Johannes van der Steen

Gaze-shift dynamics in subjects with and without symptoms of convergence insufficiency : influence of monocular preference and the effect of training

We studied gaze-shift dynamics during several gaze-shift tasks and during reading, in five subjects with convergence insufficiency (C.I., a diminished ability to converge), and in ten subjects without C.I. Furthermore, we studied the effect of vergence training in order to verify previous claims that orthoptic exercises can improve vergence performance. We recorded binocular eye movements with the scleral coil technique. Subjects switched fixation between nearby and distant light emitting diodes (LEDs) arranged in isovergence arrays (distances 35 and 130 cm) in a dimly lit room. In both the C.I. and non-C.I. group, two classes of subjects occurred: vergence responders and saccadic responders. During pure vergence tasks, saccadic responders made saccades with no or little vergence; vergence responders made vergence movements with no or small saccadic components. In saccadic responders, fixation of nearby targets was monocular. Subjects with a preferred eye, according to our determination, used the preferred eye. The five C.I. subjects showed idiosyncratic responses with insufficient vergence during most trials. They all had a tendency to alternate fixation between the left and right eye. Vergence-version tasks always elicited larger vergence components than pure vergence tasks. During a reading task, vergence angles were more accurate than during gaze-shifts between LEDs. After the pre-training sessions, nine subjects (one of which had C.I.) practised a pure vergence task three times a day for at least 2 weeks. Vergence amplitudes of four of these subjects were larger after training. We conclude that vergence training can change oculomotor performance. Although C.I. is often associated with abnormal vergence dynamics, there are no typical C.I. vergence dynamics. Unstable monocular preferences may play a role in the aetiology of C.I.

Visuomotor Impairment in Early-Stage Alzheimer's Disease: Changes in Relative Timing of Eye and Hand Movements

Although memory complaints are one of the first clinical symptoms in patients with Alzheimers disease (AD), damage to the parietal lobe, a key structure in the visuomotor coordination network, was recently identified in early-stage AD. The aim of this study was to quantify visuomotor coordination in patients with probable AD and to compare their visuomotor performance with controls using five eye-hand coordination tasks of variable complexity. Eye and hand movements were measured in 16 AD patients and 18 controls. The measurement setup consisted of a touch screen, an eye-tracking device, and a motion capturing system. We investigated eye-hand coordination by quantifying absolute and relative latencies of eye and hand movements and by analyzing eye and hand kinematics. We found that AD patients need significantly more time to initiate and execute goal-directed hand movements. AD patients are also unable to suppress reflexive eye and, to a lesser extent, hand movements. Furthermore, AD patients use a stepwise approach of eye and hand movements to touch a sequence of stimuli, whereas controls more often show an anticipatory approach. The impairments in reflex suppression of eye and hand movements, and changes in relative timing of eye-hand coordination, in AD patients support the notion that cortical networks involving the posterior parietal cortex are affected at an early disease-stage. It also suggests that the problems of AD patients to perform daily activities that require eye-hand coordination are not only caused by cognitive decline, but also by degeneration of neural networks involved in visuomotor coordination.

Changes in Timing and kinematics of goal directed eye-hand movements in early-stage Parkinson's disease

ObjectiveMany daily activities involve intrinsic or extrinsic goal-directed eye and hand movements. An extensive visuomotor coordination network including nigro-striatal pathways is required for efficient timing and positioning of eyes and hands. The aim of this study was to investigate how Parkinson’s disease (PD) affects eye-hand coordination in tasks with different cognitive complexity.MethodsWe used a touch screen, an eye-tracking device and a motion capturing system to quantify changes in eye-hand coordination in early-stage PD patients (H&Y < 2.5) and age-matched controls. Timing and kinematics of eye and hand were quantified in four eye-hand coordination tasks (pro-tapping, dual planning, anti-tapping and spatial memory task).ResultsIn the pro-tapping task, saccade initiation towards extrinsic goals was not impaired. However, in the dual planning and anti-tapping task initiation of saccades towards intrinsic goals was faster in PD patients. Hand movements were differently affected: initiation of the hand movement was only delayed in the pro-tapping and dual planning task. Overall, hand movements in PD patients were slower executed compared to controls.InterpretationWhereas initiation of saccades in an extrinsic goal-directed task (pro-tapping task) is not affected, early stage PD patients have difficulty in suppressing reflexive saccades towards extrinsic goals in tasks where the endpoint is an intrinsic goal (e.g. dual planning and anti-tapping task). This is specific for eye movements, as hand movements have delayed responses in the pro-tapping and dual planning task. This suggests that reported impairment of the dorsolateral prefrontal cortex in early-stage PD patients affects only inhibition of eye movements. We conclude that timing and kinematics of eye and hand movements in visuomotor tasks are affected in PD patients. This result may have clinical significance by providing a behavioral marker for the early diagnosis of PD.

