Optokinetic Nystagmus Research Articles

The Effect of Weighted Contact Lens on Physiological Nystagmus in Young Healthy Subjects

Background and Aim: Contact lenses correct the visual functioning of patients with low vision due to congenital nystagmus. This research presents a new method to reduce nystagmus using contact lenses in healthy subjects. Methods: Thirty-three normal people (13 women, 20 men) aged 18 to 25 with an average age of 23.3 years participated in this study. In the studied subjects, nystagmus was evoked by an optokinetic stimulus. Then, it was measured and recorded. Next, the Conventional Contact Lens (CCL) and a special lens that was designed and made heavier than the conventional lenses were placed in the eyes of the participants. Once again, nystagmus was recorded with the optokinetic stimulus while the contact lens was placed in the participant’s eyes. Results: No significant difference was observed for the Slow Phase Velocity (SPV) and gain of nystagmus with and without CCL (p>0.05), but this parameter had a significant difference with and without Weighted Contact Lenses (WCL) (p<0.05). Also, the comparison between the two lenses demonstrated a significant difference (p<0.05), which indicates the positive effect of the WCL in reducing the SPV and gain of nystagmus. Conclusion: Using weighted contact lenses can significantly reduce the SPV and gain of optokinetic nystagmus in healthy subjects. Investigating the effect of this lens in inhibiting pathological nystagmus is recommended in future research. Keywords: Nystagmus; optokinetic nystagmus; weighted contact lens

Impaired pre-synaptic plasticity and visual responses in auxilin-knockout mice

Auxilin (DNAJC6/PARK19), an endocytic co-chaperone, is essential for maintaining homeostasis in the readily releasable pool (RRP) by aiding clathrin-mediated uncoating of synaptic vesicles. Its loss-of-function mutations, observed in familial Parkinson's disease (PD), lead to basal ganglia motor deficits and cortical dysfunction. We discovered that auxilin-knockout (Aux-KO) mice exhibited impaired pre-synaptic plasticity in layer 4 to layer 2/3 pyramidal cell synapses in the primary visual cortex (V1), including reduced short-term facilitation and depression. Computational modeling revealed increased RRP refilling during short repetitive stimulation, which diminished during prolonged stimulation. Silicon probe recordings in V1 of Aux-KO mice demonstrated disrupted visual cortical circuit responses, including reduced orientation selectivity, compromised visual mismatch negativity, and shorter visual familiarity-evoked theta oscillations. Pupillometry analysis revealed an impaired optokinetic response. Auxilin-dependent pre-synaptic endocytosis dysfunction was associated with deficits in pre-synaptic plasticity, visual cortical functions, and eye movement prodromally or at the early stage of motor symptoms.

Flexible Learning Models Utilizing Different Neural Plasticities

The existing models for vestibulo-ocular reflex (VOR) and optokinetic response (OKR) learning utilize neural circuit structure and capture a few characteristics of these two learning systems. However, it remains unclear how the error signals guide these learning processes. Here, we propose novel dynamic learning models using error feedback in a flexible fashion to account for both VOR and OKR learning. We first used a feedback modulation model and found the error signals play an essential guiding role in gain compensation of wild-type mice. However, this feedback modulation model cannot accurately reproduce gain changes during the recovery period. Therefore, we propose a non-uniform feedback modulation model using flexible plasticity learning rules of different memory sites to take into account the effect of classical linearity models in both training and recovery periods. To further study learning characteristics of gain reduction, we introduce a reversal-phase feedback modulation model and explore the contribution of synaptic plasticity to adaptive learning, in which characteristics and bidirectional synaptic plasticity in the VOR-decrease learning mode can be fully recovered. Taken together, our results suggest that, to explain VOR and OKR learning systems, one needs dynamical models with flexible and multiple components at different or same sites of neuronal circuits.

