Takuya Uemura

Eye-Head Coordination During Lateral Gaze in Normal Subjects

To elucidate the characteristics of eye-head coordination during lateral gaze, eye, head and gaze displacements to 10 degrees, 20 degrees, 30 degrees, 40 degrees, and 50 degrees target presentations were analysed quantitatively in 10 normal subjects. Head displacement was recorded without mechanical restraint by a newly devised apparatus containing two terrestrial magnetic sensors. Eye movements were recorded using d.c. electro-oculography through bitemproal leads. (1) As the target angle increased, the latency of eye movement increased while that of head movements decreased. (2) The rise times of eye and head movements increased almost linearly with the target angle. (3) The maximum velocity of eye movement averaged 292 degrees/sec at 10 degrees, increased to 398 degrees/sec at 20 degrees, and remained unchanged thereafter. The maximum velocity of head movement increased linearly with the target angle. (4) The head displacement at the end of eye saccade became relatively larger as the target angle increased, though the sum of eye and head displacements, i.e. gaze, agreed with the target angle. (5) At the final resting position, the percentage of target angle attained by head displacement decreased from 93% to 10 degrees to 62% at 50 degrees. However, gaze displacement was exactly the same as the target angle, with little dispersion for each angle of gaze shift, indicating that the head rotation detector is an accurate device for recording horizontal head movement under natural conditions.

Midsagittal pontomedullary brain stem section: Effects on ocular adduction and nystagmus

Abstract Oculomotor function was studied after midsagittal section of the brain stem in rhesus monkeys. After lesions that involved both the medulla and pons, there was permanent paralysis of adduction during conjugate eye movements and divergent strabismus. Analysis of the lesions indicated that activity responsible for ocular adduction had crossed the brain stem in a localized region at the level of the abducens nuclei. The adductive paralysis was probably due to interruption of axons of abducens internuclear neurons that ascend in the medial longitudinal fasciculus (MLF). In view of the functional relationship of this region to ocular adduction and its close anatomic relationship to the MLF, we propose that it be called the MLF decussation. Because the eyes beat synchronously after deep interruption of vestibular commissural fibers, the latter are not essential for the production of quick phases of nystagmus. After medullary lesions, animals had spontaneous downward nystagmus and perverted caloric nystagmus. Optokinetic after-nystagmus was lost. The perverted nystagmus appears due to unmasking of anterior canal responses, secondary to a loss of inhibitory activity that normally crosses the brain stem in the vestibular commissural system.

Studies of the Vestibulo-Ocular Reflex and Visualvestibular Interactions During Active Head Movements

The ratio of slow phase eye speed to head speed (Gain) during voluntary sinusoidal head rotations at 0.33, 0.67 and 1.0 Hz was studied in normal subjects under various target presentations. With mental arithmetic in the dark, the mean value of the Gain was 0.8 irrespective of turning frequencies. When subjects looked at or imagined (in the dark) a spatially fixed target, the Gain was always maintained at unity. The Gain measured with a head-fixed target was 0.22, 0.33 and 0.54 at 0.33, 0.67 and 1.0 Hz, respectively. However, imagining a target in this condition failed to suppress the Gain obtained with mental arithmetic in the dark. When a target moved twice as fast as the head (pursuit of the reflected image in a head-fixed mirror), the Gain was -0.60, -0.11 and 0.38 at 0.33, 0.67 and 1.0 Hz, respectively.

Autonomic dysfunction on the affected side in Meniere's disease.

For ascertaining the existence of autonomic dysfunction on the affected side as being the cause of Menieres disease, the mecholyl tests were conducted by means of conjunctival instillation in normal subjects as well as in patients with Menieres disease, labyrinthitis and vestibular neuritis. The rate at which significant miosis (more than 10%) appeared in the mecholyl test was 3.1% among normal subjects, whereas the rate among Menieres disease patients on the affected side was significantly higher during the attack, quasi-attack and interval stages. The appearance rate among Menieres disease patients on the unaffected side was not different from that in normal subjects during any of the three stages. None of the patients with labyrinthitis or vestibular neuritis showed significant miosis on the affected side alone in the mecholyl test. This indicates that abnormality of vestibular-autonomic reflex in itself does not cause a positive reaction in the mecholyl test. Hence it can be concluded that the cause of Menieres disease is related to the existence of autonomic dysfunction on the affected side.

Compensatory eye movement and gaze fixation during active head rotation in patients with labyrinthine disorders.

Compensatory eye movement and gaze fixation during active head rotation were studied in patients with unilateral and bilateral loss of vestibular function. Patients with bilateral lesions were asked to perform mental arithmetic tasks in the dark. Although compensatory eye movements of these patients corresponded to 38–46% of compensatory movements in normal subjects, the ability of patients with lesions to visually fix on a stationary target was markedly impaired. Visual fixation on moving targets attached to the head (head-fixed targets) was also measured and found to be good. For patients with unilateral lesions, in the early stages of the disease, findings during rotations to the intact side resembled those for normal subjects, while results of rotations to the affected side resembled those for patients with bilateral lesions.

