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Biomedical subjects

R W Baloh

Publications and source records attributed to R W Baloh.

At least 145 records · Page 8Linked to original sources
PubMed1988

Eye movements induced by linear acceleration on a parallel swing.

1. Horizontal and vertical eye movements were induced in normal human subjects by sinusoidal linear acceleration on a parallel swing. The swing frequency was 0.3 Hz and the peak horizontal and vertical acceleration ranged from 0.17 to 0.48 and 0.03 to 0.34 g, respectively. Eye movements were recorded with the scleral search coil technique. 2. With the subjects seated in the dark to stimulate the otolith-ocular reflex, swing displacement along the interaural axis induced horizontal eye movements with a mean sensitivity to translation (ST) (peak eye velocity/peak swing velocity) of 3.8 to 4.7 degrees/m and a mean phase shift (eye velocity re swing velocity) of -152 to -160 degrees. Vertical eye movements had ST and phase values comparable to those of the horizontal eye movements. When the subjects sat facing forward so that the horizontal linear accelerations occurred in the occipitonasal axis, almost identical vertical but no consistent horizontal eye movements were induced. In each case the horizontal and vertical eye movements were proportional to the horizontal and vertical displacement of the swing. 3. With the subject seated in the light looking to an earth-fixed target (synergistic visual-vestibular interaction), the gain (peak eye velocity/peak target velocity) of induced eye movements was near 1, and the phase was compensatory (i.e., approximately -180 degrees) for all stimuli (even at target velocities at which the pursuit gain was less than 1). Subjects were able to suppress the otolith-ocular responses by fixating on a target attached to the swing. The ST decreased by an order of magnitude compared with measurements in the dark without a fixation target. 4. Subjects were able to augment the ST (horizontal and vertical) by imagining an earth-fixed target. Halving the distance of the imagined target approximately doubled the ST. 5. In two of three subjects tested, the ST measured with mental alerting in the dark adaptively increased (approximately doubled) after 20 min of continuous synergistic visual-vestibular interaction. The subject who did not show an adaptive increase in ST began with the highest value of the 10 normal subjects. 6. We conclude that during linear accelerations of the head the otolith signal is correctly interpreted as head movement and not rotation of the gravity vector. The otolith-ocular reflex interacts with the visual pursuit system to improve ocular stability during translational head movements.

Adult↗
PubMed1988

A comparison of the dynamics of horizontal and vertical smooth pursuit in normal human subjects.

We compared horizontal and vertical smooth pursuit recorded with a scleral contact lens technique at multiple sinusoidal frequencies (0.2-1.6 Hz) and peak velocities (12.5-100 degrees.s-1) in 10 normal subjects. The gain was significantly higher (p less than 0.05) and the harmonic distortion significantly lower (p less than 0.05) for horizontal pursuit compared to vertical pursuit for all stimuli except the lowest frequency and peak velocity. Both horizontal and vertical pursuit exhibited a phase lag that was minimal at lower frequencies but reached a mean of about 37 degrees at 1.6 Hz. This difference between horizontal and vertical pursuit could be explained by current models of the smooth pursuit system if one postulates a lower saturation level of retinal error velocity for vertical pursuit compared to horizontal pursuit.

Adult↗
PubMed1987

Saccadic eye movements in myasthenia gravis.

The peak velocities of horizontal saccades were measured in patients with myasthenia gravis (MG) to determine whether they can differentiate MG from other causes of ophthalmoplegia. Eye movements were recorded with electrooculography (EOG) or infrared scleral reflection (IR) in 42 patients with MG, 26 patients with sixth cranial nerve palsy (CNP), 19 patients with chronic progressive external ophthalmoplegia (PEO) and 28 normal subjects. Despite limitation of ductions in MG, the group means of velocities of 10 deg saccades recorded with IR were similar in MG and normal subjects. With EOG, small but statistically significant decreases in mean velocities of 10, 20 and 30 deg saccades were found in MG, compared to those in normal subjects. Twenty-one to 28% of MG patients had velocities outside of the normal range (outliers). In contrast, the group means in CNP and PEO were markedly lower than those in MG and normal subjects. The frequencies of outliers were 89 to 100% in CNP and 88 to 100% in PEO. Measurement of saccadic velocities can be helpful in differentiating MG from other causes of ophthalmoplegia.

Adolescent↗
PubMed1987

Benign positional vertigo: clinical and oculographic features in 240 cases.

We report the clinical and oculographic features in 240 patients with benign positional vertigo (BPV). In each case, after a rapid position change from the sitting to head-hanging position, a stereotyped torsional paroxysmal positional nystagmus was visually observed and recorded with electronystagmography (ENG). The mean age of onset was 54 years, with a range of 11 to 84 years. In slightly more than one-half of the cases (122/240) a likely diagnosis was determined. The most common identifiable causes were head trauma (17%) and viral neurolabyrinthitis (15%). Females outnumbered males approximately two to one in the idiopathic group. Abnormalities on bithermal caloric testing were found in 47% of patients. Only two patients, both with well-documented neurologic disorders, had central signs on ENG. Our data are consistent with a peripheral, posterior semicircular canal origin of BPV.

