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PubMed2005

[Intermittent diplopia after prolonged downward gaze to the right: what is the differential diagnosis?].

In general, intermittent diplopia evokes suspicion of ocular myasthenia gravis. However, other etiologies such as Brown syndrome or myokymia of the superior oblique may provoke intermittent diplopia. We present a case of intermittent diplopia due to a tumor in the cavernous sinus. A 59-year-old patient reported intermittent diplopia after prolonged downward gaze to the right. All other gaze directions failed to provoke symptoms. In 1992, the diagnosis of inactive macroadenoma of the pituitary gland was established and the patient underwent surgery and radiation therapy. At physical examination, prolonged downward gaze to the right of about 2 minutes provoked paresis of abduction, slight ptosis, and restriction of elevation on the left side, corresponding to sixth nerve palsy and palsy of the superior branch of the third nerve on the left side. MRI showed a relapse of the macroadenoma with infiltration of the cavernous sinus on the left side. The patient underwent surgery then focal radiation (gamma-knife). The clinical course was favourable and at the follow-up examination six months later, no diplopia was reported.

Abducens Nerve Diseases↗

PubMed2000

Ocular pursuit responses to repeated, single-cycle sinusoids reveal behavior compatible with predictive pursuit.

The link between anticipatory smooth eye movements and prediction in sinusoidal pursuit was investigated by presentation of series of identical, single-cycle, sinusoidal target motion stimuli. Stimuli occurred at randomized intervals (1.2-2.8 s) but were preceded by an audio warning cue 480 ms before each presentation. Cycle period (T) varied from 0.64 to 2.56 s and target displacement from 4 to 20 degrees in separate series. For T </= 1.28 s, responses to the first stimulus of each series exhibited a time delay across the whole cycle (mean = 121 ms for T = 0.8 s). But, in the second and subsequent (steady-state) presentations, anticipatory movements, proportional to target velocity, were made and time delay was significantly reduced (mean = 43 ms for T = 0.8 s). Steady-state time delays were comparable to those evoked during continuous sinusoidal pursuit and less than pursuit reaction time. Even when subjects did not follow the target in the first presentation, they responded to the second presentation with reduced time delay. Throughout the experiments, three types of catch trial (A-C) were introduced. In A, the target failed to appear as expected after the warning cue. Anticipatory smooth movements were initiated, reaching a peak velocity proportional to prior target velocity around 200 ms after expected target onset. In B, the target stopped midway through the cycle. Even if the target remained on and was stationary, the eye movement continued to be driven away from the stationary target with a velocity similar to that of prior responses, reaching a peak velocity that was again proportional to expected target velocity after >/=205 ms. In C, the amplitude of the single sinusoid was unexpectedly increased or decreased. When it decreased, eye velocity throughout the first half-cycle of the response was close to that executed in response to prior stimuli of higher velocity and did not return to an appropriate level for 382-549 ms. Conversely, when amplitude increased, eye velocity remained inappropriately low for the first half-cycle. Results of A and C indicate that subjects are able to use velocity information stored from prior presentations to initiate an oculomotor drive that predominates over visual feedback for the first half-cycle. Results of B indicate that the second part of the cycle is also preprogrammed because it continued despite efforts to suppress it by fixation. The results suggest that initial retinal velocity error information can be sampled, stored, and subsequently replayed as a bi-directional anticipatory pattern of movement that reduces temporal delay and could account for predictive control during sinusoidal pursuit.

Adaptation, Physiological↗

PubMed2002

The vestibulo-ocular reflex in three dimensions.