Saccadic binocular coordination in alternating exotropia

We studied the coordination of binocular eye movements in human subjects with alternating exotropia (divergent strabismus). Binocular saccades were recorded in six subjects during binocular and monocular viewing. Subjects were instructed to make saccades between two continuously lit targets (LEDs) presented in an isovergence array (with the straight-ahead target 130 cm from the eyes) in a dimly lit room. For saccades up to 20 degrees amplitude, there were no large differences in the dynamics of the saccades between control and exotropic subjects. However, for larger amplitudes subjects frequently alternated the eye of fixation during saccades. That is, subjects fixated the left target with the left eye and the right target with the right eye. The alternation in eye fixation at the end of the saccade was taken into account in the programming of the saccades. The amplitudes of the alternating saccades were approximately equal to the target amplitude minus the strabismus angle. We conclude that for those saccades where alternation occurs, there is not only a change in the eye of fixation, but also a change in the target representation provided by either eye. Thus, in this group of strabismic patients, saccades may be programmed in a retina-centered coordinate system, if we assume that for making a saccade to a new target in the contralateral visual field its representation on the temporal retinal field of the currently fixating eye is suppressed and the retinotopic target information is derived from the non-fixating eye. In executing the saccade, the non-fixating eye automatically becomes the fixating eye.

Quantification of Visual Orienting Responses to Coherent Form and Motion in Typically Developing Children Aged 0–12 Years

PURPOSE Brain damage or brain development disorders can affect (the maturation of) visual processing functions, such as form and motion detection. The aim of our study was to investigate visual orienting responses of children to a coherent form and motion stimulus as a measure for maturation of visual information processing. METHODS The 213 typically developing children aged 0-12 years included in this study were shown a 100% coherent form and motion expansion stimulus on a remote eye tracking monitor. Orienting eye movements were quantified in terms of ocular motor reaction time to fixation (RTF). Children were divided in age groups, and their performance was compared to 30 healthy adults with a mean age of 24.49 years (SD 3.62 years). RESULTS The RTF values of coherent form in children up to six years old were significantly higher compared to the adult group (P < 0.05, Dunnett post-hoc test). For motion, mature levels were reached at eight years old. RTF values depended on stimulus type (F(1,168) = 240.8, P < 0.001) and age (F(11,168) = 25.8, P < 0.001), and there was a significant age by stimulus type interaction (F(11,168) = 2.2, P < 0.05). CONCLUSIONS Remote eye tracking may provide objective insight into the maturation of visual information processing of coherent form and motion without complex instructions or active cooperation. The quantification of typical visual orienting behavior in childhood may be used as a reference for children with brain dysfunction.

Mini-Mental State Examination subscores indicate visuomotor deficits in Alzheimer's disease patients: A cross-sectional study in a Dutch population

In diagnostics of Alzheimers disease (AD), the Mini‐Mental State Examination (MMSE) questionnaire is frequently used to test cognitive decline. The final subtest of the MMSE, in which patients have to copy two interlocking pentagons, tests a variety of visuomotor functions. Recent imaging studies suggest that visuomotor function could decline in early stage AD, as a result of degeneration of the brain networks involved. The goal of the present study was to compare memory and visuomotor function in AD patients, reflected by the MMSE subscores for orientation, recall and interlocking pentagons.

