A developmental study of smooth pursuit eye movements in normal children from 7 to 15 years of age

Reliability of a Smooth Pursuit Eye-Tracking System (EyeGuide Focus) in Healthy Adolescents and Adults

Mild traumatic brain injury (mTBI) is the most common brain injury, seen in sports, fall, vehicle, or workplace injuries. Concussion is the most common type of mTBI. Assessment of impairments from concussion is evolving, with oculomotor testing suggested as a key component in a multimodality diagnostic protocol. The aim of this study was to evaluate the reliability of one eye-tracking system, the EyeGuide Focus. A group of 75 healthy adolescent and adult participants (adolescents: n = 28; female = 11, male = 17, mean age 16.5 ± 1.4 years; adults n = 47; female = 22; male = 25, mean age 26.7 ± 7.0 years) completed three repetitions of the EyeGuide Focus within one session. Intraclass correlation coefficient (ICC) analysis showed the EyeGuide Focus had overall good reliability (ICC 0.79, 95%CI: 0.70, 0.86). However, a familiarization effect showing improvements in subsequent trials 2 (9.7%) and 3 (8.1%) was noticeable in both cohorts (p < 0.001) with adolescent participants showing greater familiarization effects than adults (21.7% vs. 13.1%). No differences were observed between sexes (p = 0.69). Overall, this is the first study to address the concern regarding a lack of published reliability studies for the EyeGuide Focus. Results showed good reliability, suggesting that oculomotor pursuits should be part of a multimodality assessment protocol, but the observation of familiarization effects suggests that smooth-pursuit testing using this device has the potential to provide a biologically-based interpretation of the maturation of the oculomotor system, as well as its relationship to multiple brain regions in both health and injury.

Age-Related Effects on the Spectrum of Cerebral Visual Impairment in Children With Cerebral Palsy

Background

Cerebral Visual Impairment (CVI) is a very common finding in children affected by Cerebral Palsy (CP). In this paper we studied the characteristics of CVI of a large group of children with CP and CVI, describing their neurovisual profiles according to three different age subgroups (subgroup 1: infants 6 months–2 years; subgroup 2: pre-school age 3–5 years; subgroup 3: school age ≥ 6 years).

Methods

We enrolled 180 subjects (104 males, mean age 66 ± 42.6 months; range 6–192 months) with CP and CVI for the study. We carried out a demographic and clinical data collection, neurological examination, developmental or cognitive assessment, and a video-recorded visual function assessment including an evaluation of ophthalmological characteristics, oculomotor functions, and basic visual functions. In school-aged children, we also performed an evaluation of their cognitive-visual profiles.

Results

There were signs of CVI in all the three subgroups. Subgroup 1 (62 children) and subgroup 2 (50 children) were different for fixation (p = 0.02), visual acuity (p = 0.03) and contrast sensitivity (p < 0.01), being more frequently impaired in younger children. Comparing subgroup 2 with subgroup 3 (68 children), the older children presented more frequently myopia (p = 0.02) while the younger ones esotropia (p = 0.02) and alteration in smooth pursuit (p = 0.03) and saccades (p < 0.01). Furthermore, fixation, smooth pursuit, visual acuity, contrast sensitivity and visual filed (p < 0.01) were more frequently impaired in younger children (subgroup 1) compared to the older ones. Multiple correspondence analysis (MCA) confirmed the different neurovisual profiles according to age: younger children with CP showed more signs of CVI compared to the older ones. 34 out of 68 children belonging to subgroup 3 underwent the cognitive visual evaluation; an impairment of cognitive visual skills was detected in 21 subjects.

Conclusion

Younger children with CP showed more signs of CVI compared to the older ones, likely for the physiological maturation of visual system and mechanisms of neuroplasticity. In this direction, we suggest an early neurovisual evaluation to detect any weak visual functions.

Reliance on visual feedback from ocular accommodation on motor skills in children with developmental coordination disorder and typically developing controls

Children with developmental coordination disorder (DCD) present with marked impairments in motor skills, including visual-motor integration. Oculomotor anomalies are more prevalent in children with DCD than typically developing children. Children with DCD further demonstrate altered use of visual feedback compared to typically developing controls. We investigated whether the accommodation system, a key component of the oculomotor system, contributes to visual feedback during fine and gross motor skills performance; and whether children with DCD demonstrate differences in reliance on visual feedback from accommodation. Minus dioptre lenses were used to maximally induce accommodation and impede accommodation dynamics. Children with DCD and typically developing controls performed motor skills tests assessing balance, upper limb coordination, visual-motor performance, gross and fine dexterity. Motor skills performance in controls was significantly affected by impeded accommodation in all tasks. Children with DCD demonstrated reliance on accommodation feedback in upper limb and visual-motor tasks only. Children with DCD may be less reliant on visual feedback obtained from accommodation due to adaptive mechanisms to overcome faulty information in the presence of oculomotor anomalies. These results strengthen our previous findings that accommodation anomalies contribute to motor skills impairment, and suggest that performance on these motor tasks is heavily reliant on visual feedback from accommodation.