Eye Movement Reflexes Indicate the Homing Direction in the Path-Integrating Fiddler Crab, Uca pugilator

As animals execute essential behaviors like foraging, they must orient with respect to the space around them, requiring some neural/behavioral mechanism for spatial navigation. One such navigation mechanism is path integration, whereby animals recall their starting point by creating a memory-stored home vector. In some animals, this is stored in an egocentric frame of reference; however, it remains unclear what comprises this in animals’ spatial memory. The fiddler crab Uca pugilator makes an excellent model to investigate the nature of the egocentric frame of reference because they appear to path integrate using self-motion cues to form an egocentric vector. We hypothesized that the home vector direction is governed by the optokinetic system, since the eye–body angle explicitly reflects the deviation of the body axis from home direction as optokinetic eye movements stabilize the eyes against body rotation. To test this hypothesis, we monitored eye and body movements during foraging excursions of crabs showing varying degrees of visual stabilization. We found that crabs with good eye stability had more accurate home vectors than those with poor eye stability, and the quantitative degree of stability accurately predicted the crabs’ perception of home direction. These results suggest that eye movement reflexes may establish the homing direction in path integrating fiddler crabs.

A circuit suppressing retinal drive to the optokinetic system during fast image motion

Optokinetic nystagmus (OKN) assists stabilization of the retinal image during head rotation. OKN is driven by ON direction selective retinal ganglion cells (ON DSGCs), which encode both the direction and speed of global retinal slip. The synaptic circuits responsible for the direction selectivity of ON DSGCs are well understood, but those sculpting their slow-speed preference remain enigmatic. Here, we probe this mechanism in mouse retina through patch clamp recordings, functional imaging, genetic manipulation, and electron microscopic reconstructions. We confirm earlier evidence that feedforward glycinergic inhibition is the main suppressor of ON DSGC responses to fast motion, and reveal the source for this inhibition—the VGluT3 amacrine cell, a dual neurotransmitter, excitatory/inhibitory interneuron. Together, our results identify a role for VGluT3 cells in limiting the speed range of OKN. More broadly, they suggest VGluT3 cells shape the response of many retinal cell types to fast motion, suppressing it in some while enhancing it in others.

Deep learning framework for neurological diseases diagnosis through near-infrared eye video and time series imaging algorithms

Internet of Things (IoT) solutions have greatly evolved recently with the application of Artificial Intelligence (AI). Indeed, AI enriches the IoT with intelligence capabilities. In particular, AI methods are highly effective in the scope of the Internet of Medical Things (IoMT) for the applications requiring decision support for doctors. In this work, we propose a Deep Learning (DL) framework for the classification of Parkinson’s disease (PD) and Progressive Supranuclear Palsy (PSP). In contrast to the state-of-the-art solutions relying on only the saccade test for the classification of these neurodegenerative diseases, we collect a dataset while the subjects perform five exercises including saccade, spontaneous nystagmus, optokinetic nystagmus, pursuit, and gaze test. We then extract the pupil features (coordinates, area, minor axis, and major axis) using the image segmentation DL model and represent them as images using Gramian Angular Difference Field (GADF) time series imagining algorithm. The resultant images are supplied to the proposed disease-detection model for running the classification procedure. The best classification results were obtained for the optokinetic exercise with the accuracy of 96.9%, 90.8%, and 96.9% for the left, right, and both eyes, respectively.

Vestibular and Oculomotor Findings in Vestibular Migraine Patients.

