Magnetic Scleral Search Coil Research Articles

Post-traumatic peripheral vestibular disorders (excluding positional vertigo) in workers following head injury

Benign paroxysmal positional vertigo has typically been reported to be the most common cause of post-traumatic dizziness. There is however paucity in the literature about other peripheral vestibular disorders post-head injury. This article provides an overview of other causes of non-positional dizziness post-head trauma from our large institutional experience. The UHN WSIB Neurotology database (n = 4291) between 1998 and 2018 was retrospectively studied for those head-injured workers presenting with non-positional peripheral vestibular disorders. All subjects had a detailed neurotological history and examination and vestibular testing including video nystagmography, video head impulse testing (or a magnetic scleral search coil study), vestibular-evoked myogenic potentials, and audiometry. Imaging studies included routine brain and high-resolution temporal bone CT scans and/or brain MRI. Based on a database of 4291 head-injured workers with dizziness, 244 were diagnosed with non-positional peripheral vertigo. Recurrent vestibulopathy (RV) was the most common cause of non-positional post-traumatic vertigo. The incidence of Meniere’s disease in the post-traumatic setting did not appear greater than found in the general population. The clinical spectrum pertaining to recurrent vestibulopathy, Meniere’s disease, delayed endolymphatic hydrops, drop attacks, superior semicircular canal dehiscence syndrome, and uncompensated peripheral vestibular loss are discussed.

Gentamicin Vestibulotoxicity: Further Insights From a Large Clinical Series.

To review insights gained from a 21-year experience with gentamicin-induced vestibulotoxicity including differences in vestibulotoxicity between single daily dosing (SDD) and multiple daily dosing (MDD) regimens. Retrospective case series. Tertiary care center. Patients with gentamicin vestibulotoxicity referred to the Hertz Multidisciplinary Neurotology Clinic between January 1993 and September 2014. None. Spectrum of vestibular dysfunction measured using videonystagmography, vestibular evoked myogenic potentials, video head impulse testing, and magnetic scleral search coil testing. Of 53 patients with gentamicin-induced vestibulotoxicity, 24 received SDD and 29 received MDD treatment. The most common indications for treatment were sepsis, endocarditis, and osteomyelitis. Angular acceleration receptor function (semicircular canals) was more commonly affected than linear acceleration receptor function (otolithic organ of the saccule; 100% vs. 62%). A significant proportion of patients (53%) developed vestibulotoxicity in the absence of nephrotoxicity and 40% experienced vestibulotoxicity in a delayed fashion up to 10 days posttreatment cessation (mean 3.9 ± 0.7). Therapeutic monitoring did not necessarily prevent delayed vestibulotoxicity. Nephrotoxicity was less common for SDD compared with MDD (60% vs. 35%, p = 0.01). However, the SDD group experienced vestibulotoxicity at a lower cumulative dose (6.3 vs. 7.0 g, p = 0.04) and shorter duration of therapy (20.7 vs 29.4 d, p = 0.02). Our study further highlights important insights regarding gentamicin-induced vestibulotoxicity. While SDD is associated with decreased risk for nephrotoxicity compared with MDD, it confers a higher risk for vestibulotoxicity.

Development and validation of a high-speed video system for measuring saccadic eye movement.

Laboratory-based retroreflective and magnetic scleral search-coil technologies are the current standards for collecting saccadometric data, but such equipment is costly and cumbersome. We have validated a novel, portable, high-speed videocamera-based system (Exilim EX-FH20, Casio, Tokyo, Japan) for measuring saccade reaction time (RT) and error rate in a well-lit environment. This system would enable measurements of pro- and antisaccades in athletes, which is important because antisaccade metrics provide a valid tool for concussion diagnosis and determining an athlete's safe return to play. A total of 529 trials collected from 15 participants were used to compare saccade RT and error rate measurements of the high-speed camera system to a retroreflective video-based eye tracker (Eye-Trac 6: Applied Sciences Laboratories, Bedford, MA). Bland-Altman analysis revealed that the RT measurements made by the high-speed video system were 11 ms slower than those made by the retroreflective system. Error rate measurements were identical between the two systems. An excellent degree of reliability was found between the system measurements and in the ratings of independent researchers examining the video data. A strong association (r = .97) between the RTs determined via the retroreflective and high-speed camera systems was observed across all trials. Our high-speed camera system is portable and easily set up, does not require extensive equipment calibration, and can be used in a well-lit environment. Accordingly, the camera-based capture of saccadometric data may provide a valuable tool for neurological assessment following a concussive event and for the continued monitoring of recovery.

