Читать книгу Vestibular Disorders - Группа авторов - Страница 20

To test saccades, ask the patient to rapidly fixate on 2 stationary objects (clinician’s thumb and index finger) placed 50 cm apart and observe saccadic latency, velocity, accuracy, and conjugacy. Saccadic abnormalities are not expected in peripheral vestibular disorders. Disconjugate slowing of horizontal saccades is an abnormality observed in internuclear ophthalmoplegia, which is caused by lesions affecting the median longitudinal fasciculus. A unilateral median longitudinal fasciculus lesion results in selective slowing of adducting saccades on testing horizontal saccades to the unaffected side. The abducting eye may sometimes demonstrate disconjugate nystagmus (i.e., the nystagmus is more marked in the abducting than the adducting eye). In an acutely dizzy patient, an internuclear ophthalmoplegia might imply a brainstem stroke or demyelination. Saccadic dysmetria, in particular hypermetria, is seen in cerebellar disease. The saccade overshoots and returns to the target. Ipsipulsion, with hypermetria of ipsilateral saccades and hypometria of contralateral saccades, occurs in a lateral medullary infarct [14].

To test pursuit, ask the patient to follow the clinician’s finger moving no faster than 20 deg/s in both the horizontal and vertical directions. Look for broken or saccadic pursuit. Because many parts of the neuraxis participate in smooth pursuit, broken pursuit does not contribute greatly in identifying the site of a lesion. Age, level of alertness, intoxication, and neurodegenerative disorders affecting the cerebellum and basal ganglia can impair smooth pursuit. Deficits in smooth pursuit are usually accompanied by impaired visual cancellation of the VOR [15].