Vestibular migraine (VM) is the most frequent etiology of recurrent spontaneous episodic vertigo. Vestibular and oculomotor abnormalities have been described in VM; however, the diagnosis is currently based on symptoms. The objective of this study was to determine the most frequent abnormalities in videonystagmography (VNG), caloric testing (Cal) and video head impulse test (vHIT) in patients with VM. A retrospective cohort study was conducted, including all VM and probable VM patients seen from January 2021 to July 2022. Demographics, auditory symptoms and results via VNG, Cal and vHIT were evaluated. VNG results were compared with a control group. Sixty patients, 81.7% with VM and 18.3% with probable vestibular migraine, were included. VNG revealed the following abnormalities: 21.7% spontaneous nystagmus; 33.3% positional nystagmus, mostly central; 26.7% optokinetic nystagmus; 56.7% smooth pursuit abnormalities and 70% saccade test abnormalities, mostly velocity and latency. An abnormal unilateral caloric response was seen in 22.9%, while vHIT revealed a low gain in at least one canal in 21.7%, and saccades were seen in at least one canal with normal gains in 18.3%. Concordant results between Cal and lateral vHIT were seen in 77.1% of cases. Although VM is a clinical diagnosis, vestibular and oculomotor abnormalities are commonly seen. The most frequent oculomotor findings were an abnormal saccade test, abnormal smooth pursuit and central positional nystagmus.

Impaired Direction Selectivity in the Nucleus of the Optic Tract of Albino Mice.

Human albinos have a low visual acuity. This is partially due to the presence of spontaneous erroneous eye movements called pendular nystagmus. This nystagmus is present in other albino vertebrates and has been hypothesized to be caused by aberrant wiring of retinal ganglion axons to the nucleus of the optic tract (NOT), a part of the accessory optic system involved in the optokinetic response to visual motion. The NOT in pigmented rodents is preferentially responsive to ipsiversive motion (i.e., motion in the contralateral visual field in the temporonasal direction). We compared the response to visual motion in the NOT of albino and pigmented mice to understand if motion coding and preference are impaired in the NOT of albino mice. We recorded neuronal spiking activity with Neuropixels probes in the visual cortex and NOT in C57BL/6JRj mice (pigmented) and DBA/1JRj mice with oculocutaneous albinism (albino). We found that in pigmented mice, NOT is retinotopically organized, and neurons are direction tuned, whereas in albino mice, neuronal tuning is severely impaired. Neurons in the NOT of albino mice do not have a preference for ipsiversive movement. In contrast, neuronal tuning in visual cortex was preserved in albino mice and did not differ significantly from the tuning in pigmented mice. We propose that excessive interhemispheric crossing of retinal projections in albinos may cause the disrupted left/right direction encoding we found in NOT. This, in turn, impairs the normal horizontal optokinetic reflex and leads to pendular albino nystagmus.

From the eye to the wing: neural circuits for transforming optic flow into motor output in avian flight.

Avian flight is guided by optic flow-the movement across the retina of images of surfaces and edges in the environment due to self-motion. In all vertebrates, there is a short pathway for optic flow information to reach pre-motor areas: retinal-recipient regions in the midbrain encode optic flow, which is then sent to the cerebellum. One well-known role for optic flow pathways to the cerebellum is the control of stabilizing eye movements (the optokinetic response). However, the role of this pathway in controlling locomotion is less well understood. Electrophysiological and tract tracing studies are revealing the functional connectivity of a more elaborate circuit through the avian cerebellum, which integrates optic flow with other sensory signals. Here we review the research supporting this framework and identify the cerebellar output centres, the lateral (CbL) and medial (CbM) cerebellar nuclei, as two key nodes with potentially distinct roles in flight control. The CbM receives bilateral optic flow information and projects to sites in the brainstem that suggest a primary role for flight control over time, such as during forward flight. The CbL receives monocular optic flow and other types of visual information. This site provides feedback to sensory areas throughout the brain and has a strong projection the nucleus ruber, which is known to have a dominant role in forelimb muscle control. This arrangement suggests primary roles for the CbL in the control of wing morphing and for rapid maneuvers.

OKN-Fast: Objective visual acuity threshold measurement using the optokinetic response.