Vestibular Outcomes in Bilateral Posterior Semicircular Canal Occlusion for Refractory Benign Positional Vertigo.

Bilateral posterior semicircular canal (PSCC) occlusion is a successful treatment of bilateral benign positional vertigo (BPV) refractory to particle repositioning manoeuvers. Little about the effects on the vestibular ocular reflex (VOR) postoperatively, which is the intent of this study. All patients who underwent bilateral posterior canal occlusion for BPV at the University Health Network by the senior author (J.A.R.) between 2001 and 2017 with pre- and postoperative vestibular testing were included in the study.All patients underwent a detailed history and neuro-otological examination including dynamic visual acuity (DVA). Laboratory testing including video head impulse testing or magnetic scleral search coil testing, video nystagmography, cervical and ocular vestibular evoked myogenic potentials and audiological testing before and following their procedure at 1, 6, and 12 months postoperatively. Three patients were included in the study, all females, with a mean age of 41 years (range 36-44 yr). All patients had developed bilateral BPV after head trauma. Mean length of follow-up was 26 months (range 6-84 mo). All patients demonstrated a reduction in the vertical VOR of between 0.37 and 0.57/s at 1 month postocclusion. Between 6 and 12 months postoperatively, an improvement in their vertical VOR between 0.45 and 0.75/s was observed. Clinically, all patients reported complete resolution of their positional vertigo with a negative Dix-Hallpike bilaterally at follow-up. None reported oscillopsia, which was confirmed with DVA testing. Bilateral PSCC occlusion results in a reduction in the vertical VOR of the PSCCs.Over a 6 to 12 month time period improvement in the VOR gain can be demonstrated, most likely due to central compensation. There is clinical correlation with improvement in DVA testing. Bilateral PSCC occlusion is a safe and effective treatment for bilateral BPV proved refractory to particle repositioning manoeuvers.

Retrospective review of oscillopsia: etiologies and clinical characteristics

Background: Oscillopsia can result from dysfunction involving the vestibuloocular reflex (VOR). Few studies have detailed the full spectrum of clinical characteristics and laboratory findings of this disabling condition. Objectives: To review causes and clinical characteristics of oscillopsia. Methods: Retrospective review of clinical records of a series of patients with oscillopsia from the University Health Network Multidisciplinary Neurotology Clinic. Results: Review of 109 patients with oscillopsia showed near equal sex distribution and a mean age of 54.9 years (standard deviation 15.7). The most common peripheral vestibular causes were ototoxicity (19.3%) and Meniere’s disease (10.1%). The most common central cause involved cerebellar degeneration (7.3%). Only 43.1% complained of vertigo at any time. Head impulse testing demonstrated bilateral refixation saccades in 70% of patients, while over 95% had a loss of dynamic visual acuity ?5 lines on LogMAR chart testing. Some 38.8% of patients demonstrated normal caloric responses, whereas only 26.5% exhibited evidence of a bilateral caloric loss. Over 50% of patients maintained otolithic function as demonstrated by cervical vestibular evoked myogenic potential testing. Most patients demonstrated low VOR gains bilaterally on magnetic scleral search coil testing. Conclusions: A wide spectrum of clinical characteristics was identified in patients with oscillopsia. It is important for the physician to perform a thorough history, physical examination (including head impulse and dynamic visual acuity), and laboratory investigations. Keywords: Bilateral vestibular loss, magnetic scleral search coil, oscillopsia, vestibuloocular reflex

Design, simulation and evaluation of uniform magnetic field systems for head-free eye movement recordings with scleral search coils.

