Patients with vestibular disease may complain of vertigo, oscillopsia, or the visual consequences of nystagmus.1 Vertigo means whirling or spinning, but the term is also used to describe other illusions of motion, and implies vestibular imbalance. Oscillopsia consists of illusory, oscillatory movements of the seen environment. When oscillopsia occurs with head movements, it usually implies loss of vestibular function. Oscillopsia also may occur when the head is stationary in patients with spontaneous nystagmus. In this chapter, we review current treatments for vertigo, oscillopsia, and the visual consequences of nystagmus from the standpoint of known pathophysiology.
In interpreting and treating symptoms resulting from vestibular disorders, it is helpful to consider the nature of the demands placed on the vestibular system during natural activities, especially locomotion. The purpose of the vestibulo-ocular reflex (VOR) is to maintain clear and stable vision during natural head movements. A major threat to clear vision is posed by the head perturbations occurring during locomotion. This fact was pointed out by the anonymous physician J.C. who had lost vestibular function because of aminoglycosides2; he wrote, “During a walk I found too much motion in my visual picture of the surroundings to permit recognition of fine detail. I learned that I must stand still in order to read the lettering on a sign.”
The range of peak velocities and predominant frequencies of head rotations measured in 20 normal subjects as they walked or ran in place are summarized in Figure 14.1. Note that although peak head velocity is generally below 150 deg/sec, the predominant frequencies range from 0.5 to 5 Hz.3,4 The latter value exceeds the frequencies that vestibular physiologists have conventionally used to test patients in the laboratory but generally corresponds to the bedside head-impulse test.5 Besides head rotations, linear movements or “translations” occur during locomotion.6 However, recent studies indicate that head translations are less of a threat to vision than are rotations, unless subjects view near targets during locomotion.7,8 This information about the range and nature of head perturbations that occur during natural activities such as locomotion is useful in formulating strategies to rehabilitate patients with vestibular disorders, especially if the functional goal of therapy is the ability to walk normally, without aids.
Summary of the ranges of (A) maximum velocity and (B) frequency of rotational head perturbations that occur during walking or running in place. Distributions of data from 20 normal subjects are displayed as Tukey box graphs, which show selected percentiles of the data. All values beyond the 10th and 90th percentiles are graphed individually as points. Reproduced with permission.1
Pathophysiology of Vertigo
During locomotion, our multisensory inputs—visual, vestibular, and somatosensory—allow a unified perception of self-motion that is ...