Spontaneous Abnormal Vertical Eye Movements of Coma.

Patients in coma may exhibit several different types of spontaneous ocular movements. Three forms of spontaneous vertical movements have been distinguished based on the relative velocities of their downward and upward phases. The pathophysiological basis of all these movements has remained obscure. Two patients are reported who demonstrated all three types of spontaneous vertical movements (ocular bobbing, ocular dipping, and reverse ocular bobbing), implying that the movements may all be differing manifestations of the still unknown pathophysiological process.

So far it has only been possible to detect horizontal and vertical eye movements during real time; torsional eye movements have to be calculated from video-tape that have been processed several times, and each investigation takes considerable time. We developed a real time binocular infra red video eye tracker for routine clinical examination which allows real time graphical visualization of horizontal, vertical and torsional eye movements with a bandwidth of 12 Hz (25 Hz refresh frequency). Eye movements in three dimensions can now be obtained as easy as has been done before with electronystagmography for the horizontal component. In contrast to previous systems described, we analyze only those parts of the video-frame that are essential for detection of all three eye movements. This results in a huge data-reduction accompanied by a speed-up of analysis. The black pupil centre is detected by an iterative process of analyzing several horizontal and vertical lines of the even video field. The algorithm searches for regions of minimal intensity. Horizontal and vertical eye rotation is then calculated and transformed into Fick's coordinates. Based upon the centre of the pupil four concentric segments are defined in the iris to detect torsion and to enable correction for false rotation. Torsion is detected by cross-correlation of each segment and estimated from the outcome of the correlation coefficients. All transformations are established by predefined stored transformation matrices thus making real time calculations for transformation unnecessary. After corrections for eccentricity and assuming that fixation of the subjects tested was perfect, accuracy appears to be within 0.3 degrees-1.0 degrees for all three dimensions. Linearity after all corrections is within 4-9% within a visual field of 60 x 40 degrees (horizontal x vertical).

Investigation of cue-based vertical and horizontal eye movements with electroencephalographic and eye-tracking data

To investigate the characteristics of the head movements and the mechanisms of gaze, stabilization during walking and running, eye and head movements were recorded in 10 normal subjects and 8 patients with labyrinthine lesions, who repeated stepping (1.OHz) and running (1.5Hz) on the same spot. 1. In normal subjects, head displacements during stepping were limited in the vertical, right-left and anteroposterior directions (0.8, 1.5 and 1.5cm on average, respectively), and the head rotations and the eye movements were also small. During running, the increase in the vertical head displacement (5.5cm on average) induced rhythmical pitching motions of the head and vertical eye movements. 2. In patients with labyrinthine lesions, both the horizontal head displacement and the rotation amplitude became twice as large as those in normal subjects during either locomotion, however, horizontal eye movements did not correspondingly increase. The vertical head displacements during running resembled those of normal subjects, but the amplitude of pitching motion of the head significantly decreased. 3) The spatial stabilization of the head during stepping in normal subjects indicated that walking is a suitable locomotion for gaze stabilization. On the other hand, the head was more unstable during running, however, the pitching motions of the head resulting from vertical head displacements seemed to reduce the concussion of the head and produce vertical compensatory eye movements which maintained the gaze stabilization. 4) In patients with labyrinthine lesions, the horizontal eye movements did not compensate the horizontal head movements during walking and running. Furthermore, since the pitching motions of the head could not be produced rhythmically during running, the vertical body oscillations were directly conducted to the head. The abnormalities of the head movements in addition to the insufficient compensations may cause oscillopsia in these patients. 5) The present study indicated that the head stabilization is essential to maintain the gaze stabilization during walking and running and that the semicircular canals-ocular reflexes act a major role in these mechanisms.

Patients with anoxic coma had a cyclic, downward dipping motion of the eyes. The sign is different from ocular bobbing, seizure-related eye deviation, oculogyric crisis, and roving eye movement. Its distinguishing characteristics are slow downward with rapid upward movement, a nadir at the extreme of downgaze, and spontaneous roving horizontal eye movements. Based on necropsy findings in one case and lesions of the basal ganglia evident on computerized tomographic scan in another, it is proposed that cortical dysfunction with damage to the basal ganglia may cause ocular dipping.