A hidden Markov model for analyzing eye-tracking of moving objects : Case study in a sustained attention paradigm

Eye-tracking provides an opportunity to generate and analyze high-density data relevant to understanding cognition. However, while events in the real world are often dynamic, eye-tracking paradigms are typically limited to assessing gaze toward static objects. In this study, we propose a generative framework, based on a hidden Markov model (HMM), for using eye-tracking data to analyze behavior in the context of multiple moving objects of interest. We apply this framework to analyze data from a recent visual object tracking task paradigm, TrackIt, for studying selective sustained attention in children. Within this paradigm, we present two validation experiments to show that the HMM provides a viable approach to studying eye-tracking data with moving stimuli, and to illustrate the benefits of the HMM approach over some more naive possible approaches. The first experiment utilizes a novel 'supervised' variant of TrackIt, while the second compares directly with judgments made by human coders using data from the original TrackIt task. Our results suggest that the HMM-based method provides a robust analysis of eye-tracking data with moving stimuli, both for adults and for children as young as 3.5-6 years old.

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.

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.

Sensorimotor dysfunctions as primary features of autism spectrum disorders

Motor impairments in autism spectrum disorders (ASD) have received far less research attention than core social-communication and cognitive features. Yet, behavioral, neurophysiological, neuroimaging and histopathological studies have documented abnormal motor system development in the majority of individuals with ASD suggesting that these deficits may be primary to the disorder. There are several unique advantages to studying motor development in ASD. First, the neurophysiological substrates of motor skills have been well-characterized via animal and human lesion studies. Second, many of the single- gene disorders associated with ASD also are characterized by motor dysfunctions. Third, recent evidence suggests that the onset of motor dysfunctions may precede the emergence of social and communication deficits during the first year of life in ASD. Motor deficits documented in ASD indicate disruptions throughout the neuroaxis affecting cortex, striatum, the cerebellum and brainstem. Questions remain regarding the timing and development of motor system alterations in ASD, their association with defining clinical features, and their potential for parsing heterogeneity in ASD. Pursuing these questions through neurobiologically informed translational research holds great promise for identifying gene-brain pathways associated with ASD.

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.

Perception of individual and joint action in infants and adults

Infants and adults frequently observe actions performed jointly by more than one person. Research in action perception, however, has focused largely on actions performed by an individual person. Here, we explore how 9- and 12-month-old infants and adults perceive a block-stacking action performed by either one agent (individual condition) or two agents (joint condition). We used eye tracking to measure the latency of participants' gaze shifts towards action goals. Adults anticipated goals in both conditions significantly faster than infants, and their gaze latencies did not differ between conditions. By contrast, infants showed faster anticipation of goals in the individual condition than in the joint condition. This difference was more pronounced in 9-month-olds. Further analyses of fixations examined the role of visual attention in action perception. These findings are cautiously interpreted in terms of low-level processing in infants and higher-level processing in adults. More precisely, our results suggest that adults are able to infer the overarching joint goal of two agents, whereas infants are not yet able to do so and might rely primarily on visual cues to infer the respective sub-goals. In conclusion, our findings indicate that the perception of joint action in infants develops differentially from that of individual action.

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.

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.

Methodological approaches in developmental neuroimaging studies

Pediatric neuroimaging is increasingly providing insights into the neural basis of cognitive development. Indeed, we have now arrived at a stage where we can begin to identify optimal methodological and statistical approaches to the acquisition and analysis of developmental imaging data. In this article, we describe a number of these approaches and how their selection impacts the ability to examine and interpret developmental effects. We describe preferred approaches to task selection, definition of age groups, selection of fMRI designs, definition of regions of interest (ROI), optimal baseline measures, and treatment of timecourse data. Consideration of these aspects of developmental neuroimaging reveals that unlike single-group neuroimaging studies, developmental studies pose unique challenges that impact study planning, task design, data analysis, and the interpretation of findings.