The purpose of this paper is to review the kinematics and dynamics of the vestibulo-ocular reflex (VOR) in three dimensions. We give a brief, didactic tutorial on vectors and matrices and their importance as representational schemes for describing the kinematics and dynamics of the angular and linear accelerations that activate the vestibular system. We show how the vectors associated with angular and linear head accelerations are transformed by the peripheral and central vestibular systems to drive the oculomotor system to produce eye movements in three-dimensional space. We also review critical questions and controversies related to the compensatory and orientation behavior of the VOR. One such question is how the central vestibular system distinguishes tilts of the head, which generate interaural linear acceleration from translations along the interaural axis. Another question is how the velocity-position integrator is implemented centrally. The review has been placed in the context of a model that explains the behavior of the VOR in three dimensions. Model processes have been related to peripheral and central neural behavior in order to gain insight into the nature of the three-dimensional organization and the controversial questions that are addressed.

Adaptation, Physiological↗

PubMed1997

Contributions of regularly and irregularly discharging vestibular-nerve inputs to the discharge of central vestibular neurons in the alert squirrel monkey.

The discharge of neurons in the vestibular nuclei was recorded in alert squirrel monkeys while they were being sinusoidally rotated at 2 Hz. Type I position-vestibular-pause (PVP I) and vestibular-only (V I) neurons, as well as a smaller number of other type I and type II eye-plus-vestibular neurons were studied. Many of the neurons were monosynaptically related to the ipsilateral vestibular nerve. Eye-position and vestibular components of the rotation response were separated by multiple regression. Anodal currents, simultaneously delivered to both ears, were used to eliminate the head-rotation signals of irregularly discharging (I) vestibular-nerve afferents, presumably without affecting the corresponding signals of regularly discharging (R) afferents. R and I inputs to individual central neurons were determined by comparing rotation responses with and without the anodal currents. The bilateral currents, while reducing the background discharge of all types of neurons, did not affect the mean vestibular gain or phase calculated from a population of PVP I neurons or from a mixed population consisting of all type I units. From this result, it is concluded that I inputs are canceled at the level of secondary neurons. The cancellation may explain why the ablating currents do not affect the gain and phase of the vestibulo-ocular reflex. While cancellation was nearly perfect on a population basis, it was less so in individual neurons. For some neurons, the ablating currents decreased vestibular gain, while for other neurons the vestibular gain was increased. The former neurons are interpreted as receiving a net excitatory (I-EXC) I input, the latter neurons, a net inhibitory (I-INH) input. When compared with the corresponding R inputs, the I inputs were usually small and phase advanced. Phase advances were larger for I-EXC than for I-INH inputs. The sign and magnitude of the I inputs were unrelated to other discharge properties of individual neurons, including discharge regularity and the phase of vestibular responses measured in the absence of the ablating currents. Unilateral currents were used to assess the efficacy of ipsilateral and contralateral pathways. Ipsilateral pathways were responsible for almost all of the effects seen with bilateral currents. The results suggest that the vestibular signals carried by central neurons, even by those neurons receiving a monosynaptic vestibular-nerve input, are modified by polysynaptic pathways.

Animals↗

PubMed1995

Management of strabismus due to orbital myositis.

We report on 5 consecutive patients seen at the botulinum toxin clinic at Moorfields Eye Hospital with an ocular motility disorder secondary to orbital myositis. CT scans demonstrated involvement of one or both of the medial recti in the inflammatory process in all 5 patients. In addition 1 patient had involvement of both the lateral recti and the right superior rectus. Two patients had been treated with oral steroids, 3 with non-steroidal anti-inflammatory agents, and 1 with orbital radiotherapy. Prior to toxin injection 3 patients had an esotropia (ranging from 4 delta to 30 delta) and two an exotropia (52 delta and 85 delta). A vertical imbalance was present in 3, and all 5 patients had symptomatic diplopia. A total of six injections were given to 5 patients, 2 of whom later went on to have surgery. Toxin injection reduced the angle of the deviation to less than 10 delta in 4 patients, all of whom are now asymptomatic. The fifth patient has persistent diplopia despite two operations to correct a large exotropia. We discuss the role of botulinum toxin and surgery in the management of strabismus due to orbital myositis.

