Infrared Eye Tracker Research Articles

Oscillatory alpha-band suppression mechanisms during the rapid attentional shifts required to perform an anti-saccade task.

Neuroimaging has demonstrated anatomical overlap between covert and overt attention systems, although behavioral and electrophysiological studies have suggested that the two systems do not rely on entirely identical circuits or mechanisms. In a parallel line of research, topographically-specific modulations of alpha-band power (~8-14 Hz) have been consistently correlated with anticipatory states during tasks requiring covert attention shifts. These tasks, however, typically employ cue-target-interval paradigms where attentional processes are examined across relatively protracted periods of time and not at the rapid timescales implicated during overt attention tasks. The anti-saccade task, where one must first covertly attend for a peripheral target, before executing a rapid overt attention shift (i.e. a saccade) to the opposite side of space, is particularly well-suited for examining the rapid dynamics of overt attentional deployments. Here, we asked whether alpha-band oscillatory mechanisms would also be associated with these very rapid overt shifts, potentially representing a common neural mechanism across overt and covert attention systems. High-density electroencephalography in conjunction with infra-red eye-tracking was recorded while participants engaged in both pro- and anti-saccade task blocks. Alpha power, time-locked to saccade onset, showed three distinct phases of significantly lateralized topographic shifts, all occurring within a period of less than 1s, closely reflecting the temporal dynamics of anti-saccade performance. Only two such phases were observed during the pro-saccade task. These data point to substantially more rapid temporal dynamics of alpha-band suppressive mechanisms than previously established, and implicate oscillatory alpha-band activity as a common mechanism across both overt and covert attentional deployments.

An objective and automated method for assessing surgical skill in endoscopic sinus surgery using eye‐tracking and tool‐motion data

Assessment of surgical skill plays a crucial role in determining competency, monitoring educational programs, and providing trainee feedback. With the changing health care environment, it will likely play an important role in credentialing and maintenance of certification. The ideal skill assessment tool should be unbiased, objective, and accurate. We hypothesize that tool-motion data-how a surgeon moves his/her instruments-and eye-gaze data-what a surgeon looks at when he/she operates-contain sufficient information to quantitatively and objectively evaluate surgical skill. We investigate this hypothesis by developing a statistical model of surgery and testing the model experimentally in the context of endoscopic sinus surgery (ESS). A total of 378 trials were recorded from 7 expert and 13 novice surgeons while they were performing a series of 9 different ESS tasks. Data was collected using an electromagnetic tracker to record the surgeon's tool and endoscope motions. In addition, the location of surgeon's eye gaze was recorded using an infrared eye tracker camera. This data was fit to the statistical model and used to test the accuracy of skill assessment. The skill of expert surgeons was identified correctly for 94.6% of tasks. For surgeries performed by novice surgeons the proposed model properly recognizes the skill level with 88.6% accuracy. We present an objective and unbiased method for assessing the skill of endoscopic sinus surgeons. Experimental results show that the proposed method successfully identifies the skill levels of both expert and novice surgeons.

Differential representation of auditory categories between cell classes in primate auditory cortex

A comprehensive understanding of the neural mechanisms of cognitive function requires an understanding of how neural representations are transformed across different scales of neural organization: from within local microcircuits to across different brain areas. However, the neural transformations within the local microcircuits are poorly understood. Particularly, the role that two main cell classes of neurons in cortical microcircuits (i.e. pyramidal neurons and interneurons) have in auditory behaviour and cognition remains unknown. In this study, we tested the hypothesis that pyramidal cells and interneurons in the auditory cortex play a differential role in auditory categorization. To test this hypothesis, we recorded single-unit activity from the auditory cortex of rhesus monkeys while they categorized speech sounds. Based on the spike-waveform shape, a neuron was classified as either a narrow-spiking putative interneuron or a broad-spiking putative pyramidal neuron. We found that putative interneurons and pyramidal neurons in the auditory cortex differentially coded category information: interneurons were more selective for auditory categories than pyramidal neurons. These differences between cell classes may be an essential property of the neural computations underlying auditory categorization within the microcircuitry of the auditory cortex.

