5: Examination of the Central Ocular Motor Systems

I. CENTRAL SYSTEMS FOR THE CONTROL OF EYE MOVEMENTS

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

Five central systems control voluntary and reflex eye movements. 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).

1. Saccadic system: saccade = to jerk or reign 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?

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         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. Frontotegmental 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 in. apart and ask the patient (Pt) to look at one and then the other. Move the targets around to require the Pt ...