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PubMed1998

Dissociated vertical deviation and head tilts.

INTRODUCTION: The association of anomalous head posture and dissociated vertical deviation does not seem to be appreciated, as evidenced by the paucity of literature linking these two conditions. METHOD: The series describes 14 patients who had an anomalous head posture and dissociated vertical deviation. The assumed head tilts appeared to decrease the magnitude and improve the motor control of dissociated vertical deviation. RESULTS: Twelve of 14 patients tilted their heads contralateral to the eye with the dissociated vertical deviation, or away from the eye with a larger amount of dissociated vertical deviation if the disorder was bilateral. Two patients tilted their heads to the same side as the eye with the dissociated vertical deviation. Forced head tilt-testing in the opposite direction showed an increase in the magnitude of the dissociated vertical deviation or poorer control of the deviation. Dissociated vertical deviation was not related to oblique muscle dysfunction. Peripheral fusion was demonstrated in 10 patients, as evidenced by low-grade stereopsis or Worth 4 dot fusion at near. One patient did not show any demonstrable fusion with conventional tests. Another did not show evidence of stereopsis, but Worth 4 dot testing was not performed. Two other patients were too young to cooperate with sensory testing. Anomalous head posture was controlled or minimized after the control of the dissociated vertical deviation by surgery in four patients. Two patients showed improved stereopsis after surgery for dissociated vertical deviation. CONCLUSION: Dissociated vertical deviation should be included in the differential diagnosis of an ocular cause of head tilts. Forced contralateral head tilttesting will confirm whether dissociated vertical deviation is the cause if motor control of the dissociated vertical deviation worsens or becomes manifest rather than latent. The presence of an anomalous head posture in patients with dissociated vertical deviation can be improved with strabismus surgery.

Adult↗
PubMed1998

Role of vestibular adaptation in vestibular rehabilitation.

Recovery of gaze and postural stability in human beings with vestibular deficits is well documented. The mechanisms that contribute to this recovery form the basis for the exercises used in the rehabilitation of these patients. These mechanisms include the central preprogramming of eye movements and of postural responses, the potentiation of the cervico-ocular reflex, modification of saccadic eye movements, and the substitution of visual and somatosensory cues for the lost vestibular cues. The mechanism most successful in contributing to recovery, however, is probably adaptation of the vestibular system itself. Understanding the various compensatory mechanisms and their limitations for improving gaze and postural stability should lead to more effective treatment of these patients.

Adaptation, Physiological↗
PubMed1978

Ocular saccades in Duane's syndrome.

Since Hering's law might be affected when paradoxical innervation exists, 10 patients with Duane's syndrome were studied. Eye movements were measured by binocular recording of electro-oculogram. Our study shows clearly that the sound eye's motility is also affected. When adduction of the affected eye is present, Hering's law holds, whereas when adduction is limited this law cannot be demonstrated.

Adolescent↗
PubMed1997

Inertial vestibular coding of motion: concepts and evidence.

Central processing of inertial sensory information about head attitude and motion in space is crucial for motor control. Vestibular signals are coded relative to a non-inertial system, the head, that is virtually continuously in motion. Evidence for transformation of vestibular signals from head-fixed sensory coordinates to gravity-centered coordinates have been provided by studies of the vestibulo-ocular reflex. The underlying central processing depends on otolith afferent information that needs to be resolved in terms of head translation related inertial forces and head attitude dependent pull of gravity. Theoretical solutions have been suggested, but experimental evidence is still scarce. It appears, along these lines, that gaze control systems are intimately linked to motor control of head attitude and posture.

Animals↗
PubMed1978

Epileptic discharges triggered by eye convergence.

A 27-year-old man with major motor and minor seizures showed focal epileptic discharges and electrical seizures triggered by eye convergence. Other voluntary ocular movements failed to evoke reflex epileptic discharges. Eye convergence triggered discharges even after the eyelids were strapped open with tapes and the pupillary and accommodation reflexes were temporarily paralyzed. This patient also showed pattern-sensitive focal epileptic discharges arising from the same area of the brain as those induced by eye convergence, but he was not photosensitive.

Adult↗
PubMed1979

[Monocular circumduction nystagmus (author's transl)].