Multicenter validation of a bedside antisaccade task as a measure of executive function

To create and validate a simple, standardized version of the antisaccade (AS) task that requires no specialized equipment for use as a measure of executive function in multicenter clinical studies. The bedside AS (BAS) task consisted of 40 pseudorandomized AS trials presented on a laptop computer. BAS performance was compared with AS performance measured using an infrared eye tracker in normal elders (NE) and individuals with mild cognitive impairment (MCI) or dementia (n = 33). The neuropsychological domain specificity of the BAS was then determined in a cohort of NE, MCI, and dementia (n = 103) at UCSF, and the BAS was validated as a measure of executive function in a 6-center cohort (n = 397) of normal adults and patients with a variety of brain diseases. Performance on the BAS and laboratory AS task was strongly correlated and BAS performance was most strongly associated with neuropsychological measures of executive function. Even after controlling for disease severity and processing speed, BAS performance was associated with multiple assessments of executive function, most strongly the informant-based Frontal Systems Behavior Scale. The BAS is a simple, valid measure of executive function in aging and neurologic disease.

Effect of subthalamic deep brain stimulation on turning kinematics and related saccadic eye movements in Parkinson disease

BackgroundPersons with Parkinson disease (PD) experience turning difficulty, often leading to freezing of gait and falls. Visual information plays a significant role in locomotion and turning, and while the effects of deep brain stimulation (DBS) on oculomotor function have been well documented, the effects of DBS on oculomotor function during turning and on turning itself have yet to be fully elucidated. ObjectiveTo determine the effects of STN DBS on turning performance and related oculomotor performance in PD. MethodsEleven subjects with PD and DBS of the subthalamic nucleus performed a seated voluntary saccade task and standing 180° turns in DBS OFF and DBS ON conditions. Oculomotor data were captured using an infrared eye tracking system while segment rotations were measured using 3-D motion capture. ResultsDuring the seated saccade task, DBS did not improve saccade amplitude or latency. DBS also did not improve gait velocity and stride length during forward walking. During turning, DBS improved turn performance (turn duration), reduced the number of saccades performed during the turns, and increased the amplitude and velocity of the saccade initiating the turn. DBS decreased the intersegmental latencies (eye–head, eye–foot, and head–trunk) but this effect was lost for eye–head and eye–foot after controlling for the duration of the first gait cycle. ConclusionsDBS significantly improves turn performance and related oculomotor performance. These findings add to the growing list of therapeutic benefits offered by DBS.

Saccade Abnormalities in Autopsy-Confirmed Frontotemporal Lobar Degeneration and Alzheimer Disease

Deficits in the generation and control of saccades have been described in clinically defined frontotemporal dementia (FTD) and Alzheimer disease (AD). To determine the saccade abnormalities associated with autopsy-defined cases of frontotemporal lobar degeneration (FTLD) and of AD, because clinical FTD syndromes can correspond to a number of different underlying neuropathologic FTD and non-FTD diagnoses. An infrared eye tracker was used to record visually guided saccades to 10° targets and antisaccades in subjects with autopsy-confirmed FTD and subjects with autopsy-confirmed AD, a mean (SE) of 35.6 (10.0) months prior to death, and age-matched normal controls. Twelve subjects with FTD had an FTLD-TAR DNA-binding protein 43 pathology, 15 had an FTLD-tau pathology, and 1 subject showed an FTLD-fused in sarcoma protein pathology. Receiver operating curve statistics were used to determine the diagnostic value of the oculomotor variables. Neuroanatomical correlates of oculomotor abnormalities were investigated using voxel-based morphometry. Memory and Aging Center, Department of Neurology, University of California, San Francisco. A total of 28 subjects with autopsy-confirmed FTD, 10 subjects with autopsy-confirmed AD, and 27 age-matched normal controls. All subjects with FTD or AD were impaired relative to normal controls on the antisaccade task. However, only FTLD-tau and AD cases displayed reflexive visually guided saccade abnormalities. The AD cases displayed prominent increases in horizontal saccade latency that differentiated them from the FTD cases. Impairments in velocity and gain were most severe in individuals with progressive supranuclear palsy but were also present in other tauopathies. By using vertical and horizontal saccade velocity and gain as our measures, we were able to differentiate patients with progressive supranuclear palsy from other patients. Vertical saccade velocity was strongly correlated with dorsal midbrain volume. Decreased visually guided saccade velocity and gain are suggestive of underlying tau pathology in FTD, with vertical saccade abnormalities most diagnostic of progressive supranuclear palsy.