The precise measurement of eye movements is important for investigating vision, oculomotor control and vestibular function. The magnetic scleral search coil technique is one of the most precise measurement techniques for recording eye movements with very high spatial (≈ 1 arcmin) and temporal (>kHz) resolution. The technique is based on measuring voltage induced in a search coil through a large magnetic field. This search coil is embedded in a contact lens worn by a human subject. The measured voltage is in direct relationship to the orientation of the eye in space. This requires a magnetic field with a high homogeneity in the center, since otherwise the field inhomogeneity would give the false impression of a rotation of the eye due to a translational movement of the head. To circumvent this problem, a bite bar typically restricts head movement to a minimum. However, the need often emerges to precisely record eye movements under natural viewing conditions. To this end, one needs a uniform magnetic field that is uniform over a large area. In this paper, we present the numerical and finite element simulations of the magnetic flux density of different coil geometries that could be used for search coil recordings. Based on the results, we built a 2.2 × 2.2 × 2.2 meter coil frame with a set of 3 × 4 coils to generate a 3D magnetic field and compared the measured flux density with our simulation results. In agreement with simulation results, the system yields a highly uniform field enabling high-resolution recordings of eye movements.

Avoiding a neurosurgical approach: the transmastoid repair of semi‐circular canal dehiscence with magnetic scleral search coil measurement of postoperative vestibular function

Clinical OtolaryngologyVolume 35, Issue 2 p. 156-158 Avoiding a neurosurgical approach: the transmastoid repair of semi-circular canal dehiscence with magnetic scleral search coil measurement of postoperative vestibular function D.D. Pothier, D.D. Pothier Department of Otolaryngology Head and Neck Surgery, Toronto General Hospital, University Health Network, Toronto, ON, Canada. Department of Otorhinolaryngolohy-Head and Neck Surgery, College of Medicine, Yeungnam University, KoreaE-mail: [email protected]Search for more papers by this authorC.H. Bae, C.H. Bae Department of Otolaryngology Head and Neck Surgery, Toronto General Hospital, University Health Network, Toronto, ON, Canada. Department of Otorhinolaryngolohy-Head and Neck Surgery, College of Medicine, Yeungnam University, KoreaE-mail: [email protected]Search for more papers by this authorP.K. Das-Purkayastha, P.K. Das-Purkayastha Department of Otolaryngology Head and Neck Surgery, Toronto General Hospital, University Health Network, Toronto, ON, Canada. Department of Otorhinolaryngolohy-Head and Neck Surgery, College of Medicine, Yeungnam University, KoreaE-mail: [email protected]Search for more papers by this authorJ.A. Rutka, J.A. Rutka Department of Otolaryngology Head and Neck Surgery, Toronto General Hospital, University Health Network, Toronto, ON, Canada. Department of Otorhinolaryngolohy-Head and Neck Surgery, College of Medicine, Yeungnam University, KoreaE-mail: [email protected]Search for more papers by this author D.D. Pothier, D.D. Pothier Department of Otolaryngology Head and Neck Surgery, Toronto General Hospital, University Health Network, Toronto, ON, Canada. Department of Otorhinolaryngolohy-Head and Neck Surgery, College of Medicine, Yeungnam University, KoreaE-mail: [email protected]Search for more papers by this authorC.H. Bae, C.H. Bae Department of Otolaryngology Head and Neck Surgery, Toronto General Hospital, University Health Network, Toronto, ON, Canada. Department of Otorhinolaryngolohy-Head and Neck Surgery, College of Medicine, Yeungnam University, KoreaE-mail: [email protected]Search for more papers by this authorP.K. Das-Purkayastha, P.K. Das-Purkayastha Department of Otolaryngology Head and Neck Surgery, Toronto General Hospital, University Health Network, Toronto, ON, Canada. Department of Otorhinolaryngolohy-Head and Neck Surgery, College of Medicine, Yeungnam University, KoreaE-mail: [email protected]Search for more papers by this authorJ.A. Rutka, J.A. Rutka Department of Otolaryngology Head and Neck Surgery, Toronto General Hospital, University Health Network, Toronto, ON, Canada. Department of Otorhinolaryngolohy-Head and Neck Surgery, College of Medicine, Yeungnam University, KoreaE-mail: [email protected]Search for more papers by this author First published: 11 April 2010 https://doi.org/10.1111/j.1749-4486.2010.02088.xCitations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume35, Issue2April 2010Pages 156-158 RelatedInformation

