Smooth pursuit eye movements in children

Visuomotor Synchronization: Military Normative Performance

INTRODUCTION

Cognitive processes such as perception and reasoning are preceded and dependent on attention. Because of the close overlap between neural circuits of attention and eye movement, attention may be objectively quantified with recording of eye movements during an attention-dependent task. Our previous work demonstrated that performance scores on a circular visual tracking task that requires dynamic synchronization of the gaze with the target motion can be impacted by concussion, sleep deprivation, and attention deficit/hyperactivity disorder. The current study examined the characteristics of performance on a standardized predictive visual tracking task in a large sample from a U.S. Military population to provide military normative data.

MATERIALS AND METHODS

The sample consisted of 1,594 active duty military service members of either sex aged 18-29 years old who were stationed at Fort Hood Army Base. The protocol was reviewed and approved by the U.S. Army Medical Research and Materiel Command Institutional Review Board. Demographic, medical, and military history data were collected using questionnaires, and performance-based data were collected using a circular visual tracking test and Trail Making Test. Differences in visual tracking performance by demographic characteristics were examined with a multivariate analysis of variance, as well as a Kolmogorov-Smirnov test and a rank-sum test. Associations with other measures were examined with a rank-sum test or Spearman correlations.

RESULTS

Robust sex differences in visual tracking performance were found across the various statistical models, as well as age differences in several isolated comparisons. Accordingly, norms of performance scores, described in terms of percentile standings, were developed adjusting for age and sex. The effects of other measures on visual tracking performance were small or statistically non-significant. An examination of the score distributions of various metrics suggested that strategies preferred by men and women may optimize different aspects of visual tracking performance.

CONCLUSION

This large-scale quantification of attention, using dynamic visuomotor synchronization performance, provides rigorously characterized age- and sex-based military population norms. This study establishes analytics for assessing normal and impaired attention and detecting changes within individuals over time. Practical applications for combat readiness and surveillance of attention impairment from sleep insufficiency, concussion, medication, or attention disorders will be enhanced with portable, easily accessible, fast, and reliable dynamic eye-tracking technologies.

Evaluation of Predictive Motor Control With Two Touchscreen Tablet-Based Tests: Reliability and Validity in School-Aged Children

As predictive motor control is an important index of neuromotor development and maturation, we developed two touchscreen tablet-based tests of this function. Our aim was to investigate the reliability and validity of both a rapid manual interception test and a pursuit tracking test, using a sample of 124 children (62 boys and 62 girls) from two age groups (7-8-year-oldss and 9-10-year-olds). Participants performed both tablet tests with a stylus (sample rate 100 Hz) with both a visible and a temporarily invisible moving target. Confirmatory factor analyses and omega coefficients showed that both tests were univariate methods that provided a reliable assessment of the latent factor related to predictive visuomotor control. As would be expected, compared to younger children, older children performed better on both manual interception and pursuit tracking. The correlations between the latent factors of the two tests at 95% confidence intervals (-.276, -.608) suggested shared variance. Thus, the touchscreen-tablet based tests of rapid manual interception and manual pursuit tracking appear psychometrically suitable for assessing the neuromotor ability of predictive control in 7-10-year-old children.

Immature brain structures were associated with poorer eye movement performance at 8 years of age in preterm born children

AIM

Eye movements have rarely been explored in preterm born children. The aim of this study was to compare horizontal eye movements in children born preterm and full term when they reached 8 years of age.

METHODS

Eye movements were recorded in 24 preterm born children (18 boys) and 26 matched controls (19 boys), recruited by a French hospital, using an eye tracker. This identified different types of visually guided saccades, namely step, gap, overlap and antisaccades and pursuit eye movements. The saccades task measured the latency and the percentage of anticipatory and express saccades and errors. The pursuit task measured the gain and percentage of intrusive saccades.

RESULTS

This study confirmed that children born at 24-28 weeks of gestation demonstrated a global deficit in inhibitory processes compared to children born full term. The saccades were less precise in the preterm group, anticipatory and express saccades were elevated and there was a high occurrence of intrusive saccades during pursuit movements.

