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Biomedical subjects

R W Baloh

Publications and source records attributed to R W Baloh.

At least 37 records · Page 2Linked to original sources
PubMed1978

Is the adaptation model a valid description of the vestibulo-ocular reflex?

The pendulum model of the vestibulo-ocular reflex, including the effects of adaptation, has been evaluated using the responses of 36 normal subjects to impulsive stimuli of 128 and 256 degree/s. Estimates of the model parameters such as the time constants, the slow velocity threshold, and the minimum stimulus required to produce an after-nystagmus have been obtained using a new analytical technique. Although some of the data support the validity of the adaptation model, evidence is presented to demonstrate that the overall applicability of the model is limited.

Acclimatization↗
PubMed1978

Internuclear ophthalmoplegia. I. Saccades and dissociated nystagmus.

Saccades (horizontal and vertical) and dissociated nystagmus were quantitatively assessed in four patients with internuclear ophthalmoplegia. Two patients had bilateral medial longitudinal fasciculus (MLF) lesions associated with multiple sclerosis and two had unilateral lesions associated with brain stem vascular disease. Adducting saccades made on the side of an MLF lesion were slowed in each patient (P less than .01). At the same time, abducting saccades in the contralateral eye had normal velocity, but consistently overshot the target. After the overshoot, the eye returned to the target with an exponentially decaying course. With large angular deviations (usually more than 15 degrees), the abducting eye developed nystagmus characterized by slow components that moved toward the midposition with an initially high velocity followed by a segment of slower velocity. The adducting eye had either no nystagmus or a low-amplitude nystagmus characterized by a rounded junction between the fast and slow component. The saccade abnormalities and waveform of the dissociated nystagmus can be explained by a pulse-step mismatch at the agonist motoneurons.

Adult↗
PubMed1978

Internuclear ophthalmoplegia. II. Pursuit, optokinetic nystagmus, and vestibulo-ocular reflex.

Smooth pursuit, optokinetic nystagmus (OKN) and the vestibulo-ocular reflex (VOR) were studied in four patients with internuclear ophthalmoplegia (two with bilateral and two with unilateral lesions). Horizontal smooth pursuit by an adducting eye on the side of a medial longitudinal fasciculus (MLF) lesion was normal in three of four patients; vertical pursuit was abnormal in all four. The horizontal VOR gain of slow components made by an adducting eye on the side of an MLF lesion was normal in all four patients. The vertical VOR gain was decreased in the two patients tested. It is concluded that either there are pathways independent of the MLF for horizontal pursuit and vestibular signals that are not available to vertical signals, or vertical pursuit and vestibular eye movements require a higher rate of oculomotor neuron firing than equal-velocity horizontal eye movements.

Adult↗
PubMed1978

Eye movements in ataxia-telangiectasia.

The spectrum of eye movement disorders in six patients with ataxia-telangiectasia at different stages of progression was assessed quantitatively by electrooculography. All patients demonstrated abnormalities of voluntary and involuntary saccades. The youngest and least involved patient had significantly increased reaction times of voluntary saccades, but normal accuracy and velocity. The other patients demonstrated increased reaction times and marked hypometria of horizontal and vertical voluntary saccades. Saccade velocity remained normal. Vestibular and optokinetic fast components (involuntary saccades) had normal amplitude and velocity but the eyes deviated tonically in the direction of the slow component. We conclude that patients with ataxia-telangiectasia have a defect in the initiation of voluntary and involuntary saccades in the earliest stages. These findings are distinctly different from those in other familial cerebellar atrophy syndromes.

Adolescent↗
PubMed1978

Linear model for visual-vestibular interaction.

The results of experiments are evaluated in terms of a simple model for the interaction of eye movement responses to simultaneous optokinetic and vestibular stimuli. The model predictions agree with the results of these experiments and explain many clinical observations concerning the effect of vision on nystagmus. The model accounts for the dominance of the visual system's response over the vestibular system's response at low frequencies. It also accounts for the inability of patients with decreased smooth pursuit system response to suppress the vestibulo-ocular reflex during simultaneous optokinetic and vestibular stimulations. The model provides useful information for the design of combined optokinetic and vestibular stimuli for test vestibulo-ocular reflexes.

Eye Movements↗
PubMed1978

Vestibular-optokinetic interactions in normal subjects and in patients with peripheral vestibular dysfunction.

