Asymmetry Of Optokinetic Nystagmus Research Articles

Evaluation of Optokinetic Nystagmus Asymmetry in Surgically Treated Infantile Esotropia Patients

Evaluation of Optokinetic Nystagmus Asymmetry in Surgically Treated Infantile Esotropia Patients

Esotropia and Exotropia Preferred Practice Pattern®

Esotropia and Exotropia Preferred Practice Pattern®

Optokinetic nystagmus of Chiari Malfromation. The aim of our study is to determine the special characteristics of disorders of the Optokinetic nystagmus in the early stages of Chiari Malformation

Background Diagnosis and treatment of cochleovestibular dysfunction becomes complicated in case of genetically based combination of pathology. The Chiari Malformation (CM) is a congenital development defect and associated with the caudal displacement of cerebellum and brain stem. The aim of this study is to determine the special characteristics of disorders of the Optokinetic nystagmus in the early stages of CM. At the otorhinolaryngology department of North-West State Medical University named after I.I.Mechnikov (Russia, St Petersburg), 54 cases (patients aged 16–69 ) were studied. All patients showed the symptoms of cochleovestibular dysfunction. Methods The Optokinetic nystagmus was taken in a dark-room using VNGULMAR system manufactured by the German company “Heinemann Medizintechnik GmBH” running software developed by the French company Synapsys. The fixed speed horizontal and vertical Optokinetic stimulus on screen (20 o/s) was applied with distracted and focused attention of the patients. All the studies were conducted before the calloric test (CT) and after CT. The intensity of Optokinetic nystagmus was assessed as per SSC (speed of slow component) of nystagmus. Later on the relative asymmetry in Optokinetic nystagmus was calculated for each same name pair of horizontal and vertical Optokinetic reactions. Results The studies showed that in order to diagnose CM in the early stages it is important not only to identify the asymmetry in horizontal and vertical Optokinetic nystagmus but to mark the value and the sign of asymmetry as well. The sign of asymmetry is especially important after CT. Patients with the low placement of cerebellar tonsil Optokinetic reactions are more susceptible to CT. Conclusions Therefore, in the early stages of CM and “in the risk group”, i.e. the patients with low placement of cerebellar tonsil, before the neurological symptoms have taken place and we have only vestibular dysfunction, the videonystagmography with quantitative evaluation of Optokinetic reaction becomes a voluble source of important diagnostic information and an indication for MRI studies.

Up-down asymmetry in vertical vection

To investigate whether up-down asymmetry similar to that reported in vertical optokinetic nystagmus (OKN), that is, larger OKN responses for upward motion than for downward motion, would appear in vertical vection, we conducted three experiments. In all three experiments, participants viewed a vertically moving random-dot pattern. In Experiments 1 and 2, participants reported vection using a joystick. After each trial, they were also asked to rate the vection magnitude experienced during the stimulus presentation. In Experiment 3, eye movements and vection magnitude (rated after each trial) in response to the stimulus were measured. The results of Experiment 1 showed larger vection magnitude for the upward motion of the stimulus than for the downward motion of it. However, vection onset latency did not change much with stimulus motion direction. Experiment 2 revealed that the up-down asymmetry in vection manifested progressively during the latter part of the stimulus presentation period. Experiment 3 showed clear up-down asymmetry in both OKN and vection magnitude. These results not only indicate that up-down asymmetry similar to that reported in vertical OKN appears in vertical vection, but they also support the notion that the mechanisms underlying vection and OKN are closely related to each other.

OKN Asymmetry in Human Subjects: A Literature Review

Optokinetic nystagmus (OKN) is a reflex eye movement induced by motion of the whole or a large proportion of the visual field. It can be horizontal, vertical, and torsional in direction and consists of two basic components, a slow tracking movement and a rapid recovery saccade. Two forms of OKN exist: “look” and “stare” OKN. There is strong evidence that horizontal OKN is symmetrical in normal healthy adults and that the OKN gains can be influenced by a variety of different factors including target size, shape, contrast, and velocity. Vertical OKN on the other hand is less well understood, although there is a belief that vertical OKN is asymmetrical with an upward preference. Recent publications contradict this assertion. In this article a comprehensive literature review was carried out to determine whether a vertical OKN asymmetry exists in healthy subjects and to explain any anomalous findings.