Comparison of saccadic peak velocities between electro-oculography, video-oculography and scleral search coil

Peak velocity of saccadic eye movements is a crucial motor parameter in clinical neurology and oculomotor research. However, it may differ depending on the technique recording eye movements. Electrooculography (EOG) is easy and comfortable to handle but its signal is noisy and it may overestimate peak velocity of upwards saccades (Yee et al. 1985). Videooculography (VOG) and the magnetic Scleral Search Coil System (SSC) both show high spatial and temporal resolution but also have some technical flaws. VOG does not work when eyes are closed. SSC is invasive, expensive and decreases peak velocity compared to VOG (Frens and van der Geest 2002). For the first time, we recorded saccades and compared them intraindividually using all three recording techniques with open and closed eyes.

The clinical utility of search coil horizontal vestibulo-ocular reflex testing

Conclusion. Testing of the horizontal vestibulo-ocular reflex (VOR) with head rotations (including head impulses) using the magnetic scleral search coil technique (SCT HHI) provides valuable additional diagnostic information in patients with persistent dizziness, oscillopsia or imbalance. It identifies high and low frequency/acceleration vestibular abnormalities that are frequently missed using other methods. Objectives. To evaluate the diagnostic utility of SCT measurement of the horizontal VOR in the multidisciplinary neurotology clinic of a tertiary referral centre. Patients and methods. The records of 127 consecutive patients referred for persistent dizziness, oscillopsia, imbalance, or with clinical findings suggestive of high frequency/acceleration vestibular dysfunction were reviewed. All had been tested with clinical head impulses, bithermal calorics and vestibular-evoked myogenic potentials. VOR gain (peak eye velocity/peak head velocity) had been measured both in response to sinusoidal oscillations in a rotating chair (0.1–11Hz) and to manually delivered horizontal head rotations (peak head velocities 50–500°/s) using SCT. Results. Agreement between the different test modalities of horizontal semicircular canal function was moderate. Relative to SCT HHI, clinical HHI showed the highest sensitivity and the lowest specificity (both 70%). SCT HHI appeared to have the greatest diagnostic yield, when compared with calorics and SCT ROT (23% of all abnormalities shown were detected only by SCT HHI) and also allowed detection of significant asymmetries in patients with bilateral vestibular dysfunction.

Saccadic Eye Movement Velocity Measured with the Infrared Reflection and Search Coil Eye-Tracking Systems in Patients with Thyroid-Associated Ophthalmopathy

Background Assessment of changes in saccade velocity may be useful in the early detection of thyroid-associated ophthalmopathy (TAO). Two eye-tracking systems were used to measure the velocity of saccadic eye movements in patients with TAO. Method Fourteen patients with active TAO and 14 healthy controls were enrolled for recordings with two eye-tracking systems: the magnetic scleral search coil (MSC; Skalar Medical) and the infrared reflection systems (IR; Orbit XY-1000). The MSC is generally considered the “gold standard” method for tracking of rapid eye movements. The IR system uses novel computer technology and is based on sampling of reflected infrared light from the surface of the eyes. Main sequence plots constructed from the recorded saccadic peak velocity and amplitude were analyzed for differences between patients and healthy controls. Results There were no significant differences between patients with TAO and healthy controls in the constructed main sequence plots of maximum velocity (VMAX) and the slope constant (C). Conclusions Main sequence analysis of saccadic eye movements was not useful for detecting TAO in this experimental setting with either of the two eye-tracking methods. This is hypothesized to be due to compensation for the early orbital changes in TAO by neural adaptation of the saccades in the brain stem. The contradictory results between this and previous studies cannot be easily explained. We assume that there is a large heterogeneity in the saccadic eye movement performance in both the normal population and the TAO-population. Also, differences in the study design may cause dissimilar outcomes and hence incoherent conclusions. A non-invasive recording system that is able to generate a minimum amount of intra- and inter-individual variability and a study design where normal variability can be reduced to a minimum may be useful for future identification of early eye muscle changes in TAO.