CONCLUSION

These findings suggest that preterm born children have immature brain structures, particularly the parietal and frontal cortexes that are responsible for both saccade and pursuit performance. These could have been the cause of the abnormal inhibitory control measured in this study.

Influence of prior and visual information on eye movements in amblyopic children

This study analyzed the characteristics of pursuit and assessed the influence of prior and visual information on eye velocity and saccades in amblyopic and control children, in comparison to adults. Eye movements of 41 children (21 amblyopes and 20 controls) were compared to eye movements of 55 adults (18 amblyopes and 37 controls). Participants were asked to pursue a target moving at a constant velocity. The target was either a 'standard' target, with a uniform color intensity, or a 'noisy' target, with blurry edges, to mimic the blurriness of an amblyopic eye. Analysis of pursuit patterns showed that the onset was delayed, and the gain was decreased in control children with a noisy target in comparison to amblyopic or control children with a standard target. Furthermore, a significant effect of prior and visual information on pursuit velocity and saccades was found across all participants. Moreover, the modulation of the effect of visual information on the pursuit velocity by group, that is amblyopes or controls with a standard target, and controls with a noisy target, was more limited in children. In other words, the effect of visual information was higher in control adults with a standard target compared to control children with the same target. However, in the case of a blurry target, either in control participants with a noisy target or in amblyopic participants with a standard target, the effect of visual information was larger in children.

Quantitative Characterization of Smooth Pursuit Eye Movements in School-Age Children Using a Child-Friendly Setup

PURPOSE

It could be argued that current studies investigating smooth pursuit development in children do not provide an optimal measure of smooth pursuit characteristics, given that a significant number have failed to adjust their setup and procedures to the child population. This study aimed to characterize smooth pursuit in children using child-friendly stimuli and procedures.

METHODS

Eye movements were recorded in 169 children (4-11 years) and 10 adults, while a customized, animated stimulus was presented moving horizontally and vertically at 6°/s and 12°/s. Eye movement recordings from 43 children with delayed reading, two with nystagmus, two with strabismus, and two with unsuccessful calibration were excluded from the analysis. Velocity gain, proportion of smooth pursuit, and the number and amplitude of saccades during smooth pursuit were calculated for the remaining participants. Median and quartiles were calculated for each age group and pursuit condition. ANOVA was used to investigate the effect of age on smooth pursuit parameters.

RESULTS

Differences across ages were found in velocity gain (6°/s P < 0.01; 12°/s P < 0.05), as well as the number (12°/s P < 0.05) and amplitude of saccades (12°/s P < 0.05), for horizontal smooth pursuit. Post hoc tests showed that these parameters were different between children aged 7 or younger and adults. No significant differences were found across ages in any smooth pursuit parameter for the vertical direction (P > 0.05).

CONCLUSIONS

Using child-friendly methods, children over the age of 7 to 8 years demonstrated adultlike smooth pursuit.

TRANSLATIONAL RELEVANCE

Child-friendly procedures are critical for appropriately characterizing smooth pursuit eye movements in children.

Oculomotor Assessment in Children

Oculomotor evaluation as part of videonystagmography is an integral tool in the assessment of vestibular function providing a global assessment of the neurological pathways associated with oculomotor function. The value of an oculomotor evaluation for pediatric evaluation is well established; however, many questions can also arise with the application to the pediatric population. Oculomotor function is age dependent which can have a significant effect on the test results obtain in children. The underlying neural substrates and age effects are discussed across the literature with specific results from recent research using clinical oculomotor equipment and protocols. The evidence suggests there are several key differences in the pediatric population compared with adults. These include longer saccade latencies, reduced smooth pursuit gain, increased optokinetic asymmetry, increased variability in all responses, and increased artifact in saccade and smooth pursuit testing.

Oculomotor and Vestibular Findings in Gaucher Disease Type 3 and Their Correlation with Neurological Findings

Objectives

To evaluate the function of the oculomotor and vestibular systems and to correlate these findings with the clinical status of patients with Gaucher disease type 3 (GD3). The goal of this cross-sectional and longitudinal study was to find oculomotor biomarkers for future clinical trials.