Visual Stimulation Tests: Testing Methods, Interpretation and Pitfalls

An eye tracking test (ETT), saccade, optokinetic nystagmus (OKN) test and optokinetic-after nystagmus (OKAN) test are the visual stimulation tests most commonly performed. In this article, I will examine the methods, interpretation of the results and pitfalls of those tests. The function of smooth pursuit is evaluated in an ETT. Smooth pursuit is very susceptible to central nervous system damage. Because smooth pursuit is easily affected by the age and arousal, these conditions should be considered in evaluating the results of an ETT. In saccade, the latent time, maximal eye speed and accuracy are evaluated. Saccade may be occasionally the only test that can detect the failure of the central nervous system. OKN is divided into two types by the instructions to the examinees. When examinees are instructed to look at the stripes so as to count them, one by one, OKN is Schau-Nystagmus. When examinees are instructed to stare vacantly in front of them, OKN is Stier-Nystagmus. Schau-Nystagmus differs significantly from Steir-Nystagmus in terms of the speed and form of nystagmus. It is important to clarify the instructions given to the patient. In a qualitative analysis of OKN, nystagmus are superimposed over the stripes with a computer and pursuit movements and catching movements of the target are separately examined. OKN is able to be evaluated in detail in a qualitative analysis, whereas the optokinetic pattern test (OKP) is a clinically convenient method for visually detecting slow and fast phase asymmetry of OKN. OKAN has been thought to be concerned with the velocity storage mechanism. Therefore OKAN test is significant in the study of the function of the peripheral and central vestibular system.

Horizontal and Vertical Look and Stare Optokinetic Nystagmus Symmetry in Healthy Adult Volunteers

Look optokinetic nystagmus (OKN) consists of voluntary tracking of details in a moving visual field, whereas stare OKN is reflexive and consists of shorter slow phases of lower gain. Horizontal OKN is symmetrical in healthy adults, whereas symmetry of vertical OKN is controversial. Horizontal and vertical look and stare OKN symmetry was measured, and the consistency of individual asymmetries and the effect of varying stimulus conditions were investigated. Horizontal and vertical look and stare OKN gains were recorded in 15 healthy volunteers (40 degrees /s) using new methods to delineate look and stare OKN. Responses with right and left eye viewing were compared to investigate consistency of individual OKN asymmetry. In a second experiment, the symmetry of stare OKN was measured in nine volunteers varying velocity (20 degrees /s and 40 degrees /s), contrast (50% and 100%), grating contrast profile (square or sine wave), and stimulus shape (full screen or circular vignetted). There was no horizontal or vertical asymmetry in look or stare OKN gain for all volunteers grouped together. However, individual vertical asymmetries were strongly correlated for left and right eye viewing (look: r = 0.77, P = 0.0008; stare: r = 0.75, P = 0.001) and for look and stare OKN (r = 0.66, P = 7.3 x 10(-5)) because of a strong correlation for downward moving stimuli (r = 0.73, P = 0.002). Horizontal and vertical asymmetries were not significantly affected by variations in stimulus parameter. Although no horizontal or vertical OKN asymmetries existed for volunteers grouped together, vertical OKN was characterized by idiosyncratic asymmetries that remained consistent for an individual. Look and stare OKN gain is strongly associated for downward moving stimuli.

Multiple sensitive periods in human visual development: Evidence from visually deprived children

Psychophysical studies of children deprived of early visual experience by dense cataracts indicate that there are multiple sensitive periods during which experience can influence visual development. We note three sensitive periods within acuity, each with different developmental time courses: the period of visually-driven normal development, the sensitive period for damage, and the sensitive period for recovery. Moreover, there are different sensitive periods for different aspects of vision. Relative to the period of visually driven normal development, the sensitive period for damage is surprisingly long for acuity, peripheral vision, and asymmetry of optokinetic nystagmus, but surprisingly short for global motion. A comparison of results from unilaterally versus bilaterally deprived children provides insights into the complex nature of interactions between the eyes during normal visual development.

