Ronald J. Tusa

Computerized dynamic visual acuity test in the assessment of vestibular deficits.

OBJECTIVE The study was designed to measure dynamic visual acuity (DVA) during head movement as an assessment of the functional impact of vestibular deficits. STUDY DESIGN The study design was a prospective, clinical study. SETTING The study was performed in a tertiary, ambulatory referral center. PATIENTS Forty-two normal subjects, 29 patients with unilateral vestibular loss, and 26 patients with bilateral vestibular hypofunction who were 19-87 years of age were examined. INTERVENTION Diagnostic intervention was performed. MAIN OUTCOME MEASURE Main outcome measures included the reliability, sensitivity, and specificity of a computerized test that measures visual acuity during head movement in normal subjects and in patients with vestibular deficits. RESULTS The computerized DVA test was reliable in both normal subjects (intraclass correlation coefficient [ICC] r=0.87) and in patients with vestibular deficits (ICC r=0.83). The sensitivity of the DVA test was 94.5% and the specificity was 95.2%. The positive predictive value (individuals who test positive on the DVA test who will have a vestibular deficit) was 96.3%. The negative predictive value (individuals who test negative on the DVA test who will not have a vestibular deficit) was 93%. CONCLUSIONS The computerized DVA test is reliable and is able to distinguish among normal subjects and patients with vestibular deficits.

Vertical dynamic visual acuity in normal subjects and patients with vestibular hypofunction.

Objective This study was designed to measure visual acuity during active vertical head movement and to examine its relationship to subjective reports of oscillopsia. Study Design This was a prospective, clinical study. Setting The study was performed in a tertiary, ambulatory referral center. Patients Thirty normal subjects, 13 patients with unilateral vestibular hypofunction, 11 patients with bilateral vestibular loss, and 10 patients with nonvestibular dizziness were examined. Vestibular loss was confirmed with caloric or rotary chair testing. Intervention Diagnostic. Main Outcome Measure Reliability, sensitivity, and specificity of a computerized test that measures visual acuity during active vertical head movement. Subjective complaint of oscillopsia was measured by use of a visual analog scale. Results The active vertical head movement test was reliable both for normal subjects (intraclass correlation coefficient, r = 0.89) and for patients with dizziness (intraclass correlation coefficient, r = 0.94). Age contributed significantly to active vertical head movement in normal subjects and in patients with dizziness over the age of 46 years but not in younger subjects. Older subjects had a decrement in active vertical head movement compared with younger subjects. Subjective reports of oscillopsia did not correlate positively with active vertical head movement. Conclusion The active vertical head movement test is a reliable measure of visual acuity during active vertical head motion. The effect of age on active vertical head movement may reflect the physiologic impact of neuronal loss with aging. The poor correlation between active vertical head movement and reports of oscillopsia may be caused by the predictability of head movements during the active vertical head movement test compared with the unpredictability of head movements during walking.

Animal Models for Visual Deprivation‐Induced Strabismus and Nystagmus

Abstract: The development of gaze‐stabilizing systems depends on normal vision during infancy. Monkeys reared with binocular lid suture (BLS) for the first 25‐40 days of life have strabismus, optokinetic nystagmus deficits, latent nystagmus, and decreased binocular cells in the visual cortex and nucleus of the optic tract. When BLS is extended to 55 days, pendular and congenital nystagmus also occurs. Eyelids in infant monkeys are hairless and thin, but BLS still degrades sensory fusion, motion, and form perception. To determine to what extent these visual properties are critical in the development of normal gaze stabilization, we examined infant monkeys reared with one opaque contact lens over one eye, alternated to the fellow eye every other day (AMO); and monkeys reared in a 3‐Hz strobe environment. Monkeys reared with AMO develop strabismus, but have normal optokinetic nystagmus and no spontaneous nystagmus. Area 17 is monocular, but the medial temporal area and the nucleus of the optic tract are binocular. Monkeys reared in strobe light develop pendular nystagmus but not strabismus. We were puzzled by the results of the AMO monkeys until we examined infant monkeys with BLS that were prevented from seeing form through the lids. This was done by leaving the tarsal plate intact behind the eyelid. They developed similar to the AMO monkeys. These results suggest that disruption of sensory fusion during infancy (BLS, AMO) causes strabismus. If strabismus occurs while the monkeys have some form vision from each eye (BLS without tarsal plate), then the nucleus of the optic tract becomes monocular, which causes optokinetic nystagmus deficits and latent nystagmus. Infant monkeys reared without visual motion develop pendular nystagmus.

Strategies for balance rehabilitation: fall risk and treatment.

Abstract: Identification of fall risk for patients with known vestibular hypofunction is important because it affects the management and the level of independence of these patients. Patients with bilateral vestibular loss, overall, have a greater incidence of falls than the general community‐dwelling population over the age of 65 years. In younger patients, the incidence of falls may be related to severity of vestibular loss and to overconfidence or a lack of caution in activities. Preliminary reports suggest that vestibular rehabilitation can reduce the fall risk in patients with vestibular loss.