Methods

Twenty-six patients with GD3 were assessed for eligibility and 21 were able to perform at least one task. Horizontal and vertical reflexive saccades, smooth pursuit, gaze-holding, optokinetic nystagmus, and horizontal vestibulo-ocular reflex (VOR) were examined by video-oculography/video-head impulse test and compared concurrently with 33 healthy controls. The Scale for the Assessment and Rating of Ataxia (SARA), the modified Severity Scoring Tool (mSST), and Grooved Pegboard Test (GPT) were administered to assess overall neurological function. Eleven patients were also re-assessed after 1 year.

Results

Nine out of 17 patients exhibited gaze-holding deficits. One patient had upbeat nystagmus. Three patients presented with bilateral abducens palsy in combination with central oculomotor disorders, suggesting a bilateral involvement of the abducens nucleus. Horizontal angular VOR gain was reduced in all patients (0.66 ± 0.37) compared with controls (1.1 ± 0.11, p < 0.001). Most strongly correlated with clinical rating scales were peak velocity of downward saccades (SARA: ρ = −0.752, p < 0.0005; mSST: ρ = −0.611, p = 0.003; GPT: ρ = −0.649, p = 0.005) and duration of vertical saccades (SARA: ρ = 0.806, p < 0.001; mSST: ρ = 0.700, p < 0.0005; GPT: ρ = 0.558, p = 0.02) together with the VOR gain (SARA: ρ = −0.63, p = 0.016; mSST: ρ = −0.725, p = 0.003; GPT: ρ = −0.666, p = 0.004). Vertical smooth pursuit gain decreased significantly at follow-up.

Interpretation

This study shows neuronal degeneration of the brainstem and cerebellum with combined involvement of both supranuclear and nuclear oculomotor structures and the vestibular system in GD3. We also identified oculomotor parameters that correlate with the neurological status and can be used as biomarkers in future clinical trials.

Visual Tracking in Development and Aging

A moving target is visually tracked with a combination of smooth pursuit and saccades. Human visual tracking eye movement develops through early childhood and adolescence, and declines in senescence. However, the knowledge regarding performance changes over the life course is based on data from distinct age groups in isolation using different procedures, and thus is fragmented. We sought to describe the age-dependence of visual tracking performance across a wide age range and compare it to that of simple visuo-manual reaction time. We studied a cross-sectional sample of 143 subjects aged 7-82 years old (37% male). Eye movements were recorded using video-oculography, while subjects viewed a computer screen and tracked a small target moving along a circular trajectory at a constant speed. For simple reaction time (SRT) measures, series of key presses that subjects made in reaction to cue presentation on a computer monitor were recorded using a standard software. The positional precision and smooth pursuit velocity gain of visual tracking followed a U-shaped trend over age, with best performances achieved between the ages of 20 and 50 years old. A U-shaped trend was also found for mean reaction time in agreement with the existing literature. Inter-individual variability was evident at any age in both visual tracking and reaction time metrics. Despite the similarity in the overall developmental and aging trend, correlations were not found between visual tracking and reaction time performances after subtracting the effects of age. Furthermore, while a statistically significant difference between the sexes was found for mean SRT in the sample, a similar difference was not found for any of the visual tracking metrics. Therefore, the cognitive constructs and their neural substrates supporting visual tracking and reaction time performances appear largely independent. In summary, age is an important covariate for visual tracking performance, especially for a pediatric population. Since visual tracking performance metrics may provide signatures of abnormal neurological or cognitive states independent of reaction time-based metrics, further understanding of age-dependent variations in normal visual tracking behavior is necessary.

Effect of Stimulus Type and Motion on Smooth Pursuit in Adults and Children

PURPOSE

This study presents a two-degree customized animated stimulus developed to evaluate smooth pursuit in children and investigates the effect of its predetermined characteristics (stimulus type and size) in an adult population. Then, the animated stimulus is used to evaluate the impact of different pursuit motion paradigms in children.

METHODS

To study the effect of animating a stimulus, eye movement recordings were obtained from 20 young adults while the customized animated stimulus and a standard dot stimulus were presented moving horizontally at a constant velocity. To study the effect of using a larger stimulus size, eye movement recordings were obtained from 10 young adults while presenting a standard dot stimulus of different size (1° and 2°) moving horizontally at a constant velocity. Finally, eye movement recordings were obtained from 12 children while the 2° customized animated stimulus was presented after three different smooth pursuit motion paradigms. Performance parameters, including gains and number of saccades, were calculated for each stimulus condition.