Asymmetry of the Optokinetic Nystagmus in Lesion of the Central Nervous System

Unilateral lesions of the central nervous system (CNS) may be associated with a reduction of the optokinetic nystagmus (OKN) slow component in the direction of the lesion. The aim of our study was to assess the role played in these cases by the direct injury of the OKN pathways and/or by a possible associated visual field defect. Monocular OKN was elicited with black and white stripes moving temporally-to-nasally (TN) or nasally-to-temporally (NT) at velocities of 15, 30, 45 and 60 degrees /s. Patients with cortical or chiasmal lesions associated with visual field defects were investigated. OKN was considered asymmetrical if the gain difference between TN and NT stimulation was not within 2 standard deviations of an age-matched control group (n = 86). We examined 12 patients with cortical lesions and 4 patients with chiasmal lesions. Asymmetric OKN gain was measured in 7 patients with cortical lesions associated with a visual field defect, and in 2 patients with chiasmal compression and bitemporal hemianopia. In 2 patients with isolated occipital lesions, OKN asymmetry was explained by the associated visual field defect. The interpretation of OKN asymmetry in patients with CNS lesions should not only consider a direct lesion of the OKN pathways but also a sensory deficit due to a visual field defect.

Infantile Esotropia: An Inevitable Legacy?

Introduction and PurposeTo investigate the clinical signs and electrooculographic (EOG) records in first-degree relatives of patients with infantile esotropia.Subjects and MethodEight families were randomly selected with at least one member with Ciancia syndrome, a common form of infantile esotropia. Both patients and normal relatives underwent a complete visual and ocular motility examination. The pursuit, optokinetic nystagmus (OKN) and saccadic eye movements were recorded by EOG.ResultsEvery family had either clinical and/or EOG anomalies in the examination of apparently normal relatives. A wide spectrum of abnormalities was found. Fourteen relatives had clinical abnormalities, with reduced stereopsis being the most frequently found. Twelve had EOG anomalies, especially in the OKN tracings.ConclusionInfantile esotropia should be considered a familial disease, where relatives who fail to meet all the criteria for the diagnosis still show some of its features. We suggest that asymmetry of OKN, impairment of pursuit movements, reduced stereopsis, and nystagmus in abduction are subclinical signs of the condition, which are frequently present in otherwise normal relatives. We highlight the importance of a positive family history of strabismus to further understand the genetic factors responsible for the transmission of infantile esotropia.

Optokinetic nystagmus in strabismus: are asymmetries related to binocularity?

Strabismus may be associated with an asymmetry of monocular horizontal optokinetic nystagmus (OKN). It is unclear whether OKN asymmetries are associated with deficiency in binocular and/or stereovision. In the current study, patients with different degrees of binocularity were investigated. OKN was examined in the dominant and nondominant eyes of four groups of patients: (1) no measurable binocularity (NB), (2) poor binocularity (PB)-that is, showing binocularity on the Bagolini Test and/or rudimentary stereovision, (3) good binocularity (GB) with good stereoacuity after squint surgery, and (4) a control group. Monocular OKN was elicited with black-and-white stripes moving temporally to nasally (TN) or nasally to temporally (NT) at velocities of 15, 30, 45, and 60 deg/s. Eye movements were recorded with infrared oculography. Only subjects in the NB group showed a significant OKN asymmetry, with preference for TN stimulation in dominant and nondominant eyes. Subjects with PB did not have significant OKN asymmetries but reduced OKN gains in both stimulus directions. Subjects with GB had normal mean OKN gains without asymmetry. Larger OKN asymmetries were correlated with younger age at detection of strabismus if NB and GB were grouped together, but not if each group was analyzed separately. For the first time, a large groups of patients classified by level of binocular vision has been investigated. The results show that OKN gain and asymmetry are associated with the development of binocular vision. OKN investigation may be helpful to identify patients with binocularity or binocular potential in strabismus.