The vestibulo-ocular reflex (VOR) during rotation, optokinetic nystagmus (OKN), and interactions between the vestibulo-ocular and optokinetic systems were studied quantitatively in 10 normal human subjects, 15 patients with unilateral horizontal semicircular canal paralysis (UP), and 11 patients with bilateral horizontal semicircular canal paralysis (BP). The OKN gain (eye velocity/drum velocity) was not significantly different between the normal subjects and the patient groups. During tests in which rotatory and visual stimuli were presented simultaneously, the contribution to the observed eye movements by the VOR was only one-fourth to one-third of its gain during rotation in the dark in the normal subjects and UP patients. These interactive tests did not differentiate UP patients from normal subjects but did separate BP patients from normal subjects.

Adult↗
PubMed1978

The spectrum of audiologic and vestibular findings in patients with Meniere's disease.

A retrospective study of 55 patients with Meniere's disease suggested a subgrouping based on presentation of auditory symptoms. Patients were defined as "definite" (documented fluctuating hearing loss and episodic vertigo), "probable" (history of fluctuating hearing loss and episodic vertigo) and "possible" (history of fluctuating tinnitus and episodic vertigo). An in-depth discussion of the natural history, audiometric and vestibular findings is presented.

Adult↗
PubMed1977

Primary position upbeat nystagmus. A clinicopathologic study.

Eye movements were studied with electro-oculography in a patient with primary position, large amplitude, upbeat nystagmus. The upbeat nystagmus increased in amplitude on upward gaze, decreased on downward gaze, and was not altered by loss of fixation. The patient could not produce smooth pursuit movements upward or to the left, but had normal saccadic and vestibular induced eye movements in all directions. At necropsy, a low grade glioma was found involving primarily the medulla and caudal pons. The inferior olives and prepositus hypoglossal nuclei were diffusely infiltrated with tumor. These results suggest (1) primary position upbeat nystagmus is due to a defect in the upward smooth pursuit system, (2) the lower brain stem at the level of the inferior olives and nucleus prepositus hypoglossi is important in the mediation of vertical pursuit, and (3) primary position upbeat nystagmus can result from damage to several nuclei and interconnecting pathways in the caudal brain stem and midline cerebellum involved in control of vertical smooth pursuit.

Ataxia↗
PubMed1977

Subclinical eye movement disorders in patients with multiple sclerosis.

Eye movements were quantitatively evaluated in 16 patients with well-documented multiple sclerosis who had minimal or no clinically apparent eye movement disorder. Induced saccade and pursuit eye movements were recorded with electro-oculography and analyzed with newly developed programs on a laboratory digital computer. Thirteen of the 16 patients had significant (p less than 0.05) impairment of saccades and/or smooth pursuit when compared with 25 normal subjects tested in our laboratory. The type and frequency of abnormalities were as follows: saccade dysmetria, eight; delayed saccade reaction time, five; bilateral saccade slowing, four; slowing of adducting saccades only (medial longitudinal fasciculus syndrome), one; and impaired smooth pursuit, both directions, three, and one direction only, three. In addition, four patients had vestibular nystagmus with eyes closed, and one patient had typical rebound nystagmus. These data suggest that quantitative assessment of eye movements in patients with suspected multiple sclerosis can help in identifying the important "second lesion."

Adult↗
PubMed1976

Rapid eye movements in myasthenia gravis. II. Electro-oculographic analysis.

Voluntary saccades were studied by electro-oculography in ten patients with myasthenia gravis (MG) and in eight patients with other types of ophthalmoplegia. Despite limited range of eye movements, maximum velocities of 20 degree and 40 degree saccades in patients with MG were not significantly different from those in normal individuals, whereas maximum velocities in patients with other types of ophthalmoplegia were significantly decreased. In some myasthenic patients, small amplitude saccades were hypermetric and had high velocities, appearing clinically as "quiver" movements characteristic of MG. In MG the preservation of saccades with high initial velocities, even in the presence of severe ophthalmoplegia, suggests that muscle fibers generating rapid movements during saccades (twitch fibers) can be relatively spared when muscle fibers responsible for maintenance of excentric gaze (tonic fibers) are severely affected.

Adolescent↗
PubMed1976

A study of congenital nystagmus: waveforms.

Eighteen patients with congenital nystagmus were studied with the techniques of electronystagmography and computer analysis. We found several complex wave forms of congenital nystagmus in the primary position of gaze above those of jerk and pendular nystagmus as defined clinically. An etiologic classification of motor fixation defect and sensory fixation defect nystagmus based on waveforms is not justified. Ocular tracking studies demonstrate that the smooth pursuit system is operational in congenital nystagmus and substantiate the belief that the fast component of jerk nystagmus is a corrective movement generated by the saccadic system. Patients with congenital nystagmus are able to produce voluntary saccades with normal velocity-amplitude relationships.

Adolescent↗
PubMed1976

Positional vertigo with cerebellar astrocytoma.

