Biomedical subjects

R W Baloh

Publications and source records attributed to R W Baloh.

At least 109 records · Page 6Linked to original sources

PubMed1994

Dynamic visual acuity: a test for oscillopsia and vestibulo-ocular reflex function.

A method has been developed of clinically quantifying dynamic visual acuity (DVA), the acuity during imposed head motion in the pitch axis. In this method, visual acuity is measured using a computer-controlled projection system during vertical, sinusoidal relative motion either of the optotypes (the letters to be read) or of a servodriven swinging chair in which subjects are seated. In normal persons, the vestibulo-ocular reflex (VOR) functions adequately during imposed head movements to limit retinal image instability, making DVA independent of head velocity. During head movements the wearing of telescopic spectacles, which magnify the visual effects, can overwhelm even normal visual-vestibular interactions, producing retinal image instability leading to creation of artificial experimental oscillopsia in normal subjects. With the head stationary, optotype motion at frequencies and velocities beyond the capabilities of visual tracking also results in retinal image motion. Using these methods, DVA for both optotype and head motion was found to be degraded in a predictable fashion when the velocity of the image on the retina exceeded 2 degrees per second. In two patients with total peripheral vestibular loss, DVA was markedly impaired during head motion. As a result of the VOR deficit, this impairment of DVA was observed, even without the use of telescopic spectacles, and was predictably related to the velocity of imposed head motion. Dynamic visual acuity during imposed head motion is a quantitative and clinically feasible measure of oscillopsia that reflects functionally significant abnormalities of the VOR.

Adult↗

PubMed1993

Disequilibrium of unknown cause in older people.

Many older people complain of a sense of unsteadiness when standing or walking and many are fearful of falling. The cause of this disequilibrium is often difficult to determine even after thorough clinical evaluation. To better understand the pathogenesis of this symptom in a community-dwelling population, we studied 26 patients > 75 years old who complained of disequilibrium in whom no cause was evident after clinical evaluation. Each patient and each of 26 age-matched controls underwent a comprehensive evaluation that included a history and examination, a questionnaire, functional scales, a gait and balance scale, mini-mental state testing, audiometry, visual acuity, visual tracking, rotational vestibular testing, and quantitative posturography. Although none had Romberg's sign, patients tended to sway more and do poorer on semiquantitative gait and balance testing than did controls. Patients showed few differences from controls for most other measurements. However, 7 patients, designated Group V, had profoundly reduced vestibular function. In the remaining 19 patients (Group D), the average vestibular function was still significantly lower than controls. Sway velocity measured with posturography was increased in the patients compared with controls, particularly in Group V patients. Measures of vestibular function correlated with increased sway velocity both in Group D alone and among all study participants. Quantitative measurement of vestibular function should be considered in older people complaining of disequilibrium, particularly if the cause is not apparent after the initial evaluation.

Activities of Daily Living↗

PubMed1993

The effect of aging on visual-vestibuloocular responses.

To determine age-related changes in oculomotor function we measured vestibuloocular (VOR), optokinetic (OKN), and visual-vestibular responses in a large group of normal subjects over the age of 75 years and compared the results with those from a group of young adults. Compared with the young subjects, older subjects had: (1) an amplitude-dependent decrease in VOR gain, (2) a shorter dominant VOR time constant, (3) a lower OKN slow-phase velocity saturation, and (4) a decreased ability to enhance and suppress the VOR with vision. These functional changes in older subjects are presumably secondary to well-documented, age-related changes in the sensory and neural elements of the visual-vestibulooculomotor pathways. They may be a contributory factor to the common complaints of dizziness and dysequilibrium in people over the age of 75 years.

Adolescent↗

PubMed1993

Optokinetic-vestibular interaction in patients with increased gain of the vestibulo-ocular reflex.

We studied optokinetic nystagmus (OKN), optokinetic afternystagmus (OKAN) and visual-vestibular interaction in five patients with markedly elevated vestibulo-ocular reflex (VOR) gain due to cerebellar atrophy. All had impaired smooth pursuit, decreased initial slow phase velocity of OKN, and impaired ability to suppress the VOR with real or imagined targets. OKN slow phase velocity gradually built up over 25-45 s, reaching normal values for low stimulus velocities (< or = 30 deg/s). Initial velocity of OKAN was increased, but the rate of decay of OKAN was normal. These findings can be explained by models that include separate velocity storage and variable gain elements shared by the vestibular and optokinetic systems.

Adult↗

PubMed1993

Horizontal semicircular canal variant of benign positional vertigo.

