Conjugate Eye Movements Research Articles

Evidence for three-dimensional cortical control of gaze from epileptic patients

Electrophysiological studies in primates indicate that the eye fields of the cerebral hemispheres control gaze in three-dimensional space, and contain neurons that encode both conjugate (versive) and vergence eye movements....

Dynamic Characterization of Agonist and Antagonist Oculomotoneurons During Conjugate and Disconjugate Eye Movements

In this report, we provide the first quantitative characterization of the relationship between the spike train dynamics of medial rectus oculomotoneurons (OMNs) and eye movements during conjugate and disconjugate saccades. We show that a simple, first-order model (i.e., containing eye position and velocity terms) provided an adequate model of neural discharges during both on and off-directed conjugate saccades, while a second-order model, which included a decaying slide term, significantly improved the ability to fit neuronal responses by approximately 10% (P<0.05). To understand how the same neurons drove disconjugate eye movements, we evaluated whether sensitivities estimated during conjugate saccades could be used to predict responses during disconjugate saccades. For the majority of neurons (68%), a conjugate-based model failed, and instead neurons preferentially encoded the position and velocity of the ipsilateral eye. Similar to our previous results with abducens motoneurons, we also found that position and velocity sensitivities of OMNs decreased with increasing velocity, and the simulated population drive of OMNs during disconjugate saccades was less (approximately 10%) than during conjugate saccades. Taken together, our results provide evidence that the activation of the antagonist, as well as agonist, motoneuron pools must be considered to understand the neural control of horizontal eye movements across different oculomotor behaviors. Moreover, we propose that the undersampling of smaller motoneurons (e.g., nontwitch) was likely to account for the missing drive observed during disconjugate saccades; these cells are thought to be more specialized for vergence movements and thus could provide the additional input required to command disconjugate eye movements.

Síndrome opsoclono-mioclono-atáxico paraneoplásico

Opsoclonus myoclonus ataxia syndrome (OMAS) is a very infrequent paraneoplastic or postinfectious movement disorder, which may occur at any age, most commonly between 6 and 36 months of age. In four days, a previously healthy 30-month-old girl progressively developed gait instability, intention tremor, dysarthric speech, irritability and altered sleep. Physical and neurological examination did not reveal additional deficits. She had had a transient exanthema without fever three weeks before. Basic blood analysis, serologies, cultures, urine toxin detection, EEG and cerebral CT were normal. Lumbar puncture showed minimal lymphocytosis. On the fifth day following the onset of symptoms, the ataxia worsened, precluding sitting, and the tremor was aggravated by intentional myoclonus. Chaotic saccadic, large amplitude multidirectional but conjugated eye movements appeared. An opsoclonus (OMAS) was suspected and a chest X-ray and CT revealed a paravertebral thoracic mass. Surgery confirmed a localized ganglioneuroblastoma. Blood neuron-specific enolase and urine catecholamine levels were normal. Opsoclonus disappeared with high doses of prednisone and following surgery. Ataxia improved but the patient still required low daily doses of steroids for one year. Conclusions. The diagnosis of OMAS is based on clinical findings. Opsoclonus is a specific clinical sign that all clinicians must recognize. The presence of opsoclonus should always prompt the search for a neural-crest tumour, as one of the most important precipitating causes. The prognosis of this tumour is usually excellent, but neurological symptoms frequently relapse due to the tapering of steroids.

Opsoklonus-Myoklonus-Syndrom

Introduction: Opsoclonus-myoclonus-syndrome (OMS) is a rare, idiopathic or paraneoplastic syndrome, which is predominantly characterized by opsoclonus (rapid, multi-directional conjugate eye movements), a movement disorder in terms of a myoclonic ataxia and irritability. In adulthood an association with different types of cancer has been reported, whereas in childhood neuroblastomas (NB) are found frequently.

Vergence deficits in patients with cerebellar lesions

The cerebellum is part of the cortico-ponto-cerebellar circuit for conjugate eye movements. Recent animal data suggest an additional role of the cerebellum for the control of binocular alignment and disconjugate, i.e. vergence eye movements. The latter is separated into two different components: fast vergence (to step targets) and slow vergence (to ramp and sinusoidal targets). The aim of this study was to investigate whether circumscribed cerebellar lesions affect these dynamic vergence eye movements. Disconjugate fast and slow vergence, conjugate smooth pursuit and saccades were binocularly recorded by a scleral search coil system in 20 patients with acute cerebellar lesions (all ischemic strokes except for one) and 20 age-matched healthy controls. Patients showed impairment of slow vergence while fast vergence was unaffected. Slow vergence gain to sinusoidal targets was significantly reduced, both in convergence and divergence direction. Divergence but not convergence velocity to ramp targets was reduced. Conjugate smooth pursuit eye movements to sinusoidal and to step-ramp targets were impaired. Patients had saccadic hypometria. All defects were particularly expressed in patients with vermis lesions. In contrast to recent animal data fast vergence was not impaired in any of our patient subgroups. We conclude that (i) the human cerebellum, in particular the vermis, is involved in the processing of dynamic vergence eye movements and (ii) cerebellar lesions elicit dissociable effects on fast and slow vergence.