Visual acuity (VA) is the gold-standard measure for the assessment of visual function, but it is challenging to obtain in non-verbal adults and young children. We present OKN-Fast, an objective, automated method for estimation of VA using a reflexive eye movement called optokinetic nystagmus (OKN) that does not require a verbal response from the patient (VA-OKN). We tested the method in a cohort of healthy adults (n=12) with good vision, who were also blurred using a lens. On average OKN-Fast reduced the number of trials needed to determine threshold by half, as compared to a gold standard trial-by-trial assessment. The VAs determined by OKN and ETDRS were similar when blurred (no statistically significant difference). However, a significant bias of logMAR 0.2 was observed for the good vision condition. VA-OKN was highly repeatable with limits of agreement (LOA) similar to those found for ETDRS charts when blurred. However, this VA-OKN was only moderately correlated with VA measured using a ETDRS chart (r2 = 0.55). These results suggest that further optimization is warranted.Clinical Relevance- This work provides an automated approach for the estimation of visual acuity in non-verbal populations such as young children or non-verbal adults.

Glial modulation of the parallel memory formation.

Actions from glial cells could affect the readiness and efficacy of learning and memory. Using a mouse cerebellar-dependent horizontal optokinetic response motor learning paradigm, short-term memory (STM) formation during the online training period and long-term memory (LTM) formation during the offline rest period were studied. A large variability of online and offline learning efficacies was found. The early bloomers with booming STM often had a suppressed LTM formation and late bloomers with no apparent acute training effect often exhibited boosted offline learning performance. Anion channels containing LRRC8A are known to release glutamate. Conditional knockout of LRRC8A specifically in astrocytes including cerebellar Bergmann glia resulted in a complete loss of STM formation while the LTM formation during the rest period remained. Optogenetic manipulation of glial activity by channelrhodopsin-2 or archaerhodopsin-T (ArchT) during the online training resulted in enhancement or suppression of STM formation, respectively. STM and LTM are likely to be triggered simultaneously during online training, but LTM is expressed later during the offline period. STM appears to be volatile and the achievement during the online training is not handed over to LTM. In addition, we found that glial ArchT photoactivation during the rest period resulted in the augmentation of LTM formation. These data suggest that STM formation and LTM formation are parallel separate processes. Strategies to weigh more on the STM or the LTM could depend on the actions of the glial cells.

Quantification of Visual Feature Selectivity of the Optokinetic Reflex in Mice

The optokinetic reflex (OKR) is an essential innate eye movement that is triggered by the global motion of the visual environment and serves to stabilize retinal images. Due to its importance and robustness, the OKR has been used to study visual-motor learning and to evaluate the visual functions of mice with different genetic backgrounds, ages, and drug treatments. Here, we introduce a procedure for evaluating OKR responses of head-fixed mice with high accuracy. Head fixation can rule out the contribution of vestibular stimulation on eye movements, making it possible to measure eye movements triggered only by visual motion. The OKR is elicited by a virtual drum system, in which a vertical grating presented on three computer monitors drifts horizontally in an oscillatory manner or unidirectionally at a constant velocity. With this virtual reality system, we can systematically change visual parameters like spatial frequency, temporal/oscillation frequency, contrast, luminance, and the direction of gratings, and quantify tuning curves of visual feature selectivity. High-speed infrared video-oculography ensures accurate measurement of the trajectory of eye movements. The eyes of individual mice are calibrated to provide opportunities to compare the OKRs between animals of different ages, genders, and genetic backgrounds. The quantitative power of this technique allows it to detect changes in the OKR when this behavior plastically adapts due to aging, sensory experience, or motor learning; thus, it makes this technique a valuable addition to the repertoire of tools used to investigate the plasticity of ocular behaviors.

A quantitative approach to study the adaptation of rhythmic eye movements and the resulting tonic eye deviation in larval zebrafish.