Monocular circumduction nystagmus is a very rare ocular movement. A type of circumduction movement, it is caused by successive movements of all the ocular muscles within the framework of a pendular nystagmus. As a monocular movement, it raises the question of the physiopathological mechanism of such a movement which is so complex and is also limited to one eye. The existence of a monocular form of circumduction nystagmus makes it necessary to revise the mechanism of pendular nystagmus.

Adult↗
PubMed1982

The AC/A ratio and convergence in hypermetropia corrected with spectacles or contact lenses.

Some hypermetropes, when corrected with contact lenses, appear to have a much smaller AC/A ratio than when corrected with spectacle lenses. Ocular convergence measured with contact lenses is greater than that measured with spectacles. Studies were carried out to establish the cause of these effects. Theoretical considerations are compared with the experimental results obtained. This study emphasizes the importance of the different amounts of magnification induced by contact lenses as compared with spectacles.

Adolescent↗
PubMed1993

Eye movement and electrophysiological findings in an infant with hemispheric pathology.

A visually unresponsive infant had a normal ophthalmological examination. Eye-movement studies using electro-oculography revealed asymmetrical binocular smooth pursuit, binocular optokinetic nystagmus and vestibulo-ocular reflex. Electrophysiological testing showed markedly asymmetrical occipital flash and pattern visual evoked potentials. Both investigations suggested a posterior right-hemispheric problem, which was confirmed with cranial ultrasound. This case study illustrates the usefulness of non-invasive techniques in neuro-ophthalmological investigations of young children.

Brain Diseases↗
PubMed1989

Congenital adduction palsy and synergistic divergence: a clinical and electro-oculographic study.

We studied two patients with a peculiar congenital disturbance of ocular motility in which the horizontal movements of the left eye were always opposite the normal expected direction. The common features were: (1) congenital monocular adduction palsy and exotropia of the left eye; (2) simultaneous abduction of both eyes (divergence) on attempted dextroversion; (3) ocular torticollis, head turned to the right; and (4) inverse nystagmus of the left eye, occurring spontaneously as well as during optokinetic and vestibular testing. Clinical and electrooculographic findings suggested a close relationship to Duane's retraction syndrome and supported the concept that innervational mechanisms were responsible for the phenomenon.

Adult↗
PubMed1989

Measurement of binocular alignment in normal monkeys and in monkeys with strabismus.

Accurate assessment of ocular alignment in monkeys is difficult because typical clinical methods require extensive cooperation by the subject or provide only a rough estimate of the misalignment. Recently, Brodie derived a geometrical model for determining the Hirschberg ratio in humans, and validated it photographically. In this study, we have applied these procedures in order to determine corresponding values for monkeys. We have found the average Hirschberg ratio for macaques to be approximately 14 degrees of rotation per millimeter corneal light reflex displacement. We extended the model to binocular viewing conditions, which allows for a description of the visual axes in Cartesian coordinates in relation to the head. Fixation errors, computed in terms of lateral and axial error vectors from intended fixation targets, were then determined for one normal monkey and for three monkeys that have a naturally occurring strabismus. Assessment of the fixation errors was made at several different distances and angles in the horizontal plane. The standard deviation for our measurements averaged 2.1 degrees. Our data indicate that measurements must be made at multiple locations throughout the visual field in order to accurately specify the pattern of misalignment. Finally, a procedure is demonstrated which specifies the misalignment in terms of a cyclopian eye, which is independent of the interocular separation.

Animals↗
PubMed2005

Activity-dependent modulation: a non-linearity in the unilateral vestibulo-ocular reflex pathways.

It is well established that the vestibulo-ocular reflex (VOR) depends not only on sensory stimulation but also on the behavioral context associated with the stimulation. Recent modeling studies suggested that including a non-linearity in the activation function of the VOR neurons achieves the desired context-dependence for the VOR without resorting to currently assumed complex cortical computations. With the non-linearity, neurons operate as non-linear summers of incoming activity with sensitivities modulated by their activation levels. In this study we examined whether such a non-linearity exists in the unilateral VOR pathways in behaving monkeys. Acoustic clicks were employed to evoke unilateral VOR responses during fixation, head motion and smooth pursuit. We found that the click-evoked unilateral VOR responses did not simply sum in a linear manner with the eye movements initiated by head or target motion. Instead, the same acoustic click evoked larger eye movements if the ongoing eye movements were in the same direction. We also showed that the interaction between the ongoing eye movement and the click-evoked response was close to being multiplicative. These results revealed a previous unknown non-linearity in the unilateral VOR pathways, which may have important implications on the neural implementation of the context-dependence for the VOR.