Vergence deficits in cerebellar lesions

The cerebellum is part of the cortico-ponto-cerebellar circuit for conjugate eye movements. Accordingly, cerebellar lesions cause smooth pursuit deficits and saccadic dysmetria. In contrast, the role of the cerebellum for disconjugate, i.e. vergence eye movements in humans is still unknown. The aim of this study was to investigate whether cerebellar lesions affect vergence eye movements.

Vergence deficits in cerebellar lesions

The cerebellum is part of the cortico-ponto-cerebellar circuit for conjugate eye movements. Accordingly, cerebellar lesions cause smooth pursuit deficits and saccadic dysmetria. In contrast, the role of the cerebellum for disconjugate, i.e. vergence eye movements in humans is still unknown. The aim of this study was to investigate whether cerebellar lesions affect vergence eye movements. Similar to conjugate eye movements, vergence can be separated into two different components: vergence to step targets (fast vergence) and vergence to ramp and sinusoidal targets (slow vergence). Eye movements (fast and slow vergence, smooth pursuit, saccades) were binocularly recorded with the scleral search coil system in 20 patients with acute cerebellar lesions (ischemic strokes) and age-matched healthy controls. Small dim laser stimuli were presented on an earth horizontal platform at the level of the subject's nose. Smooth pursuit always had a constant vergence angle (iso-vergence). The majority of patients had unilateral lesions in the territory of the posterior inferior cerebellar artery (3 patients with infarctions in the superior cerebellar artery territory, one cavernoma patient). Group analysis revealed impairment of both conjugate and disconjugate eye movements as well as reduced saccadic gain (Table). The gain of slow vergence to sinusoidal targets was reduced in the patients. Patients with vermal lesions (subgroup, n=10) had a significant lower gain compared to controls while the other patients did not differ. In contrast, fast vergence to step targets remained unimpaired (acceleration). Smooth pursuit to step-ramp targets was impaired, with increased latency, decreased initial acceleration and reduced gain. Smooth pursuit eye movement gain to sinusoidal targets was significantly reduced. Similar to vergence eye movements to sinusoidal targets, patients with vermal lesions had a lower smooth pursuit gain while the other patients did not differ from controls. We propose that (1) the cerebellum is involved in the processing of vergence eye movements, (2) the cerebellar vermis plays an important role in executing vergence eye movements and (3) neural control of fast and slow vergence appears to be separated in the cerebellum.

Abnormal Eye Movements in Children

The recognition and evaluation of abnormal eye movements in children is an essential task for the pediatric ophthalmologist that may lead to the discovery of systemic and neurologic disease and even preventable visual loss. With few exceptions, the eye movements discussed in this chapter can occur at all stages of life, but their presentation in infancy and childhood has a unique significance that merits their inclusion in this textbook on pediatric manifestations of ophthalmic disease. The first step in approaching abnormal eye movements is to categorize them into broad categories, such as ‘‘roving’’ eye movements that are commonly seen in patients who develop visual-impairment early in life, saccadic intrusions (see below), or the true forms of nystagmus. With a cursory examination, these manifestations of ocular motor pathology may be confused, but each has its own implications for diagnosis and management. Roving eye movements are very slow, large amplitude, and seemingly aimless movements of the eyes that are seen in patients who are severely blind early in life. Saccadic intrusions are relatively fast, conjugate eye movements of relatively small amplitude that often occur in short bursts or as single events. Saccadic intrusions may occur as back-andforth movements across the point of fixation (ie, ‘‘saccadic oscillations’’), or as equal amplitude movements off to one side and then back onto the point of fixation (ie, ‘‘square-wave jerks’’). For both types of saccadic intrusions, there is an almost imperceptible delay between one saccadic movement and the next (ie, intersaccadic interval). In distinction,

Eye movement deficits in children with posterior fossa tumors

Purpose: To evaluate pre- and postsurgical eye movement abnormalities in children with posterior fossa tumors. Methods: Conjugate and vergence eye movements were recorded with inferior rectus video-oculography in 25 children with posterior fossa (PF) tumors after resection of the tumor. Several children were also tested presurgically. Horizontal smooth pursuit (SPh) was elicited with a sinusoidally moving target (±10°, peak velocity, 30°/s). Horizontal and vertical OKN, optokinetic nystagmus, was assessed with a high contrast square-wave grating moving at 15, 30, and 45°/s.