Adolescent↗

PubMedDate not supplied

Geometric adjustments to account for eye eccentricity in processing horizontal and vertical eye and head movement data.

Neglecting the eccentric position of the eyes in the head can lead to erroneous interpretation of ocular motor data, particularly for near targets. We discuss the geometric effects that eye eccentricity has on the processing of target-directed eye and head movement data, and we highlight two approaches to processing and interpreting such data. The first approach involves determining the true position of the target with respect to the location of the eyes in space for evaluating the efficacy of gaze, and it allows calculation of retinal error directly from measured eye, head, and target data. The second approach effectively eliminates eye eccentricity effects by adjusting measured eye movement data to yield equivalent responses relative to a specified reference location (such as the center of head rotation). This latter technique can be used to standardize measured eye movement signals, enabling waveforms collected under different experimental conditions to be directly compared, both with the measured target signals and with each other. Mathematical relationships describing these approaches are presented for horizontal and vertical rotations, for both tangential and circumferential display screens, and efforts are made to describe the sensitivity of parameter variations on the calculated results.

Eye Movements↗

PubMed2001

Functional anatomy of nonvisual feedback loops during reaching: a positron emission tomography study.

Reaching movements performed without vision of the moving limb are continuously monitored, during their execution, by feedback loops (designated nonvisual). In this study, we investigated the functional anatomy of these nonvisual loops using positron emission tomography (PET). Seven subjects had to "look at" (eye) or "look and point to" (eye-arm) visual targets whose location either remained stationary or changed undetectably during the ocular saccade (when vision is suppressed). Slightly changing the target location during gaze shift causes an increase in the amount of correction to be generated. Functional anatomy of nonvisual feedback loops was identified by comparing the reaching condition involving large corrections (jump) with the reaching condition involving small corrections (stationary), after subtracting the activations associated with saccadic movements and hand movement planning [(eye-arm-jumping minus eye-jumping) minus (eye-arm-stationary minus eye-stationary)]. Behavioral data confirmed that the subjects were both accurate at reaching to the stationary targets and able to update their movement smoothly and early in response to the target jump. PET difference images showed that these corrections were mediated by a restricted network involving the left posterior parietal cortex, the right anterior intermediate cerebellum, and the left primary motor cortex. These results are consistent with our knowledge of the functional properties of these areas and more generally with models emphasizing parietal-cerebellar circuits for processing a dynamic motor error signal.

Adult↗

PubMed2005

Extraocular muscle surgery for extorsion after macular translocation surgery new surgical technique and clinical management.

PURPOSE: To report a new extraocular muscle surgery procedure for large-angle extorsion, and clinical management of subjective tilt and diplopia after full macular translocation (MT360). DESIGN: Consecutive retrospective case series. PARTICIPANTS: Seven patients with downward MT360 were evaluated after MT360, both before (preoperative) and after (postoperative) extraocular muscle surgery, with at least 6 months' follow-up. METHODS: Information gathered included demographics, visual acuity, ocular motility, torsion by Maddox rod, ocular history, and symptoms of visual disturbance. Surgery on extraocular muscles was performed based on the magnitude of torsion measured after MT360 surgery. MAIN OUTCOMES MEASURES: Maddox rod testing of torsion after MT360, and both preoperative and postoperative extraocular muscle surgery. RESULTS: Mean preoperative torsion was reduced from 45.4+/-11.3 degrees to 8.3+/-4.8 degrees (at 6 months after MT360) (P = 0.03). Extraocular muscle surgery slightly reduced the mean hypertropia of the operated eye (preoperative, 20+/-10 prism diopters [PD], vs. postoperative, 11+/-6 PD) (P = 0.06). Mean exotropia was affected minimally by extraocular muscle surgery (preoperative, 22+/-31 PD, vs. postoperative, 20+/-24 PD). Three patients required a second extraocular muscle surgery (performed on the fellow eye) to correct residual extorsion and diplopia. Overall, 85% (6/7) of patients were free of both diplopia and tilt after 1 or 2 extraocular muscle surgeries. CONCLUSIONS: Although our patients continued to have significant horizontal/vertical strabismus postoperatively, the extraocular muscle surgery performed was successful in reducing the torsional misalignment enough such that the remaining diplopia could be successfully ignored or suppressed.