To optimize performance during vital tasks, animals are capable of tuning rhythmic neural signals that drive repetitive behaviors, such as motor reflexes under constant sensory stimuli. In the oculomotor system, animals track the moving image during slow phases while repetitively resetting the eye position from the eccentricity during quick phases. During optokinetic response (OKR), larval zebrafish occasionally show a delayed quick phase; thus, the eyes remain tonically deviated from the center. In this study, we scrutinized OKR in larval zebrafish under a broad range of stimulus velocities to determine the parametric property of the quick-phase delay. A prolonged stimulation revealed that the slow-phase (SP) duration-the interval between two quick phases-was tuned increasingly over time toward a homeostatic range, regardless of stimulus velocity. Attributed to this rhythm control, larval zebrafish exhibited a tonic eye deviation following slow phases, which was especially pronounced when tracking a fast stimulus over an extended time period. In addition to the SP duration, the fixation duration between spontaneous saccades in darkness also revealed a similar adaptive property after the prolonged optokinetic stimulation. Our results provide a quantitative description of the adaptation of rhythmic eye movements in developing animals and pave the way for potential animal models for eye movement disorders.

Brief Oxygen Exposure after Traumatic Brain Injury Hastens Recovery and Promotes Adaptive Chronic Endoplasmic Reticulum Stress Responses.

Traumatic brain injury (TBI) is a major public health concern, particularly in adolescents who have a higher mortality and incidence of visual pathway injury compared to adult patients. Likewise, we have found disparities between adult and adolescent TBI outcomes in rodents. Most interestingly, adolescents suffer a prolonged apneic period immediately post-injury, leading to higher mortality; therefore, we implemented a brief oxygen exposure paradigm to circumvent this increased mortality. Adolescent male mice experienced a closed-head weight-drop TBI and were then exposed to 100% O2 until normal breathing returned or recovered in room air. We followed mice for 7 and 30 days and assessed their optokinetic response; retinal ganglion cell loss; axonal degeneration; glial reactivity; and retinal ER stress protein levels. O2 reduced adolescent mortality by 40%, improved post-injury visual acuity, and reduced axonal degeneration and gliosis in optical projection regions. ER stress protein expression was altered in injured mice, and mice given O2 utilized different ER stress pathways in a time-dependent manner. Finally, O2 exposure may be mediating these ER stress responses through regulation of the redox-sensitive ER folding protein ERO1α, which has been linked to a reduction in the toxic effects of free radicals in other animal models of ER stress.

Sex-related differences in retinal function in Wistar rats: implications for toxicity and safety studies.

Introduction: Wistar Han rats are a preferred strain of rodents for general toxicology and safety pharmacology studies in drug development. In some of these studies, visual functional tests that assess for retinal toxicity are included as an additional endpoint. Although the influence of gender on human retinal function has been documented for more than 6decades, preclinically it is still uncertain if there are differences in retinal function between naïve male and female Wistar Han rats. Methods: In this study, sex-related differences in the retinal function were quantified by analyzing electroretinography (ERG) in 7-9-week-old (n = 52 males and 51 females) and 21-23-week-old Wistar Han rats (n = 48 males and 51 females). Optokinetic tracking response, brainstem auditory evoked potential, ultrasonic vocalization and histology were tested and evaluated in a subset of animals to investigate the potential compensation mechanisms of spontaneous blindness. Results/Discussion: Absence of scotopic and photopic ERG responses was found in 13% of 7-9-week-old (7/52) and 19% of 21-23-week-old males (9/48), but none of female rats (0/51). The averaged amplitudes of rod- and cone-mediated ERG b-wave responses obtained from males were significantly smaller than the amplitudes of the same responses from age-matched females (-43% and -26%, respectively) at 7-9weeks of age. There was no difference in the retinal and brain morphology, brainstem auditory responses, or ultrasonic vocalizations between the animals with normal and abnormal ERGs at 21-23weeks of age. In summary, male Wistar Han rats had altered retinal responses, including a complete lack of responses to test flash stimuli (i.e., blindness), when compared with female rats at 7-9 and 21-23weeks of age. Therefore, sex differences should be considered when using Wistar Han rats in toxicity and safety pharmacology studies with regards to data interpretation of retinal functional assessments.