LIE Detection by Inducing Cognitive Load

Research on the accuracy of eyewitness testimony has expanded dramatically in recent years. Most of it concerns the issue of mistaken identification, not the problem of uncovering deceptive accounts of witnesses, which is the focus of this research. In the literature, a technique for lie detection has been proposed that induces cognitive load on liars by averting their rehearsal of deception: Time Restricted Integrity-Confirmation. The current authors tested it by instructing “witnesses” of actual crime videos to lie or tell the truth to related questions. Each of 145 adults was randomly assigned to a truth telling, an unrehearsed lying, or a rehearsed lying condition. The cognitive cues were response time, answer consistency, eye movements, and pupil dilation. Eye data were gathered with an infrared eye tracker. Truth tellers had the quickest response times and the fewest inconsistencies. Moreover, they generally had more eye movements, suggesting low cognitive loads. Discriminant analyses classified rehearsed liars, unrehearsed liars, and truth tellers up to 69% accurately, with few false positives. Further refinement is warranted.

Social and Nonsocial Content Differentially Modulates Visual Attention and Autonomic Arousal in Rhesus Macaques

The sophisticated analysis of gestures and vocalizations, including assessment of their emotional valence, helps group-living primates efficiently navigate their social environment. Deficits in social information processing and emotion regulation are important components of many human psychiatric illnesses, such as autism, schizophrenia and social anxiety disorder. Analyzing the neurobiology of social information processing and emotion regulation requires a multidisciplinary approach that benefits from comparative studies of humans and animal models. However, many questions remain regarding the relationship between visual attention and arousal while processing social stimuli. Using noninvasive infrared eye-tracking methods, we measured the visual social attention and physiological arousal (pupil diameter) of adult male rhesus monkeys (Macaca mulatta) as they watched social and nonsocial videos. We found that social videos, as compared to nonsocial videos, captured more visual attention, especially if the social signals depicted in the videos were directed towards the subject. Subject-directed social cues and nonsocial nature documentary footage, compared to videos showing conspecifics engaging in naturalistic social interactions, generated larger pupil diameters (indicating heightened sympathetic arousal). These findings indicate that rhesus monkeys will actively engage in watching videos of various kinds. Moreover, infrared eye tracking technology provides a mechanism for sensitively gauging the social interest of presented stimuli. Adult male rhesus monkeys' visual attention and physiological arousal do not always trend in the same direction, and are likely influenced by the content and novelty of a particular visual stimulus. This experiment creates a strong foundation for future experiments that will examine the neural network responsible for social information processing in nonhuman primates. Such studies may provide valuable information relevant to interpreting the neural deficits underlying human psychiatric illnesses such as autism, schizophrenia and social anxiety disorder.

Reflexive and volitional saccades: Biomarkers of Huntington disease severity and progression

Background Huntington disease (HD) is a genetic, neurodegenerative disorder characterized by chorea, behavioral co-morbidities, cognitive deficits, and eye movement abnormalities. We sought to evaluate whether reflexive and voluntary orienting prove useful as biomarkers of disease severity in HD. Methods Eleven HD subjects were evaluated with the motor subscale of the Unified Huntington Disease Rating Scale (UHDRS) and the Montreal Cognitive Assessment. Using an infrared eye tracker, we also measured latency and error rates of horizontal and vertical saccades using prosaccade and antisaccade eye movement tasks. We calculated simple and age-controlled correlations between eye movement and clinical parameters. Results Prosaccade latency correlated with total chorea score. HD patients with greater clinical severity were significantly slower in the prosaccade task. Antisaccade error rate also correlated with UHDRS motor score and total chorea score. HD patients with greater clinical severity as measured by either measure made significantly more errors in the antisaccade task. All these correlations remained significant even when age was taken into account. Conclusions The results of the present age-controlled study show for the first time that both reflexive and voluntary eye motor control in HD patients decrease with increase in disease severity suggesting declines in both motor and cognitive function. Thus, relatively simple eye movement parameters (latency and error rate) obtained from simple tasks (prosaccade and antisaccade) may serve as quantitative biomarkers of sub-cortical and cortical disease severity in HD and could aid in predicting onset, distinguishing subtypes, or evaluating disease progression and novel therapies.