Nystagmus during Attacks of Vestibular Migraine: An Aid in Diagnosis

Introduction: An estimated one-fourth to one-third of patients with migraine will experience vertigo associated with their migraine attacks. Vestibular migraine frequently presents as a diagnostic challenge as objective neurological findings consistent with this entity have not been well described. Objective: The aim of this study is to characterize eye movements of patients presenting with nystagmus during attacks of migrainous vertigo. Design: A retrospective study of 26 patients presenting with nystagmus during an acute vestibular migraine was performed. All patients were examined while symptomatic during a migraine spell, and also while asymptomatic. All patients underwent tests of vestibular function with either bithermal water caloric or rotary chair electronystagmography. Results: The most common patient was a female of perimenopausal age. Spontaneous nystagmus was seen in 19% of patients and nystagmus provoked by horizontal headshaking was seen in 35%. Nystagmus could be provoked with positional testing in 100% of symptomatic patients with fixation blocked. The positional nystagmus most commonly was sustained, of low velocity, and could be horizontal, vertical or torsional. Bithermal water caloric or rotary chair tests obtained during symptom-free intervals were normal in all patients. Conclusions: Although nystagmus characteristics are quite variable during vestibular migraine, the finding on examination of low-velocity, sustained nystagmus with positional testing in a young to middle-aged adult patient presenting with vertigo, nausea and headache is highly suggestive of vestibular migraine as long as the nystagmus dissipates when the patient is free of symptoms.

Neurophysiologic and clinical correlations of epileptic nystagmus

Epileptic nystagmus (EN) is a rare sign of seizure activity. We describe eight patients with horizontal EN and hypothesize that the frequency of ictal discharge, anatomic localization of ictal activity, and level of consciousness determine its occurrence and mechanism. We believe that EN is due to epileptic activation of a cortical saccade region; in each case, quick phases were generated away from the side of the focus, and both quick and slow phases were totally confined to the field contraversive to the seizure focus.

Perverted head-shaking nystagmus: A possible mechanism

The authors describe a patient with acute MS who developed vertigo (tumbling) and downbeat nystagmus upon horizontal head oscillation (perverted head-shaking nystagmus). The only abnormality on brain MRI was a hyperintense signal in the caudal medulla that contains the nucleus Roller and nucleus intercalatus. These nuclei project to structures involved in the velocity storage system for horizontal vestibulocular reflex (VOR) and vertical VOR, and also to the vestibular cerebellum. The authors offer possible mechanisms for perverted nystagmus in this patient.

Cervico-ocular reflex in normal subjects and patients with unilateral vestibular hypofunction.

Objective To determine whether the cervico-ocular reflex contributes to gaze stability in patients with unilateral vestibular hypofunction. Study Design Prospective study. Setting Tertiary referral center. Patients Patients with unilateral vestibular hypofunction (n = 3) before and after vestibular rehabilitation and healthy subjects (n = 7). Interventions Vestibular rehabilitation. Main Outcome Measures We measured the cervico-ocular reflex in patients with unilateral vestibular hypofunction before and after vestibular rehabilitation and in healthy subjects. To measure the cervico-ocular reflex, we recorded eye movements with a scleral search coil while the trunk moved at 0.3, 1.0, and 1.5 Hz beneath a stabilized head. To determine whether the head was truly stabilized, we measured head movement using a search coil. Results We found no evidence of cervico-ocular reflex in any of the seven healthy subjects or in two of the patients with unilateral vestibular hypofunction. In one patient with chronic unilateral vestibular hypofunction, the cervico-ocular reflex was present before vestibular rehabilitation only for leftward trunk rotation (relative head rotation toward the intact side). After 5 weeks of placebo exercises, there was no change in the cervico-ocular reflex. After an additional 5 weeks that included vestibular exercises, cervico-ocular reflex gain for leftward trunk rotation had increased threefold. In addition, there was now evidence of a cervico-ocular reflex for rightward trunk rotation, potentially compensating for the vestibular deficit. Conclusion The cervico-ocular reflex appears to be a highly inconsistent mechanism. The change of the cervico-ocular reflex in one patient after vestibular exercises suggests that the cervico-ocular reflex may be adaptable in some patients.

Ipsiversive eye deviation and epileptic nystagmus

We studied an 11-year-old boy with focal seizures in the right temporo-occipital cortex. During the seizure, there was a 1- to 2-second period of ipsiversive (rightward) conjugate eye deviation, followed by 10 to 15 seconds of horizontal jerk nystagmus with slow phases that were directed to the right and appeared linear. The patient was conscious throughout the seizure. These findings fit the description of epileptic nystagmus. We postulate that the eye deviation and slow phases of the nystagmus in this patient were induced by epileptic activation of a cerebral smooth pursuit pathway originating from temporo-occipital cortex.

Efficacy of gaze stability exercises in older adults with dizziness.

Background and Purpose: The purpose of this study was to determine whether the addition of gaze stability exercises to balance rehabilitation would lead to greater improvements of symptoms and postural stability in older adults with normal vestibular function who reported dizziness. Methods: Participants who were referred to outpatient physical therapy for dizziness were randomly assigned to the gaze stabilization (GS) group (n = 20) or control (CON) group (n = 19). Dizziness was defined as symptoms of unsteadiness, spinning, a sense of movement, or lightheadedness. Participants were evaluated at baseline and discharge on symptoms, balance confidence, visual acuity during head movement, balance, and gait measures. The GS group performed vestibular adaptation and substitution exercises designed to improve gaze stability, and the CON group performed placebo eye exercises designed to be vestibular neutral. In addition, both groups performed balance and gait exercises. Results: There were no baseline differences (P > .05) between the GS and CON groups in age, sex, affect, physical activity level, or any outcome measures. Both groups improved significantly in all outcome measures with the exception of perceived disequilibrium. However, there was a significant interaction for fall risk as measured by Dynamic Gait Index (P = .026) such that the GS group demonstrated a significantly greater reduction in fall risk compared with the CON group (90% of the GS group demonstrated a clinically significant improvement in fall risk versus 50% of the CON group). Discussion and Conclusions: This study provides evidence that in older adults with symptoms of dizziness and no documented vestibular deficits, the addition of vestibular-specific gaze stability exercises to standard balance rehabilitation results in greater reduction in fall risk.