RESULTS

The animated stimulus produced in young adults significantly higher velocity gain (mean: 0.93; 95% CI: 0.90-0.96; P = .014), position gain (0.93; 0.85-1; P = .025), proportion of smooth pursuit (0.94; 0.91-0.96, P = .002), and fewer saccades (5.30; 3.64-6.96, P = .008) than a standard dot (velocity gain: 0.87; 0.82-0.92; position gain: 0.82; 0.72-0.92; proportion smooth pursuit: 0.87; 0.83-0.90; number of saccades: 7.75; 5.30-10.46). In contrast, changing the size of a standard dot stimulus from 1° to 2° did not have an effect on smooth pursuit in young adults (P > .05). Finally, smooth pursuit performance did not significantly differ in children for the different motion paradigms when using the animated stimulus (P > .05).

CONCLUSIONS

Attention-grabbing and more dynamic stimuli, such as the developed animated stimulus, might potentially be useful for eye movement research. Finally, with such stimuli, children perform equally well irrespective of the motion paradigm used.

Clinical application of eye movement tasks as an aid to understanding Parkinson's disease pathophysiology

Parkinson's disease (PD) is a progressive neurodegenerative disorder of the basal ganglia. Most PD patients suffer from somatomotor and oculomotor disorders. The oculomotor system facilitates obtaining accurate information from the visual world. If a target moves slowly in the fronto-parallel plane, tracking eye movements occur that consist primarily of smooth-pursuit interspersed with corrective saccades. Efficient smooth-pursuit requires appropriate target selection and predictive compensation for inherent processing delays. Although pursuit impairment, e.g. as latency prolongation or low gain (eye velocity/target velocity), is well known in PD, normal aging alone results in such changes. In this article, we first briefly review some basic features of smooth-pursuit, then review recent results showing the specific nature of impaired pursuit in PD using a cue-dependent memory-based smooth-pursuit task. This task was initially used for monkeys to separate two major components of prediction (image-motion direction memory and movement preparation), and neural correlates were examined in major pursuit pathways. Most PD patients possessed normal cue-information memory but extra-retinal mechanisms for pursuit preparation and execution were dysfunctional. A minority of PD patients had abnormal cue-information memory or difficulty in understanding the task. Some PD patients with normal cue-information memory changed strategy to initiate smooth tracking. Strategy changes were also observed to compensate for impaired pursuit during whole body rotation while the target moved with the head. We discuss PD pathophysiology by comparing eye movement task results with neuropsychological and motor symptom evaluations of individual patients and further with monkey results, and suggest possible neural circuits for these functions/dysfunctions.

Learning the trajectory of a moving visual target and evolution of its tracking in the monkey

An object moving in the visual field triggers a saccade that brings its image onto the fovea. It is followed by a combination of slow eye movements and catch-up saccades that try to keep the target image on the fovea as long as possible. The accuracy of this ability to track the "here-and-now" location of a visual target contrasts with the spatiotemporally distributed nature of its encoding in the brain. We show in six experimentally naive monkeys how this performance is acquired and gradually evolves during successive daily sessions. During the early exposure, the tracking is mostly saltatory, made of relatively large saccades separated by low eye velocity episodes, demonstrating that accurate (here and now) pursuit is not spontaneous and that gaze direction lags behind its location most of the time. Over the sessions, while the pursuit velocity is enhanced, the gaze is more frequently directed toward the current target location as a consequence of a 25% reduction in the number of catch-up saccades and a 37% reduction in size (for the first saccade). This smoothing is observed at several scales: during the course of single trials, across the set of trials within a session, and over successive sessions. We explain the neurophysiological processes responsible for this combined evolution of saccades and pursuit in the absence of stringent training constraints. More generally, our study shows that the oculomotor system can be used to discover the neural mechanisms underlying the ability to synchronize a motor effector with a dynamic external event.