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.

Smooth pursuit eye movements in children

Smooth pursuit eye movements consists of slow eye movements that approximate the velocity of the eyes to that of a small moving target, so that target image is kept at or near the fovea. Little information on smooth pursuit is available in children. We used an infrared eye tracker to record smooth pursuit in 38 typically developing children, aged 8-19 years. Participants followed a visual target moving sinusoidally at +/-10 degrees amplitude, horizontally and vertically at 0.25 or 0.5 Hz. The mean horizontal smooth pursuit gains, the ratio of eye to target velocities, were 0.84 at 0.25 Hz and 0.73 at 0.5 Hz. Mean vertical smooth pursuit gains were 0.68 at 0.25 Hz and 0.45 at 0.5 Hz. Smooth pursuit gains were significantly lower for vertical in comparison to horizontal tracking, and for 0.5 Hz in comparison to 0.25 Hz tracking (P<0.0001). Smooth pursuit gains increased with age (P<0.01, Pearson's correlation tests), with horizontal gains attaining reported adult values by mid adolescence. Vertical gains had large variability among participants. The median phase, the time interval between eye and target velocities, varied between 39 and 86 ms. Phase was not influenced by age. We conclude that smooth pursuit gains are lower in children than gains reported in adults. Vertical pursuit gain is significantly lower than horizontal pursuit gain. Gains improve with age and approach adult values in mid adolescence. Children have larger phases than reported adults values indicating that prediction in the smooth pursuit system is less mature in children.

Saccadic eye movement task identifies cognitive deficits in children with schizophrenia, but not in unaffected child relatives

BACKGROUND

The delayed oculomotor response (DOR) task requires response inhibition followed by movement of gaze towards a known spatial location without a current stimulus. Abnormalities in response inhibition and in the spatial accuracy of the eye movement are found in individuals with schizophrenia and in many of their relatives, supporting the use of these saccadic abnormalities as endophenotypes in genetic studies. It is unknown whether school-age children, either with psychosis or as relatives of a schizophrenic proband, can be included.

METHOD

One hundred eighty-seven children, ages 5.8-16.0 years - 45 children with childhood-onset schizophrenia, 64 children with a first-degree relative with schizophrenia, and 84 typically developing children - completed DOR tasks with 1 and 3 second delays.

RESULTS

Children with childhood-onset schizophrenia demonstrated impaired response inhibition and impaired spatial accuracy compared to both relatives and typicals; however, relatives and typicals did not differ from each other.

CONCLUSIONS

Children with childhood-onset schizophrenia have saccadic abnormalities similar to those found in adults with schizophrenia, supporting the continuity of executive function deficits in childhood-onset with adolescent and adult-onset schizophrenia. However, saccadic tasks are not sensitive to genetic risk in non-psychotic children and 6-15-year-old children should not be included in genetic studies utilizing this endophenotype.

Voluntary control of saccadic and smooth-pursuit eye movements in children with learning disorders

Eye movement is crucial to humans in allowing them to aim the foveae at objects of interest. We examined the voluntary control of saccadic and smooth-pursuit eye movements in 18 subjects with learning disorders (LDs) (aged 8-16) and 22 normal controls (aged 7-15). The subjects were assigned visually guided, memory-guided, and anti-saccade tasks, and smooth-pursuit eye movements (SPEM). Although, the LD subjects showed normal results in the visually guided saccade task, they showed more errors in the memory-guided saccade task (e.g. they were unable to stop themselves reflexively looking at the cue) and longer latencies, even when they performed correctly. They also showed longer latencies than the controls in the anti-saccade task. These results suggest that they find it difficult to voluntarily suppress reflexive saccades and initiate voluntary saccades when a target is invisible. In SPEM using step-ramp stimuli, the LD subjects showed lower open- and closed-loop gains. These results suggest disturbances of both acceleration of eye movement in the initial state and maintenance of velocity in minimizing retinal slip in the steady state. Recent anatomical studies in LD subjects have suggested abnormalities in the structure of certain brain areas such as the frontal cortex. Frontal eye movement-related areas such as the frontal eye fields and supplementary eye fields may be involved in these disturbances of voluntary control of eye movement in LDs.

Oculomotricity in childhood: is the normal range the same as in adults?

The study of oculomotricity is done by the evaluation of three systems: saccade eye movements (MOS), optokinetic nystagmus (NO) and smooth pursuit eye movement (MORL). The joint action of these three systems allows the visual field's establishment in different movement situations.