It is well known that eye movements are highly affected by Parkinson’s disease. The majority of studies related to effects of Parkinson’s disease on eye movements have been performed for rapid eye movements during sleep. However, in the current study, eye movements during resting-state (eyes-open and eyes-closed conditions) were studied to evaluate Parkinson’s disease. To measure eye movements, vertical electrooculography (VEOG) was used. Using extracted features in time-, frequency-, and time-frequency domains of VEOG time-series, a classification analysis between healthy subjects and Parkinson’s disease patients in OFF- and ON-medication states was performed. The most-informative features for an error-correcting output codes support vector machine classifier were selected according to the multiple-comparison corrected p-values. VEOG data obtained 69.10 % and 87.27 % discrimination accuracy for OFF- and ON-medication states, respectively. Interestingly, higher discrimination was obtained for the lower frequency contents of VEOG time-series (0.1–1.25 Hz). The most discriminative features were related to the variation of amplitude and frequency content for OFF-medication, while in ON-medication the features according to the variation of VEOG amplitudes were removed from the most discriminative features list. Based on the obtained results, it was concluded that vertical eye movements of Parkinson’s disease patients had lower amplitude variation compared with healthy subjects in OFF-medication, while levodopa prescription increased such variation in vertical eye movements during the eyes-closed condition and decreased the variation during the eyes-open condition. Levodopa prescription possibly affects the amplitude variation of VEOG time-series, while it had no effect on the movement rates (frequency contents) of vertical eye movements.

Vertical saccadic eye movements are accompanied by concurrent eyelid movements in the same direction. The interstitial nucleus of Cajal (InC) controls eye position for vertical eye movements and may also control saccade-related lid position as well. This study investigates whether the InC serves as a premotor center for eyelid saccades, by employing dual-tracer methods in cats to label both the projections of the InC and the motoneurons supplying the levator palpebrae superioris (LPS) muscle, which lie in the caudal central subdivision (CCS) of the oculomotor complex. Injections of biotinylated dextran amine (BDA) into the InC anterogradely labeled axons that terminated bilaterally throughout the CCS and in the oculomotor nuclei proper. Labeled terminals lay in close association with labeled LPS motoneurons, which were retrogradely labeled following injections of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the muscle. Ultrastructural investigation revealed that most terminals contained spherical vesicles and formed asymmetric synaptic contacts with the labeled motoneurons. These results strongly suggest that the InC monosynaptically controls lid movements in conjunction with vertical eye movements, including saccades. To identify the neurons of origin for this pathway, WGA-HRP injections were centered in the CCS. These experiments indicate that lid and eye motoneurons may share a common source of bilateral InC input. Thus, a common vertical position signal may be employed to maintain the lid and eye at appropriate elevations during fixation, such that the lid sits just above the pupil, allowing unobstructed vision, but at the ready to protect the cornea.

Horizontal and vertical pursuit eye movements were analyzed quantitatively in normal subjects with the use of a charge-coupled device (CCD)-electro-oculogram. Parameters adopted for the qualification were coherence function and phase.As the speed of the target increased, the difference in phase between the target and both horizontal and vertical eye movements became larger. However, there was no significant difference in phase between horizontal and vertical eye movement.Quantitative frequency analysis of pursuit eye movements showed that eyes follow a horizontally moving target more accurately than a vertically moving target. When a target is moved vertically in the upper half of the field, the eyes follow it less accurately.

Electronystagmography (ENG) has been widely used in physiological studies of eye movements. It is generally known that ENG is at a disadvantage in recording the vertical component of eye movements, and thus there has been a great deal of difficulty in physiological studies of vertical eye movements using ENG. The eye mark recorder is an instrument which has already been used in the study of visual point movement in various situations. We tried to apply the eye mark recorder to the recording of eye movements in normal volunteers, and then compared its recording characteristics with those of ENG. When recording vertical eye movements with the eye mark recorder there is little baseline drift and no confusing waves caused by blinking, which is sometimes misinterpreted as nystagmus. The result is easy calibration of the device and more accurate measurement of the slow-phase velocity of nystagmus than ENG. Recording with the eye mark recorder is atraumatic and allows binocular visual stimulation. There are certain other techniques, such as search coil or video oculography, which allow more accurate recording of vertical eye movements than ENG. The search coil techniques, however, requires the attachment of a measuring contact lens during the examination and video oculography is still in development process, so both of them are difficult to use widely. Thus, we found that the eye mark recorder has a great advantage in recording the slow-phase eye velocity of vertical nystagmus and the vertical component of smooth eye movements in humans. We think that eye mark recorder can serve as a powerful new tool to investigate vertical OKN and OKAN.