Quantification of visual function assessment using remote eye tracking in children: validity and applicability

PURPOSE

Measurements of visual and oculomotor functions are essential for providing tailored support to visually impaired children. In young or intellectually disabled children these measurements can be difficult or even impossible to perform. Recordings of orienting gaze in response to specific visual information, made with eye tracking, may offer a solution. The aim of this study was to observe and quantify eye tracking (ET)-based gaze responses to provide information about visual and oculomotor functioning, and to compare this information with standard visual function assessments (VFA).

METHODS

One hundred and twenty-six visually impaired children from 1-14 years underwent a VFA. Next they underwent a remote ET test. Four aspects of oculomotor control (nystagmus, fixation, saccades, pursuit) and three visual functions (visual field, contrast, colour) were selected to compare both methods. Performance was assessed (1) during VFA using standard behavioural observation and test scores and (2) after ET by observing and scoring the eye movement recordings. Validity, in terms of agreement between results, was measured by correlation analyses. From the orienting gaze responses, quantitative parameters (gain, fixation duration and directional saccades) were calculated to characterize visual performance.

RESULTS

Good agreement between the two test methods was found for observational assessment of oculomotor control and visual functions (correlations ranging from rs  = 0.39 to rs  = 0.69). The quantitative parameters of visual performance showed distinct results between children with and without specific functional impairments, both in children aged 1-6 and 7-14 years.

CONCLUSION

Eye tracking-based gaze recordings are a promising tool to assess oculomotor and visual performance in a communication-free manner. Calculating quantitative parameters from specific gaze responses could assist in the characterization of functional visual performance in children, independent of age. Gaze responses are a useful addition to standard VFA in clinical practice.

Development of internal models and predictive abilities for visual tracking during childhood

The prediction of the consequences of our own actions through internal models is an essential component of motor control. Previous studies showed improvement of anticipatory behaviors with age for grasping, drawing, and postural control. Since these actions require visual and proprioceptive feedback, these improvements might reflect both the development of internal models and the feedback control. In contrast, visual tracking of a temporarily invisible target gives specific markers of prediction and internal models for eye movements. Therefore, we recorded eye movements in 50 children (aged 5-19 yr) and in 10 adults, who were asked to pursue a visual target that is temporarily blanked. Results show that the youngest children (5-7 yr) have a general oculomotor behavior in this task, qualitatively similar to the one observed in adults. However, the overall performance of older subjects in terms of accuracy at target reappearance and variability in their behavior was much better than the youngest children. This late maturation of predictive mechanisms with age was reflected into the development of the accuracy of the internal models governing the synergy between the saccadic and pursuit systems with age. Altogether, we hypothesize that the maturation of the interaction between smooth pursuit and saccades that relies on internal models of the eye and target displacement is related to the continuous maturation of the cerebellum.

Spontaneous improvement in oculomotor function of children with cerebral palsy

Eye movements are essential to get a clear vision of moving objects. In the present study, we assessed quantitatively the oculomotor deficits of children with cerebral palsy (CP). We recorded eye movements of 51 children with cerebral palsy (aged 5-16 years) with relatively mild motor impairment and compared their performance with age-matched control and premature children. Overall eye movements of children with CP are unexpectedly close to those of controls even though some oculomotor parameters are biased by the side of hemiplegia. Importantly, the difference in performance between children with CP and controls decreases with age, demonstrating that the oculomotor function of children with CP develops as fast as or even faster than controls for some visual tracking parameters. That is, oculomotor function spontaneously improves over the course of childhood. This evolution highlights the ability of lesioned brain of children with CP to compensate for impaired motor function beyond what would be achieved by normal development on its own.

Vertical and horizontal smooth pursuit eye movements in children with developmental coordination disorder

AIM

Our aim was to study horizontal and vertical smooth pursuit eye movements in children with developmental coordination disorder (DCD).

METHOD

Horizontal and vertical smooth pursuit eye movements of 91 children were studied using electro-oculography: 27 children with DCD (23 males, four females), according to the DSM-IV-TR criteria, and 64 comparison children (26 males, 38 females). All children were 7 to 12 years old (mean 9y, SD 1.5y). Among the group of children with DCD, eight had received intervention. Intervention exercised static and dynamic fixation, saccades, visual strategies, visuospatial abilities, and eye-hand coordination. A smooth pursuit gain index was calculated and statistical comparisons were made between the two groups of children.