Adolescent↗
PubMed1987

Eye movements in schizophrenia.

Smooth pursuit and other eye movements were quantitatively studied in patients with chronic schizophrenia to characterize the pattern and severity of eye movement abnormalities in this disorder. Twenty-one patients with schizophrenia, 13 patients with other psychiatric disorders (manic-depressive psychosis, schizoaffective disorder, depression and obsessive-compulsive disorder), and 19 normal subjects were studied. Horizontal eye movements were recorded with DC electro-oculography and analyzed by an online computer system. Eye velocity and closed-loop gain of pursuit, optokinetic nystagmus (OKN), vestibulo-ocular response (VOR) and visual-vestibular interactions were calculated. The latency, accuracy and peak velocity-amplitude relationships of voluntary saccades were measured. The group mean gains of pursuit and OKN of the schizophrenic patients were significantly lower than those of the normal subjects. Suppression of the VOR by fixation was impaired, and the latency of saccades was prolonged. However, the differences in group mean values were small in magnitude, and the frequencies of outliers among the schizophrenic patients were low. The patients with other psychiatric disorders had a similar pattern and severity of eye movement abnormalities. The frequency and severity of eye movement abnormalities in schizophrenic patients are lower than those indicated by previous studies that used different techniques of analysis.

Adolescent↗
PubMed1986

Vertical visual-vestibular interaction in normal human subjects.

Previous studies have described asymmetrical vertical eye movements when normal human subjects were rotated about a vertical inter-aural axis (with head rolled 90 degrees). We measured vertical eye movements induced by visual, vestibular and visual-vestibular stimuli with a magnetic scleral search coil technique while 10 normal subjects sat upright in a chair designed to rotate about the horizontal inter-aural axis at frequencies and amplitudes of natural head movements. Asymmetries in the gain of upward and downward pursuit and fixation-suppression of the VOR were found in individual subjects. However, there was no significant difference (p greater than 0.05) between the mean gain of up and down slow eye movements induced by vestibular, visual or visual-vestibular stimulation in the group of normal subjects. Systematic up-down asymmetries in vertical eye movements previously observed with testing about the vertical inter-aural axis were probably due to bias introduced by otolith stimulation and/or electro-oculographic eyelid artifact.

Adult↗
PubMed1986

Late cortical cerebellar atrophy. Clinical and oculographic features.

Ten patients with late cortical cerebellar atrophy documented with computerized tomography (CT) and magnetic resonance (MR) imaging presented a uniform pattern of oculomotor abnormalities. All had deficits in smooth pursuit and fixation suppression of the vestibulo-ocular reflex (VOR). The gain of the VOR was often increased but the dynamics of the VOR were not different from normals. Full-field optokinetic responses and visual-vestibular interaction mediated via the VOR velocity storage element were preserved. Just as in lower primates, the cerebellum in humans is a critical relay station for foveal pursuit and visual-vestibular interaction requiring foveal pursuit. Vestibular responses and visual-vestibular interaction mediated through the VOR velocity storage element are relatively independent of the cerebellum.

Adult↗
PubMed1985

Eye-movement abnormalities in ophthalmoplegia, ataxia, and areflexia (Fisher's syndrome).

Ophthalmoplegia, ataxia, and areflexia are present in a distinctive syndrome called Fisher's syndrome. Eye-movement recordings were used to analyze ophthalmoplegia and other eye-movement abnormalities in three patients. Disorders of supranuclear ocular motor pathways (palsy of upward gaze and internuclear ophthalmoplegia) and peripheral cranial nerve palsies could account for the ophthalmoplegia. In one patient, computed tomography demonstrated a lucency in the midbrain that could be correlated with palsy of upward gaze and bilateral internuclear ophthalmoplegia. Eye-movement abnormalities characteristic of lesions of the midline structures of the cerebellum were documented in two patients. A review of reported cases of Fisher's syndrome and brain-stem encephalitis suggested that these syndromes comprise a spectrum of a reversible, parainfectious process affecting the peripheral cranial nerves and CNS.

Adolescent↗
PubMed1985

Eye movements in patients with absent voluntary horizontal gaze.

Despite the complete absence of horizontal saccades, two patients with pontine gliomas had horizontal reflex eye movements within a range of +/- 20 degrees. The gain (peak eye velocity/peak stimulus velocity) and phase of the vestibulo-ocular reflex were normal, but the optokinetic gain was decreased. The latency, accuracy, and peak velocity of vertical saccades were normal. Apparently the voluntary gaze centers in the pontine reticular formation are not crucial for generating horizontal vestibular or vertical saccadic eye movements.

Adult↗
PubMed1985

Infantile cerebellar atrophy.