Intra-Individual Variability of Saccadic Velocity Measured with the Infrared Reflection and Magnetic Scleral Search Coil Methods

Background. The infrared (IR) and the magnetic scleral search coil (MSC) systems for eye tracking were studied with regard to the intra-individual variability in saccadic eye movement recordings. Method. Three healthy subjects performed similar saccadic eye movement tasks at five different occasions with both the IR (Orbit XY-1000) and the MSC (Skalar Medical) techniques. The maximum velocity (VMAX) and slope constant (C) of the main sequence plots were analyzed with regard to the coefficient of variation (CV) and the intraclass correlation coefficient (Ricc). In addition, the possible reasons for variability in the IR recordings, especially different causes for noise, were analyzed and discussed. Results. The main sequence data showed intra-individual variation with both recording systems, but the coefficient of variation was higher for VMAX with the IR compared to the MSC method. Ricc analysis showed that 36% of the variance of VMAX and 49% of the variance of C resulted from intra-individual variability in recordings of the IR system. The corresponding results for the MSC recordings regarding VMAX and C were 48% and 88%. Conclusions. Saccadic eye movement recordings yielded a larger intra-individual variability with the IR system than with the MSC system. The effect that the MSC annulus may have on the ocular motor command signal and the possible low pass filter caused by the coil slipping on the surface of the eye may partly explain the relatively lower velocity in the MSC recordings. Also, noise in the IR recordings induces peaks of eye velocity, which can be reduced considerably by filtering. However, the variability in the recordings, which was larger in the IR than in the MSC recordings, did not seem to be decreased by filtering. The basic level of noise in the recordings was not clearly associated with the amount of reduction of VMAX when the IR recordings were filtered. We suggest that artefacts of the saccadic signal, which can be related to changes in the reflecting surface of the eyes and eyelids, are important factors for explaining the variability and high-velocity peaks in the IR recordings. Lighting conditions was confirmed as a cause for noise, but temperature and air humidity changes in the goggles were not suspected to influence data in the normal experimental setting. Although noise, shortcomings of the recording technique and procedure may offer explanations for the intra-individual variability, the calibration procedure and changes in attention and fatigue of the subject should also be considered.

A comparison between the magnetic scleral search coil and infrared reflection methods for saccadic eye movement analysis

A non-invasive eye tracking system, based on pulsed infrared light (IR), was compared with the magnetic scleral search coil method (MSC) for saccadic eye movement recordings. Ten normal subjects performed horizontal and vertical saccades recorded with both methods. Eight recordings were complete and analysed for maximum peak velocity (V(MAX)) and constant (C) of the main sequence curve. The IR recordings showed significantly higher peak velocity values than the MSC system and generally more inter-individual variability. No significant difference regarding peak velocity was detected between abducting and adducting saccades or between upward and downward saccades with either of the systems. Horizontal saccades had higher peak velocities with both techniques. Comparison of the main sequence plots of the IR and MSC eye tracking techniques reveals that the IR system yields higher values of maximum peak velocity and the constant, the differences being similar for eye movements in different directions. There are various possible explanations for the lower maximum velocity of the MSC recordings, e.g. slipping of the coil annulus on the surface of the eye and a change of the oculomotor command signal induced by wearing the coil. Also, artefacts associated with the IR recording system may cause over-estimations of the saccadic velocity and, furthermore, contribute to the higher variability of the IR recordings.