RESULTS

Horizontal pursuit gain was similar in both populations, but vertical pursuit gain was significantly impaired (p<0.001, after adjusting for age as covariate), i.e. more saccadic in children with DCD (18-99%; n=27, mean 51.6%, median 48.5%, SD 23.2%) than in comparison participants (35-97%; n=63, mean 66.4%, median 65.0%, SD 15.4%). Among the DCD group, the vertical pursuit index was also significantly higher (p=0.009) in the intervention subgroup (29-99%; n=8, mean 69.4%, median 75.5%, SD 28.7%) than in the non-intervention subgroup (18-74%; n=19, mean 44.1%, median 42.5%, SD 15.9%).

INTERPRETATION

These results suggest a delay in the maturation of the pursuit system in children with DCD.

Smooth pursuit eye movements in children with strabismus and in children with vergence deficits

Purpose

The objective of our study was to examine horizontal smooth pursuit performance in strabismic children and in children with vergence deficits, and to compare these data with those recorded in a group of control age-matched children.

Methods

Binocular eye movements were recorded by video-oculography in ten strabismic children (mean age: 9.8±0.8) and seven children with vergence deficits (mean age: 10.8±0.6). Data were compared to that of age-matched control children (mean age: 9.8±0.8 years).

Results

Catch-up saccades amplitude in strabismic children and in children with vergence deficits were significantly higher than in control age-matched children. Moreover, in strabismic children the amplitude of catch-up saccades was significantly higher in rightward than in leftward direction. The number of catch-up saccades was also significantly higher in rightward than in leftward direction. The gain value of pursuits in rightward direction was significantly higher in the right eye than in the left one; for the right eye, the gain value was significantly higher in rightward than in leftward direction. Binocular coordination of pursuit was better in control age-matched children than in children with vergence deficits and than in strabismic children.

Conclusions

Binocular coordination of pursuit is abnormal in children with vergence deficits and worse in strabismic children. Binocular vision plays an important role in improving binocular coordination of pursuit.

Spontaneous blink rates in children during different types of eye movements

INTRODUCTION

The spontaneous blink rate (SBR) is variable in humans. It increases rapidly during childhood before reaching a plateau in adulthood at 10-20 blinks/minute. Our aim was to compare the SBR during different visual tasks in children.

METHODS

Thirty-nine healthy participants (mean age(SD):13.6(3.5)years, M=21), made horizontal and vertical visually-guided saccades, tracked a horizontal and vertical target, performed horizontal and vertical active sinusoidal head rotations in light and darkness while looking straight ahead (VOR task) or fixated straight ahead and in four directions of gaze. The eyes of each participant were videotaped and reviewed twice to determine the SBR. Parametric and non-parametric tests were used to analyze the data.

RESULTS

The median SBR during fixation straight ahead was seven blinks/minute, which was similar to the SBR during horizontal saccades and horizontal smooth pursuit tasks. The median SBR during vertical smooth pursuit and vertical saccades were significantly lower than during fixation (p≤0.042). The median SBR during the VOR task in light and horizontal VOR in darkness were significantly higher than during fixation (p=0.019-0.024).

CONCLUSIONS

The median SBR during visual fixation was lower than that reported previously in 5-14 years-old children during rest or 11-20 years-old subjects during quiet conversation. The median SBR was even lower during vertical smooth pursuit and saccades tasks. This may be due to differences in concentration required for visual fixation in general and vertical visual tasks more specifically. The higher SBR during the VOR may be due to drying of the eyes during head shaking.

The saccadic system does not compensate for the immaturity of the smooth pursuit system during visual tracking in children

Motor skills improve with age from childhood into adulthood, and this improvement is reflected in the performance of smooth pursuit eye movements. In contrast, the saccadic system becomes mature earlier than the smooth pursuit system. Therefore, the present study investigates whether the early mature saccadic system compensates for the lower pursuit performance during childhood. To answer this question, horizontal eye movements were recorded in 58 children (ages 5-16 yr) and 16 adults (ages 23-36 yr) in a task that required the combination of smooth pursuit and saccadic eye movements. Smooth pursuit performance improved with age. However, children had larger average position error during target tracking compared with adults, but they did not execute more saccades to compensate for their low pursuit performance despite the early maturity of their saccadic system. This absence of error correction suggests that children have a lower sensitivity to visual errors compared with adults. This reduced sensitivity might stem from poor internal models and longer processing time in young children.