Aged↗

PubMed2006

Preparatory gain modulation of visuomotor transmission for smooth pursuit eye movements in monkeys.

It has been reported that the visuomotor processing underlying the initiation of smooth pursuit eye movement is modulated in relation to the recent experience of eye movements: the initial pursuit eye velocity is larger after experiencing repeated pursuits than saccades. To assess which parameters of the previously executed pursuits play an essential role in modulating the gain of visuomotor transmission, we recorded the ocular responses of monkeys to a brief perturbing motion of the tracking target injected before the start of the eye movements. First, we compared the perturbation responses among the blocks in which the duration of executing pursuit was varied. We found that the response amplitude increased with the increase of the pursuit duration and it reached a plateau level at 100-200 ms of the duration. Second, a comparison of the perturbation responses in the blocks in which target velocity was different showed a gradual increase of the response as a function of the required pursuit velocity. Third, when the animals repeatedly performed pursuits, the response amplitude gradually increased with increasing interval between the appearance of the target and the onset of perturbation. On the other hand, such an increase was not observed when the animals repeatedly performed saccades. These results suggest that before initiating eye movements, the pursuit system modulates the gain of visuomotor transmission so as to be closely related to the properties of the repeatedly experienced eye movements and this gain modulation is triggered by the target's appearance.

Animals↗

PubMed1992

Multimeridional apparent frontoparallel plane: relation between stimulus orientation angle and compensating tilt angle.

The classical apparent frontoparallel plane (AFPP) setting is typically obtained by having the subject move a series of parallel rods farther or closer until they line up in a plane perceived to be parallel to the face plane. If there is a size difference between the two ocular images, the AFPP setting defined by the rods will exhibit a tilt from the objective frontoparallel plane, about an axis parallel to the rods. The multimeridional apparent frontoparallel plane (MAFPP) is an extension of this procedure to rod orientations other than the vertical meridian. In previous studies, it was found that oblique tilt angle settings corresponding to rod orientations of 45 degrees and 135 degrees are equal to square root 2 times the tilt angle for the vertical rod orientation for the same interocular magnification difference along the meridian perpendicular to the rods. In this study, we measured the tilt angles produced by a series of oblique rod orientations between 15 degrees and 165 degrees, inclusive. Throughout the 150 degrees range tested, the tilt angles were found to be consistently proportional to the cosecant of the rod orientation angle, the factor square root 2 previously used being a specific example of this relation. Within this range, neither empirical cues nor the induced effect cause the cosecant relation to break down. It is suggested that the MAFPP procedure can be applied more extensively than previously anticipated.

Aniseikonia↗

PubMed2004

System identification of the human vestibulo-ocular reflex during head-free tracking.

A method was developed to identify the linear, system level dynamics of the horizontal, angular vestibulo-ocular reflex (VOR) as it stabilized vision during head-free tracking of a visual target. Small amplitude, broad spectrum, stochastic torque perturbations were applied to the head while the subject tracked an unpredictable, moving target with active head and eye motions. Stochastic system identification techniques were used to design the torque and target inputs and to conduct the analysis such that the linear dynamics of the VOR, independently of the visual system's influence on eye motions, were determined. The linear analysis was limited to evaluating VOR dynamics from approximately 0.5 to 4.5 Hz. Nonlinearities in the head-neck system affected the low frequency response of the head to the torque perturbations, and the eye velocity sequence was affected by nonlinearities and degraded by noise at high frequencies. The VOR's gain was near 1.0 between about 0.5 and 2.5 Hz, and then decreased steadily to 0.85 as the frequency increased towards 4.0 Hz. The VOR phase angle was also frequency dependent and corresponded to VOR eye motions lagging the head's disturbance motion by less than 10 ms at frequencies greater than 1.0 Hz.