The authors present two surgically verified cases of cerebellar astrocytoma extending into the fourth ventricular floor. Each patient presented with positional vertigo, and electronystagmography revealed positional nystagmus indicative of a central lesion. The findings in these cases emphasize the need of looking for positional nystagmus in patients with suspected posterior fossa lesions.

Adolescent↗
PubMed1975

Neuropsychological dysfunction in children with chronic low-level lead absorption.

To investigate the relation between low-level absorption and neuropsychological function, blind evaluations were under-taken in forty-six symptom-free children aged 3-15 years with blood-lead concentrations of 40-68 mug. per 100 ml. (mean 48 mug. per 100 ml.) and in seventy-eight ethnically and socioeconomically similar controls with levels greater than mug. per 100 ml. (mean 27 mug. per (100 ml). All children lived within 6-6 km. of a large, lead-emitting smelter, and in many cases residence there had been lifelong. Mean age in the lead group was 8-3 years and in the controls 9-3. Testing with Wechsler intelligence scales for schoolchildren and preschool children (W.I.S.C. and W.P.P.S.I.) showed age-adjusted performance I.Q. to be significantly decreased in the group with higher lead levels (mean scores, W.I.S.C. plus W.P.P.S.I., 95 v. 103). Children in all ages in the lead group also had significant slowing in a finger-wrist tapping test. Full-scale I.Q., verbal I.Q., BEHAVIOUR, AND HYPERACTIVITY RATINGS DID NOT DIFFER.

Absorption↗
PubMedDate not supplied

Quantitative measurement of smooth pursuit eye movements.

Smooth pursuit eye movements were quantitatively assessed in 25 normal subjects and 22 patients. A laboratory digital computer was used to compute 200 eye velocity samples per second and to statistically compare these eye velocity measurements for five different object velocities. Of six statistics evaluated, mode eye velocity showed the least variability in normal subjects and was most frequently abnormal in patients. Compared to normal subjects, patients with brain stem degeneration and cerebellar-pontine angle tumors with brain stem compression had significant impairment of smooth pursuit. Patients with peripheral vestibular lesions and C-P angle tumors without brain stem compression did not have impaired smooth pursuit. These preliminary findings suggest that quantitative measurement of pursuit eye velocity can be a sensitive test for brain stem dysfunction.

Adult↗
PubMedDate not supplied

Eye-tracking and optokinetic nystagmus. Results of quantitative testing in patients with well-defined nervous system lesions.

Eye-tracking and optokinetic nystagmus (OKN) abmormalities in patients with focal lesions of the nervous system are reviewed. Patients with peripheral labyrinthine lesions can have deficits in smooth pursuit and OKN, but they are rapidly compensated after an acute lesion. By contrast, patients with large, cerebellopontine angle tumors have progressive impairment of pursuit and OKN as the tumor enlarges. Abnormalities of saccadic eye movements suggest intrinsic central nervous system (CNS) dysfunction. Saccade accuracy is severely impaired with cerebellar lesions, while brain stem disease frequently results in a slowing of saccade maximum velocity. Smooth pursuit and OKN abnormalities are common with all types of CNS lesions. The pattern of eye-tracking and OKN abnormality can be useful in anatomically localizing nervous system lesions.

Atrophy↗
PubMedDate not supplied

Caloric testing. 1. Effect of different conditions of ocular fixation.

Twelve normal subjects received standard caloric testing under the following conditions: 1) fixation, 2) Frenzel glasses in a dimly lit room, 3) eyes open in total darkness, and 4) eyes closed. Multiple nystagmus response parameters were evaluated and statistically compared for each condition. Fixation markedly diminished induced nystagmus and produced the largest coefficient of variation for each response parameter. Caloric testing with eyes closed resulted in periodic nystagmus suppression and a less distinct saw-toothed pattern. As with fixation, the coefficient of variation was consistently higher with eyes closed compared to eyes open in darkness or Frenzel glasses. It is concluded that caloric testing of the vestibulo-ocular reflex arc should be performed with eyes open in darkness or with Frenzel glasses.

Central Nervous System Diseases↗
PubMedDate not supplied

Caloric testing 2. results in normal subjects.

A large number of variables were examined simultaneously for 43 normal subjects over the four irrigations of a caloric test. Care was used for every step of the testing procedure and data analysis to eliminate as much of the variance in the caloric responses as possible. The normality of each variable's distribution was examined using the Wilk-Shapiro W test and corrected if necessary by the best of several transformations. The means, standard deviation, and 95% confidence intervals of the resultant data were derived. Statistical tests of temperature, sidedness, and directionality were done on the variables and several important sources of variance were found and explained.

Electrooculography↗