Assessment of Reading Behavior with an Infrared Eye Tracker after 360° Macular Translocation for Age-Related Macular Degeneration

PURPOSE. Macular translocation (MT360) is complex surgery used to restore reading in exudative age-related macular degeneration (AMD). MT360 involves retinal rotation and subsequent oculomotor globe counterrotation and is not without significant surgical risk. This study attempts to gauge the optimal potential of MT360 in restoring reading ability and describe the quality and extent of recovery. METHODS. The six best outcomes were examined from a consecutive series of 23 MT360 cases. Reading behavior and fixation characteristics were examined with an infrared eye tracker. Results were compared to age-matched normal subjects and patients with untreated exudative and nonexudative AMD. Retinal sensitivity was examined with microperimetry to establish threshold visual function. RESULTS. MT360 produced significant improvements in visual function over untreated disease and approximated normal function for reading speed and fixation quality. Relative to the comparative groups, eye tracking revealed the MT360 cohort generated a greater number of horizontal and vertical saccades, of longer latency and reduced velocity. In contrast, saccadic behavior when reading (forward and regressive saccades) closely matched normal function. Microperimetry revealed a reduction in the central scotoma with three patients recovering normal foveal sensitivity. CONCLUSIONS. Near normal reading function is recovered despite profound surgical disruption to the anatomy (retinal/oculomotor). MT360 restores foveal function sufficient to produce a single stable locus of fixation, with marked reduction of the central scotoma. Despite the limitations on saccadic function, the quality of reading saccadic behavior is maintained with good reading ability. Oculomotor surgery appears not to limit reading ability, and the results of retinal surgery approximate normal macular function.

Decreased Fragile X Mental Retardation Protein Expression Underlies Amygdala Dysfunction in Carriers of the Fragile X Premutation

The fragile X premutation provides a unique opportunity for the study of genetic and brain mechanisms of behavior and cognition in the context of neurodevelopment and neurodegeneration. Although the neurodegenerative phenotype, fragile X-associated tremor/ataxia syndrome, is well described, evidence of a causal link between the premutation and psychiatric disorder earlier in life, clear delineation of a behavioral/cognitive phenotype, and characterization of the physiological basis of observed symptoms have been elusive. We completed functional magnetic resonance imaging targeting the amygdala with an emotion-matching task and concurrent infrared eye tracking, FMR1 molecular genetic testing, and neuropsychological assessment in 23 men with the premutation (mean age = 32.9 years) and 25 male control subjects (mean age = 30.1 years). Premutation carriers had significantly smaller left and right amygdala volume and reduced right amygdala activation during the task relative to control subjects. Although both elevated FMR1 messenger RNA and reduced fragile X mental retardation protein (FMRP) were associated with the reduced activation, multiple regression analysis suggested that reduced FMRP is the primary factor. Premutation carriers also had higher ratings of autism spectrum symptoms than control subjects, which were associated with the reduced amygdala response. Although prior studies have emphasized a toxic gain-of-function effect of elevated messenger RNA associated with the premutation, the current results point to the role of reduced FMRP in alterations of brain activity and behavior.