Gaze-Stabilizing Deficits and Latent Nystagmus in Monkeys With Early-Onset Visual Deprivation: Role of the Pretectal NOT

We studied the role of the pretectal nucleus of the optic tract (NOT) in the development of monocular optokinetic nystagmus (OKN) asymmetries and latent nystagmus (LN) in two monkeys reared with binocular deprivation (BD) caused by binocular eyelid suture for either the first 25 or 55 days of life. Single-unit recordings were performed in the right and left NOT of both monkeys at 2-3 yr of age and compared with similar unit recordings in normally reared monkeys. We also examined ocular motor behavior during electrical stimulation of the NOT and during pharmacological inactivation and activation using GABA(A) agonists and antagonists. In BD animals a large proportion of NOT units was dominated by the contralateral eye, in striking contrast to normal animals where 100% of NOT units were sensitive to stimuli delivered to either eye. In the 55-day BD animal no binocularly sensitive neurons were found, while in the 25-day BD animal 60% of NOT units retained at least some binocular sensitivity. Differences in direction sensitivity were also observed in BD animals. We found that 56% of units in the 55-day BD monkey and 10% of units in the 25-day BD monkey responded preferentially to contraversive visual motion. In contrast, only 5% of the NOT units encountered in normally reared monkeys respond preferentially during contraversive visual motion, the rest were most sensitive to ipsiversive visual motion. NOT neurons of BD monkeys showed a wide range of speed sensitivities similar to that of normal monkeys. Unilateral electrical stimulation of the NOT in BD animals induced a conjugate nystagmus with slow phases directed toward the side of stimulation. When we blocked the activity of NOT units with muscimol, a potent GABA(A) agonist, LN was abolished. In contrast, LN was increased when spontaneous activity of the NOT was enhanced with bicuculline, a GABA(A) antagonist. Our results indicate that the NOT in BD monkeys plays an important role in the OKN deficits and LN generation during monocular viewing. We hypothesize that the large proportion of units dominated by the contralateral eye contribute to the development of monocular OKN asymmetries and LN.

Directional motion asymmetry in infant VEPs — which direction?

Monocular viewing during early infancy reveals asymmetries in optokinetic nystagmus (OKN) and visual evoked potentials (VEPs). This study investigates the VEP asymmetry to see if it is consistent in direction with the OKN asymmetry. Steady-state VEPs were recorded from infants (5–21 weeks) viewing gratings that underwent successive displacements in the same direction, leftward or rightward. In addition, transient VEPs were recorded to the two directions of an oscillating stimulus. Both tests produced larger VEP amplitudes for nasal-to-temporal compared to temporal-to-nasal movement. Horizontal eye movements were monitored by EOG while viewing these stimuli to test whether the asymmetry was a consequence of eye movements. No difference in eye movements as a function of the stimulus was found, excluding differences in retinal slip as an explanation of the asymmetry. The stronger neural response for nasal-to-temporal displacements is opposite to the asymmetry of OKN. Oculomotor and VEP asymmetries may be related; however this relationship is not simply that the stronger neural response, indicated by the VEP, leads to a stronger optokinetic response.

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.

Monocular horizontal OKN in observers with early- and late-onset strabismus

Several reports on monocular optokinetic nystagmus (OKN) in observers with strabismus have found that asymmetry of OKN tends to occur in both eyes of observers with an early onset of strabismus but only in the deviating eye of those with a later onset of strabismus. Our objective was to quantify and compare the magnitude of the OKN asymmetry in each eye as a function of observer’s age at onset of strabismus. We studied monocular OKN in ten observers with early-onset (up to 24 months of age), seven observers with late-onset (after 24 months of age) unilateral strabismus, and 12 normally sighted control observers. In the deviating eye, observers with early-onset strabismus showed large OKN asymmetries in favour of nasalward motion while observers with late-onset strabismus showed smaller OKN asymmetries in that eye. The majority of early- and late-onset observers showed near normal OKN in the non-deviating eye although the early-onset observers showed bilateral asymmetries more often. These findings may be due to both age at onset of strabismus and chronological age and are discussed in terms of the issue of plasticity or recovery of function.