AIM

To compare the value of oculomotricity in normal adults and children to confirm, or not if it is viable to use the same parameters of adults normality to children's exams interpretation.

STUDY DESIGN

Clinical with transversal cohort.

MATERIAL AND METHOD

We studied MOS, NO and MORL in 50 normal children and in 35 adults and the results were compared by the t Student test.

RESULTS

The data analysis showed significant difference between children and adults (significance at level +/- = 0.05)

DISCUSSION

In the literature we have found evidence that myelinization of the vestibular pathways happen at about 16 weeks and the pyramidal tracts, at 24 months. Oculomotricity is finished at this time. Other papers describe the importance of these tests in the diagnostic of neurological diseases, visual alterations and as predictors of the risk of schizophrenia development but they do not report the normal range in children. In our study we found increased latency of MOS, increase in gain of NO, reduction in gain and increase in the distortion of MORL in children if compared to adults, which is in accordance with the literature. These alterations can be explained by the low attention during the tests and the immaturity of ocular movements' control in children.

CONCLUSION

Therefore, the establishment of a parameter of normality to the oculomotricity in childhood is necessary for the correct analysis of the oculography to avoid misinterpretation of the exam.

Smooth pursuit eye movements are associated with phonological awareness in preschool children

Phonological awareness is strongly related to reading ability, but reports are more conflicting concerning the association of high level oculomotor skills with reading. Here, we show that phonological awareness is specifically associated with the ability to perform smooth pursuit eye movements in preschool children. Two large independent samples of preschool children (n=838 and n=732) aged 5-6.4 years, without history of neurological disorder, were examined by school medical doctors for visual and oculomotor problems. Nineteen percent of the children in the first sample and 14% in the second failed at the clinical evaluation of smooth pursuit eye movements, and 17 and 15%, respectively, presented another visual or oculomotor problem. Ten short cognitive tests were performed by the same children. Visual and oculomotor problems other than a failure on smooth pursuit were not consistently related to the cognitive tasks, with one exception, the visual recognition of letters. Children who failed at smooth pursuit obtained lower scores at a number of cognitive tasks, and especially phonological awareness tasks and copy of visually presented trajectories. Poor working memory and/or failure of anticipation during the tracking of a visual or auditory stimulus related to frontal cortex immaturity may explain these associations in preschool children.

Directional asymmetry in smooth ocular tracking in the presence of visual background in young and adult primates

The smooth pursuit system moves the eyes in space accurately while compensating for visual inputs from the moving background and/or vestibular inputs during head movements. To understand the mechanisms underlying such interactions, we examined the influence of a stationary textured visual background on smooth pursuit tracking and compared the results in young and adult humans and monkeys. Six humans (three children, three adults) and six macaque monkeys (five young, one adult) were used. Human eye movements were recorded using infrared oculography and evoked by a sinusoidally moving target presented on a computer monitor. Scleral search coils were used for monkeys while they tracked a target presented on a tangent screen. The target moved in a sinusoidal or trapezoidal fashion with or without whole body rotation in the same plane. Two kinds of backgrounds, homogeneous and stationary textured, were used. Eye velocity gains (eye velocity/target velocity) were calculated in each condition to compare the influence of the textured background. Children showed asymmetric eye movements during vertical pursuit across the textured (but not the homogeneous) background; upward pursuit was severely impaired, and consisted mostly of catch-up saccades. In contrast, adults showed no asymmetry during pursuit across the different backgrounds. Monkeys behaved similarly; only slight effects were observed with the textured background in a mature monkey, whereas upward pursuit was severely impaired in young monkeys. In addition, VOR cancellation was severely impaired during upward eye and head movements, resulting in residual downward VOR in young monkeys. From these results, we conclude that the directional asymmetry observed in young primates may reflect a different neural organization of the vertical, particularly upward, pursuit system in the face of conflicting visual and vestibular inputs that can be associated with pursuit eye movements. Apparently, proper compensation matures later.

Early expression of a pathophysiological feature of schizophrenia: saccadic intrusions into smooth-pursuit eye movements in school-age children vulnerable to schizophrenia

OBJECTIVE

Neurodevelopmental hypotheses of schizophrenia propose that the responsible pathology occurs much earlier than the usual onset of illness in late adolescence. Nonspecific neurocognitive and behavioral deficits found in children vulnerable to schizophrenia support this hypothesis. This report describes early deficits in a putative genetic endophenotype, saccadic intrusions into smooth-pursuit eye movements (SPEM).

