Signs and Symptoms | vestibular

Common Signs and Symptoms

NYSTAGMUS

Nystagmus is characterized by an involuntary movement of the eyes, which may reduce vision or be associated with other, more serious, conditions that limit vision. Nystagmus may be one of several infantile types or may be acquired later in life. There are many types of adult-onset acquired nystagmus. These are often associated with oscillopsia (the experience of the world 'wiggling'), poor vision, and loss of balance. Often acquired nystagmus is a result of neurological problems and may respond to certain drugs, depending on the cause of the nystagmus (American Nystagmus Network, 2002).

(Gupta, 2014)

VERTIGO

Vertigo is an unpleasant distortion of static gravitational orientation, or an erroneuous perception of motion of either the sufferer or the environment. It is not a disease entity, but rather the outcome of many pathological or physiological processes. Vertigo is best described as a multisensory and sensorimotor syndrome with perceptual, postural, ocular motor, and autonomic manifestations induced by either

unusual and therefore unadapted (motion) stimulation of the intact sensory systems, or
Pathological (lesional) dysfunction (Brandt, 2013).

People suffering vertigo feel as if they are moving when they are not. Often it feels like a spinning or swaying movement (Post and Dickerson, 2010).

OSCILLOPSIA

Oscillopsia is an illusion of an unstable vision, made up of the perception of to-and-fro movement of the environment. The notion of oscillopsia refers to the interaction between the physiological mechanisms resulting in movements of the eyes and those keeping a stable visual perception (Tilikete, Pisella, Pelisson, & Vighetto, 2007). Oscillopsia may result either from impaired ocular stability or impaired compensation or suppression of afferent visual information resulting from normal eye movements. Understanding the exact mechanisms of oscillopsia may lead to novel treatment (Tilikete and Vighetto, 2011).

SACCADES

Saccades are rapid, ballistic movements of the eyes that abruptly change the point of fixation. They range in amplitude from the small movements made while reading, for example, to the much larger movements made while gazing around a room. Saccades can be elicited voluntarily, but occur reflexively whenever the eyes are open, even when fixated on a target (Purves et al., 2001).

SMOOTH PURSUIT

Smooth Pursuit is a voluntary eye movement that allows tracking of a slow moving target to maintain its position on the fovea. During smooth pursuit, vision remains clear, unlike saccade where vision is interrupted. A time delay of approximately 100-200 ms occurs before smooth pursuit begins after acquiring a target to track. The smooth pursuit system responds to both position and velocity errors, but the velocity seems to be more important, especially in initiating the movement. Oftentimes, smooth pursuit involves a saccade to bring the fovea on the target, followed by a continuous eye movement that matches the velocity of the target so that the target does not slip off the fovea. In general, smooth pursuit eye movements are initiated only when following a target (or the remembered motion of a target); that is, without visual stimulus, voluntary smooth pursuit eye movements do not occur (Enderle, 2010).

VESTIBULAR OCULAR REFLEX

Vestibulo-ocular movements stabilize the eyes relative to the external world, thus compensating for head movements. These reflex responses prevent visual images from “slipping” on the surface of the retina as head position varies. The action of vestibulo-ocular movements can be appreciated by fixating an object and moving the head from side to side; the eyes automatically compensate for the head movement by moving the same distance but in the opposite direction, thus keeping the image of the object at more or less the same place on the retina. The vestibular system detects brief, transient changes in head position and produces rapid corrective eye movements. Sensory information from the semicircular canals directs the eyes to move in a direction opposite to the head movement. While the vestibular system operates effectively to counteract rapid movements of the head, it is relatively insensitive to slow movements or to persistent rotation of the head (Purves et al., 2001).

(OpenStax College, 2013)