We describe a family whose members have a dominantly inherited, early-onset, nonprogressive syndrome that includes spontaneous upbeating nystagmus and mild gait ataxia. Magnetic resonance imaging showed localized atrophy of the cerebellar vermis. Several families described in the literature resemble our family but differ in mode of inheritance, age at onset, rate of progression, or clinical findings. We believe this family represents a unique type of inherited early-onset atrophy of the cerebellar vermis.

Adult↗
PubMed1985

Dorsal midbrain syndrome: clinical and oculographic findings.

We report clinical and oculographic findings in seven patients with the dorsal midbrain syndrome (Parinaud's syndrome). All presented with limited upward voluntary gaze and convergence nystagmus with attempted upward voluntary gaze. Quantitative analysis of vertical eye movements documented characteristic abnormalities of saccades with relative preservation of reflex eye movements (ie, vestibular, optokinetic, and visual-vestibular). Vertical saccade velocity was only slightly decreased in five patients with tumors, indicating that the vertical burst neurons in the mesencephalic reticular formation and their efferent pathways to the oculomotor neurons were minimally damaged. On the other hand, two patients with probable brainstem encephalitis exhibited marked slowing of vertical saccades, indicating that the burst neurons, or their efferent pathways to the oculomotor neurons, were severely damaged.

Adolescent↗
PubMed1985

Atypical brainstem encephalitis: magnetic resonance imaging and oculographic features.

A 50-year-old woman had primary position upbeating nystagmus, abnormalities of the lower cranial nerves, mild cerebellar signs, and CSF lymphocytosis. CT and MRI showed enlargement of the pons. Eye movement recordings revealed impaired pursuit and optokinetic nystagmus, and visual-vestibular interactions were absent. The patient improved spontaneously.

Brain Stem↗
PubMed1985

Rotational testing in patients with bilateral peripheral vestibular disease.

We performed quantitative low and high frequency rotational testing in 17 patients with bilateral peripheral vestibular deficits. A characteristic pattern of decreased gain and increased phase lead at low frequencies of sinusoidal stimulation and decreased time constant to impulsive stimulation was observed in most patients. The results of caloric testing correlated with the results of low frequency rotational testing but not with the results of high frequency testing. Only 2 patients complained of oscillopsia at the time of testing and both of these had decreased vestibulo-ocular reflex gain at low and high frequencies of sinusoidal rotation.

Adult↗
PubMed1985

Velocities of vertical saccades with different eye movement recording methods.

Voluntary vertical saccades were recorded in five normal human subjects with electro-oculography (EOG), an infrared, limbus tracking system (IR), and a magnetic scleral search coil method. The peak velocity-amplitude relationships of up and down saccades were measured during refixations across the center of the orbit and within the upper and lower fields of the orbit. The search coil was the most accurate method and did not reveal significant differences between the group mean velocities of up and down saccades in the different fields of the orbit. However, subjects can have idiosyncratic differences in velocities between up and down saccades. EOG overestimated the velocities of up saccades. IR underestimated the velocities of up saccades. The search coil was used to record vertical saccades in adduction and abduction. Horizontal eccentric gaze did not significantly affect the velocities of vertical saccades.

Adult↗
PubMed1984

Episodic vertical oscillopsia and downbeat nystagmus in a Chiari malformation.

A 36-year-old woman had intermittent downbeat nystagmus. Between episodes of downbeat nystagmus, eye movements were normal, except for stationary positional nystagmus and decreased vestibulo-ocular responses (VOR) to rotation. Smooth pursuit, optokinetic nystagmus, and visual-VOR interactions, which are usually impaired in patients with downbeat nystagmus and cerebellar dysfunction, were normal. Computed tomography and findings during a suboccipital craniotomy demonstrated a mild Chiari malformation, type 1. Episodic downbeat nystagmus that is not associated with other ocular motor abnormalities due to cerebellar dysfunction can be an initial sign of a Chiari malformation.

Adult↗
PubMed1984

Changes in the human vestibulo-ocular reflex after loss of peripheral sensitivity.

Quantitative rotational testing was used to study changes in the vestibulo-ocular reflex of patients with unilateral and bilateral peripheral vestibular lesions. Compared with normal subjects, the patients exhibited a characteristic pattern of decreased gain and increased phase lead at low frequencies of sinusoidal stimulation and decreased time constants on impulsive stimulation. By contrast, gain and phase measurements on high-frequency-low-amplitude sinusoidal stimulation were often normal. In the patients with bilateral lesions, the results of caloric testing correlated with the results of low-frequency rotational testing but not with the results of high-frequency testing. There are two main clinical implications of these findings. First, patients with absent response to caloric stimulation (unilateral or bilateral) may have a normal response to high-frequency sinusoidal rotation (i.e., the frequencies that constitute most natural head movements). This probably explains why such patients do not report oscillopsia. Second, low-frequency sinusoidal rotational testing and caloric testing are more sensitive than high-frequency sinusoidal or impulsive rotational testing for detecting early loss of vestibular sensitivity due, for example, to ototoxic drugs.

Adult↗