Structural Features of the Basal Lamina in Reissner's Membrane of the Guinea Pig

The structural features of the basal lamina in Reissners membrane were examined electron microscopically using tannic acid fixation, poly-cationic staining (ruthenium red), and mono-cationic staining (safranin O). Tannic acid fixation revealed 5-10-nm filaments which ran perpendicularly between the lamina densa and the cytoplasmic surface of squamous epithelial cells. Ruthenium red staining showed a lattice-like arrangement of anionic sites on both sides of the lamina densa. Safranin O staining revealed filamentous networks at the same sites. These structural features of the basal lamina in the Reissners membrane were very similar to those of the glomerular and the alveolar basement membrane. Therefore, the possibility that anionic sites of Reissners membrane may play the role of a size and charge-selective barrier between the scala media and the scala vestibuli, in much the same way that the glomerular basement membrane plays the same role of barrier, must be taken into account.

Recovery of Vestibulo-Ocular Reflex and Gaze Disturbance in Patients with Unilateral Loss of Labyrinthine Function

Vestibulo-ocular reflex (VOR) gain and the ability of gaze fixation were investigated in patients with unilateral loss of labyrinthine function during the time course of compensation (four days to 6 months). A marked directional difference in the VOR gain in the acute stage (0.51 to 0.73 at four days) decreased proportionately to the logarithm of time on rotations to the affected side and to the intact side by an increase and a slight decrease of the gain, respectively. Gaze disturbance, which occurred only on rotations to the affected side, recovered in parallel with the decrease of directional difference in the VOR gain; it was still found at 1 Hz at 6 months. Recovery of gaze disturbance in unilateral lesions seems to be accomplished not only by the change in the VOR gain, but also by intensified amplification of this gain to make up for a low VOR gain.

Compensatory eye movement and gaze fixation upon passive head and body rotation and active head rotation

ZusammenfassungUm Unterschiede bei kompensatorischen Augenbewegungen und bei Blickfixation aufzudecken, wurde bei normalen Versuchspersonen und bei Patienten mit beiderseitigem Verlust der Labyrinthfunktion die passive Kopf- und Körperrotation sowie die aktive Kopfrotation durchgeführt. Bei den normalen Versuchspersonen ergaben sich keine Besonderheiten. Die Untersuchung der Patienten zeigte, daß die Beobachtung der kompensatorischen Augenbewegung und der Blickfixation während der passiven Rotation zur Aufdeckung von Störungen des vestibulookulären Reflexes nützlich ist.SummaryTo detect differences in compensatory eye movement and gaze fixation, normal subjects and patients with bilateral loss of labyrinthine functions were subjected to passive head-and-body rotation and performed active head rotation. In normal subjects, there was no difference between passive and active rotation with respect to compensatory eye movement in the dark and spatial gaze fixation; on the other hand, the ability to gaze fixedly on a head-fixed target was better during passive than active rotation. In our patients, the findings obtained upon passive rotation resembled those already reported for active rotation, indicating that observing compensatory eye movements and gaze fixation during passive rotation is useful in the detection of disorders of the vestibulo-ocular reflex.

Effect of Glycerol and Mannitol on Perilymphatic PO2 in Guinea Pig Cochlea

The effects of glycerol and mannitol on partial oxygen pressure (PO2) in perilymph were studied with a polarographic technique in the guinea pig cochlea. Following a transient reduction immediately after the intravenous injection of each drug, the oxygen tension increased to reach a peak 5 to 10 minutes later, and then decreased gradually. The magnitude and duration of the PO2 increases were larger after the administration of glycerol than after that of mannitol. These results corresponded well with the clinical experience that glycerol was more effective than mannitol in improving hearing in Menieres disease. The increase of PO2 in the cochlea, therefore, is considered to be one of the possible contributory factors for the improvement of hearing in patients with Menieres disease after glycerol administration.

Quantitative analysis of pursuit eye movements by unidirectional target motion

SummaryThe effects of a change in target speed (10°–100°/s) and amplitude (10°–80°) on smooth pursuit eye movements were analyzed in normal subjects by moving a target unidirectionally. The limit of pursuit speed adaptation changed according to changes in the target amplitude, being about 40°–50°/s at a target amplitude of 40°–80°. The minimum target amplitude needed to induce rhythmic pursuit eye movements markedly increased from 3.7° at 10°/s to 55.0° at 100°/s. The relationship between the gain (the ratio of eye speed to target speed) and the pursuit time suggested that pursuit eye speeds may depend on the pursuit time rather than absolute target speeds and that the gain might become unity even at fast target speeds, provided the critical pursuit time is given.