Acoustic Stimulation↗
PubMed1988

Vestibulo-ocular reflex and gaze functions in a patient with congenital inner ear anomalies.

We report on the vestibulo-ocular reflex (VOR) and gaze functions during horizontal rotations as well as upright locomotions in a fisherman with congenital inner ear anomalies. The finding of a marked gaze disturbance due to low VOR gain during passive rotations resembled that found in early acquired lesions. There was an improvement during active rotations, suggesting an intensified cervico-ocular reflex. Although head oscillations in the horizontal plane were abnormally large during stepping and running, they were compensated for visually even at high frequencies. The absence of complaints of oscillopsia as well as his ability to achieve proper balance seemed to be accomplished by his optokinetic ability, regularly transformed head oscillations and modified perceptive mechanisms at higher cortical levels.

Adult↗
PubMed2005

Wavelength dependence of intraocular straylight.

Wavelength dependence of retinal straylight has been a mystery since Stiles in 1929 [Stiles,W.S., 1929. The scattering theory of the effect of glare on the brightness difference threshold. Proc. R. Soc. Lond. (Biol.) 105, 131-41.] supposed it to have the strong Rayleigh type lambda(-4) dependence, typical for small particle light scattering, but which was never found. Using the accurate 'compensation comparison' approach, retinal straylight was measured from 625 to 457 nm. Subjects with a large variety of ocular pigmentation were included. Straylight was found to depend strongly on pigmentation of the eye, in addition to age. Young and well-pigmented eyes (young negroids) show nearly perfect lambda(-4) dependence. With less pigmentation (blue-eyed Caucasians), a red dominated component is added, negating the lambda(-4) dependence.

Adult↗
PubMed1975

Sylvian aqueduct syndrome as a sign of acute obstructive hydrocephalus in children.

Eight cases of obstructive hydrocephalus manifesting palsy of upward gaze and other features of the Sylvian aqueduct syndrome are reported. During the crisis of intracranial hypertension, all of them developed upward gaze palsy and variable abnormalities of the convergence mechanism such as paralysis, spasm, and convergence nystagmus. The frequent apparent blindness was probably related to gaze paralysis, since visual evoked responses were present. All these ocular abnormalities disappeared after shunting. Periaqueductal dysfunction on the basis of raised intracranial pressure is postulated as the possible mechanism for the above ocular manifestations. The 'setting sun' sign is frequently seen in infants and children with hydrocephalus and has been considered in the past to result from displacement of eyeballs by pressure from the orbital roof plate. Our observations would suggest periaqueductal dysfunction rather than the mechanical displacement as the possible mechanism for this sign.

Acute Disease↗
PubMed2000

Neurophysiological aspects of eye and eyelid movements during blinking in humans.

