Smooth pursuit development in infants

Binocular Summation for Reflexive Eye Movements: A Potential Diagnostic Tool for Stereodeficiencies

Purpose

Stereoscopic vision, by detecting interocular correlations, enhances depth perception. Stereodeficiencies often emerge during the first months of life, and left untreated can lead to severe loss of visual acuity in one eye and/or strabismus. Early treatment results in much better outcomes, yet diagnostic tests for infants are cumbersome and not widely available. We asked whether reflexive eye movements, which in principle can be recorded even in infants, can be used to identify stereodeficiencies.

Methods

Reflexive ocular following eye movements induced by fast drifting noise stimuli were recorded in 10 adult human participants (5 with normal stereoacuity, 5 stereodeficient). To manipulate interocular correlation, the stimuli shown to the two eyes were either identical, different, or had opposite contrast. Monocular presentations were also interleaved. The participants were asked to passively fixate the screen.

Results

In the participants with normal stereoacuity, the responses to binocular identical stimuli were significantly larger than those induced by binocular opposite stimuli. In the stereodeficient participants the responses were indistinguishable. Despite the small size of ocular following responses, 40 trials, corresponding to less than 2 minutes of testing, were sufficient to reliably differentiate normal from stereodeficient participants.

Conclusions

Ocular-following eye movements, because of their reliance on cortical neurons sensitive to interocular correlations, are affected by stereodeficiencies. Because these eye movements can be recorded noninvasively and with minimal participant cooperation, they can potentially be measured even in infants and might thus provide an useful screening tool for this currently underserved population.

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.

Visual tracking in very preterm infants at 4 mo predicts neurodevelopment at 3 y of age

BACKGROUND

Typically developing infants track moving objects with eye and head movements in a smooth and predictive way at 4 mo of age, but this ability is delayed in very preterm infants. We hypothesized that visual tracking ability in very preterm infants predicts later neurodevelopment.

METHOD

In 67 very preterm infants (gestational age<32 wk), eye and head movements were assessed at 4 mo corrected age while the infant tracked a moving object. Gaze gain, smooth pursuit, head movements, and timing of gaze relative the object were analyzed off line. Results of the five subscales included in the Bayley Scales of Infant Development (BSID-III) at 3 y of age were evaluated in relation to the visual tracking data and to perinatal risk factors.

RESULTS

Significant correlations were obtained between gaze gain and cognition, receptive and expressive language, and fine motor function, respectively, also after controlling for gestational age, severe brain damage, retinopathy of prematurity, and bronchopulmonary dysplasia.

CONCLUSION

This is the first study demonstrating that the basic ability to visually track a moving object at 4 mo robustly predicts neurodevelopment at 3 y of age in children born very preterm.

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.

Concordant eye movement and motion parallax asymmetries in esotropia

The role of eye movements in the perception of depth from motion was investigated in esotropia. Elevated motion parallax thresholds have been shown in strabismus [Thompson, A. M., & Nawrot, M. (1999). Abnormal depth perception from motion parallax in amblyopic observers. Vision Research, 39, 1407-1413] suggesting a global deficit in depth perception involving both stereopsis and motion. However, this motion parallax deficit in strabismus might be better explained by the role that eye movements play in motion parallax [Nawrot, M., & Joyce, L. (2006). The pursuit theory of motion parallax. Vision Research, 46, 4709-4725]. Esotropia is associated with asymmetric pursuit and optokinetic response eye movements [Demer, J. L., & von Noorden, G. K. (1988). Optokinetic asymmetry in esotropia. Journal of Pediatric Ophthalmology and Strabismus, 25, 286-292; Schor, C. M., & Levi, D. M. (1980). Disturbances of small-field horizontal and vertical optokinetic nystagmus in amblyopia. Investigative Ophthalmology and Visual Science, 19, 851-864; Tychsen, L., & Lisberger, S. G. (1986). Maldevelopment of visual motion processing in humans who had strabismus with onset in infancy. The Journal of Neuroscience, 6, 2495-2508; [Westall, C. A., Eizenman, M., Kraft, S. P., Panton, C. M., Chatterjee, S., & Sigesmund, D. (1998). Cortical binocularity and monocular optokinetic asymmetry in early-onset esotropia. Investigative Ophthalmology and Visual Science, 39, 1352-1360.]. The first experiment demonstrates that the motion parallax deficit in esotropia mirrors the pursuit eye movement asymmetry: in the direction of normal pursuit, esotropic observers had normal depth from motion parallax. A second set of experiments, conducted in normal observers, demonstrates that this motion parallax deficit is not a secondary problem due to the retinal slip created by inadequate pursuit. These results underscore the role of pursuit eye movements in the perception of depth from motion parallax.

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.

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.

Abnormal supranuclear eye movements in the child: a practical guide to examination and interpretation

Abnormal eye movements in the infant or voting child can be congenital or acquired. They may be a result of abnormal early visual development or a sign of underlying neurologic or neuromuscular disease. It is important to be able to detect these abnormalities and to distinguish them from normal but immature eye movements. The spectrum of disease in children differs from that in adults. Serious, potentially fatal but treatable disorders can be acquired in infancy, and abnormal eye movements in a sometimes apparently well child should never be labeled as congenital or benign without careful investigation. Eye movement analysis can indicate the presence of an underlying condition and help the clinician to classify different neurologic diseases. It is important to carefully examine the ocular motor system in any children at risk of neurologic disease. This review provides a practical guide to the examination and interpretation of eye movements in the child and includes recent literature on eye movement disorders of childhood. We describe supranuclear abnormalities of the ocular motor system in the order in which we would normally examine it: saccades, pursuit, convergence, vestibulo-ocular reflex, and optokinetic nystagmus. Nystagmus, internuclear ophthalmoplegia, cranial nerve abnormalities, and "miswiring" phenomena (such as Duane's syndrome and synergistic divergence) are not discussed.