To evaluate the role of neural integrators (NI) in the oculomotor system. A literature search was carried out using several electronic databases during the months of June 2014 to March 2015. The following keywords were used to generate focused results: 'neural integrators', 'gaze-holding', 'oculomotor integration', 'impaired gaze-holding', 'gaze evoked nystagmus' and 'gaze dysfunction'. Further materials were found through searching relevant articles within reference lists. Seventy-one articles were sourced for this review which analysed animal and human subjects and network models; 45 were studies of humans, 16 studies of primates, three studies of felines and one study from rats and network models. The remaining articles were literature reviews. The horizontal and vertical, including torsional, NI are located logically in the brainstem, nearby their appropriate target extraocular motoneuron nuclei for stable eye position in eccentric position. The nucleus prepositus hypoglossi (NPH) and medial vestibular nuclei (MVN) are closely linked at the caudal pons and dorsal rostral medulla, integrating horizontal conjugate eye movement. The interstitial nucleus of Cajal (INC) integrates vertical and torsional eye movement at the upper midbrain. The integrator time constant is averaged to 25seconds in human horizontal and animal vertical NI to perform its function. Case reports revealed that dysfunction of horizontal NI also resulted in vertical ocular deviations, indicating some overlap of horizontal and vertical gaze control. Furthermore, pharmacological inactivation of NI exposed a population of inhibitory neurotransmitters that permits its mechanism of action; allowing for smooth conjugate movement. Neural integrators operate to integrate eye velocity and eye position information to provide signals to extraocular motoneurons to attain and maintain a new position. Therefore, NI allow image stabilization during horizontal and vertical eye movements at eccentric positions for comfortable single vision.

Congenital abnormal eye movement without gaze nystagmus.

Objective: The aim of this study is to investigate how well eye movement times in visual target selection tasks by an eye input device follows the typical Fitts" Law and to compare vertical and horizontal eye movement times.BR Background: Typically manual pointing provides excellent fit to the Fitts" Law model. However, when an eye input device is used for the visual target selection tasks, there were some debates on whether the eye movement times in can be described by the Fitts" Law. More empirical studies should be added to resolve these debates. This study is an empirical study for resolving this debate. On the other hand, many researchers reported the direction of movement in typical manual pointing has some effects on the movement times. The other question in this study is whether the direction of eye movement also affects the eye movement times.BR Method: A cursor movement times in visual target selection tasks by both input devices were collected. The layout of visual targets was set up by two types. Cursor starting position for vertical movement times were in the top of the monitor and visual targets were located in the bottom, while cursor starting positions for horizontal movement times were in the right of the monitor and visual targets were located in the left.BR Results: Although eye movement time was described by the Fitts" Law, the error rate was high and correlation was relatively low (R² = 0.80 for horizontal movements and R² = 0.66 for vertical movements), compared to those of manual movement. According to the movement direction, manual movement times were not significantly different, but eye movement times were significantly different.BR Conclusion: Eye movement times in the selection of visual targets by an eye-gaze input device could be described and predicted by the Fitts" Law. Eye movement times were significantly different according to the direction of eye movement.BR Application: The results of this study might help to understand eye movement times in visual target selection tasks by the eye input devices.

Eye movements serve vision, which has two different aims: changing images using saccades, i.e. rapid eye movements, and stabilizing new images on the retina using slow eye movements. Eye movements are performed by ocular motor nuclei in the brainstem, on which supranuclear pathways--originating in the cerebral cortex, cerebellum and vestibular structures--converge. It is useful for the neurologist to know the clinical abnormalities of eye movements visible at the bedside since such signs are helpful for localization. Eye movement paralysis may be nuclear or infranuclear (nerves), involving all types of eye movements, i.e. saccades as well as the vestibulo-ocular reflex (VOR), or supranuclear, in which case the VOR is usually preserved. Lateral eye movements are organized in the pons, with paralysis of adduction (and preservation of convergence) when the lesion affects the medial longitudinal fasciculus (internuclear ophthalmoplegia), paralysis of conjugate lateral eye movements when the lesion affects the abducens nucleus (VI) and the "one-and-a-half" syndrome when both these structures are involved. Vertical eye movements are organized in the midbrain, with ipsilateral oculomotor (III) paralysis and contralateral paralysis of the superior rectus muscle when the third nerve nucleus is unilaterally damaged, supranuclear upward gaze paralysis when the posterior commissure is unilaterally damaged and supranuclear downward gaze paralysis (often coupled with upward gaze paralysis) when the mesencephalic reticular formations are bilaterally damaged. Numerous types of abnormal eye movements exist, of which nystagmus is the most frequent and usually due to damage to peripheral or central vestibular pathways. Cerebral hemispheric or cerebellar damage results in subtle eye movement abnormalities at the bedside, in general only detected using eye movement recordings, because of the multiplicity of eye movement pathways at these levels and their reciprocal compensation in the case of a lesion. Lastly, eye movements can also help the neuroscientist to understand the organization of the brain. They are a good model of motricity allowing us, using eye movement recordings, to study the afferent pathways of the cortical areas that trigger them, and thus to analyze relatively complex neuropsychological processes such as visuo-spatial integration, spatial memory, motivation and the preparation of motor programs.