Altered Mental Status and a Retro-auricular Mass

A 29-year-old woman was found lying unconscious in the shower. There was a two-day history of headache and dizziness. In the emergency room, she was initially stuporous (Glasgow Coma Scale 10/15), afebrile, bradycardic and hypertensive. She exhibited roving, conjugate eye movements, left facial paresis (including frontalis), left ptosis, diffuse hypotonia, extensor plantar responses bilaterally and a 1.5 cm warm, fluctuant mass with surrounding erythema behind the left ear (Figure 1). Otoscopy revealed a bulge in the posterior wall of the left external auditory canal.

Conjugate eye movements and gamma power modulation of the EEG in persistent vegetative state

Background Power in the gamma band EEG increases during saccades in normal subjects. Objective To develop a potential method to quantify signs of cortical responsiveness in persistent vegetative state (PVS) we quantified gamma range EEG in association with conjugate slow ballistic eye movements (SBEM). Methods The EEG and the simultaneous electro-oculogram were recorded in 14 (8F/6M) PVS patients. Clinical scoring was based on the Glasgow Coma Scale (GCS) and Coma Rating Scale (CRS). The Wavelet Transform, followed by Hilbert transform was applied to the EEG and gamma power distribution was quantified relative to the timing of an eye movement. We correlated the clinical and the neurophysiological measures. Results Gamma activity was present in all PVS patients. Its power was modulated in association with eye movements only in less severely affected patients, with minimum power prior to, and maximum power during the eye movement. In severely affected patients there was no evidence of a temporal relationship between gamma power and the phase of the eye movement. Conclusions Detecting changes in the time course of gamma power in relation to conjugate ballistic eye movements provides a quantitative neurophysiological method for prospective longitudinal studies to explore if the preservation of this CNS function relates to the potential for recovery in PVS patients.

Systematic perceptual distortion of 3D slant by disconjugate eye movements

When an observer pursues an object moving away from him or her, both eyes rotate in the opposite direction, and this type of disconjugate eye movement can generate eye movement-induced disparities in the case of dynamic objects that are present around the pursuit object. Such disparities are not usually generated by conjugate eye movement. The aim of this study was to determine whether eye movement-induced disparities could be calibrated with eye position information. Observers were requested to judge the slant of an object defined by the spatiotemporal pattern of occlusion during disconjugate eye movement. Interestingly, the observers’ perception of the slant of the target object was systematically distorted, although the perceptual distortion decreased somewhat in the presence of a salient reference around the target. This suggests that eye movement-induced disparities are not calibrated properly with eye position information.

New facilitation exercise using the vestibulo-ocular reflex for ophthalmoplegia: preliminary report

To study the effect of facilitation exercises using the vestibulo-ocular reflex on ophthalmoplegia due to brainstem injury. A single-baseline design (A-B: A without specific therapy, B with specific therapy) across individual subjects. Inpatient rehabilitation facility. Eight patients with ophthalmoplegia (total of 15 affected muscles) due to brainstem injury. Basic rehabilitative treatment that included physical therapy, occupational therapy and/or speech therapy for impairments such as hemiplegia, ataxia or dysarthria was administered for two weeks (control treatment). Then, two facilitation exercise sessions (100 times/day, five days/week for two weeks) were administered in addition to the basic rehabilitative treatment for four weeks to the eight patients with ophthalmoplegia. Ophthalmoplegia was evaluated at study entry and at the end of each two-week session. The goal of the facilitation exercises is to facilitate voluntary eye movement using conjugated eye movements in the direction opposite to passive movements of the head. To assess ophthalmoplegia we measured the distance between the internal/external corneal margin and the canthus of the affected eye on images recorded on a video tape recorder. After the initial two-week basic rehabilitative treatment, the distance between the corneal margin and canthus decreased slightly. Subsequently, after each of the two facilitation exercise sessions, there were significant reductions in the distance between the corneal margin and canthus compared with that at the beginning of the respective facilitation exercise session. Facilitation exercises significantly improved the horizontal movement of eyes with ophthalmoplegia due to brainstem injury.