A circuit suppressing retinal drive to the optokinetic system during fast image motion

A circuit suppressing retinal drive to the optokinetic system during fast image motion

Nanoparticles Enhance Solubility and Neuroprotective Effects of Resveratrol in Demyelinating Disease.

Resveratrol is a natural polyphenol which may be useful for treating neurodegenerative diseases such as multiple sclerosis (MS). To date, current immunomodulatory treatments for MS aim to reduce inflammation with limited effects on the neurodegenerative component of this disease. The purpose of the current study is to develop a novel nanoparticle formulation of resveratrol to increase its solubility, and to assess its ability to prevent optic nerve and spinal cord degeneration in an experimental autoimmune encephalomyelitis (EAE) mouse model of MS. Resveratrol nanoparticles (RNs) were made using a thin rehydration technique. EAE mice received a daily oral administration of vehicle, RNs or unconjugated resveratrol for one month. They were assessed daily for clinical signs of paralysis and weekly for their visual acuity with optokinetic responses (OKR). After one month, their spinal cords and optic nerves were stained for inflammation and demyelination and retinal ganglion cells immunostained for Brn3a. RNs were stable for three months. The administration of RNs did not have any effect on clinical manifestation of EAE and did not preserve OKR scores but reduced the intensity of the disease. It did not reduce inflammation and demyelination in the spinal cord and the optic nerve. However, RNs were able to decrease RGC loss compared to the vehicle. Results demonstrate that resveratrol is neuroprotective by reducing RGC loss. Interestingly, neuroprotective effects and decreased disease severity occurred without reduction of inflammation or demyelination, suggesting this therapy may fill an unmet need to limit the neurodegenerative component of MS.

Longitudinal Outcomes of Cumulative Impact Exposure on Oculomotor Functioning in Professional Motorsport Drivers

Professional motorsport drivers are regularly exposed to biomechanical forces comparable with those experienced by contact and collision sport athletes, and little is known about the potential short-term and long-term neurologic sequelae. To determine whether cumulative impact exposure is associated with oculomotor functioning in motorsport drivers from the INDYCAR professional open-wheel automobile racing series. This is a longitudinal retrospective cohort study conducted across 3 racing seasons (2017-2019). Statistical analyses were conducted in November 2021. Data were retrieved from a secondary care setting associated with the INDYCAR series. INDYCAR series drivers who participated in 3 professional level racing seasons and were involved in at least 1 contact incident (ie, crash) in 2 of the 3 seasons were included in the study. Cumulative acceleration and deceleration forces and total contact incidents (ie, crashes) measured via accident data recorder third generation chassis and ear accelerometers. Postseries oculomotor performance, including predictive saccades, vergence smooth pursuit, and optokinetic nystagmus, was measured annually with a head-mounted, clinical eye tracking system (Neurolign Dx 100). Thirteen drivers (mean [SD] age, 29.36 [7.82] years; all men) sustained median resultant acceleration forces of 38.15 g (observed range, 12.01-93.05 g; 95% CI, 30.62-65.81 g) across 81 crashes. A 2-way multivariate analysis of variance did not reveal a statistically significant association between ear and chassis average resultant g forces, total number of contact incidents, and racing season assessed (F9,12 = 0.955; P = .54; Wilks Λ = 0.44). In this cohort study of professional drivers from the INDYCAR series, there were no statistically significant associations among cumulative impact exposure, racing season assessed, and oculomotor performance. Longitudinal studies across racing seasons using multidimensional examination modalities (eg, neurocognitive testing, advanced imaging, biomarkers, and physical examination) are critical to understand potential neurological and neurobehavioral sequelae and long-term consequences of cumulative impact exposure.

