Impact of the Vestibular System on the Visual System

Anatomy of the Vestibular System

Types of Vestibular Input

Vestibular Canals

Vestibulo-Ocular Reflex

Demonstration of Normal VOR Response Head moving Eyes moving Image on retina remains stationary

Demonstration of Abnormal VOR Response Head moving Eyes moving Image on retina moving resulting in blur and smearing of image

Head Thrust Test  This test is used to evaluate for unilateral vestibular function. In this test, the patient’s head is turned 15-30 degrees from center and then rapidly rotated to the other side with the patient focusing on the examiner’s eyes. Patients with unilateral vestibular weakness will have a catch-up saccade when rotated rapidly.

Impact on Visual System WHY WE GET DIZZY During normal head rotations, the eye rotates opposite to the head, thus canceling the motion of the head. This tends to stabilize the image of the world on the retina. VESTIBULAR INPUT WITHOUT VISION During very prolonged head rotations with the eyes closed, the drive to the VOR stops (falsely telling the brain that one is stationary). If at this point you open your eyes, you see the world moving and you feel dizzy. VISUAL SENSE OF MOTION WITHOUT VESTIBULAR DRIVE Visual input on its own can drive the VOR (the optokinetic response). This visual input can elicit a false perception of motion. For example, a false sense of motion often occurs when looking out a car window and an adjacent car starts to move. COMBINED VISUAL AND VESTIBULAR INPUT During a prolonged head rotation in the light, both the signal from the cupula and visual input reaches the vestibular nuclei. Visual input builds up as the signal from the cupula dies away, thus compensating for the loss of cupula drive. Motion sickness occurs when the two signals are in conflict. Suppose you are inside the cabin of a boat during a storm. Your vestibular afferents are telling you that you are moving. Because you and the cabin are moving together, the visual system senses that you are not moving. To avoid motion sickness the best bet is to go out on the deck and look at the horizon. One theory for the feeling of nausea is that the brain interprets this conflict as poisoning and responds by eliciting vomiting to clear the poison.

Symptoms of a Vestibular Disorder   VERTIGO AND DIZZINESS Spinning or whirling sensation; an illusion of movement of self or the world (vertigo) Lightheaded, floating, or rocking sensation (dizziness) Sensation of being heavily weighted or pulled in one direction. BALANCE AND SPATIAL ORIENTATION Imbalance, stumbling, difficulty walking straight or turning a corner Clumsiness or difficulty with coordination Difficulty maintaining straight posture; tendency to look downward to confirm the location of the ground Head may be held in a tilted position Tendency to touch or hold onto something when standing, or to touch or hold the head while seated Sensitivity to changes in walking surfaces or footwear Muscle and joint pain (due to struggling with balance) Difficulty finding stability in crowds or in large open spaces COGNITIVE Difficulty concentrating and paying attention; easily distracted Forgetfulness and short-term memory lapses Confusion, disorientation, difficulty comprehending directions or instructions Difficulty following speakers in conversations, meetings, etc., especially when there is background noise or movement Mental and/or physical fatigue out of proportion to activity

Symptoms of a Vestibular Disorder VISION Trouble focusing or tracking objects with the eyes; objects or words on a page seem to jump, bounce, float, or blur or may appear doubled Discomfort from busy visual environments such as traffic, crowds, stores, and patterns Sensitivity to light, glare, and moving or flickering lights; fluorescent lights may be especially troublesome Sensitivity to certain types of computer monitors and digital televisions Tendency to focus on nearby objects; increased discomfort when focusing at a distance Increased night blindness; difficulty walking in the dark Poor depth perception OTHER Nausea or vomiting, "Hangover" or "seasick" feeling in the head Motion sickness Sensation of fullness in the ears Headaches Slurred speech Sensitivity to pressure or temperature changes and wind currents Pain, pressure, or other symptoms with certain dietary changes (e.g., high sodium)

VT Activities with Vestibular Integration Mirror Fixations Add a Balance Board or Physio-ball to any activity Infinity Walk Back to Back Ball Pass/ Over Head Through Legs Ball Pass Fruit Ninja