopia: onset, duration, vertical or horizontal, monocular or binocular, and positions that improve or worsen the diplopia. This can help differentiate a new onset of fourth nerve palsy from a congenital condition that has decompensated. Patients with trochlear nerve palsy typically have worse diplopia on downgaze and gaze opposite the affected eye. If the onset is due to trauma, determine the mechanism of injury. Blunt trauma to the head, especially directly at the orbit, is a common cause of acquired trochlear nerve palsy.
A detailed medical history and review of systems can aid in detecting the root cause of the palsy. Determine risk factors for stroke, including any history of hypertension, dyslipidemia, diabetes mellitus, smoking, and past cardiovascular incidents. Surgical history should be assessed for past intracranial or orbital surgeries. Constitutive symptoms such as fever, malaise, and neck stiffness suggest meningitis. Neurologic findings can indicate a compressive lesion of the trochlear nucleus, fascicle, or nerve. Diagnosis of other diseases such as HIV infection and demyelinating diseases is pertinent as they also are associated with fourth nerve palsy. In older patients, giant cell arteritis also should be ruled out. [20, 21]
Physical Examination
Inspect the patient for compensatory torticollis, typically to the opposite side of the affected superior oblique. However, some patients tilt toward the side of the affected muscle to create greater separation and suppression of the double vision. Other patients have no torticollis because of poor vision or existing amblyopia.
The 3-step test can be useful in evaluation of vertical diplopia caused by a paretic cyclovertical muscle. However, results of this test can be misleading in the setting of restrictive ophthalmopathy, multiple muscle involvement, skew deviation, and an absent trochlear nerve, so results should be interpreted cautiously and combined with imaging findings and a detailed history for definitive diagnosis. [22, 23] Each step reduces by half the number of possible affected muscles until only 1 remains, as follows:
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The first step is to identify the hypertropic eye in primary gaze. This implicates depressors of hypertropic eye or elevators of hypotropic eye.
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The second step is to ascertain if hypertropia is worse on left gaze or right gaze. This will identify 4 muscles that act in that direction of gaze.
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The third step is to determine if hypertropia is worse on right head tilt or left head tilt.
The Bielschowsky head-tilt test stimulates intorsion of the globe on the side to which the head is tilted and extorsion of the globe on the side away from which the head is tilted. [24] Intorters and extorters of each globe have opposite vertical functions, and, when there is a paretic muscle, unopposed vertical action of other muscle makes hyperdeviation more apparent in that field of action. Only the paretic muscle will have been implicated in each step of the test.
In the case of bilateral fourth nerve palsy, interpretation of the 3-step test may be confusing. [25] Right hypertropia manifests on right head tilt, and left hypertropia manifests on left head tilt. Other findings, such as V-pattern esotropia and large amounts of excyclotorsion, also are suggestive of bilateral disease.
Cyclotorsion may be measured using the double Maddox rod test. [12, 26, 27] Details are as follows:
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Patients are seated in a dark room to minimize their reliance on environmental cues.
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Red Maddox rod is placed before each eye with axes oriented obliquely at about 5-10° from the vertical. A prism could be placed in front of one eye to vertically separate the images; this would help the patient to compare the 2 images better.
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Patient is asked to rotate 1 frame until the 2 lines are parallel.
Patients with bilateral disease typically show more than 10° of excyclotorsion.
The upright-supine test can differentiate skew deviation from other causes of vertical strabismus. Measure the patient’s vertical misalignment while in the upright position. Then, measure again while the patient is supine. A decrease of more than 50% in supine is a positive result. The vertical misalignment caused by skew deviation depends on head position, whereas it would not change in trochlear nerve palsy. Based on a study by Wong et al, this test has 76% sensitivity and 100% specificity. [28]
Examine fundus photography for ocular torsion. The disc-fovea angle is used to estimate the amount of ocular torsion and can be measured as the angle between the line from the optic disc center to the fovea and a horizontal line through the optic disc center. [27] Dieterich et al discovered a 2°-8° ocular torsion in patients with trochlear nerve palsy, and Lefevre et al observed 10.7° ± 3.8° of excyclotorsion in the paretic eye and 8.8° ± 5.7° in the nonparetic eye. [29, 30] In a study by Roh et al, this test was more sensitive (100%) than both the Lancaster red-green test and double Maddox rod test. [31]
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A 2-year-old girl with compensatory left head tilt due to congenital right superior oblique palsy.
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Postoperative photo of same girl; note marked improvement of head tilt.
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Patient with traumatic bilateral superior oblique palsy; note right hypertropia on right head tilt and left hypertropia on left head tilt.
