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Biomedical subjects

V Honrubia

Publications and source records attributed to V Honrubia.

At least 109 records · Page 6Linked to original sources
PubMed1983

Effect of eccentric gaze on pursuit.

The effect of eccentric gaze on pursuit eye movements was studied with electro-oculography in normal human subjects and a patient with defective pursuit. Sinusoidal target trajectories were centered about the primary position of gaze and eccentric, horizontal positions of gaze. Eccentric gaze decreased pursuit gain (eye velocity/target velocity) when the eyes moved farther eccentrically in the orbits and increased pursuit gain when the eyes moved toward the centers of the orbits. The magnitude of these effects increased with increasing eccentricity of gaze, increasing peak target velocity, and decreasing pursuit gain during tracking of target trajectories centered about the primary position. These effects can be caused by the elastic forces of the extraocular muscles, globe and other orbital tissues. The pursuit subsystem cannot compensate for these factors at high target velocities, or when it is impaired by pathologic lesions.

Cerebellar Diseases↗
PubMed1983

Effects of an optokinetic background on pursuit eye movements.

The effects of an optokinetic background on pursuit eye movements was studied in four normal human subjects and seven patients with impaired pursuit and/or optokinetic nystagmus (OKN). Eye movements were recorded by DC electro-oculography and eye movement velocity was analyzed by a digital, microprocessor system. Tracking of a small laser target was performed against a featureless, white screen, a stationary OKN background that filled the entire visual field and an OKN background moving at constant velocity. The OKN background significantly affected pursuit in all subjects. The stationary background or background moving in the direction opposite to that of the laser target impaired pursuit; whereas, the background moving in the same direction as that of the target improved pursuit. The effects of the background on pursuit were greater in subjects with lower pursuit gains during tracking against the screen. An algebraic summation of independently induced pursuit and OKN eye movements could not account for all of the experimental observations.

Eye Movements↗
PubMed1981

Eye movement abnormalities in rod monochromacy.

Eye movements were studied quantitatively using electro-oculography in seven patients with rod monochromacy. Attention was given to eye movement abnormalities that could help to differentiate rod monochromacy from other forms of congenital nystagmus. Horizontal nystagmus in center gaze had pendular and jerk waveforms with much lower amplitude than that in patients with other forms of congenital nystagmus and visual acuity of 20/200-20/400. Slow build-up of slow component velocity over many seconds and directional asymmetry of optokinetic nystagmus (OKN) were observed during monocular optokinetic stimulation. The directional asymmetry of OKN was characterized by a higher OKN gain (eye velocity/OKN drum velocity) during rotation of the OKN drum in the temporal-to-nasal direction in the visual field, than that during drum rotation in the nasal-to temporal direction. Similar directional asymmetry and slow build-up are found in afoveate animals, such as the rabbit, during monocular optokinetic stimulation, but are not found in normal human subjects or in patients with other forms of congenital nystagmus.

Adolescent↗
PubMed1981

Eye movements in patients with Wallenberg's syndrome.

We studied electro-oculographic and videotape recordings of eye movements in six patients with Wallenberg's syndrome. With fixation, all patients had a spontaneous rotatory nystagmus with the fast phase directed toward the intact side. With loss of fixation, the patients' eyes deviated tonically toward the side of the lesion. Voluntary and involuntary saccades had larger amplitude when directed toward the side of the lesion than away from it. The spontaneous nystagmus predictably interacted with all slow eye movements, producing asymmetric smooth-pursuit, optokinetic, and vestibular responses. In addition, smooth-pursuit and optokinetic responses were decreased significantly in both directions compared to normal subjects. Fixation suppression of vestibular nystagmus also was impaired in both directions. We concluded that two different types of oculomotor bias were present in these patients--a velocity bias and a position bias. The former resulted from damage to the caudal lateral vestibular nuclei, and the latter from interruption of cerebellopontine pathways.

Adult↗
PubMed1981

Physiological and anatomical characteristics of primary vestibular afferent neurons in the bullfrog.