Smooth pursuit and fixation ability in children with Tourette syndrome

OBJECTIVE

The smooth pursuit eye movements and fixation ability of children aged 8 to 16 years with Tourette syndrome (TS) were examined.

BACKGROUND

Although several studies have examined the saccadic ability of patients with TS, there have been only a few studies examining pursuit ability in TS.

METHOD

Pursuit gain (eye velocity/target velocity) and intrusive saccades during fixation were measured in children with TS-only, TS+attention deficit hyperactivity disorder (ADHD), and TS+ADHD+obsessive compulsive disorder (OCD), and in controls (8 to 16 y). Two pursuit tasks and 1 fixation task were used. In random pursuit 1 (RP1), each step and ramp cycle began from fixation; in random pursuit 2 (RP2), each cycle followed the next. In the fixation task, children were required to maintain fixation on a center dot and ignore distractor stimuli.

RESULTS

All children had significantly higher pursuit gains in RP2 than in RP1 when pursuing a 30 degrees/s moving target. In addition, in RP2, the TS+ADHD+OCD group displayed significantly higher pursuit gains relative to the TS-only, TS+ADHD, and control groups. In the fixation task, the TS+ADHD group exhibited significantly more intrusive saccades than the TS+ADHD+OCD and control groups.

CONCLUSIONS

Our findings support an enhanced oculomotor ability in the TS+ADHD+OCD group and the presence of an online gain control mechanism during ongoing pursuit. These findings are discussed in more detail.

Predictive smooth eye pursuit in a population of young men: I. Effects of age, IQ, oculomotor and cognitive tasks

Smooth eye pursuit is believed to involve the integration of an extraretinal signal formed by an internal representation of the moving target and a retinal signal using the visual feedback to evaluate performance. A variation of the smooth eye pursuit paradigm (in which the moving target is occluded for a short period of time and subjects are asked to continue tracking) designed to isolate the predictive processes that drive the extraretinal signal was performed by 1,187 young men. The latency to the onset of change in pursuit speed, the time of decelerating eye-movement speed and the steady state residual gain were measured for each subject and correlated with measures of other oculomotor (closed-loop smooth eye pursuit, saccade, antisaccade, active fixation) and cognitive tasks (measuring sustained attention and working memory). Deceleration time increased with increasing age, while education, general IQ and cognitive variables had no effect on predictive pursuit performance. Predictive pursuit indices were correlated to those of closed-loop pursuit and antisaccade performance, but these correlations were very weak except for a positive correlation of residual gain to saccade frequency in the fixation task with distracters. This correlation suggested that the maintenance of active fixation is negatively correlated with the ability to maintain predictive pursuit speed. In conclusion, this study presents predictive pursuit performance in a large sample of apparently healthy individuals. Surprisingly, predictive pursuit was weakly if at all related to closed-loop pursuit or other oculomotor and cognitive tasks, supporting the usefulness of this phenotype in the study of frontal lobe integrity in normal and patient populations.

Vertical and horizontal smooth pursuit eye movements in children: a neuro-developmental study

An evaluation of eye movements is very useful in neurological disorders but is complicated by issues such as maturation and lack of normative data in children. In order to address these issues we studied smooth pursuit eye movements of 65 normal children aged 7-11 years old. The gain of horizontal smooth pursuit (HSP) was higher than the gain of the vertical smooth pursuit (SP) and this difference had a statistical tendency to disappear with aging from 7 to 11 years. These data suggest that, in the cerebral regions involved in the control of SP, i.e. posterior parietal and superior temporal lobe regions, the networks for VSP mature latter than those for HSP.