Adult↗

PubMed2005

The specificity and sensitivity of uninhibited COR in labyrinthine-defective patients.

The Cervico-ocular reflex (COR), which depends on proprioceptive afferents from neck muscles to the vestibular nucleus, makes little contribution to the stabilization of gaze in humans. If labyrinthine function is lost because of disease, however, the COR may increase in gain and assume greater importance in generating compensatory eye rotations during natural head movements. We tested the COR, i.e., eye movement responses to rotation of the trunk about the earth fixed head (swinging test with fixed head STFH). If the vestibular function is intact, normally there should be no nystagmus. A total of 88 labyrinthine defective patients and 78 controls were studied. Of the 166 subjects evaluated, 88 presented some kind of alteration (either central or peripheral) and had STFH results showing "no inhibition" in 85 patients. Therefore, the STFH's sensibility is 96.6%. The remaining 3.4% were false negatives (i.e., pathology that could not be detected by the test). Of the 166 subjects evaluated, 78 had normal results and normal STFH. Therefore, STFH's specificity was 100%. We conclude that the study of the COR through STFH is a simple, useful, and clinically reliable test which should improve our knowledge of the interesting relationship between VOR and COR.

Eye Movements↗

PubMed2005

Effect of 3,4-diaminopyridine on the postural control in patients with downbeat nystagmus.

Downbeat nystagmus (DBN) is a common, usually persistent ocular motor sign in vestibulocerebellar midline lesions. Postural imbalance in DBN may increase on lateral gaze when downbeat nystagmus increases. 3,4-Diaminopyridine (3,4-DAP) has been shown to suppress the slow-phase velocity component of downbeat nystagmus and its gravity-dependent component with concomitant improvement of oscillopsia. Because the pharmacological effect is thought to be caused by improvement of the vestibulocerebellar Purkinje cell activity, the effect of 3,4-DAP on the postural control of patients with downbeat nystagmus syndrome was examined. Eye movements were recorded with the video-based Eyelink II system. Postural sway and pathway were assessed by posturography in lateral gaze in the light and on eye closure. Two out of four patients showed an improvement of the area of postural sway by 57% of control (baseline) on eye closure. In contrast, downbeat nystagmus in gaze straight ahead and on lateral gaze did not benefit in these two patients, implying a specific influence of 3,4-DAP on the vestibulocerebellar control of posture. It was concluded that 3,4-DAP may particularly influence the postural performance in patients with downbeat nystagmus.

4-Aminopyridine↗

PubMed2001

The association between nonstrabismic anisometropia, amblyopia, and subnormal binocularity.

PURPOSE: To determine if thresholds exist for the development of amblyopia and subnormal binocularity with various types of anisometropia and to compare these with existing guidelines for the treatment or observation of anisometropia. DESIGN: The records of all previously untreated patients evaluated for isolated refractive error during a 42-month period were reviewed to assess the association between anisometropia, amblyopia, and subnormal binocularity. PARTICIPANTS: Three hundred sixty-one (361) patients with anisometropia and 50 nonanisometropic control participants, examined over a 42-month period, with no history of treatment for refractive error, amblyopia, or other ocular pathologic characteristics were evaluated. METHODS: Uncorrected visual acuity in each eye, monofixation response, and degree of stereopsis were recorded for each patient. Patients with unequal or subnormal uncorrected visual acuity were retested with cycloplegic refraction. If the visual acuity was still abnormal, patients were retested while wearing spectacles. MAIN OUTCOME MEASURES: Degree and type of anisometropia were compared with incidence and severity of amblyopia and subnormal binocularity. RESULTS: Spherical myopic anisometropia (SMA) of more than 2 diopters (D) or spherical hypermetropic anisometropia (SHA) of more than 1 D results in a significant increase in the incidence of amblyopia and decrease in binocular function when compared with nonanisometropic patients (P = 0.05). Increasing levels of SMA and SHA beyond these thresholds result in increased incidence and severity of amblyopia. Cylindrical myopic anisometropia (CMA) or cylindrical hyperopic anisometropia (CHA) of more than 1.5 D results in a significant increase in amblyopia and a decrease in binocular function (P = 0.05). Levels of CMA and CHA more than 1.5 D result in an increased incidence and severity of amblyopia. CONCLUSIONS: This study supports existing guidelines for the treatment or observation of anisometropia and characterizes the association between the type and degree of anisometropia and the incidence and severity of amblyopia and subnormal binocularity.