Symptomatic high frequency/acceleration vestibular loss: consideration of a new clinical syndrome of vestibular dysfunction

ConclusionSymptomatic high frequency/acceleration vestibular loss is a distinct clinical entity that can be missed on conventional ENG with caloric testing. Under certain circumstances, symptomatic patients with a high frequency/acceleration vestibular loss should undergo an MSSC study for confirmation, if required.ObjectiveTo document that normal electronystagmography (ENG) with conventional bithermal caloric testing is inadequate for diagnosing clinically significant high frequency/acceleration vestibular loss.Material and methodsPatients with clinical symptoms and signs of persistent peripheral vestibular dysfunction despite normal conventional bithermal caloric testing on ENG underwent high frequency/acceleration horizontal magnetic scleral search coil (MSSC) eye movement studies. The clinical findings and results from audiometric tests, conventional ENG with bithermal caloric tests and MSSC tests were reviewed.ResultsEleven patients were identified as having an abnormal MSSC study, indicating a high frequency/acceleration vestibular loss consistent with their clinical history despite normal or equivocal bithermal caloric responses on conventional ENG. Although valuable, ENG caloric testing evaluates lateral semicircular canal function and should be considered a non-physiological test primarily of low frequency vestibular function. High frequency/acceleration head thrust testing clinically detected a “high frequency/acceleration vestibular loss” in 8/11(72.7%) cases.

The vestibulo-ocular reflex in fourth nerve palsy: deficits and adaptation

The effects of fourth nerve palsy on the vestibulo-ocular reflex (VOR) had not been systematically investigated. We used the magnetic scleral search coil technique to study the VOR in patients with unilateral fourth nerve palsy during sinusoidal head rotations in yaw, pitch and roll at different frequencies. In darkness, VOR gains are reduced during incyclotorsion, depression and abduction of the paretic eye, as anticipated from paresis of the superior oblique muscle. VOR gains during excyclotorsion, elevation and adduction of the paretic eye are also reduced, whereas gains in the non-paretic eye remain normal, indicating a selective adjustment of innervation to the paretic eye. In light, torsional visually enhanced VOR (VVOR) gains in the paretic eye remain reduced; however, visual input increases vertical and horizontal VVOR gains to normal in the paretic eye, without a conjugate increase in VVOR gains in the non-paretic eye, providing further evidence of selective adaptation in the paretic eye. Motions of the eyes after fourth nerve palsy exemplify monocular adaptation of the VOR, in response to peripheral neuromuscular deficits.

Ocular motor myotonic phenomenon in myotonic dystrophy

Objective: To detect disconjugate ocular motor abnormalities and a possible extraocular muscle myotonic phenomenon in patients with myotonic dystrophy (MyD). Methods: The magnetic scleral search coil technique was used to...

Opsoclonus in three dimensions: oculographic, neuropathologic and modelling correlates

Opsoclonus is a dyskinesia consisting of involuntary, arrhythmic, chaotic, multidirectional saccades, without intersaccadic intervals. We used a magnetic scleral search coil technique to study opsoclonus in two patients with paraneoplastic complications of lung carcinoma. Eye movement recordings provided evidence that opsoclonus is a three-dimensional oscillation, consisting of torsional, horizontal, and vertical components. Torsional nystagmus was also present in one patient. Antineuronal antibody study revealed the presence of anti-Ta (Ma2 onco-neuronal antigen) antibodies in one patient, which had previously been associated only with paraneoplastic limbic encephalitis and brainstem dysfunction, but not opsoclonus, and only in patients with testicular or breast cancer. Neuropathologic examination revealed mild paraneoplastic encephalitis. Normal neurons identified in the nucleus raphe interpositus (rip) do not support postulated dysfunction of omnipause cells in the pathogenesis of opsoclonus. Computer simulation of a model of the saccadic system indicated that disinhibition of the oculomotor region of the fastigial nucleus (FOR) in the cerebellum can generate opsoclonus. Histopathological examination revealed inflammation and gliosis in the fastigial nucleus. This morphological finding is consistent with, but not necessary to confirm, damage to afferent projections to the FOR, as determined by the model. Malfunction of Purkinje cells in the dorsal vermis, which inhibit the FOR, may cause opsoclonus by disinhibiting it.