METHOD

SPEM were recorded in 189 children aged 6-15 years: 49 children with schizophrenia, 60 nonpsychotic first-degree relatives, and 80 typically developing children.

RESULTS

Children with schizophrenia demonstrated poorer gain and a significantly increased frequency of leading saccades and large anticipatory saccades; however, only leading saccades differentiated first-degree relatives from typical children. Admixture analysis indicates that 94% of children with schizophrenia, 50% of first-degree relatives, and 19% of typically developing children have abnormally increased frequencies of leading saccades.

CONCLUSIONS

Typically developing young school-age children have a leading saccade phenotype similar to that of adults, suggesting this brain function is fully developed by early school-age years. The abnormal leading saccade phenotype, a schizophrenia-associated familial brain dysfunction, is present by 6 years of age, more than a decade before the highest risk for onset of psychosis. Treatment and prevention strategies will need to consider the early neurodevelopmental nature of schizophrenia.

Children's pursuit eye movements: a developmental study

We examined the pursuit eye movements of adults and three groups of children 4-6, 8-10, 12-16 years of age. The first experiment compared tracking performance of a partially occluded target with that of a fully visible target. The second experiment examined pursuit abilities of children using a non-cognitive source of information for motion, i.e., proprioception. In this experiment, we compared the ability to track one's own strobe-illuminated finger with the tracking of the experimenter's finger. In the first experiment, only children 4-6 years of age had difficulty inhibiting the tendency to look towards the visible portion of the partially occluded target. They also had significantly fewer epochs of pursuit relative to teenagers and adults. The older children's pursuit eye movements (8-10) were neither significantly different from the youngest nor from the two older groups. In the second experiment, all participants pursued their own finger better than the experimenter's finger, but the youngest children had significantly fewer epochs of pursuit relative to adults. Pursuit of a partially occluded target and incorporation of proprioceptive signals to drive smooth pursuit eye movements are abilities present at four years of age that continue to develop with increasing age.

Eye movement dysfunction as a biological marker of risk for schizophrenia

OBJECTIVE

Our aim was to review smooth pursuit eye movement (SPEM) studies in schizophrenia and groups at high risk for schizophrenia, with a view to evaluating the utility of SPEM dysfunction as a biological marker of risk for schizophrenia.

METHOD

Smooth pursuit eye movement studies, related saccade function and the unresolved issues in this area of schizophrenia research were addressed. The different perspectives on the trait marker status of SPEM dysfunction, provided by both high-risk studies and related developmental research were considered. Attention was also given to the relationship between eye movement dysfunction and symptom profiles.

RESULTS

Converging evidence points to the robust and specific nature of SPEM dysfunction in schizophrenia, and highlights the role of frontal lobe and a related network dysfunction. The vast majority of 'high risk' studies support the view that SPEM dysfunction is also genetically specific to schizophrenia, and is not simply due to the overt expression of this illness. Studies assessing SPEM in relation to symptomatology show an association with the Disorganisation syndrome in particular.

CONCLUSIONS

Evidence for the specificity of SPEM dysfunction to diagnosed schizophrenia, as well as to healthy individuals with a genetic vulnerability to schizophrenia, suggests that the SPEM task has efficacy as a test of gene carrier status in schizophrenia, and therefore as a trait marker of risk for schizophrenia. Future studies should seek to explore the relationships between SPEM and other eye movement dysfunctions (antisaccades, express saccades), in view of evidence that some of these dysfunctions also show specificity for schizophrenia.

Smooth pursuit eye movements in schizophrenia and attentional dysfunction: adults with schizophrenia, ADHD, and a normal comparison group

BACKGROUND

Smooth pursuit eye movement (SPEM) abnormalities are found in schizophrenia. These deficits often are explained in the context of the attentional and inhibitory deficits central to schizophrenia psychopathology. It remains unclear, however, whether these attention-associated eye movement abnormalities are specific to schizophrenia or are a nonspecific expression of attentional deficits found in many psychiatric disorders. Adult attention-deficit/hyperactivity disorder (ADHD) is an alternative disorder with chronic attentional and inhibitory dysfunction. Thus, a comparison of SPEM in adult schizophrenia and adult ADHD will help assess the specificity question.

METHODS

SPEM is recorded during a 16.7 degrees per second constant velocity task in 17 adults with ADHD, 49 adults with schizophrenia, and 37 normal adults; all groups included individuals between ages 25-50 years.