Eye tracking performance and the boundaries of the schizophrenia spectrum

In order to investigate the nature of the eye tracking impairment in schizophrenia spectrum we measured pursuit gain with a constant velocity target using a quantitative (RMS error in pursuit gain) and, on an exploratory basis, a qualitative (quality of tracking) measure. We utilized a sample consisting of three clinically characterized groups: patients with schizophrenia (SZ), their first degree non-psychotic relatives, subjects with schizotypal personality disorder (SPD), and healthy volunteers (HV). Thirty three SZ patients, 19 SPD subjects, 66 non-psychotic relatives (all clinically assessed for schizophrenia spectrum psychopathology—DSM-IIIR) and 18 HV were evaluated using an infrared eye tracking system. Targets were constant velocity trapezoids at 5°/s (slow) and 16°/s (fast). The quality of the eye tracking was independently evaluated by at least two raters (ICC: 0.92). The RMS measures at the two velocities (quantitative measure) and the quality of the tracking obtained for each velocity were entered separately into a two factor repeated measures ANOVA, with velocity and diagnosis as the independent measures. For the quantitative ratings (RMS error), a significant effect for velocity was found, with all subjects performing worse at the higher velocity, but there was no significant velocity by diagnosis interaction. In addition, an overall significant effect for diagnosis was found in the four-group ANOVA. In post hoc multiple comparison tests, SZ subjects performed significantly worse from the HV and the relatives. SPD subjects were not different from patients with schizophrenia (or from any group—and their performance was intermediate between the HV and the SZ). Relatives of the patients with schizophrenia were different from SZ subjects, but not different from SPD or HV subjects. Similar results were obtained in the exploratory qualitative ratings. Clinical symptoms did not correlate significantly with quantitative or qualitative performance in any group. We have found that the performance of SPD subjects is intermediate between that of patients with schizophrenia and the healthy volunteers in both qualitative and quantitative (exploratory) measures. Indeed, SPD subjects comprise the only group not statistically different from schizophrenic patients in quantitative or qualitative ratings.

Fixation Stability: A Comparison between the Nidek MP-1 and the Rodenstock Scanning Laser Ophthalmoscope in Persons with and without Diabetic Maculopathy

Impaired fixation stability is associated with reduced reading speed. In previous research, fixation stability has been assessed using an infrared eye tracker or a confocal scanning laser ophthalmoscope. The new MP-1 microperimeter from Nidek Technologies (Padova, Italy) provides another option for the assessment of fixation. Here the authors compare fixation stability values measured using the MP-1 microperimeter and the Rodenstock scanning laser ophthalmoscope (SLO; Rodenstock GmbH, Munich, Germany) in persons with and without diabetic maculopathy. Sixteen normally sighted volunteers and 21 patients with diabetic maculopathy were recruited. Fixation stability was recorded monocularly on the SLO and the MP-1 in counterbalanced order while participants fixated a red 1 degree cross. Fixation data collected from each instrument were used to calculate a bivariate contour ellipse area (BCEA) that encompassed 68% of fixation points. For control subjects, MP-1 BCEA values were larger than SLO by 0.25 log min arc(2), though the difference was small (10%) and of borderline significance (MP-1, 2.51 log min arc(2); SLO, 2.26 log min arc(2); P = 0.06). In patients with diabetic maculopathy there was no significant difference between MP-1 and SLO values (MP-1, 2.94 log min arc(2); SLO, 2.90 log min arc(2); P = 0.88). No significant difference was found in BCEA values from the SLO and MP-1 in control subjects and patients with diabetic maculopathy. The authors suggest that the similarity between BCEA values, together with the consistent and reliable operation of the MP-1, make it a useful and viable alternative to the SLO in the assessment of fixation.

The Cerebellar Dysplasia of Chiari II Malformation as Revealed by Eye Movements

Chiari type II malformation (CII) is a developmental deformity of the hindbrain. We have previously reported that many patients with CII have impaired smooth pursuit, while few make inaccurate saccades or have an abnormal vestibuloocular reflex. In contrast, saccadic adaptation and visual fixation are normal. In this report, we correlate results from several eye movement studies with neuroimaging in CII. We present a model for structural changes within the cerebellum in CII. Saccades, smooth pursuit, the vestibulo-ocular reflex, and visual fixation were recorded in 21 patients with CII, aged 8-19 years and 39 age-matched controls, using an infrared eye tracker. Qualitative and quantitative MRI data were correlated with eye movements in 19 CII patients and 28 controls. Nine patients with CII had abnormal eye movements. Smooth pursuit gain was subnormal in eight, saccadic accuracy abnormal in four, and vestibulo-ocular reflex gain abnormal in three. None had fixation instability. Patients with CII had a significantly smaller cerebellar volume than controls, and those with normal eye motion had an expanded midsagittal vermis compared to controls. However, patients with abnormal eye movements had a smaller (non-expanded) midsagittal vermis area, posterior fossa area and medial cerebellar volumes than CII patients with normal eye movements. The deformity of CII affects the structure and function of the cerebellum selectively and differently in those with abnormal eye movements. We propose that the vermis can expand when compressed within a small posterior fossa in some CII patients, thus sparing its ocular motor functions.