Ocular dominancy in conjugate eye movements at reading distance

We recorded conjugate eye movements to elucidate whether ocular dominancy was present at reading distance in 21 normal volunteers with the right-handedness by using a video-oculographic (VOG) measurement. This included the velocity of smooth pursuits, and the latency and velocity of saccades. We defined the dominant eye for each subject by means of the near–far alignment test and 20 subjects showed the right dominant eyes. Although the ocular dominancy was not found in the velocity of smooth pursuit and vertical saccades, the velocity of horizontal saccades in the dominant eyes was faster than that in the non-dominant eyes. These results suggest that the dominant eye is functionally activated prior to non-dominant eye in horizontal saccades at reading distance, which thus indicates the functional dominancy of the dominant eye in conjugate eye movements.

Binocular Coordination in Fore/Aft Motion

Stabilization of images on the fovea during either fore/aft translation of a subject or fore/aft movement of a visual target in front of a stationary observer imposes complex geometrical requirements that depend upon the eccentricity of the object of interest with respect to the eyes. Each eye needs to be rotated independently with varying proportions of conjugate (version) and disconjugate (vergence) eye movements to maintain fixation of the target. Here, we describe binocular coordination in the early response to translational movements of normal subjects along their naso-occipital axis. We recorded the responses evoked by small (about 4 cm), abrupt (about 0.7 g), fore/aft translations in four normal subjects while they viewed a near target. In the forward and backward starting positions the target was 15 or 10.5 cm away, respectively. Each subject was tested with the target centered between the eyes, aligned on the right eye, and placed to the right of the right eye by approximately 3 cm. The three conditions differed only in the lateral eccentricity of the target, yet the geometrical requirements for image stabilization are very different: pure vergence, one eye still, or mostly version. We found that the eye-movement responses closely matched what was needed for visual stabilization of the target, though responses to stimuli calling for divergence were less accurate than those for convergence. The latency of these responses ranged from 40 to 65 ms and achieved about 80% of the ideal response by 90 to 100 ms after the onset of the stimulus. Next, we asked whether these eye movements were generated by the vestibular system or by high-level strategies for image stabilization, such as pursuit. Thus, in a second set of experiments we used the mean profile of fore\aft body motion computed for each subject to drive a small visual target across the same distances and in the same eccentricities used during body translations. We found that visually driven responses had longer latencies (by at least 80 ms, ranging from 144 to 155 ms) and slower dynamics (with significantly lower peak eye velocities), highlighting the different subsystems producing the two types of responses. Saccades were also an important component of the response to both visual and vestibular stimuli, less frequent during the centered-target configuration and more frequent during viewing of eccentric targets. Visual stimuli evoked saccadic corrections more often and at shorter latencies than did vestibular stimuli. Both smooth and saccadic eye movements were appropriately disconjugate and their pattern depended on whether the eyes were converging or diverging.

Periodic alternating gaze deviation associated with schizencephaly and optic nerve hypoplasia

A 3-year-old girl presented with alternating horizontal gaze deviations lasting 20 to 30 seconds interspersed with brief 5- to 10-second periods of normal ocular motility. She had schizencephaly and optic nerve hypoplasia. This is the first case description of the entity of periodic alternating gaze deviation with these disorders. CASE REPORT A 3-year-old girl was referred for visual evaluation because of trouble following objects. Her mother stated that she could not remember ever taking a picture of her daughter when her eyes were aligned in the primary position. She noted that they were consistently directed in either right gaze or left gaze. She was diagnosed with schizencephaly by prenatal ultrasound and postnatal magnetic resonance imaging. She was severely delayed physically and cognitively and she could not walk without assistance. She was the product of an uncomplicated Cesarean delivery. Medications included polyethylene glycol for constipation and levothyroxine for hypothyroidism. Family history was unremarkable. There was no history of seizures. The examination showed difficulty fixating and following especially when the eyes were deviated in eccentric gaze. She blinked to threat only from her left visual field and mostly when her eyes were moving between either eccentric positions of gaze. Extraocular motility showed full conjugate eye movements without strabismus. Her eyes appeared forced into either extreme right or left gaze and this would last 20 to 30 seconds before they would drift to primary position for 5 to 10 seconds and then move into the opposite eccentric horizontal eye position. The eyes never deviated up or down. During the periods of eccentric gaze, she would turn her head in a contraversive manner to maintain fixation at objects in front of her. In the interictal period, she would manifest some nystagmus that beat either to the left or to the right, whichever direction that the eyes were pointing. This appeared similar to end-gaze nystagmus. During these interictal periods, she would have normal optokinetic and vestibular responses, but not during the gaze deviations when there were no responses. Eyelids were normal and face was symmetric with good eyelid closure. There was no proptosis present clinically. Pupils were equal and briskly reactive, but there was a left afferent pupillary defect. Ocular media were clear OU. Funduscopy revealed bilaterally hypoplastic nerves without pallor (Figure 1). She was alert and had minimal speech output, and muscle tone was normal throughout. Orthotics were in place on her lower extremities. Her MRI scan demonstrated a large left lateral ventricle that communicated with a subarachnoid space through the posterior parietal lobe (Figure 2). There was ectopic gray matter lining the ventricle.

