Lea Averbuch-Heller

Comparison of horizontal, vertical and diagonal smooth pursuit eye movements in normal human subjects.

We compared horizontal and vertical smooth pursuit eye movements in five healthy human subjects. When maintenance of pursuit was tested using predictable waveforms (sinusoidal or triangular target motion), the gain of horizontal pursuit was greater, in all subjects, than that of vertical pursuit; this was also the case for the horizontal and vertical components of diagonal and circular tracking. When initiation of pursuit was tested, four subjects tended to show larger eye accelerations for vertical as opposed to horizontal pursuit; this trend became a consistent finding during diagonal tracking. These findings support the view that different mechanisms govern the onset of smooth pursuit, and its subsequent maintenance when the target moves in a predictable waveform. Since the properties of these two aspects of pursuit differ for horizontal and vertical movements, our findings also point to separate control of horizontal and vertical pursuit.

Torsional eye movements in patients with skew deviation and spasmodic torticollis Responses to static and dynamic head roll

Article abstract-We measured torsional eye movements induced by sinusoidal rotation or static tilt of the head in roll while viewing a far or near target in 4 patients with skew deviation due to brainstem lesions, 4 patients with spasmodic torticollis (ST), 2 patients with unilateral eighth nerve section (VIIIS), and 10 normal subjects. Torsional nystagmus was present in all 4 patients with skew deviation. In subjects and patients, responses to both sinusoidal and static roll were larger while viewing the far target, consistent with factors dictated by geometry. Response gains to sinusoidal roll were abnormal in 3 patients with skew (increased in one, decreased in two), abnormal in 3 with ST (increased in 1, decreased in 2), and in abnormal both VIIIS patients (decreased). Greater abnormalities were evident in 3 skew patients while rolling away from the side of their brainstem lesions and in both VIIIS patients while rolling toward their lesioned ears. There were similar but less pronounced changes during static head roll. We conclude that patients with skew, ST, and VIIIS may all have abnormal ocular counter-rolling that is more evident during dynamic testing while viewing a far target. Such abnormalities endure because of the limited influence exerted by vision on torsional eye movements. NEUROLOGY 1997;48: 506-514

Unsatisfactory Treatment of Acquired Nystagmus With Retrobulbar Injection of Botulinum Toxin

PURPOSE We quantified the effects of botulinum toxin injected into the retrobulbar space of patients with acquired nystagmus with prominent vertical or torsional components. METHODS We measured binocular eye rotations in three planes before and after injection of botulinum toxin (10, 12.5, or 25 units) into the retrobulbar space of one eye of each of three patients, ages 28 to 37 years, with acquired pendular nystagmus. RESULTS Retrobulbar injection of botulinum toxin abolished or reduced all components of the nystagmus in the treated eye in all three patients for about two to three months. The patient who received 25 units developed complete external ophthalmoplegia and blepharoptosis. The other two patients retained some voluntary movements but developed diplopia. In one patient, visual acuity improved from Jaeger 5 to Jaeger 1. In a second patient, filamentary keratitis developed, and visual acuity declined from Jaeger 2 to Jaeger 7; keratitis was a recurrent problem one year after the botulinum toxin injection. In the third patient with predominantly torsional nystagmus, visual acuity was unchanged at Jaeger 2. No patient was pleased with the results, because of blepharoptosis, diplopia, or discomfort (from keratitis), and none elected to repeat the procedure. CONCLUSIONS The side effects of botulinum toxin administered by retrobulbar injection limit its therapeutic value in the treatment of acquired nystagmus. Even smaller doses that do not abolish nystagmus may produce troublesome diplopia.

Square-wave jerks induced by pallidotomy in parkinsonian patients

Article abstract Square-wave jerks (SWJs) are small, inappropriate saccades that intrude on steady fixation by taking the eye away from the target and then returning it after approximately 200 msec. The pathophysiology of SWJs is unknown; they have not been attributed to any specific lesion. We found that unilateral pallidotomy substantially increased the frequency of SWJs in three patients with Parkinson’s disease. This effect is likely due to imbalance in the fixation system caused by asymmetric reactivation of prefrontal cortex via ascending thalamocortical projections. Alternatively, disruption of nigral projections to the superior colliculus might be responsible.

Oscillopsia suppression and foveation-period variation in congenital, latent, and acquired nystagmus

We studied the relative importance of clear and stable epochs of vision and extraretinal signals of eye movements in suppressing illusory motion of the world (oscillopsia) in eight subjects with two types of infantile nystagmus, congenital nystagmus (CN) and latent/manifest latent nystagmus (LMLN), and two acquired forms of nystagmus (AN), pendular and jerk. Three subjects with CN and no oscillopsia did not always exhibit well-developed foveation periods, unless their CN was therapeutically damped. Two subjects with CN and AN had transient oscillopsia that coincided in time and plane with the lack of well-developed foveation. Two subjects with AN and oscillopsia had well-developed foveation (one after gabapentin). One subject with LMLN and vertical AN experienced oscillopsia solely in the plane of the AN, despite the presence of good foveation in both planes. Our findings argue against the role of foveation periods in suppression of oscillopsia. In CN, lack of well-developed foveation does not result in o...