The Effects of Sleep Deprivation on Flight Performance, Instrument Scanning, and Physiological Arousal in Pilots

The effects of 34 hr of continuous wakefulness on flight performance, instrument scanning, subjective fatigue, and EEG activity were measured. Ten fixed-wing military pilots flew a series of 10 simulator profiles, and root mean squared error was calculated for various flight parameters. Ocular scan patterns were obtained by magnetic head tracking and infrared eye tracking. Flying errors peaked after about 24 to 28 hr of continuous wakefulness in line with peaks in subjective fatigue and EEG theta activity, and they were not directly attributable to degradation of instrument scanning, which was very consistent across pilots and largely unaffected by the sleep deprivation.

Bahrain 2009: NIDEK Presentations During the 10th Middle East African Council of Ophthalmology International Congress

Correspondence: Ayman N. Hashem, MD, FRCS, Magrabi Eye & Ear Hospital, PO Box 7344, Jeddah 21462, Saudi Arabia. Tel: 96 2636 5000; E-mail: ayman.nasr@magrabi.com.sa T his year’s supplement to the Journal of Refractive Surgery is an interesting compilation of articles comprised of actively solicited papers from authors worldwide and the 2009 NIDEK Advanced Vision Excimer Laser Platform (NAVEX) Seminar held in conjunction with the 10th Middle East African Council of Ophthalmology (MEACO) International Congress, which was held in Manama, Kingdom of Bahrain. The Kingdom of Bahrain was the fi rst country in the Persian Gulf to have oil wells, which resulted in largely replacing the traditional pearl industry of this country. In keeping with this pioneering spirit, the authors in this issue have addressed a number of topics that signify the process of change over time. For example, the traditional laser centration technique on the line of sight may not be optimal for all patients as presented by Okamoto and colleagues. Another example is the use of the OPDScan II/Station for the evaluation of phakic intraocular lenses (IOLs) rather than traditional aberrometers as presented by Hashem and colleagues and Hamdi. Change also implies adaptability, a hallmark of NIDEK’s philosophy. NIDEK introduced NAVEX and over the past decade has incorporated a number of technologies to keep it a forerunner in the fi eld. Two examples are the incorporation of one of the fi rst active cyclotorsion error compensation modules in an excimer laser and a 1-KHz active eye tracker. With corneal topographic, aspheric, wavefront-guided, and fully prolate ablations, NIDEK remains a leader in the Middle East and worldwide for its diagnostic and therapeutic applications in vision correction. Traditionally, NIDEK has maintained a commitment to a dynamic and comprehensive education for its users by gathering surgeons worldwide to exchange ideas. This year’s meeting was no different, and practice patterns were realized to be similar regardless of region or country. In this issue, outcomes of topography-guided treatments (customized aspheric treatment [CATz]), wavefront-guided treatments (optical path difference customized aspheric treatment [OPDCAT]), and optimized aspheric transition zone treatments (OATz) are presented. Amoozadeh and colleagues report keratocyte density after LASIK and PRK using the Confoscan 3. Waring summarizes the clinical implications of recent technological additions to the CXIII and Quest excimer lasers in the form of increased accuracy of laser spot placement with the new 1-kHz infrared eye tracker, which provides the potential for attaining perfect customized corneal treatment. El Danasoury presents his experience with CATz in retreating highly irregular corneas. I would like to thank Rich Bains, consultant to NIDEK Co Ltd, for his professional contribution and initial edits of the original manuscripts. My sincerest appreciation to Alaa M. El Danasoury, MD, and Hamed M. Anwar, MD, for the spirit of teamwork and the support with this issue. Finally, I would especially like to thank George O. Waring III, MD, Editor-in-Chief, for inviting me to be the guest editor of this supplement. The articles included in this supplement, editorially reviewed by myself and Dr Waring, receive “S” pagination, indicating the commercial sponsorship of the non-peer reviewed suppplement.