Intracellular recordings were made in the VIIIth nerve of the bullfrog (Rana catesbiana) to measure the membrane characteristics and obtain records of spontaneous and evoked spike activity of primary semicircular canal afferents. Physiological stimulation of the canals was achieved by rotating the preparation on a servomotor driven turntable with the animals' head centered in the rotational axis. The responses of each neuron to sinusoidal rotations at frequencies of 0.05Hz, 0.5Hz and for impulsive accelerations of 400 deg/sec2 were obtained. Membrane characteristics measured included the cell resting and action potential amplitude, and spike-activation threshold for applied currents. Physiologically characterized neurons were injected with horseradish peroxidase by applying pneumatic pressure and/or iontophoretic currents to the micropipettes containing 5% HRP in 1 M KCI. Following survival times of 12--48 h, the VIIIth nerve and attached vestibular end organ was removed for histochemical processing using a diaminobenzidine procedure to visualize the HRP reaction product. Light microscopy was used to discern the anatomical features of the neurons and to trace their peripheral dendritic trajectories from the ganglion to their termination(s) in the crista. Our studies have revealed that the bullfrog's primary vestibular afferents are characterized by a broad range of soma and axon diameters which correspond to an equally broad range of spontaneous and evoked activity characteristics. The largest neurons had more irregular spontaneous firing rates and consistently exhibited the greatest gain and smallest phase shifts with respect to head acceleration. These neurons consistently terminated at or near the central region of the crista. On the other hand, the smallest neurons were characterized by having the most regular spontaneous discharge patterns, the lowest gains, and greatest phase shifts with respect to head acceleration. Our findings are thus consistent with the view that the anatomical features of the primary vestibular neurons are important in determining the neuron's physiological characteristics. In terms of response dynamics our observations indicate that the receptors in the frog's crista ampullaris are heterogeneous and differentially sensitive to a wide range of stimulus frequencies.

Afferent Pathways↗
PubMed1981

A study of congenital nystagmus: vestibular nystagmus.

The vestibulo-ocular response (VOR) to rotatory stimuli was studied by electro-oculography in 41 patients with congenital nystagmus. The pattern of the VOR and the gain of the slow component velocity (peak eye velocity/peak chair velocity) were normal in 55 per cent of the patients. In 10 per cent of patients an abnormal pattern of the VOR in which the eyes deviated tonically in the direction of the slow component of the VOR was found. In these patients a mild defect in the generation of vestibular fast components might be present since the slow component velocity (SCV) appeared to be normal, but the amplitude and frequency of fast components were decreased. Thirty-two per cent of patients demonstrated persistence of an intense nystagmus with eyes opened in the dark. However, summation of the smooth movement velocity of the nystagmus and the SCV of a probably normal VOR could be demonstrated. The VOR was basically normal in patients with congenital nystagmus with or without associated ocular lesions.

Electrooculography↗
PubMed1980

Optokinetic nystagmus and parietal lobe lesions.

In an attempt to define better the mechanism of impaired optokinetic nystagmus (OKN) caused by parietal lobe lesions, we recorded the eye movements of two patients. One had a slowly enlarging parietal glioma, and the other, an infarction involving the parietal and occipital lobes. In both patients, ipsilateral foveal pursuit and full-field pursuit of a surrounding optokinetic drum were impaired while voluntary and involuntary saccades (fast components) were normal. Foveal pursuit was impaired more than full-field pursuit, suggesting the existence of two separate pathways by which visual signals for OKN slow phases reach the oculomotor centers in the brainstem. We conclude that the ipsilateral slow phase OKN deficit seen in our patients resulted from damage to the foveal pursuit pathway that runs from the occipitoparietal association area to the ipsilateral brainstem horizontal gaze center.

Adult↗
PubMed1980

Effects of halothane on the vestibulo-ocular reflex.

The differential effect of halothane on the characteristics of fast and slow components of vestibular nystagmus was investigated in rabbits. Eye movements were monitored using the "magnetic search coil" method and evaluated with the aid of a laboratory minicomputer. Low concentrations of halothane act preferentially on the fast component. There is a shift of the position threshold of fast component generation toward the periphery of the orbit and a diminution of the eye velocity during this nystagmus phase. Higher steady state concentrations of halothane reduced the velocity of the slow components whereby there is an increase in the amplitude of stimulation necessary to produce vestibulo-ocular responses of a magnitude to exceed the threshold of fast components. The results support the hypothesis that there are independent neural pathways for the production of fast and slow components of nystagmus whose neurons have different sensitivities to anesthetic agents.

Animals↗
PubMed1980

Identification of the location of vestibular lesions on the basis of vestibulo-ocular reflex measurements.