Adolescent↗

PubMed1994

Subcortical contributions to head movements in macaques. II. Connections of a medial pontomedullary head-movement region.

1. In the companion article, a variety of head movements were elicited by stimulation in, and adjacent to, the gigantocellular reticular nucleus (Cowie and Robinson 1994). We refer to this area, caudal to the abducens nucleus, as the gigantocellular head movement region. In the present paper, the anatomical connections of this region, as determined by injections of wheat-germ agglutinin conjugated horseradish peroxidase (WGA-HRP), are reported. The majority of efferent and afferent connections were with areas related to head movements. 2. Efferent fibers from the region projected via two paths to the caudal medulla and upper cervical spinal cord. Labeled fibers descended in the anterolateral funiculus of the ipsilateral spinal cord to terminate in lateral parts of the ventral horn. A second pathway descended bilaterally in the medial longitudinal fasciculus to the anterior funiculi and medial portions of the ventral gray. These efferents paralleled the head-movement topography demonstrated physiologically. Other projections included efferents to the interstitial nucleus of Cajal, caudal field H of Forel, paramedian pontine reticular formation, and caudal vestibular nuclei. Other efferent fibers projected to the trigeminal, facial, and hypoglossal nuclei, as well as to the parvocellular reticular field, which contains interneurons for these motor groups. However, no efferent or afferent labeling involved the ocular motor nuclei. 3. Afferents to the gigantocellular head movement region arose mainly from head-movement areas. In all animals, labeled cells were found in the intermediate and deep layers of the caudal superior colliculus. Labeled neurons also were found in the caudal field H of Forel, interstitial nucleus of Cajal, pontine medial tegmentum including the pontine paramedian reticular formation, nucleus subcoeruleus, and vestibular nuclear complex. Caudally, filled cells were located in the parvocellular, magnocellular, dorsal, and ventral reticular nuclei, the supraspinal nucleus, and the upper cervical ventral horn. 4. In one animal, the ipsilateral frontal cortex contained retrogradely labeled neurons. These cells were found in layer V of cortical areas 4 and 6. Other afferent cells were found consistently in the periventricular and periaqueductal gray matter. 5. A control injection into the caudal vestibular nuclear complex showed projections to the gigantocellular reticular formation and labeled cells in the vestibular and parvocellular reticular nuclei. These observations show that the connections of the gigantocellular region are not typical of all head movement sites. 6. These data indicate that the gigantocellular head-movement region has the requisite efferent and afferent connections to function in the subcortical control of head, but not eye, movements.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1997

The artifact of retinoscopy revisited: comparison of refractive error measured by retinoscopy and visual evoked potential in the rat.

