CHAPTER 7

Diagnostic Evaluation of Strabismus and

Torticollis

History and Presenting Features of Strabismus

When obtaining the history from a patient with strabismus, the clinician should document, if possible, the age of onset of a deviation or symptom. Old photographs may be useful for this purpose. In addition, the clinician should seek to answer the following questions about the deviation or symptom:

Did its onset coincide with trauma or illness?

Is the deviation constant or intermittent?

Is it present for distance or near vision or both?

Is it unilateral or alternating?

Is it present only when the patient is inattentive or fatigued?

Does the child close 1 eye (squint)?

Is the deviation associated with double vision or eyestrain?

Previous treatment should be reviewed, including amblyopia therapy, spectacle correction, and eye muscle surgery. While obtaining the history, the clinician should observe the patient, noting such factors as head positioning, head movement, attentiveness, and motor control. See Chapter 1 for discussion of general considerations and strategies for examination of the pediatric patient.

Assessment of Ocular Alignment

Positions of Gaze

The primary position of gaze is the position of the eyes when fixating straight ahead on an object at infinity. For practical purposes, infinity is considered to be 6 m (20 ft), and for this position the head should be straight.

The cardinal positions are the 6 positions of gaze in which the prime mover is 1 muscle of each eye, together called yoke muscles (see Chapter 5). The midline positions are straight up and straight down from primary position. These latter 2 gaze positions help the clinician determine the elevating and depressing capabilities of the eye, but they do not isolate any 1 muscle because 2 elevator and 2 depressor muscles affect midline gaze positions.

The diagnostic positions of gaze consist of these 9 gaze positions: the 6 cardinal positions, straight up and straight down, and primary position. For patients with vertical strabismus, the diagnostic positions of gaze also include forced head tilt to the right and left (see the section 3-Step Test, later in the chapter). Near fixation and reading position (depending on the patient’s symptoms) complete the list of clinically important alignment measurements. Several formats are available for documenting

findings of these tests (Fig 7-1).

Figure 7-1 Three examples of methods for recording the results of ocular alignment testing.

Tests for measuring ocular alignment can be grouped into 3 basic types: cover tests, corneal light reflex tests, and subjective tests.

Cover Tests

Foveal fixation in each eye, attention, cooperation, and the ability to make eye movements are all necessary for cover testing. If a patient is unable to maintain constant fixation on an accommodative target, cover tests should not be used. There are 3 main types of cover tests: the cover-uncover test, the alternate cover test, and the simultaneous prism and cover test. All can be performed at distance or near fixation.

The monocular cover-uncover test is the most important test for detecting manifest strabismus and for differentiating a heterophoria from a heterotropia (Fig 7-2). As each eye is covered, the examiner watches for any movement in the opposite, noncovered eye; such movement indicates a heterotropia. If there is no movement of the noncovered eye, movement of the covered eye as the cover is applied and movement in the opposite direction (a fusional movement) as the cover is removed indicates a heterophoria. If the patient has a heterophoria, the eyes will be straight before and after the coveruncover test; the deviation appears during the test as a result of interruption of binocular vision. A patient with a heterotropia, however, starts with a deviated eye and, after testing, ends with the same eye or—in the case of an alternating heterotropia—the opposite eye deviated. In some patients with heterophoria, the eyes are straight before testing, but they dissociate into a manifest deviation (heterotropia) after the occlusion interrupts binocular vision.

Figure 7-2 The monocular cover-uncover test.

The alternate cover test (Fig 7-3A) detects both latent and manifest deviations. Testing should be performed at both distance and near fixation. The deviation is quantified by using prisms to eliminate the eye movement as the occluder is switched from eye to eye (prism alternate cover test; Fig 7-3B). It may be necessary to use both horizontally and vertically placed prisms. This measures the total deviation; it does not distinguish between latent (heterophoria) and manifest (heterotropia) components of the deviation.