Disjunctive Optokinetic Nystagmus in a Naturally Esotropic Macaque Monkey: Interaction between Nasotemporal Asymmetries of Versional Eye Movement and Convergence

Objective: To assess the interaction between versional and vergence eye movements in normal and strabismic monkeys. Methods: Horizontal optokinetic nystagmus (OKN) and vergence were measured using the magnetic scleral search coil technique in a normal adult monkey and a strabismic monkey who had naturally occurring early-onset esotropia. Mean eye velocity and vergence angles were calculated during the slow phases of OKN. Results: The strabismic monkey had a nasotemporal asymmetry of OKN favoring nasally directed motion in each eye. During monocular optokinetic stimulation, mean eye velocities were substantially greater for the adducting as compared to the abducting eye. The velocity of the abducting eye was between 55 and 80% of the velocity of the adducting eye (p < 0.01). As a consequence of the disjunctive movements, the eyes converged an average of 4 ± 2.8° during OKN. Saccadic analysis documented normal lateral rectus function in each eye. Neither an OKN asymmetry nor disjunctive OKN was observed in the normal monkey. Conclusion: Disjunctive OKN in the esotropic monkey suggests that the cerebral maldevelopment responsible for nasally biased OKN also contributes to nasal biases in vergence pathways.

Saccades and smooth pursuit in myotonic dystrophy.

Reflexive saccades, remembered saccades, antisaccades, fixation and smooth pursuit were recorded in seven subjects with myotonic dystrophy (MD) and seven age-matched controls using the magnetic scleral search coil technique. Neuropsychological performance was assessed using the Wisconsin Card Sort Test and measures of verbal fluency. Subjects with MD showed significantly elevated error rates in the antisaccade and remembered saccade paradigms, consistent with prefrontal dysfunction, and these two measures of distractibility were significantly correlated with each other. Saccadic latencies, square wave jerk frequency, and smooth pursuit peak velocity gain showed no significant difference between the two groups, although the peak velocity of all classes of saccades was significantly reduced in patients with MD. These results extend the findings of previous studies of oculomotor function in MD, and provide novel evidence for a central contribution to abnormalities of eye movements in this condition.

Oculomotor function in amyotrophic lateral sclerosis: Evidence for frontal impairment

Saccadic eye movements, fixation, and smooth pursuit were recorded in 17 subjects with amyotrophic lateral sclerosis (ALS) and 11 age-matched controls using a magnetic scleral search coil. Reflexive, remembered and antisaccades, and smooth pursuit at four target velocities were studied. Subjects with ALS showed significantly elevated error rates (distractibility) and latency in the antisaccade and remembered saccade paradigms but no abnormality of reflexive saccades. The frequency of small saccades that intruded on steady fixation (square-wave jerks) was also increased in ALS subjects. Peak velocity gain of smooth pursuit and performance on the Wisconsin Card Sort Test did not differ significantly between the two groups. These findings are consistent with prefrontal dysfunction in ALS and provide an independent source of support for the thesis that the pathology of this condition invades frontal cortex.

Reorientation of Poststimulus Nystagmus in Tilted Humans1

Recent studies indicate that the direction of postrotatory nystagmus and optokinetic afternystagmus reorients toward earth-horizontal in tilted subjects. To further examine this phenomenon in humans, we studied 8 adults (4M, 4F) with no history of neurologic or otologic disease. Vestibular stimulation consisted of yaw off-vertical axis rotation (OVAR) trapezoids with eyes open in the dark at 60 degrees/s constant velocity with a tilt angle of 30 degrees and a deceleration at 100 degrees/s2 to a stop in either the right-ear-down or the left-ear-down position. The optokinetic stimulus consisted of 5 degrees wide black and white stripes projected against a cylindrical visual surround 1 m in diameter rotated at a constant velocity of 30 degrees/s. The projector, visual surround, and subject were all tilted by 30 degrees; subjects were placed either in the right-ear-down or left-ear-down position. Eye position was measured using the magnetic scleral search coil technique. Each trial was scrutinized for the presence of reorientation of nystagmus in the subject's roll plane by looking for vertical nystagmus in the appropriate direction. Results indicated that reorientation of postrotatory nystagmus following OVAR was variable but often present. Reorientation of optokinetic afternystagmus was neither as consistent nor as robust as that seen following OVAR. These findings confirm that humans exhibit a predilection for eye rotations in the earth-horizontal plane.(ABSTRACT TRUNCATED AT 250 WORDS)