PURPOSE: The validity of retinoscopy in small eyes has not been clearly established due to uncertainty regarding the source of the ocular reflections assessed during this procedure. A widely cited model which proposes that their origin is the inner limiting membrane of the retina was evaluated in the rat by comparing refractive errors measured by retinoscopy to those measured by visual evoked potentials (VEPs). METHODS: Ten rats were refracted both by cycloplegic streak retinoscopy and by VEP while viewing 0.05 to 0.15 cpd square-wave gratings-reversed at 1.875 Hz. Spherical aberration of the rat eye was assessed as a potentially confounding variable in VEP refraction by sequential retinoscopic refractions across the rat's natural pupil through a 1.5-mm pinhole. RESULTS: All animals were moderately to highly hyperopic by both methods (range = +4.5 to +18.5 D). Spherical aberration was minimal (median = 3.5 D of overcorrected aberration). The median difference between retinoscopic refractions and those by VEP was not significant (+1.94 D more hyperopia by retinoscopy; p = 0.062, Wilcoxon signed rank) but was significantly less than the +9.64 D difference predicted by an inner limiting membrane model (upper 95% limit = +3.76 D). CONCLUSION: This suggests that the origin of the retinoscopic reflex is located in the outer retina rather than at the inner limiting membrane. Correction factors for retinoscopy in small eyes may be smaller than previously assumed.

Animals↗

PubMed1996

Combined eye-head gaze shifts to visual and auditory targets in humans.

We studied the characteristics of combined eye-head gaze shifts in human subjects to determine whether they used similar strategies when looking at visual (V), auditory (A), and combined (V + A) targets located at several target eccentricities along the horizontal meridian. Subjects displayed considerable variability in the combinations of eye and head movement used to orient to the targets, ranging from those who always aligned their head close to the target, to those who relied predominantly on eye movements and only moved their head when the target was located beyond the limits of ocular motility. For a given subject, there was almost no variability in the amount of eye and head movement in the three target conditions (V, A, V + A). The time to initiate a gaze shift was influenced by stimulus modality and eccentricity. Auditory targets produced the longest latencies when located centrally (less than 20 degrees eccentricity), whereas visual targets evoked the longest latencies when located peripherally (greater than 40 degrees eccentricity). Combined targets (V + A) elicited the shortest latency reaction times at all eccentricities. The peak velocity of gaze shifts was also affected by target modality. At eccentricities between 10 and 30 degrees, peak gaze velocity was greater for movements to visual targets than for movements to auditory targets. Movements to the combined target were of comparable speed with movements to visual targets. Despite the modality-specific differences in reaction latency and peak gaze velocity, the consistency of combinations of eye and head movement within subjects suggests that visual and auditory signals are remapped into a common reference frame for controlling orienting gaze shifts. A likely candidate is the deeper layers of the superior colliculus, because visual and auditory signals converge directly onto the neurons projecting to the eye and head premotor centers.

Acoustic Stimulation↗

PubMed2006

The sub-clinical see-saw nystagmus embedded in infantile nystagmus.

A transient, decompensated vertical phoria in an individual with infantile nystagmus syndrome (INS) resulted in two images that oscillated vertically-a diplopic oscillopsia. Ocular motor studies during the vertical oscillopsia recreated by vertical prisms, led to the identification of a sub-clinical see-saw nystagmus (SSN), present under the prism-induced diplopic condition. Retrospective analysis of ocular motor recordings made prior to the above episode of vertical diplopia revealed the presence of that same sub-clinical SSN. The SSN had not been detected previously despite extensive observations and recordings of this subject's pendular IN over a period of forty years. Three- dimensional search-coil data from fourteen additional INS subjects (with pendular and jerk waveforms) confirmed the existence of sub-clinical SSN embedded within the clinically detectable horizontal-torsional IN in seven of the fifteen and a sub-clinical, conjugate, vertical component in the remaining eight. Unlike the clinically visible SSN found in achiasma, the cause of this sub-clinical SSN is hypothesized to be due to a failure of the forces of the oblique muscles (responsible for the torsional component of the IN) to balance out the associated forces of the vertical recti; the net result is a small, sub-clinical SSN. Thus, so-called "horizontal" IN is actually a horizontal-torsional oscillation with a secondary, sub-clinical SSN or conjugate vertical component. The suppression of oscillopsia by efference copy in INS appears to be accomplished for each eye individually, even in a binocular individual. However, failure to fuse the two images results in oscillopsia of one of them.

Diplopia↗