The registration of eye movements by electrooculography may be useful only as an auxiliary diagnostic method in evaluating a paralytic condition of the extraocular muscles. François and Derouck79 were first to point out that the velocity of eye movements registered in this way may yield useful clinical information regarding severity of the paralysis and recognition of return of function during recovery. Similar studies were conducted by Mackensen166 and further pursued and applied to clinical ophthalmology by A. B. Scott and coworkers,240 Metz,171–173 Metz and coworkers, 177–180 W. E. Scott,242 W. E. Scott and Nankin,245 and many others. These investigators showed that the systematic study of saccadic velocity may be useful in distinguishing between a mechanical and a paretic limitation of ocular motility. A study of saccadic velocity may be used also in conjunction with other diagnostic methods, such as the forced duction test or determination of generated muscle force, to assess the function of a paralyzed muscle. If paralysis exists, the velocity of eye movement into the field of action of the paralyzed muscle will be markedly decreased (Fig. 20–11), the normal rapid saccade being replaced by a slow, drifting eye movement. If the motility defect is caused by a mechanical obstacle, the saccadic velocity of an eye movement into the field of apparent paresis will be normal. Kirkham and coworkers138 used saccadic velocity measurements to distinguish between bilateral abducens paralysis and divergence paralysis (see also Chapter 22).
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FIGURE 20–11. Electro-oculographic registration of eye movements in a patient with left cranial nerve VI paresis. Positive deflection, gaze to right. Negative deflection, gaze to left. Arrows denote decreased saccadic velocity upon gaze into the paretic field of gaze. (From Mackensen G: Okulographie. In Hamburger FA, Hollwich F, eds: Augenmuskellähmungen, vol 46. Stuttgart, Ferdinand Enke Verlag, 1966.)
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An astute observer can detect the difference in eye movement velocities with the naked eye in many cases, thereby eliminating the need for registering eye movement.