The neural relationships between eyelid movements and eye movements during spontaneous, voluntary, and reflex blinking in a group of healthy subjects were examined. Electromyographic (EMG) recording of the orbicularis oculi (OO) muscles was performed using surface electrodes. Concurrently, horizontal and vertical eye positions were recorded by means of the double magnetic induction (DMI) ring method. In addition, movement of the upper eyelid was measured by a specially designed search coil, placed on the upper eyelid. The reflex blink was elicited electrically by supraorbital nerve stimulation either on the right or the left side. It is found that disconjugate oblique eye movements accompany spontaneous, voluntary as well as reflex blinking. Depending on the gaze position before blinking, the amplitude of horizontal and vertical components of the eye movement during blinking varies in a systematic way. With adduction and downward gaze the amplitude is minimal. With abduction the horizontal amplitude increases, whereas with upward gaze the vertical amplitude increases. Unilateral electrical supraorbital nerve stimulation at low currents elicits eye movements with a bilateral late component. At stimulus intensities approximately two to three times above the threshold, the early ipsilateral blink reflex response (R(1)) in the OO muscle can be observed together with an early ipsilateral eye movement component at a latency of approximately 15 ms. In addition, during the electrical blink reflex, early ipsilateral and late bilateral components can also be identified in the upper eyelid movement. In contrast to the late bilateral component of upper eyelid movement, the early ipsilateral component of upper eyelid movement appears to open the eye to a greater degree. This early ipsilateral component of upper eyelid movement occurs more or less simultaneously with the early eye movement component. It is suggested that both early ipsilateral movements following electrical stimulation do not have a central neural origin. Late components of the eye movements slightly precede the late components of the eyelid movement. Synchrony between late components of eyelid movements and eye movements as well as similarity of oblique eye movement components in different types of blinking suggest the existence of a premotor neural structure acting as a generator that coordinates impulses to different subnuclei of the oculomotor nucleus as well as the facial nerve nucleus during blinking independent from the ocular saccadic and/or vergence system. The profile and direction of the eye movement rotation during blinking gives support to the idea that it may be secondary to eyeball retraction; an extra cocontraction of the inferior and superior rectus muscle would be sufficient to explain both eye retraction and rotation in the horizontal vertical and torsional planes.

Adult↗
PubMed1987

[The language of the eye. Expressive functions of the eye].

The eye is an effective and frequently used means of communication. Innate ocular signals express basic feelings and are identical all over the world. Acquired signals depend on cultural status, intelligence, and education. Eye diseases and orbital anomalies can provide misleading impressions, because they can be confused with true eye signals or because they can trigger innate reaction mechanisms. Surgically, the eye can often be improved as an emittor of signals; the message, however, has to be composed by the patient.

Emotions↗
PubMed1995

Short-term adaptation of the phase of the vestibulo-ocular reflex (VOR) in normal human subjects.

We investigated the effects of short-term vestibulo-ocular reflex (VOR) adaptation on the gain and phase of the VOR, and on eccentric gaze-holding in darkness, in five normal human subjects. For 1 h, subjects sat in a chair that rotated sinusoidally at 0.2 Hz while surrounded by a visual stimulus (optokinetic drum). The drum was rotated relative to the chair, to require a VOR with either a phase lead or lag of 45 deg (with respect to a compensatory phase of zero) with no change in gain, or a gain of 1.7 or 0.5 with no change in phase. Immediately before and after each training session, VOR gain and phase were measured in the dark with 0.2 Hz sinusoidal rotation. Gaze-holding was evaluated following 20 deg eccentric saccades in darkness. Adaptation paradigms that called only for a phase lead produced an adapted VOR with 33% of the required amount of phase change, a 20% decrease in VOR gain, and an increased centripetal drift after eccentric saccades made in darkness. Adaptation paradigms that called for a phase lag produced an adapted VOR with 29% of the required amount of phase change, no significant change in VOR gain, and a centrifugal drift after eccentric saccades. Adaptation paradigms requiring a gain of 1.7 produced a 15% increase in VOR gain with small increases in phase and in centripetal drift. Adaptation paradigms requiring a gain of 0.5 produced a 31% decrease in VOR gain with a 6 deg phase lag and a centrifugal drift. The changes in drift and phase were well correlated across all adaptation paradigms; the changes in phase and gain were not. We attribute the effects on phase and gaze-holding to changes in the time constant of the velocity-to-position ocular motor neural integrator. Phase leads and the corresponding centripetal drift are due to a leaky integrator, and phase lags and the corresponding centrifugal drift are due to an unstable integrator. These results imply that in the short-term adaptation paradigm used here, the control of drift and VOR phase are tightly coupled through the neural integrator, whereas VOR gain is controlled by another mechanism.

Adaptation, Psychological↗
PubMed1984

A preliminary investigation of the information carrying potential of voluntary eye movements.

This paper reports the preliminary findings of a study on the information carrying potential of voluntary eye movements. An ocular communication device, originally developed at the Denver Research Institute, was used to determine how fast information can be transmitted by voluntary eye movements. The tentative findings are that: a maximum information throughput of roughly 10 bits/s is possible and the DRI device merits further development. The primary relevance of this study is to the development of communication aids for the severely handicapped.

Communication Devices for People with Disabilities↗