One-kilohertz Eye Tracker and Active Intraoperative Torsion Detection in the NIDEK CXIII and Quest Excimer Lasers

To describe recent technological additions to the NIDEK CXIII and Quest excimer lasers. A summary article with data from previous published studies outlining the benefits of newer technology. The addition of a 1-kHz infrared eye tracker decreased the spread of laser spot placement from a mean of 228.79 microm without a tracker to 38.47 microm with the eye tracker. The addition of real-time torsion error correction produced a statistically significantly lower cylinder dispersion, mean manifest refractive cylinder, and error of angle postoperatively in eyes that underwent LASIK. The incorporation of an ultrahigh speed eye tracker and active cyclotorsion correction surpasses the minimal technology criteria required for accurate wavefront-based ablations.

Developmental Eye Movement Test: What is it Really Measuring?

The Developmental Eye Movement (DEM) test is commonly used as a clinical visual-verbal ocular motor assessment tool. However, while the DEM test ratio has been reported to correlate with horizontal saccadic eye movements, there have been no published comparative studies of the DEM test and objective eye movement measures. The aim of this study was to compare DEM test performance with explicit quantification of saccadic eye movements, reading performance, symptomatology and visual processing speed, to assess the validity of the DEM test in clinical practice. One hundred fifty-eight children aged 8 to 11 years completed the DEM test and a battery of eye movement tasks, recorded by a Microguide 1000 infrared eye tracker. All subjects completed a symptomatology survey. Reading performance and visual processing data was collected for 77 and 75 children, respectively. One hundred twenty-nine of the 158 subjects (81.65%) passed the DEM test. There was no significant correlation between any component of DEM test performance and quantitative eye movement parameters (gain, latency, asymptotic peak velocity, and number of corrective saccades) or symptomatology. There were significant correlations between DEM test outcome and reading performance, and with visual processing speed. DEM test performance does not correlate with saccadic eye movement skills or symptomatology. However, it is related to reading performance and visual processing speed. This study suggests that although DEM test times may not correlate directly with eye movement parameters, they do correlate with aspects of reading performance and thus may serve a diagnostic role in clinical practice.

A very inexpensive MRI-compatible method for dichoptic visual stimulation

Here I describe a very simple, very effective, and very inexpensive method of dichoptic stimulus presentation, designed for use in a head-only MRI scanner with a standard back-projection system. The method can also be used outside of the scanner. Images are presented separately and simultaneously to the two eyes, without the use of colored lenses, with no constraints on stimulus properties (other than size: stimuli must be less than half of the width of the viewing screen), no degradation in luminance reaching the eye, and zero crosstalk between the two eyes. Simultaneous infrared eye tracking and/or pupilometry can also be performed. Components include a two-part cardboard divider (one part in the bore of the magnet, and one in the head coil) and prism lenses (readily obtainable from the local eyeglass shop) cut to fit scanner-compatible eyeglass frames. The total cost (in 2007) was approximately US$ 300.

The Vestibulo-ocular Reflex During Active Head Motion in Chiari II Malformation

Chiari type II malformation (CII) is a developmental anomaly of the cerebellum and brainstem, which are important structures for processing the vestibulo-ocular reflex (VOR). We investigated the effects of the deformity of CII on the angular VOR during active head motion. Eye and head movements were recorded using an infrared eye tracker and magnetic head tracker in 20 participants with CII [11 males, age range 8-19 years, mean (SD) 14.4 (3.2) years]. Thirty-eight age-matched healthy children and adolescents (21 males) constituted the control group. Participants were instructed to 'look' in darkness at the position of their thumb, placed 25 cm away, while they made horizontal and vertical sinusoidal head rotations at frequencies of about 0.5 Hz and 2 Hz. Parametric and non-parametric tests were used to compare the two groups. The VOR gains, the ratio of eye to head velocities, were abnormally low in two participants with CII and abnormally high in one participant with CII. The majority of participants with CII had normal VOR performance in this investigation. However, the deformity of CII can impair the active angular VOR in some patients with CII. Low gain is attributed to brainstem damage and high gain to cerebellar dysfunction.