Effect of infantile strabismus on visuomotor development in the squirrel monkey (Saimiri sciureus): Optokinetic nystagmus, motion VEP and spatial sweep VEP

PURPOSE. To determine whether squirrel monkeys made artificially strabismic in infancy had ocular fixation abnormalities, directional asymmetries of horizontal optokinetic nystagmus (OKN) and asymmetries of motion visually evoked potentials (MVEPs) similar to those of humans with infantile strabismus. METHODS. Esotropia was produced in a newborn squirrel monkey by surgical tenotomy of both lateral rectus muscles. The alignment and eye rotations of the monkey were examined longitudinally and VEP testing was performed at the age of one year. Visual acuity was measured using spatial frequency sweep VEPs (SSVEP) in response to grating stimulation. OKN was tested under conditions of monocular viewing using full-visual-field, vertically oriented, moving stripes. MVEPs in response to horizontal motion were recorded with the animal sedated to reduce the possibility of eye movement artifact. RESULTS. The artificially strabismic squirrel monkey displayed a constant, comitant esotropic strabismus accompanied by latent nystagmus. Monocular SSVEP acuity was subnormal in one eye, consistent with mild monocular strabismic amblyopia. The monkey demonstrated asymmetric OKN favoring nasally-directed stimulus motion when viewing with either eye. Monocular MVEPs were also characterized by a horizontal asymmetry with a directional bias inverted 180 degrees between the right and the left eyes. The eye movements and MVEP asymmetries were similar to those observed in strabismic macaque monkeys and humans with early-onset strabismus. Neither the OKN asymmetry nor the MVEP asymmetry was evident in a normal squirrel or normal macaque monkey. CONCLUSION. The artificially strabismic squirrel monkey is an appropriate eye movement and VEP model for the study of neural mechanisms in human infantile strabismus.

Prediction of early-onset esotropia from components of the infantile squint syndrome: Schor CM, Fusano RE, Wilson N, et al. Invest Ophthalmol Vis Sci 1997;38:719-40

To examine the association between components of the infantile squint syndrome (ISS) and age of onset of esotropia among subjects in the Cooperative Amblyopia Classification Study (CACS).Fifty subjects were classified retrospectively as having early-onset esotropia (EOE) and 150 subjects were classified as having late-onset esotropia (EOE), depending on whether symptoms of (or treatment for) strabismus occurred before the first birthday or between the first and ninth birthdays, respectively. The authors compared the degree to which latent nystagmus (LN), dissociated vertical deviation (DVD), monocular asymmetry of optokinetic nystagmus (MOKN), monocular asymmetry of smooth pursuit (MSP), and perceived monocular speed bias (MSB) predicted EOE.Slow-phase velocity of MOKN and MSP were faster in response to nasal than to temporal target motion. In contrast, MSB revealed that targets of equal velocity were perceived as moving faster temporally than nasally. The authors evaluated MOKN, MSP, and MSB as dichotomous and as continuous predictors. Dichotomous analysis showed significant associations between DVD and asymmetries of MOKN in the preferred eye of subjects with EOE. Univariate logistic regression models, based on DVD and LN as well as on continuous measures of MOKN, MSP, and MSB, revealed predictive power for all ISS components except LN. In the preferred eye, MSP asymmetry was the strongest single predictor of EOE; multivariate analysis revealed that prediction of EOE improved with the inclusion of DVD.Multivariate analysis indicated that dichotomous measures of DVD and continuous measures of MSP were independent predictors of EOE in a population of 8- to 40-year-old subjects with strabismus. In the preferred eye, MOKN asymmetry was predictive of EOE in the absence of information about MSP. Predictive values of all ISS components depended heavily on the baseline prevalence of EOE in the target population.