Progressive Supranuclear Palsy

Progressive supranuclear palsy (PSP) has been reported as a disorder mainly characterized by a tendency to fall, vertical supranuclear gaze palsy, and constriction of the body axis, akinesia, and cognitive impairment. Patients presenting with these typical clinical features are diagnosed as having the PSP-Richardson syndrome (PSP-RS). Electronystagmography (ENG) is useful for the detection of ocular motility disorder, which is the main feature of PSP. In cases of PSP, ocular motility disorder in the vertical direction occurs from the initial stage of the disease, and is characterized by prolonged latency and reduced velocity of the saccadic eye movement in the vertical direction. Horizontal saccadic eye movement disorder also occurs after the intermediate stage. Square wave jerks (SWJ) are often recognized from the initial stage of the disease. In terms of nystagmus, the quick phase is impaired due to impaired saccadic eye movements, and impairment of optokinetic nystagmus also starts from the quick phase movements. Pursuit (smooth) eye movement may also be impaired as the disease progresses. On the other hand, the vestibulo-ocular reflex is maintained even after disease progression to a late stage.

Optokinetic Nystagmus: Five Reasons Why Every Neurologist Should Evaluate It (P3-9.006)

<h3>Objective:</h3> To highlight the clinical utility of optokinetic nystagmus (OKN) through five illustrative video cases. <h3>Background:</h3> Bedside evaluation of OKN allows for rapid assessment of smooth pursuit (slow phase) and saccades (fast phase). Specific abnormalities of OKN have localizing value and may also suggest specific neurologic disorders. <h3>Design/Methods:</h3> We provide five video cases where OKN was helpful in localization and/or diagnosis. Video cases are provided from https://novel.utah.edu/Gold/. <h3>Results:</h3> (1) OKN can be used to make an early diagnosis of progressive supranuclear palsy before there is ophthalmoparesis. Vertical OKN can demonstrate absent or attenuated saccades, particularly when compared to a normal response to horizontal OKN. (2) A subtle sign of internuclear opthalmoparesis, when there is no obvious limitation of adduction, can be demonstrated with horizontal OKN by noting a slow (lagging) adducting saccade. (3) In patients with dorsal midbrain (Parinaud) syndrome, upgaze is often limited or absent, and the characteristic finding of convergence-retraction nystagmus (CRN) can be easily appreciated when an optokinetic stimulus is moved downward (e.g., downward slow phase followed by CRN instead of an upward fast phase). (4) Patients with a homonymous hemianopsia due to an occipital lesion will have normal OKN; whereas, patients with a homonymous hemianopsia due to a parietal lesion will have absent OKN when the stimulus is directed toward the side of the lesion. (5) In patients who claim to have binocular or monocular blindness, the presence of OKN (when monocular, with the good eye covered) is highly suggestive of functional vision loss. Observing OKN does not prove that the patient’s visual function is normal, but does rule out blindness. <h3>Conclusions:</h3> Assessing optokinetic nystagmus with a flag, tape, drum, or the examiner’s fingertips is a portable, inexpensive, and rapid bedside examination to localize and diagnose a variety of neurologic and neuro-ophthalmic disorders. <b>Disclosure:</b> Dr. Hale has nothing to disclose. Dr. Reich has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Best Doctors. Dr. Reich has received personal compensation in the range of $500-$4,999 for serving as a Consultant for UpToDate. Dr. Reich has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Enterin. Dr. Reich has received personal compensation in the range of $0-$499 for serving on a Scientific Advisory or Data Safety Monitoring board for NIH. Dr. Reich has received personal compensation in the range of $10,000-$49,999 for serving as an Expert Witness for Various law firms. The institution of Dr. Reich has received research support from ninds. Dr. Reich has received publishing royalties from a publication relating to health care. Dr. Reich has received publishing royalties from a publication relating to health care. Dr. Gold has received personal compensation in the range of $500-$4,999 for serving as an Editor, Associate Editor, or Editorial Advisory Board Member for Springer .