A pilot study of gabapentin as treatment for acquired nystagmus

The effects of the anticonvulsant gabapentin were measured on vision and eve movements in three patients with acquired pendular nystagmus. In two patients, the nystagmus was associated with multiple sclerosis and, in the other, it followed brainstem stroke. A single oral 600 mg dose of gabapentin produced improvement of vision due to changes in ocular oscillations in all three patients. The effect was sustained after five weeks of treatment in two patients who elected to continue taking gabapentin 900-1500 mg/day. The results of this pilot study suggest that a controlled trial of gabapentin should be conducted to evaluate its role in the treatment of acquired forms of nystagmus.

Dysfunction of pontine omnipause neurons causes impaired fixation: macrosaccadic oscillations with a unilateral pontine lesion

Macrosaccadic oscillations of eyes (MSO) are regarded as a form of saccadic dysmetria secondary to cerebellar dysfunction. They are usually conjugate, horizontal, and symmetric in both directions of gaze. Using magnetic search coils, we studied a patient with MSO that developed five years following head injury and involved synchronously horizontal, vertical, and torsional planes. The MSO were characterized by directional pre-ponderance and were associated with ipsilateral pontine lesion. We propose a disturbance of fixation mechanisms due to unilateral disinhibition of saccadic burst neurons in three planes. This could arise from either primary or secondary dysfunction of omnipause neurons due to impaired input from the contralateral superior colliculus. The delayed onset is suggestive of denervation supersensitivity as the underlying pathophysiology.

Clinical evidence of extraocular muscle fiber-type specificity of botulinum toxin

Objective: To compare the effects of botulinum toxin on static and dynamic aspects of eye movements, and thereby elucidate the mechanisms of its action on eye muscles. Background: Laboratory evidence indicates that static alignment and saccades are subserved by different extraocular muscle fiber types, and botulinum toxin may cause specific dysfunction of the fibers controlling static alignment. Diplopia is a well-known side effect of periorbital botulinum toxin injections in humans, and may be a clinical correlate of the laboratory findings. Methods: Search coil recording of eye movements was performed in one patient with systemic botulism, and in three patients with diplopia following periorbital injection of botulinum toxin A. Results: In the patient with acute botulism, eye movement alignment, range, and saccadic velocity profiles were abnormal. In three patients with iatrogenic diplopia, static alignment was abnormal but movement range and saccadic velocities were within normal limits. Edrophonium improved the range of movements and saccadic velocities in the patient with systemic botulism but was ineffective in reversing ocular misalignment in the one iatrogenic patient to whom it was administered. Conclusions: Precise alignment is subserved by orbital singly innervated muscle fibers, and the effects of botulinum toxin are greatest on these fibers. This predilection is apparent when the toxin dose is very small, as must have been the case in our patients with iatrogenic diplopia. The lack of a response to edrophonium probably reflects structural damage to muscle fibers. In contrast, larger doses of toxin produce an acute dysfunction of all extraocular muscle fiber types, which is responsive to edrophonium and consequently reflects partial blockade at the neuromuscular junction.

Tracking of illusory target motion: differences between gaze and head responses.

We compared ocular and eye-head tracking responses to an illusion of diagonal motion produced when vertical movement of a small visual target was synchronized to horizontal movement of a background display. In response to sinusoidal movement, smooth ocular pursuit followed vertical target motion, with only a small horizontal component. In response to regular stepping movement, all anticipatory saccades were in the direction of the illusion; these erroneous oblique movements were followed by corrective horizontal saccades. When the head was free to move, it usually showed a diagonal trajectory that, for both sinusoidal and stepping target motion, was always in the direction of the illusion; no corrective movements were present. Thus, for our illusory stimuli, eye and head tracking showed qualitative differences that imply that ocular tracking was ultimately controlled by actual target motion but head tracking was controlled by illusory target motion.

Latent and congenital nystagmus in Down syndrome.

OBJECTIVES Although nystagmus has been reported in Down syndrome (DS), it has been poorly characterized, because most investigators have relied on clinical observations rather than on eye movement recordings. This study was conducted to investigate nystagmus in DS, using quantitative measurements of eye movements. METHODS Ocular motility and visual functions were examined in 26 unselected adults with DS and compared with those in an age-matched group of 35 subjects with other causes of mental retardation. The eye movements of those with clinically evident nystagmus were recorded with the infrared technique. We also recorded the eye movements of a child with DS and nystagmus. RESULTS Nystagmus was identified in six (23%) adults with DS and in none in the control group. All six patients showed latent/manifest latent nystagmus (LMLN), prominent with the covering of one eye, and esodeviations of 10 to 30 prism diopters. Eye movement recordings confirmed LMLN with its exponentially decaying waveform. Frequencies ranged from 2 to 5 Hz and amplitudes from 5 degrees to 20 degrees. While attempting to fixate straight ahead in the absence of visual cues, three subjects exhibited shifts in the mean eye position. In contrast with the findings in adults, the only child with DS examined had both congenital nystagmus and LMLN waveforms. CONCLUSIONS The predominant type of nystagmus in the study subjects with DS is LMLN. The high prevalence of LMLN may reflect abnormal integration of visuospatial information that is typical of DS. The concurrent presence of congenital nystagmus in a child but only LMLN in the adults with DS raises the possibility of age-related waveform changes or could reflect sample variation.