Modification of Vertical OKN and Vertical OKAN Asymmetry in Humans During Parabolic Flight

Characteristics of human vertical optokinetic nystagmus (OKN) and afternystagmus (OKAN) were examined by ISCAN imaging system on the ground and on board NASA's KC-135 aircraft in a parabolic flight study. The aircraft produced alternating periods of micro-(ca. 10(-2) G) and hyper-(ca. 1.8 G) gravitoinertial forces. Each phase lasted approximately 20 to 25 s. As compared to the baseline data on the ground, there was a significant increase of downward OKN/OKAN, whereas the upward OKN/OKAN did not change significantly in either micro- or hyper-G. As a consequence, the asymmetry of vertical OKN/OKAN, normally seen on the ground, was lost. It is postulated that the increase of downward OKN/OKAN in non-1-G conditions was governed by two different mechanisms. In micro-G, the normal inhibition effect in 1 G on the downward eye movement mediated by otolith organ activity to vertical velocity storage was removed. In hyper-G, downward OKN/OKAN was facilitated by augmented otolith-ocular reflex because of increased gravitoinertial force, so as to produce enhanced compensatory downward eye movement.

Contribution of chromatic mechanisms to the production of small-field optokinetic nystagmus (OKN) in normals and strabismics

The contribution of chromatic mechanisms to motion processing is currently debated. Although OKN as a measure of motion processing has been employed for chromatic stimuli, the contribution of chromatic mechanisms to the production of OKN has not been assessed directly. We measured voluntary-pursuit and involuntary-stare OKN responses to drifting patterns defined by colors modulated in a cone based color space which isolates luminance and color mechanisms. Results show that OKN responses are reduced for isoluminant stimuli, particularly for the stare conditions. The greatest reduction in responses occur for isoluminance stimuli that isolate the S cones. These results suggest that the chromatic mechanisms may have reduced input to the neural substrate that produces involuntary-stare OKN or that stare OKN has different temporal characteristics when stimulated by chromatic and luminance mechanisms. We also measured OKN asymmetries in several convergent strabismics in response to isoluminant and luminance patterns and compared their response to previous reports of horizontal OKN asymmetries in normal neonate infants. The results question the validity of either the modeling of OKN asymmetries in strabismus as incomplete development or the comparison of adult eye movement records evaluated with criteria for OKN with psychophysical forced choice evaluation of ocular drift in infants.

Clinical optokinetic nystagmus asymmetry in treated esotropes.

Monocular optokinetic nystagmus (OKN) asymmetry is associated with disruption of early binocular visual development. Three groups of treated esotropic patients and a group of normal controls were evaluated for the presence of clinically detectable monocular OKN asymmetry. Clinical assessment of monocular OKN asymmetry was performed by observing eye movements in response to a hand-held rotating drum. Asymmetry was quantitated on a scale of 0 to +3 OKN asymmetry. Clinical OKN asymmetry was evaluated in the following groups of patients: those with congenital esotropia treated with very early surgery achieving high-grade stereo acuity (group 1); those with congenital esotropia treated with late surgery achieving no stereopsis (group 2); those with acquired esotropia achieving high-grade stereo acuity after treatment with spectacle correction (group 3); and normal controls (group 4). Two of the three patients in group 1 showed +3 OKN asymmetry despite having high-grade stereo acuity; the third one, who was surgically aligned earliest (13 weeks), demonstrated +1 OKN asymmetry. This patient achieved orthotropia, 40 seconds stereo acuity, perfect Randot stereo acuity, and had no dissociated vertical deviation or latent nystagmus. All 10 patients in group 2 (those with late alignment-after 1 year-and no stereo acuity) showed +3 OKN asymmetry. All four patients in group 3 (those with acquired hypermetropic esotropia and high-grade stereo acuity after treatment) and all 10 patients in the normal control group showed no OKN asymmetry. Clinically obvious monocular OKN asymmetry can occur in patients with congenital esotropia who are aligned early and develop high-grade stereo acuity. Even brief periods of strabismus during the early period of binocular motor development can result in persistent OKN asymmetry. This suggests that binocular motor processing may develop distinct from, and prior to, the development of high-grade stereo acuity. OKN asymmetry appears to be a clinical sign of an insult to early binocular motor development.