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A. The eyes move at two speeds, fast and slow (Dell’Osso and Daroff, 1999)

  1. Physiologic fast eye movements, saccades, include:

    1. All voluntary horizontal and vertical eye movements.

    2. The kickback phase of jerk nystagmus, whether pathologic or physiologically induced by caloric or optokinetic stimuli.

    3. Rapid eye movements in sleep.

  2. Pathologic fast eye movements, opsoclonus and ocular flutter, are faster than any saccades that the person can produce by volitional eye movements and are described later.

  3. Slow eye movements include:

    1. Smooth pursuit.

    2. Vergences (convergence/divergence).

    3. The deviation phase of vestibular and optokinetic nystagmus.

B. The five eye-movement systems tested by the neurologic examination (NE)

Five central systems control voluntary and reflex eye movements (Bender, 1980; Bender et al 1998). Voluntary selection of a visual target requires saccadic action to move the eyes to the target. After that, fixation, fusion, following, and focusing (vergences and the control of refraction) proceed more or less automatically (Table 5-1).

TABLE 5-1The Five Major Eye-Movement Systems

  1. Saccadic system: saccade = to jerk or rein in. Saccadic movement describes eye movements by increments or jerks, like a ratchet (Kennard et al., 1994).

    1. Self-demonstration of saccades:

      1. Look straight ahead. Then, while keeping your head completely still, move your eyes all the way to the right and hold them there.

      2. With your head still, very slowly try to move your eyes as continuously and smoothly as possible all the way from the right to the left. Attend to how your eyes move. Do they move continuously and smoothly or by incremental jerks? ___________________________________________________

        You will experience your eye movements as jerks, that is, saccades. Try this experiment on other people and observe their saccades.

    2. You cannot move your eyes smoothly voluntarily. All volitional eye movements require saccades.

    3. Fronto-tegmental corticobulbar pathways are thought to mediate all such saccades (Fig. 5-1).

    4. The supplementary motor area, substantia nigra, superior colliculus, vermis, fastigial nucleus, reticular formation, and vestibular system play roles in saccadic production and accuracy.

    5. To test for saccadic accuracy: Hold up your index fingers about 18 inches apart and ask the patient (Pt) to look at one and then the other. ...

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