1. The spike activity of deep cerebellar nuclear neurons was recorded in the alert cat during spontaneous and during vestibularly and visually induced eye movements. 2. Neurons were classified according to their location in the nuclei, their antidromic activation from projection sites, their sensitivity to eye position and velocity during spontaneous eye movements, and their responses to vestibular and optokinetic stimuli. 3. Type I EPV (eye position and velocity) neurons were located mainly in the posterior part of the fastigial nucleus and activated antidromically almost exclusively from the medial longitudinal fasciculus close to the oculomotor complex. These neurons, reported here for the first time, increased their firing rate during saccades and eye fixations towards the contralateral hemifield. Their position sensitivity to eye fixations in the horizontal plane was 5.3 +/- 2.6 spikes s-1 deg-1 (mean +/- S.D.). Eye velocity sensitivity during horizontal saccades was 0.71 +/- 0.52 spikes s-1 deg-1 s-1. Variability of their firing rate during a given eye fixation was higher than that shown by abducens motoneurons. 4. Type I EPV neurons increased their firing rate during ipsilateral head rotations at 0.5 Hz with a mean phase lead over eye position of 95.3 +/- 9.5 deg. They were also activated by contralateral optokinetic stimulation at 30 deg s-1. Their sensitivity to eye position and velocity in the horizontal plane during vestibular and optokinetic stimuli yielded values similar to those obtained for spontaneous eye movements. 5. Type II neurons were located in both fastigial and dentate nuclei and were activated antidromically from the restiform body, the medial longitudinal fasciculus close to the oculomotor complex, the red nucleus and the pontine nuclei. Type II neurons were not related to spontaneous eye movements. These neurons increased their firing rate in response to contralateral head rotation and during ipsilateral optokinetic stimulation, and decreased it with the oppositely directed movements. 6. Saccade-related neurons were located mostly in the fastigial and dentate nuclei. Fastigial neurons were activated antidromically from the medial longitudinal fasciculus, while dentate neurons were activated from the red nucleus. These neurons fired a burst of spikes whose duration was significantly related to saccade duration. Dentate neurons responded during the omni-directional saccades, while some fastigial neurons fired more actively during contralateral saccades. 7. These three types of neuron represent the output channel for oculomotor signals of the posterior vermis and paravermis. It is proposed that type I EPV neurons correspond to a group of premotor neurons directly involved in oculomotor control.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of the medial longitudinal fasciculus (MLF) in voluntary and vestibular eye movements was investigated by both lesion and single fiber recording experiments in alert monkeys. Bilateral lesions of the MLF rostral to the abducens nucleus produce strikingly different deficits in vertical and horizontal eye movements. As already described by others, all adducting movements except for vergence were slowed. In addition, there was a shortterm reduction in the gain of the horizontal vestibulo-ocular reflex (VOR) with modest changes in the phase shift of eye movements due to sinusoidal head rotation. On the other hand, vertical fixation, smooth pursuit and the vertical VOR were severely impaired for as long as a month after the lesion. Both the vertical VOR and smooth pursuit were virtually abolished and a vertical gaze evoked nystagmus, composed of normal saccades followed by a drift to the midline, was present. The deficits in vertical and horizontal eye movement could be accounted for by destruction of the MLF fibers revealed by single unit recording. Based on their discharge properties, two fiber types, histologically verified to travel in the MLF at the level of the trochlear nucleus, could be distinguished. The first discharged only with horizontal eye movements and behaved like a medial rectus motoneuron; these fibers emitted a burst of spikes prior to and during adducting saccades, increased their tonic activity with adductive fixations, and exhibited a modulated firing rate during the VOR. The second discharged with vertical head velocity when the animal was oscillated about the interaural axis; in addition, these fibers exhibited constant firing rates which were a function of eye position and paused for all saccades. Loss of the first fibers would impair all adducting eye movements whereas loss of the second fibers would impair holding the eye in the upper and lower field of gaze and the slow phase of the WOR but not vertical saccades. These studies demonstrate a neural substrate for anterior internuclear ophthalmoplegia and further suggest that an examination of vertical eye movements might be a sensitive indicator of MLF lesions.