RESULTS

Smooth pursuit gain and the frequency of anticipatory and leading saccades are worse in schizophrenic subjects, with normal and ADHD subjects showing no differences on these variables.

CONCLUSIONS

Many attention-associated SPEM abnormalities are not present in most subjects with ADHD, supporting the specificity of these findings to the attentional deficits seen in schizophrenia.

Familial transmission of risk factors in the first-degree relatives of schizophrenic people

Schizophrenia is a complex illness with multiple pathophysiologic factors that contribute to its psychopathology. One strategy to identify these factors is to observe them in isolation from each other, by characterizing their expression in the relatives of schizophrenic probands. By Mendel's second law, each genetic factor should be independently distributed in a sibship, so that each can be observed by itself, uncomplicated by the general problems of the illness. Such independently distributed phenotypes are obviously useful for genetic analyses; however, they can also be considered together, to model how various brain dysfunctions may combine to produce psychoses. In addition to a sensory gating deficit linked to the alpha 7-nicotinic acetylcholine receptor locus, schizophrenics and their families have a number of other deficits, including decreased hippocampal volume on magnetic resonance images and increased plasma levels of the dopamine metabolite homovanillic acid. Although such research is far from complete, a heuristic model combining a sensory gating deficit, decreased hippocampal neuron capacity, and increased dopaminergic neurotransmission is consonant with current understanding of the neuropsychology of schizophrenia.

The effects of age on a smooth pursuit tracking task in adults with schizophrenia and normal subjects

BACKGROUND

Performance during a smooth pursuit eye movement (SPEM) task has been proposed as a marker of genetic risk for schizophrenia, although the precise component of SPEM tracking most associated with genetic risk remains undetermined. Normal adult aging is associated with deterioration on SPEM tasks; it remains unclear whether investigations of SPEM abnormalities will allow inclusion of older subjects in genetic studies. This study examines 1) the effect of normal aging on several components of SPEM performance; and 2) whether schizophrenic-normal differences found in young adults continue over a broad adult age span.

METHODS

SPEM was recorded during a 16.7 degrees per sec constant velocity task in 64 normal adults, ages 18 to 79 years, and 58 schizophrenic subjects, ages 18 to 70 years.

RESULTS

Smooth pursuit gain, the percent of total eye movements due to catch-up saccades, the frequency of large anticipatory saccades, and the frequency of leading saccades all deteriorate with increasing age. After correction for age, schizophrenic to control differences persist on most eye movement variables with the largest effect sizes for leading saccades (1.56) and smooth pursuit gain (1.17).

CONCLUSIONS

The tendency to use saccades to anticipate target motion, even in small steps (leading saccades), deserves further attention as a potential marker useful in genetic analyses.

Elementary phenotypes in the neurobiological and genetic study of schizophrenia

This review describes the strategy of using elementary phenotypes for neurobiological and genetic linkage studies of schizophrenia. The review concentrates on practical aspects of selecting the phenotype and then understanding the confounds in its measurement and interpretation. Examples from the authors' studies of deficits in P50 inhibition and smooth pursuit eye movement dysfunction are presented. These two phenotypes share considerable similarity in their neurobiology, including a similar response to nicotine. They also appear to co-segregate with the genetic risk for schizophrenia as autosomal co-dominant phenotypes. Although most schizophrenic patients inherit these abnormalities unilinealy, i.e., from one parent, apparent bilineal inheritance produces a more severe illness, observed clinically as childhood-onset schizophrenia. The initial study showing linkage of the P50 deficit to the chromosome 15q14 locus of the alpha 7-nicotinic acetylcholine receptor is an example of the potential usefulness of these phenotypes for combined genetic and neurobiological study of schizophrenia.

Deficient cancellation of the vestibular ocular reflex in schizophrenia

Schizophrenia has long been associated with difficulties in visual tracking of a moving object. Deficits are most notable in tracking tasks that require inhibition of saccades during active smooth pursuit. In order to assess whether there is a more global problem in inhibition of other eye movement systems while the smooth pursuit system is active, this study examined cancellation of the vestibular ocular reflex (VOR). Cancellation of the VOR occurs in a task in which the subject is rotated while looking at a target that is also being rotated. This requires the subject to use the pursuit system to override the VOR, maintain the eye at a stable location within the orbit, and thus retain visual gaze upon the target. Thirteen individuals with schizophrenia and 15 normals were assessed during clockwise rotation at 60 degrees s-1. Schizophrenic subjects had a significant increase in counterclockwise slow velocity eye movements, suggesting an impaired ability to cancel the VOR. Cancellation of the VOR is thus another example of a breakthrough of an alternative eye movement system while the smooth pursuit system is active. Because of the simplicity of the VOR and its suitability for animal modeling, investigation of this phenomenon may delineate more precisely the mechanisms of visual tracking dysfunction in schizophrenia.

