The major task in evaluating a child with a motility abnormality is trying to determine whether it is caused by a "common strabismus" or a potentially more serious acquired disorder. The acute nature of the presentation, which is often helpful in adults, can be confusing in children as many benign entities such as accommodative esotropia can "suddenly" appear. In addition, many congenital motility disturbances such as Brown's syndrome and Duane's syndrome can go unnoticed for quite some time. Careful observation for compensatory head positions, variability, or signs of aberrant regeneration may give a clue as to the acquired nature of the disorder. Examination of old photographs can be extremely useful in dating the onset of the strabismus. Because strabismus is often secondary to other ophthalmic abnormalities, a thorough eye exam including cycloplegic refraction (to rule out accommodative factors) is necessary. Because most neuro-ophthalmic motility disorders result from a weakness of one or more of the extraocular muscles, the motility evaluation hinges on whether the ocular rotations are normal. Although this can be difficult in children, various methods are available.
Begin by having the child look in the various fields of gaze. Colorful toys, noisy objects, or lights can be helpful in accomplishing this task. Occasionally, the child will resist looking in certain gaze positions, and other methods must be employed to assess a limitation. One of the most useful is the "doll's head maneuver." Because the child is often very apprehensive, he or she will remain fixated on the examiner instead of looking at the toy or light. In such circumstances, the examiner can rotate the child's head, thereby forcing the eyes into the desired position (Fig. 2-5). In doing so, any weakness can be determined just as effectively as having the child look into that gaze position.
A second maneuver using the same vestibular response can be employed with very young infants. It involves having the examiner rotate the infant in a circle (Fig. 2-6). This action stimulates the semicircular canals and forces the infant's eyes toward the direction of rotation.7 Its main utility is in horizontal motility defects. This action also causes a jerk nystagmus to occur upon cessation, with the fast component to the opposite direction. Thus, when rotating an infant to the examiner's right, the child will exhibit a deviation to its left (examiner's right) with a right jerk nystagmus. This approach is extremely helpful in identifying sixth nerve palsies.
Occasionally, a child presents with an esotropia and, because of strong visual cross-fixation, attempts at assessing abduction are futile. In such circumstances, a trial of alternately patching the eyes in the clinic or at home may demonstrate the patient's normal ocular rotation. The Bielschowsky head tilt
test, although not usually quantifiable in young children, can be used to detect an isolated cyclovertical muscle paresis. A vertical deviation seen while tilting the child's head to the side should raise the suspicion that a paralytic condition exists and further investigation is warranted.
Last, one can use the optokinetic drum or tape to assess ocular motor function. By rotating the drum to the patient's left, a pursuit movement to the left followed by a fast eye movement to the right (saccade) is elicited. Optokinetic testing is useful for monocular motility disorders because it helps demonstrate slower incomplete saccadic movements in paralytic extraocular conditions that are neurogenic, myoneural, or myopathic.7 In addition, it can help to demonstrate weaknesses of gaze function and the absence of saccades in the presence of pursuit movements (congenital motor apraxia).
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