What is included in the physical exam to evaluate trochlear nerve palsy (fourth nerve palsy)?

Updated: Oct 08, 2019
  • Author: Zafar A Sheik, MD, MD; Chief Editor: Andrew G Lee, MD  more...
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Answer

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 three-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. [21, 22] Each step reduces by half the number of possible affected muscles until only 1 remains, as follows:

  • The first step is to identify the hypertropic eye in primary gaze. This implicates depressors of hypertropic eye or elevators of hypotropic eye.
  • 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.
  • 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 globe on the side to which head is tilted and extorsion of globe on the side away from which head is tilted. [23] 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 case of bilateral fourth nerve palsy, interpretation of 3-step test may be confusing. [24] 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.


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