Anticipatory saccades during smooth pursuit eye movements and familial transmission of schizophrenia

BACKGROUND

Smooth pursuit eye movement (SPEM) abnormalities are a putative marker of genetic risk for schizophrenia. Accurate SPEM performance requires the subject to activate neural systems responsible for smooth pursuit tracking, while simultaneously suppressing activity of neurons responsible for saccadic movements that would move the eye ahead of the target. This study examined whether specific aspects of SPEM dysfunction cosegregate with genetic risk in parents of schizophrenic probands.

METHODS

Eighteen probands and their parents had SPEM recorded. Parents with an ancestral history of schizophrenia were hypothesized to be more likely than their spouses without such a history to carry a genetic risk for schizophrenia.

RESULTS

Ten families had a single parent with a positive ancestral history for schizophrenia. The frequency of anticipatory saccades, which were mostly small, and the fraction of total eye movement that they represented were the only measures that differentiated the more likely genetic carrier parents in these families from their spouses and age-matched normals.

CONCLUSIONS

Failure to suppress saccadic anticipation of target motion during smooth pursuit appears an aspect of SPEM dysfunction related to presumed genetic risk for schizophrenia.

Eye movements, prematurity and developmental co-ordination disorder

Horizontal pursuit eye movements were investigated in two separate groups of children: One group exhibited developmental co-ordination disorder (n = 8) whilst another group of children were born prematurely (n = 8). Both studies found a reduced gain in pursuit eye movements when the respective populations were compared with control groups (n = 32). A difference was also found in the ability of some children to temporally synchronize their tracking response to the stimulus, which was indicative of poor predictive control rather than lags in the control system. We suggest that horizontal eye movements may be a sensitive indicator of more general motor deficits during childhood development.

Blink rate in childhood-onset schizophrenia: comparison with normal and attention-deficit hyperactivity disorder controls

Several lines of evidence have implicated central dopaminergic pathways in the modulation of blink rate. In the present study, blink rate during smooth pursuit was examined in 17 children with childhood-onset schizophrenia, on and off of clozapine, and compared to that of age-matched normal children and unmedicated children with attention-deficit hyperactivity disorder (ADHD). As has been observed in adolescent and adult schizophrenics, blink rate was significantly higher in schizophrenic children relative to normal and ADHD controls. Within the schizophrenic group, blink rate did not significantly change with the introduction of clozapine and was not related to clinical variables. Blink rate was positively correlated with deterioration in smooth pursuit in normal subjects.

Smooth pursuit eye movements in childhood-onset schizophrenia: comparison with attention-deficit hyperactivity disorder and normal controls

Abnormalities of the smooth pursuit eye movements of adults with schizophrenia have been well described. We examined smooth pursuit eye movements in schizophrenic children, contrasting them with normal and attention-deficit hyperactivity disorder (ADHD) subjects, to determine whether there is continuity of eye movement dysfunction between childhood- and adult-onset forms of schizophrenia. Seventeen schizophrenic children with onset of illness by age 12, 18 ADHD children, and 22 normal children were studied while engaged in a smooth pursuit eye tracking task. Eye tracking variables were compared across the three groups. Schizophrenic children exhibited significantly greater smooth pursuit impairments than either normal or ADHD subjects. Within the schizophrenic group, there were no significant relationships between eye tracking variables and clinical variables, or ventricular/brain ratio. Childhood-onset schizophrenia is associated with a similar pattern of smooth pursuit abnormalities to that seen in later-onset schizophrenia.

Early expression of smooth-pursuit eye movement abnormalities in children of schizophrenic parents

OBJECTIVE

Disordered smooth-pursuit eye movements (SPEM) and, specifically, small anticipatory saccades that disrupt SPEM have been hypothesized to be a marker of genetic vulnerability to schizophrenia. This study compares SPEM in children of schizophrenic parents with normally developing control children to assess whether SPEM abnormalities are also present in a subset of at-risk children.