We report the clinical features and results of quantitative eye-movement testing in 13 patients with episodic positional vertigo and nonfatiguing direction-changing horizontal positional nystagmus (beating to the right with the head turned to the right and beating to the left with the head turned to the left). The benign history and lack of associated neurologic findings support a peripheral localization of the lesion. This syndrome probably represents a horizontal semicircular canal variant of benign positional vertigo. Free-floating debris in one horizontal canal may explain many of the clinical and oculographic findings.

Adult↗

PubMed1993

Novel brainstem syndrome associated with prostate carcinoma.

Two patients successfully treated for prostatic cancer developed a progressive neurologic syndrome beginning with loss of voluntary horizontal eye movements followed by severe, persistent muscle spasms of the face, jaw, and pharynx. Both had mild gait unsteadiness, and one exhibited facial and abdominal myoclonus. Extensive diagnostic studies, including MRIs of the brainstem (with and without contrast), were normal. CSF examination showed mild pleocytosis and elevated IgG. Quantitative eye movement recordings documented selective involvement of voluntary horizontal saccades with sparing of horizontal slow eye movements. Neither patient had antineuronal antibodies in the blood. Postmortem examination revealed perivascular chronic inflammatory cells and microglial infiltration of the pons and medulla. One patient also had perivascular infiltrates in both mesial temporal lobes. Neuronal loss was localized to the pontine tegmentum, the medullary sensory nuclei, and the cerebellum. Brainstem motor nuclei were preserved. The clinical and pathologic findings suggest an autoimmune process (probably paraneoplastic) with selective damage to a subpopulation of brainstem neurons critical for horizontal eye movements and recurrent inhibition of bulbar nuclei.

Adenocarcinoma↗

PubMed1993

Dysequilibrium in older people.

The Council on Scientific Affairs of the California Medical Association presents the following inventory of items of progress in neurology. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established, both as to scientific fact and important clinical significance. The items are presented in simple epitome, and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, researchers, and scholars to stay abreast of these items of progress in neurology that have recently achieved a substantial degree of authoritative acceptance, whether in their own field of special interest or another. The items of progress listed below were selected by the Advisory Panel to the Section on Neurology of the California Medical Association, and the summaries were prepared under its direction.

Accidental Falls↗

PubMed1993

Visual-vestibular interaction in humans during active and passive, vertical head movement.

We studied visual-vestibular interaction (VVI) in 9 normal human subjects using active and passive vertical head rotations. Gain and phase of the vertical vestibulo-ocular reflex (VOR) and visually enhanced vestibulo-ocular reflex (VVOR) were measured for single frequency sinusoidal motion, as well as for sinusoidal motion of continuously increasing frequency, over the range of 0.4 to 4.0 Hz. In addition to measurement of VVOR during normal vision, telescopic spectacles having a magnification of 1.9x were used to challenge VVI to facilitate measurement of visual enhancement of VOR gain. In the mid-frequency range (1.6 to 2.4 Hz), the active VOR exhibited gain closer to compensatory than did the passive VOR; at other frequencies, active and passive VOR gains were similar. VVOR gain during normal vision was compensatory for both active and passive motion throughout the frequency range tested. VVOR gain with 1.9x telescopic spectacles was greater than VOR gain at all frequencies tested, including up to 3.2 Hz for passive head movements, and up to 4.0 Hz for active head movement. However, gain enhancement with telescopic spectacles was consistently greater during active than during passive head movement. Phase errors for the VOR and VVOR were small under all testing conditions. Although active VOR and VVOR were directionally symmetrical, gain of upward slow phases differed from that of downward slow phases for passive VOR and VVOR in a manner depending on rotational frequency. For both active and passive testing, gain and phase values obtained during swept frequency rotations were similar to those obtained during single frequency sinusoidal testing. These data indicate that VVI can enhance gain of the passive vertical VOR even at frequencies above what is usually considered to be the upper limit of visual pursuit tracking. The additional enhancement observed during active head movements at these high frequencies is attributable to use of efference copy of the skeletal motor command to neck musculature.

Adult↗

PubMed1992

Otolith-ocular testing in human subjects.

Assessment of the otolith-ocular reflex of human subjects involves linear acceleration and/or changes in the orientation of the head with respect to gravity. Several such stimuli are currently under investigation regarding their applicability to the evaluation of patients with dizziness and balance disorders. Discussed in this paper are off-vertical axis rotation, eccentric rotation, pitch and roll rotation, and linear acceleration. For each of these stimuli, basic principles, normative human data, and patient data are described. Although none of these methods are currently established for clinical use, each of them, especially off-vertical axis rotation and linear acceleration, have the potential for developing into a clinically useful method for assessing otolith function in man.

Electrooculography↗

PubMed1992