Development of eye-movement control

Cognitive control of behavior continues to improve through adolescence in parallel with important brain maturational processes including synaptic pruning and myelination, which allow for efficient neuronal computations and the functional integration of widely distributed circuitries supporting top-down control of behavior. This is also a time when psychiatric disorders, such as schizophrenia and mood disorders, emerge reflecting a particularly vulnerability to impairments in development during adolescence. Oculomotor studies provide a unique neuroscientific approach to make precise associations between cognitive control and brain circuitry during development that can inform us of impaired systems in psychopathology. In this review, we first describe the development of pursuit, fixation, and visually-guided saccadic eye movements, which collectively indicate early maturation of basic sensorimotor processes supporting reflexive, exogenously-driven eye movements. We then describe the literature on the development of the cognitive control of eye movements as reflected in the ability to inhibit a prepotent eye movement in the antisaccade task, as well as making an eye movement guided by on-line spatial information in working memory in the oculomotor delayed response task. Results indicate that the ability to make eye movements in a voluntary fashion driven by endogenous plans shows a protracted development into adolescence. Characterizing the transition through adolescence to adult-level cognitive control of behavior can inform models aimed at understanding the neurodevelopmental basis of psychiatric disorders.

Physiology and pathology of eye–head coordination

Human head movement control can be considered as part of the oculomotor system since the control of gaze involves coordination of the eyes and head. Humans show a remarkable degree of flexibility in eye-head coordination strategies, nonetheless an individual will often demonstrate stereotypical patterns of eye-head behaviour for a given visual task. This review examines eye-head coordination in laboratory-based visual tasks, such as saccadic gaze shifts and combined eye-head pursuit, and in common tasks in daily life, such as reading. The effect of the aging process on eye-head coordination is then reviewed from infancy through to senescence. Consideration is also given to how pathology can affect eye-head coordination from the lowest through to the highest levels of oculomotor control, comparing conditions as diverse as eye movement restrictions and schizophrenia. Given the adaptability of the eye-head system we postulate that this flexible system is under the control of the frontal cortical regions, which assist in planning, coordinating and executing behaviour. We provide evidence for this based on changes in eye-head coordination dependant on the context and expectation of presented visual stimuli, as well as from changes in eye-head coordination caused by frontal lobe dysfunction.

Smooth ocular pursuit in Chiari type II malformation

Chiari type II malformation (CII) is a congenital anomaly of the cerebellum and brainstem, both important structures for processing smooth ocular pursuit. CII is associated with myelomeningocele and hydrocephalus. We investigated the effects of CII on smooth pursuit (SP) eye movements, and determined the effects of spinal lesion level, number of shunt revisions, nystagmus, and brain dysmorphology on SP. SP was recorded using an infrared eye tracker in 21 participants with CII (11 males, 10 females; age range 8-19y, mean 14y 3mo [SD 3y 2mo]). Thirty-eight healthy children (21 males, 17 females) constituted the comparison group. Participants followed a visual target moving sinusoidally at +/- 10 degrees amplitude, horizontally and vertically at 0.25 or 0.5Hz. SP gains, the ratio of eye to target velocities, were abnormal in the CII group with nystagmus (n= 8). The number of shunt revisions (range 0-10), brain dysmorphology, or spinal lesion level (n= 15 for lower and n= 6 for upper spinal lesion level) did not correlate with SP gains. SP is impaired in children with CII and nystagmus. Abnormal pursuit might be related to the CII dysgenesis or to effects of hydrocephalus. The lack of effect of shunt revisions and abnormal tracking in participants with nystagmus provide evidence that it is related primarily to the cerebellar and brainstem malformation.

Application of video-based technology for the simultaneous measurement of accommodation and vergence

Accommodation and vergence are two ocular motor systems that interact during binocular vision. Independent measurement of the response dynamics of each system has been achieved by the application of optometers and eye trackers. However, relatively few devices, typically earlier model optometers, allow the simultaneous assessment of accommodation and vergence. In this study we describe the development and application of a custom designed high-speed digital photorefractor that allows for rapid measures of accommodation (up to 75Hz). In addition the photorefractor was also synchronized with a video-based stereo eye tracker to allow a simultaneous measurement of accommodation and vergence. Analysis of accommodation and vergence could then be conducted offline. The new instrumentation is suitable for investigation of young children and could be potentially used for clinical populations.