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Biomedical subjects

R W Baloh

Publications and source records attributed to R W Baloh.

At least 199 records · Page 11Linked to original sources
PubMed1979

Eye movement fatigue in myasthenia gravis.

An 18-year-old woman presented with dissociated nystagmus that was first attributed to multiple sclerosis. When she attempted to maintain 30-degree horizontal gaze deviation in either direction, there was progressive weakness of the adducting eye and increasing amplitude of nystagmus in the abducting eye. The amplitude and maximum velocity of repetitive one-per-second 30-degree saccades progressively decreased over a 3-minute period. Intravenous edrophonium completely abolished the dissociated nystagmus and adducting muscle weakness, and returned the saccade maximum velocity to normal. Her subsequent response to pyridostigmine and thymectomy confirmed the diagnosis of myasthenia gravis.

Adolescent↗
PubMed1979

Impulsive and sinusoidal rotatory testing: a comparison with results of caloric testing.

The usefulness of rotatory testing (impulsive and sinusoidal) as an indicator of impaired horizontal semicircular canal function was evaluated in 63 patients with unilateral and bilateral decreased caloric responses. The rotatory stimuli were precisely controlled over a large magnitude range and EOG recorded nystagmus responses were quantified using digital analysis techniques. Rotatory testing was consistently abnormal in patients with complete unilateral caloric paralyses but was normal in over one-half of the patients with significant but less than complete unilateral caloric paralyses. The difference in maximum slow component velocity (SVMX) of induced nystagmus after the largest rotatory stimuli was the best indicator of unilateral impaired function. The patients with bilateral decreased caloric responses demonstrated three categories of rotatory response: 1. normal at all magnitudes of stimulation, 2. decreased but present after large magnitude stimuli, and 3. absent responses. It is concluded that although rotatory testing cannot replace caloric testing it can provide useful clinical information particularly in patients suspected of having bilateral vestibular disease.

Caloric Tests↗
PubMed1979

Effect of alcohol and marijuana on eye movements.

The effects of alcohol and marijuana (tetrahydrocannabinol-THC) on saccades, smooth pursuit, and optokinetic nystagmus were quantitatively evaluated in 24 normal subjects using electro-oculographic recordings. Each subject was given an initial trial run and then tested three times (at weekly intervals) with either 0.0microgram THC or 100 microgram THC/kg bodyweight while at three different blood alcohol concentrations (0.0, 0.05 and 0.1%). A 2X3 factorial design was used. Saccades and smooth pursuit were induced by a dot of light moving in steps and ramps on a modified television set. Optokinetic nystagmus was induced by a cloth drum completely surrounding the subject and moving at a constant velocity of 30 degrees/s. Alcohol (0.05 and 0.1%) alone produced significant (p less than 0.05) impairment of saccade maximum velocity and reaction time, smooth pursuit velocity, and optokinetic slow-component velocity. The addition of THC caused performance to further deteriorate at each blood alcohol level but, in all but one instance, the added effect was not statistically significant ( greater than 0.05). At the THC and alcohol concentrations used in this study, the eye movement effects of alcohol over-shadowed those of marijuana.

Adult↗
PubMed1979

Slow build-up of optokinetic nystagmus associated with downbeat nystagmus.

Eye movement recordings in two patients with downbeat nystagmus demonstrated an unusual finding of severely impaired smooth pursuit and relatively unimpaired optokinetic nystagmus (OKN). OKN was characterized by a remarkable, slow build-up of slow-component velocity, similar to that found in afoveate animals. Optokinetic after-nystagmus (OKAN), or transient persistence of nystagmus after cessation of visual stimulation, typical of the optokinetic response of normal human subjects, was also preserved in these patients. These observations suggest that the normal contribution of smooth pursuit to the ocular motor response to rotation of the visual environment can be selectively removed by a lesion at the level of the craniocervical junction.

Adult↗
PubMed1979

Subclinical effects of chronic increased lead absorption--a prospective study. II. Results of baseline neurologic testing.

This report summarizes the results of baseline neurologic testing in a group of apparently healthy workers from a secondary lead smelter and a group of controls from nearby aluminum processing plants. The test battery included a standard neurologic examination nerve conduction measurements, quantitative oculomotor function tests and detailed audiologic studies. Lead workers and controls were intermixed so that the examiners were unaware of the status of any individual being tested. Although the lead workers reported significantly more neurologic symptoms than the controls, relatively few differences were found on quantitative neurologic testing. Decreased deep tendon reflexes occured more frequently in the lead workers than in the controls (22% vs. 11%) but the difference was of borderline significance (p=0.06) and other signs of peripheral neuropathy occurred with equal frequency in both groups. The mean motor conduction velocity and sensory latency measurements were not significantly different in the lead workers and in the controls and, of the six oculomotor function measurements, only the mean accuracy of saccadic eye movements was significantly (p less than 0.01) different in the two groups. High frequency hearing loss occurred with equal frequency and severity in both groups, consistent with the level of noise exposure in the lead and control plants.

Absorption↗
PubMed1979

Subclinical effects of chronic increased lead absorption--a prospective study. I. Study design and analysis of symptoms.

Seventy workers exposed to lead for at least one year and 35 control workers have been enrolled in a prospective study of possible neurologic effects of chronic lead absorption at or below the current standard of 80 microgram per 100 ml whole blood. The study design is described in detail. Initial results of analysis of lead-related symptoms from baseline studies indicate few differences between the exposed and nonexposed workers. The majority of differences were for central nervous system (CNS) symptoms and muscle or joint pain. Little correlation was found between symptom reporting and indices of lead absorption. The evidence suggests that factors other than lead absorption itself may be important in symptom reporting.

Absorption↗
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↗