Figure 7-10 The 3-step test. A, Step 1: A right hypertropia suggests weakness in 1 of the 2 depressors of the right eye (RIR or RSO) or in 1 of the 2 elevators of the left eye (LIO or LSR). B, Step 2: Worsening of the right hypertropia on left gaze implicates either the RSO or the LSR. Note that at the end of step 2, 1 depressor and 1 elevator of opposite eyes will be identified as the possible weak muscle. C, Step 3: The right head tilt causes intorsion of the right eye. Because this rotation depends on activation of both the RSO (a depressor) and the RSR (an elevator), weakness of the RSO will cause the right hypertropia to increase.

Step 1

Determine which eye is hypertropic (see Fig 7-2). Step 1 narrows the number of possible underacting muscles from 8 to 4. In the example shown in Figure 7-10, the right eye has been found to be hypertropic. This means that the paralysis will be found in either the depressors of the right eye (RIR, RSO) or the elevators of the left eye (LIO, LSR). Draw an oval around these 2 muscle groups (see Fig 7-10A).

Step 2

Determine whether the vertical deviation is greater in right gaze or in left gaze. In the example, the deviation is larger in left gaze. This implicates 1 of the 4 vertically acting muscles used in left gaze. Draw an oval around the 4 vertically acting muscles that are used in left gaze (see Fig 7-10B). At the end of step 2, the 2 remaining possible muscles (1 in each eye) are either both intortors or both extortors and are either both superior or both inferior muscles (1 rectus and 1 oblique). Note that in Figure 7-10B, the increased left-gaze deviation eliminates 2 inferior muscles and implicates 2 superior muscles.

Step 3

Known as the Bielschowsky head-tilt test, the final step involves tilting the head to the right and left during distance fixation. Head tilt to the right stimulates intorsion of the right eye (RSR, RSO) and extorsion of the left eye (LIR, LIO). Head tilt to the left stimulates extorsion of the right eye (RIR, RIO) and intorsion of the left eye (LSR, LSO). Normally, the 2 intortors and the 2 extortors of each eye have opposite vertical actions that cancel each other. If 1 intortor or 1 extortor is weak, the vertical action of the other ipsilateral torting muscle becomes manifest.

To continue the example, Figure 7-10C shows that when the head is tilted to the right, the right eye moves upward as it attempts to intort to maintain fixation, increasing the vertical deviation. This suggests that the vertical action of the right superior rectus muscle is unopposed, indicating that the right superior oblique muscle is weak and is the palsied muscle. (See also Chapter 11, Fig 11-3.)

Prism Adaptation Test

In the prism adaptation test, the patient is fitted with prisms to align the visual axes, which can help predict whether fusion may be restored following surgery.

Torticollis: Differential Diagnosis and Evaluation

Torticollis is an abnormal head position (AHP) due to rotation of the head around any of the 3 axes (head turn, chin-up or chin-down, or tilt), alone or in combination. Patients with torticollis are often referred to ophthalmologists as part of a comprehensive evaluation because torticollis can be associated with a variety of eye movement disorders, including strabismus. Early diagnosis and correction of ocular causes of torticollis is particularly important in children, because prolonged AHP may result in permanent facial asymmetry or secondary musculoskeletal changes. Common

causes of both ocular and nonocular torticollis appear in Table 7-2.

Table 7-2

Ocular Torticollis

Although the association between an AHP and ocular abnormality can be simply a shared underlying cause (eg, ocular tilt reaction), more often the AHP is a compensatory response to the ocular condition that results in improved binocularity, visual acuity, or centration of a limited visual field.

A patient with incomitant strabismus can often improve binocular alignment by adopting an AHP. Conditions that commonly cause an AHP include superior oblique palsy, Duane retraction syndrome, Brown syndrome, blowout fractures, and thyroid eye disease. Patients with unilateral ptosis may use a chin-up head posture to maintain binocularity.

Congenital nystagmus that damps at a null point is the most common condition in which better visual acuity is the motivation for an AHP. An AHP can also develop in jerk nystagmus that damps with gaze in the direction of the slow phase (eg, manifest latent nystagmus [fusion maldevelopment nystagmus syndrome]). Other conditions in which a need for better visual acuity drives the AHP include bilateral ptosis and refractive errors. With bilateral duction deficits (eg, congenital fibrosis of extraocular muscles), an AHP may be needed for foveation.

Patients with homonymous hemianopia and monocular patients may turn their head toward their blind side to center their visual field relative to their body. In rare cases, patients with superior oblique palsy have a paradoxical head tilt to the wrong side, which increases the separation between diplopic images, possibly to reduce the conflict between the 2 images when fusion is not possible.

Diagnostic evaluation of ocular torticollis

Ophthalmologic evaluation of the patient with torticollis focuses on determining whether there is an ocular cause for the AHP. The duration of the torticollis can be a diagnostic clue, but the history is sometimes misleading. Parents may not recognize chronic AHP; examining old photographs can be helpful in this situation. Cycloplegic retinoscopy is performed to look for uncorrected refractive errors. Motility testing should be done with particular attention to gaze positions opposite those favored by the AHP. Nystagmus is usually obvious, but subtle nystagmus may be visible only during slit-lamp or fundus examination. Fundus examination may reveal extorsion suggestive of superior oblique palsy or conjugate torsion (extorsion in 1 eye and intorsion in the other), as seen in the ocular tilt reaction. If placing the patient in the supine position eliminates the head tilt, a