METHOD

With infrared oculography, SPEM was examined in 13 children of schizophrenic parents and 19 normally developing controls (aged 6 to 15 years). Measures of smooth-pursuit gain and root mean square error were used in addition to more specific measures of catch-up saccades and anticipatory saccades.

RESULTS

Children of schizophrenic parents differed from normally developing controls on gain and root mean square error, but not on catch-up saccades. Small anticipatory saccades were significantly more frequent in the at-risk group. The percentage of total eye movements due to anticipatory saccades identified 54% of the at-risk group (compared with none of the control group) as performing more than two standard deviations above (worse than) the control mean.

CONCLUSIONS

The presence of increased anticipatory saccades is evidence for an oculomotor dysfunction that may be a phenotype of the genetic risk for schizophrenia, expressed years prior to the possible development of clinical illness.

Developmental trends in pursuit eye movements among preschool children

The purpose of this study was to investigate the developmental differences in pursuit eye movements among preschool children. The subjects were 28 children aged 3 to 6 years old and 5 adults aged 22 to 37 years. The target was moved sinusoidally on the horizontal plane at 0.3-, 0.5-, and 0.7-Hz stimulus frequency. The power ratio which represented the smoothness of eye movements and the phase difference between eye movements and target movement was calculated. The power ratio decreased with increased stimulus frequency for all subjects, indicating that eye movements became less smooth. At all stimulus frequencies, the power ratio was higher for adults than for children. Among the three age groups of children, there was no statistically significant difference on this parameter. The phase shifted from a small amount of lead for no lag to the lag with faster stimulus frequency in adults, but the gap was not statistically significant. For children, there was a statistically significant difference across age groups on change in the phase difference. These findings may suggest that the developmental differences in pursuit eye movements of children across ages 3 to 6 years were clear in what related to the phase difference.

Saccadic eye movements in normal children from 8 to 15 years of age: a developmental study of visuospatial attention

This cross-sectional study used saccadic eye movements, as measured by infrared occulography, to assess several aspects of visuospatial attention in normal children ages 8-15 years. Saccadic latency (a global measure of the ability to shift visuospatial attention), the ability to suppress extraneous saccades during fixation, and the ability to inhibit task-provoked anticipatory saccades all improve with age. However, the pattern of development differs for different tasks; saccadic latency shortens at a linear rate across the age range 8-15 years, while the capacity to inhibit anticipatory saccades matures by 12-13 years of age, and the ability to suppress saccades matures by 10 years of age. Analyses of age-related changes in oculomotor measures of attention may provide a novel approach in the study of children with attentional difficulties.

Childhood-onset schizophrenia: timely neurobiological research

OBJECTIVE

To review timely research on childhood-onset schizophrenia in view of advances in biological research on, and neurodevelopmental theories of, the later-onset disorder.

METHOD

Research issues are outlined including further clarification of ICD- and DSM-defined childhood schizophrenia, and differentiation from autism "spectrum" and other subtle, chronic developmental disorders. Key neurobiological advances are reviewed for which child studies are relevant and feasible.

CONCLUSION

It is anticipated that narrowly defined childhood-onset schizophrenics will constitute a predominantly male population. A high rate of family illness or chromosomal and/or brain developmental abnormalities, which will be instructive regarding the pathophysiology of later-onset schizophrenia, is expected.

Eye movement task related to frontal lobe functioning in children with attention deficit disorder

OBJECTIVE

Attention-deficit hyperactivity disorder (ADHD) has been postulated to be related to dysfunction of the prefrontal cortex. In the oculomotor delayed response task, a subject is cued as to where he or she should look (shift visual gaze to) but must delay a short period and then shift gaze to the location where the cue previously existed but no longer exists (a memory-guided saccade). Dependent measures from this task provide information on three functions tentatively tied to prefrontal cortex functioning: the ability to inhibit response (during the delay period), preparation of motor response (inversely tied to the latency of shifting visual gaze), and accuracy of working visuospatial memory (accuracy of the memory-guided saccade).

METHOD

Thirteen children with ADHD and 10 normal controls, aged 9 to 12 years, were tested using an 800-msec delay period.

RESULTS

Children with ADHD showed, relative to normal controls, deficits on inhibiting response during the delay period but no differences in latency (preparation of motor response) or accuracy of visuospatial memory.

CONCLUSIONS

These results support the hypothesis that the primary deficit in ADHD is difficulty in inhibition of response. This deficit may be associated with pathology located outside the dorsolateral prefrontal cortex.