affected ear with positive pressure (pressure against tragus), and conjugate eye movement away from the affected ear with negative pressure. Positive findings are suggestive of perilymphatic fistula, and sometimes Ménière’s disease. Smooth pursuit, saccadic eye movements, and vergence Once baseline ocular motility and alignment have been established, the examiner assesses smooth pursuit and saccadic eye movements as well as vergence. Smooth pursuit testing assesses the quality of eye movement while the patient tracks a slowly moving target in all directions. The smooth pursuit system is used to maintain a moving target on the fovea of the retina during head movement at low velocities. While the vestibular system acts to maintain gaze at higher velocities, this system is driven by cortical regions in addition to the cerebellum and brainstem (Leigh & Zee, 2006). The examiner asks the patient to track a discrete target (pencil, finger) from 18 to 24 inches away. The object should move 30° from center in each direction at a speed of about 20° per second while the patient maintains a stationary head position. The examiner is looking for a smooth trajectory of oculomotor motion in all directions (lateral, vertical, diagonal). Saccadic eye movement is rapid conjugate eye movement to place the fovea on a target. The examiner holds two discrete targets within the patient’s peripheral field of vision and asks the patient to look quickly between the two targets while keeping the head in a stationary position. If the patient’s eyes do not meet the target and a refixation on the target is observed, this is called a corrective saccade . The patient should normally be able to reach the target in one movement. Abnormal findings in saccadic and smooth pursuit eye movements are indicative of lesions in the brainstem or cerebellum and would warrant referral to a physician for further diagnostic consultation. To examine vergence, the examiner holds a discrete object (finger, pencil) 2 feet away from the patient’s nose and slowly brings it toward the bridge of the nose until the target becomes double. The eyes should converge and the pupils should constrict. Normal convergence occurs at about 4 inches. Patients having difficulty with convergence will experience double vision of the target when it is farther than 4 inches from the bridge of the nose. should wear his or her glasses if needed for distance visual correction. The patient recites the lowest line (smallest font size) they can read clearly on the chart. The examiner stands behind the patient, firmly grasping the head with both hands on either side of the head. The patient’s head is then moved side to side in a smooth rotational trajectory at a frequency of 2 Hz (two full side-to-side cycles per second) while the patient recites the lowest line on the Snellen chart he or she can read clearly. If the VOR is functioning normally, the patient’s eyes will move in the opposite direction of head movement at the same frequency, allowing for visual fixation on the target (eye chart). Normally, a patient’s visual acuity will be somewhat reduced under these conditions as head-eye movement is not a perfect 1:1 relationship, and he or she can demonstrate up to a two-line degradation (increase in font size, moving up on the chart) over the baseline visual acuity line. DVA is abnormal if there is a three-or-more-line degradation, indicating difficulty with gaze stabilization (Herdman & Clendaniel, 2014). It is important for the examiner to maintain a smooth horizontal trajectory of head movement to ensure that any degradation of visual acuity can be attributed to diminished VOR function and not to distortion of the target. Using a metronome, which can be accessed online, will ensure that the test is performed at the proper
in the direction of the nystagmus (direction-changing nystagmus) in that right-beating nystagmus will occur with gaze to the right, changing to left-beating nystagmus with gaze to the left (see Table 1). Table 1: Peripheral Versus Centrally Mediated Nystagmus
Peripheral Mediated
Centrally Mediated
Visual Fixation Decreased
No change or increase
Direction
Horizontal and torsional Increased w/gaze to fast phase
Either torsional or vertical No change or reverses direction
Gaze
In acute stages of peripheral lesions, spontaneous nystagmus can be seen with center gaze, as well as gaze to the right and left. This is called third-degree nystagmus. Within the first few days of recovery, nystagmus will be seen only at center gaze and gaze away from the side of the lesion – in the direction of the fast phase (second- degree nystagmus). As recovery continues over the course of a week or so, nystagmus can be seen only during gaze away from the side of the lesion (first-degree nystagmus). As nystagmus can be suppressed with visual fixation in the patient with peripherally mediated nystagmus, the use of Frenzel lenses or infrared goggles during examination will help the examiner appreciate the presence of the nystagmus. Pressure-induced nystagmus should also be assessed. In this test, the examiner looks for drift of the eyes or the presence of mixed vertical and torsional nystagmus while pressure is induced in three ways: The patient puts pressure against the tragus of the ears (with his or her fingers) and exerts an external pressure (Hennebert’s sign), the patient closes his or her glottis and bears down (valsalva), or the patient attempts to blow out through pinched nostrils. A positive Hennebert’s sign demonstrates conjugate eye movement away from the Vestibular function Tests of the functional integrity of the vestibular system are designed to incorporate movements that stimulate vestibular system activity in order to elicit the VOR. As the motor output of the vestibular system is reflected in the oculomotor system, measuring VOR responses will give information about vestibular system function. Initial assessment of VOR function is to have the patient fix the vision on a target while moving the head side to side, stimulating the horizontal semicircular canals to elicit a VOR response through the MLF to maintain gaze stabilization. The examiner slowly moves the patient’s head side to side approximately 30° in both directions. The patient can look at the examiner’s nose as the target, while the examiner assesses the patient’s ability to maintain visual fixation on that target. The examiner then assesses the vestibulo-ocular reflex cancellation (VORc). In this test, the patient follows a moving target with the head and eyes, maintaining ocular position in the center of the orbits. This requires input from higher cortical centers to override the VOR, with abnormal findings indicative of a centrally mediated lesion. A more quantitative assessment of VOR is the Dynamic Visual Acuity (DVA) test. In this test, the examiner uses a Snellen eye chart to assess the patient’s baseline visual acuity. The patient can be either sitting or standing, as appropriate, the proper distance from the eye chart, and
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