Quantitative analysis of electro-oculographic recordings of eye movement in response to precise visual and vestibular stimuli makes possible the differentiation of three categories of vestibular syndromes due to pathological changes in three different parts of the visual vestibulo-ocular reflex arc: (1) decreased vestibulo-ocular reflex gain (e.g., decrease in slow component velocity), but normal fast components and visual-vestibular interaction (labyrinth and eighth nerve); (2) normal slow component velocity but abnormal fast components to all stimuli (pontine or medullar reticular formation); and (3) normal slow component velocity to vestibulo-ocular stimulaton but abnormal visual-vestibular interaction as well as normal fast components (visual-motor pathways or cerebellum).

Cerebellar Diseases↗
PubMed1980

Study of congenital nystagmus: optokinetic nystagmus.

A severe defect of optokinetic nystagmus (OKN) was found in 46 patients with congenital nystagmus. Abnormal patterns of OKN, such as superimposition of pendular oscillations on the optokinetic slow component and inversion of OKN, were observed. Optokinetic gain (eye movement velocity/drum velocity) was decreased compared to that in normal subjects, and optokinetic after-nystagmus, or transient persistence of OKN after cessation of visual stimulation, was absent. These findings suggest that there is a defect in the subcortical optokinetic system in congenital nystagmus. Optokinetic responses did not clearly differentiate patients who had ocular lesions that impair vision, such as ocular albinism and opacities of the ocular media, from patients who did not have such lesions. Similar abnormal patterns of OKN were found in both groups of patients, although optokinetic gain tended to be lower in patients with ocular lesions than in those without lesions.

Electrooculography↗
PubMed1980

Visual tracking of auditory stimuli.

A white noise sound stimulus was emitted successively in an anechoic chamber across 24 loudspeakers equally spaced in the horizontal plane in a semicircle with diameter of 11 ft. Eye movements produced by each of 20 normal-hearing young adults in the center of this arc who tracked the sound at 10 different velocities (15--180 degrees/sec) were recorded with standard ENG methods. During each rotating cycle of the stimulus the eyes were able to follow the sound with discrete saccades, but did not produce nystagmic-like movements. Increased stimulus velocity resulted in (1) diminution of the amplitude of the tracking cycles, (2) decrease in the number of saccades, and (3) increase in the average velocity of the eye. Ss performed better with lights on than off. The additional quantitative findings from the present study further indicate the limitation in the ability of human Ss to localize a moving acoustic source in space.

Acoustic Stimulation↗
PubMed1980

On-line analysis of eye movements using a digital computer.

We describe a microcomputer system for on-line analysis of eye movement recordings. Quantitative data from the patient and statistical comparison with normative data is available within seconds of test completion. Three types of eye movements are analyzed--voluntary saccades, smooth pursuit, and nystagmus. The first two are induced by a computer-controlled laser dot projected onto a screen and the third by a computer-controlled optokinetic drum, caloric infusion, and rotatory chair. The computer algorithm differentiates the eye position signal to yield an instantaneous eye velocity record. Saccades are identified based on their characteristic velocity profile. For pursuit and nystagmus. The first two are induced by a computer-controlled laser dot projected onto a screen and the third by a computer-controlled optokinetic drum, caloric infusion, and rotatory chair. The computer algorithm differentiates the eye position signal to yield an instaneous eye velocity record. Saccades are identified based on their characteristic velocity profile. For pursuit and nystagmus, the velocity record is modified by linearly interpolating across segments in which saccades occurred. The gain (output eye velocity/input eye velocity) is calculated after Fourier analysis of the data.

Computers↗
PubMed1979

Modification of constant optokinetic nystagmus by vestibular stimuation.

Experiments were conducted to quantify the effect of a vestibular stimulation of known magnitude on a constant optokinetic nystagmus (OKN). Ten normal human subjects were tested with varying magnitudes of vestibular stimuli that were superimposed on a constant 30 degrees optokinetic stimulus. The gain of the vestibular system in the dark was 0.42 +/- 0.11, and the gain in the light during superimposition testing was 0.12 +/- 0.02. From these results, predictions were made that the degree of vestibular imbalance necessary to produce an asymmetric OKN would generate a spontaneous nystagmus in the dark, which would be equivalent to 20 to 30 degrees. Data from a large group of patients were used for corroboration of the results.

Adult↗