Adjustment of the vestibulo-ocular reflex gain as a function of perceived target distance in humans

The human vestibulo-ocular reflex (VOR) was investigated during active head movements in yaw while subjects were asked to view targets located at 20, 30, 40, 60, 90, and 120 cm distance aligned with eye level. Binocular video cameras were used to study conjugate eye movements and binocular convergence. Perceived target distance was determined during head oscillation by having the subjects move a cursor to the remembered position of the previously seen targets. The changes in VOR gain with viewing distance were found to be more closely related to perceived target distance than to actual target distance or fixation distance. This result suggests that the adjustment of VOR gain with viewing distance is under stronger cognitive control than would be expected of a simple motor reflex.

Ophthalmoplegic migraine

Ophthalmoplegic migraine is a rare presentation of migraine complicated by an isolated oculomotor paresis. Vasodilation of extracranial vessels is believed to underlie the headache, and vasoconstriction to account for the ophthalmoplegia. Whether the vascular insult involves the central or peripheral portions of the oculomotor nerve is still uncertain. We describe a child who presented with ophthalmoplegic migraine and was demonstrated to have a deficiency of the near triad documented by eye movement and pupillary recordings. Voluntary conjugate eye movements—saccades, smooth pursuit, and optokinetic nystagmus—were normal. Vergence amplitudes appropriate to fixation distance were elicited for Snellen optotypes but not to a point source of light. Concurrent measures of pupillary diameter failed to reveal significant modulation to either stimulus. Brain magnetic resonance imaging scan was normal, and there was no contrast enhancement of the oculomotor nerve at its exit from the midbrain. Both the oculomotor paresis and concurrent presence of a deficiency of the near triad localized the vascular insult to the oculomotor nerve complex in the brainstem.

Attenuation of perceived motion smear during vergence and pursuit tracking

When the eyes move, the images of stationary objects sweep across the retina. Despite this motion of the retinal image and the substantial integration of visual signals across time, physically stationary objects typically do not appear to be smeared during eye movements. Previous studies indicated that the extent of perceived motion smear is smaller when a stationary target is presented during pursuit or saccadic eye movements than when comparable motion of the retinal image occurs during steady fixation. In this study, we compared the extent of perceived motion smear for a stationary target during smooth pursuit and vergence eye movements with that for a physically moving target during fixation. For a target duration of 100 ms or longer, perceived motion smear is substantially less when the motion of the retinal image results from vergence or pursuit eye movements than when it results from the motion of a target during fixation. The reduced extent of perceived motion smear during eye movements compared to fixation cannot be accounted for by different spatio-temporal interactions between visual targets or by unequal attention to the moving test spot under these two types of conditions. We attribute the highly similar attenuation of perceived smear during vergence and pursuit to a comparable action of the extra-retinal signals for disjunctive and conjugate eye movements.

Pontine omnipause activity during conjugate and disconjugate eye movements in macaques.

Previous reports have shown that saccades executed during vergence eye movements are often slower and longer than conjugate saccades. Lesions in the nucleus raphe interpositus, where pontine omnipause neurons (OPNs) are located, were also shown to result in slower and longer saccades. If vergence transiently suppresses the activity of the OPNs just before a saccade, then reduced presaccadic activity might mimic the behavioral effects of a lesion. To test this hypothesis, 64 OPNs were recorded from 7 alert rhesus monkeys during smooth vergence and saccades with and without vergence. The firing rate of many OPNs was modulated by static vergence angle but not by version and showed transient changes during slow vergence without saccades. This modulation was smooth, and not the abrupt pause seen for saccades, indicating that OPNs do not act as gates for vergence commands. We confirmed that saccades made during both convergence and divergence are significantly slower and longer than conjugate saccades. OPNs paused for all saccades, and the pause lead (interval between pause onset and saccadic onset) was significantly longer for saccades with convergence, in agreement with our hypothesis. Contrary to our hypothesis, pause lead was not longer for saccades with divergence, even though these saccades were slowed as much as those occurring during convergence. Furthermore, there was no significant correlation, on a trial-by-trial basis, between pause lead and saccadic slowing. These results suggest that it is unlikely that presaccadic slowing of OPNs is responsible for the slower saccades seen during vergence movements.