Ductions and Versions
Measurement of the Deviation
Head Tilt Test
Compensatory Anomalies of Head Position
Sensory Anomalies
Neurogenic Paralysis vs. Myogenic or Structural Restriction of Eye Movements
Forced Duction Test
Estimation of Generated Muscle Force
Eye Movement Velocity
Paralytic vs. Nonparalytic Strabismus
Congenital vs. Acquired Paralysis
Orbital Imaging Techniques
Evaluation of Visual Impairment Caused by Diplopia
Head Tilt Test

The head tilt test is alluded to in Chapter 12. The physiologic basis of the head tilt test was explained by Hofmann and Bielschowsky112 and it has become universally known as the "Bielschowsky head tilt test." However, 30 years before Hofmann and Bielschowsky, Nagel191 noted that the combined action of the superior rectus muscle and the superior oblique muscle of one eye and of the inferior rectus and inferior oblique muscles in the fellow eye causes incycloduction and excycloduction. Nagel also hinted that with a cyclovertical paresis the deviation would be more noticeable with appropriate tipping of the head. This theory was fully confirmed on clinical grounds by Hofmann and Bielschowsky, who gave the following explanation for the head tilt phenomenon. If, for instance, in a patient with a right superior oblique paresis, the head is tilted to the right shoulder, nervous impulses will arise from the otolith apparatus and be sent to all muscles concerned when both eyes are rotating around their anteroposterior axis to the left. Thus excycloduction of the left eye is produced by co-contraction of both inferior muscles and incycloduction of the right eye by co-contraction of both superior muscles. However, since the paretic right superior oblique muscle is no longer capable of counteracting the elevating and adducting component of the right superior rectus muscle, the right eye will move upward (positive Bielschowsky test; Figs. 202, 203, 204, and 2020). With the head tilted to the left, the cycloversional movement of both eyes to the right occurs without participation of the paretic muscle; hence, the visual axis will not become deviated. It goes without saying that owing to the orientation of the semicircular canals the test cannot be applied in the supine patient.

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FIGURE 202. Physiologic basis of the Bielschowsky head tilt test. A, On tilting the head to either shoulder, reflex innervation of the cyclorotatory extraocular muscles occurs from stimulation of the otolith apparatus. Head inclination to the right shoulder causes incycloduction OD and excycloduction OS and inclination to the left shoulder elicits a cycloversion to the opposite (right) direction. The muscles involved in rotating the eyes around their anteroposterior axes are indicated by their initials. The compensation of the head inclination by cyclorotation of the eyes does not fully offset the angle of inclination. B, Muscles that act synergistically during cycloductions become antagonists when elevating and depressing the globes. Under normal conditions the vertical action of the rectus muscles exceeds that of the oblique muscles; conversely, the effect of the oblique muscles on cycloduction is greater than that of the vertical rectus muscles. C, When the head is tilted to the involved side in the case of a right superior oblique paralysis, the vertical and adducting action of the right superior rectus is unopposed. Contraction of this muscle in an attempt to incycloduct the eye results in elevation of that eye, thus increasing the vertical deviation (positive Bielschowsky test). (From Noorden GK von: Atlas of Strabismus, ed 4. St Louis, MosbyYear Book, 1983.)

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FIGURE 203. Diagnosis of the paretic muscle in a patient with right hypertropia (RHT). By comparing the position of the patients eye with the drawing, one can identify the paretic muscle. A, RHT may be caused by paresis of the right superior oblique (RSO), right inferior rectus (RIR), left superior rectus (LSR), or left inferior oblique (LIO). Increased RHT in dextroversion (B), or levoversion (E), limits the number of possibly paretic muscles to two. The paretic muscle is identified by tilting the head to the right and left shoulders (C, D, F, and G). (From Noorden GK von: Atlas of Strabismus, ed 4. St Louis, MosbyYear Book, 1983.)

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FIGURE 204. Diagnosis of the paretic muscle in a patient with left hypertropia (LHT). The threestep maneuver is performed as in Figure 203. (From Noorden GK von: Atlas of Strabismus, ed 4. St Louis, MosbyYear Book, 1983.)

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FIGURE 2020. Clinical findings in a patient with a long-standing traumatic left superior oblique paralysis. The head is tilted to the right shoulder and the face is slightly turned to the right (A). In primary position this patient had a left hypertropia of 20 prism diopters (F), increasing to 30 prism diopters in dextroversion (E), with the greatest deviation (35 prism diopters) when the patient was looking up and to the right (B). The hyperdeviation was also present in the left field of gaze (D, G) where it measured 10 prism diopters (spread of comitance). Note secondary overaction of the left inferior oblique muscle (B, E) and only minimal limitation of depression when looking down and to the right (H). The Bielschowsky head tilt test is diagnostic for a left superior oblique paralysis with increase of the left hypertropia on tilting the head to the left shoulder (K, L).

The head tilt test is applicable in paresis of any of the cyclovertical muscles. However, there is less vertical difference between the two eyes upon tilting the head with paresis of vertical rectus muscles than with paresis of the oblique muscles because the vertical action of the unopposed oblique muscles is considerably less than that of the unopposed vertical rectus muscles.

Following its original description by Hofmann and Bielschowsky112 the head tilt test has become firmly established in our diagnostic armamentarium. Several modifications have evolved with which the examiner can arrive at the correct diagnosis of the offending muscle.78, 99, 100, 103, 212 The test is especially useful in distinguishing a true from a simulated superior rectus paralysis in a patient with a contralateral superior oblique paralysis who habitually fixates with the paralyzed eye (inhibitional palsy of the contralateral antagonist; see Fig. 201).

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FIGURE 201. Inhibitional palsy of the right superior rectus (upper left) in a patient with left superior oblique palsy who fixates with the paralyzed eye. Note normal right superior rectus action and marked overaction of the left inferior oblique under the translucent cover when the right eye is fixating (left), and the left eye is covered with a Spielmann translucent occluder (see Chapter 12).

We follow the diagnostic scheme popularized by Parks212 by asking the following three questions: (1) Does the patient have a right or left hypertropia in primary position? (2) Does this deviation increase in dextroversion or levoversion? (3) Does it increase with the head tilted to the right or left shoulder? Using this three-step method, one can distinguish a paretic oblique or vertical rectus muscle in most instances. Figures 203 and 204 show the various responses that may be encountered during the head tilt test.