Peaks and Troughs of Three-Dimensional Vestibulo-ocular Reflex in Humans

The three-dimensional vestibulo-ocular reflex (3D VOR) ideally generates compensatory ocular rotations not only with a magnitude equal and opposite to the head rotation but also about an axis that is collinear with the head rotation axis. Vestibulo-ocular responses only partially fulfill this ideal behavior. Because animal studies have shown that vestibular stimulation about particular axes may lead to suboptimal compensatory responses, we investigated in healthy subjects the peaks and troughs in 3D VOR stabilization in terms of gain and alignment of the 3D vestibulo-ocular response. Six healthy upright sitting subjects underwent whole body small amplitude sinusoidal and constant acceleration transients delivered by a six-degree-of-freedom motion platform. Subjects were oscillated about the vertical axis and about axes in the horizontal plane varying between roll and pitch at increments of 22.5° in azimuth. Transients were delivered in yaw, roll, and pitch and in the vertical canal planes. Eye movements were recorded in with 3D search coils. Eye coil signals were converted to rotation vectors, from which we calculated gain and misalignment. During horizontal axis stimulation, systematic deviations were found. In the light, misalignment of the 3D VOR had a maximum misalignment at about 45°. These deviations in misalignment can be explained by vector summation of the eye rotation components with a low gain for torsion and high gain for vertical. In the dark and in response to transients, gain of all components had lower values. Misalignment in darkness and for transients had different peaks and troughs than in the light: its minimum was during pitch axis stimulation and its maximum during roll axis stimulation. We show that the relatively large misalignment for roll in darkness is due to a horizontal eye movement component that is only present in darkness. In combination with the relatively low torsion gain, this horizontal component has a relative large effect on the alignment of the eye rotation axis with respect to the head rotation axis.

Behavioral Inhibition Errors in Parkinson's Disease Tested Using an Antisaccade and Antitapping Task

BACKGROUND The antisaccade (AS) paradigm is frequently used to assess errors in reflexive behavioral responses in Parkinsons disease (PD) patients. Although PD pathology of frontal-striatal circuits suggests increased errors, reports on sensitivity and specificity of the AS task are lacking. We increased the level of cognitive complexity by adding to the AS task an antitapping instruction, i.e. an antisaccade and antitapping (ASAT) task. OBJECTIVE In this study, we compared saccadic error rates between PD patients and age-matched controls in 1) an AS task, using only eye movements and 2) an ASAT task, using eye and hand movements. METHODS 30 PD patients en 30 healthy age-matched controls performed an AS task and an ASAT task. The measurement setup consisted of a touch screen, an eye tracking system and a motion capture system. Error rates and eye - and hand latencies were compared between groups. RESULTS PD patients show higher error rates in the ASAT task, but not in the AS task compared to controls. In correctly performed ASAT task trials, PD patients are on average 60 milliseconds faster to initiate an eye movement. Subject classification based on error rates and eye latencies in the ASAT task results in a sensitivity of 0.77 and a specificity of 0.63. CONCLUSIONS The results suggest that saccadic error rates and eye latencies in the cognitively more demanding ASAT task are sensitive measures to differentiate PD patients from controls. This task is a potentially useful addition to current methods to investigate visuomotor deficits in PD.

Reliability of visual orienting response measures in children with and without visual impairments.

BACKGROUND From the need for a quantitative method to examine visual processing in young children, we measured ocular orienting responses to visual stimuli (form, motion, expansion, color, contrast, cartoons). Reliability and applicability of this method were assessed. NEW METHOD 80 children (1-12 years) with visual impairments and a reference group of 118 typically developing children (1-6 years) completed two sessions. Test-retest reliability was measured by calculating differences in reaction time and fixation accuracy between the two sessions. For applicability, the cumulative percentage of children that fell within a pre-defined reliability interval was plotted against the mean number of responses. RESULTS In typically developing children none of the outcome measures significantly differed between sessions. In the children with visual impairments similar results were obtained, except for motion. This stimulus elicited significantly faster reaction times in the second session. In at least 80% of the children reliable reaction times could be calculated if 4 responses to a cartoon stimulus and 1 or 2 responses to the other stimuli were measured. COMPARISON WITH EXISTING METHOD(S) The existing method to quantify visual information processing has been refined: the range of visual functions was extended and a criterion for reliable assessment of orienting response times was established. CONCLUSIONS Objective measurement of orienting responses is a reliable method to test the initial stage of visual processing in children with and without visual impairments. A set minimum number of responses for each stimulus warrants the reliability of measurements obtained with this functional method in clinical practice.

Binocular Eye Movement Responses to Dichoptically Presented Horizontal and/or Vertical Stimulus Steps

Humans and primates with stereo vision depend on accurate binocular oculomotor control mechanisms to align their two eyes on corresponding points of a visual scene. Misalignments are sensed as the difference in the position of corresponding points of the two retinal images (binocular disparity) and are corrected by vergence eye movements. Vergence responses have been extensively investigated using dichoptically presented visual stimuli.1–3 The dynamics of horizontal and vertical vergence eye movements are also known.2,4,5 In general, vertical vergence dynamic properties are inferior to horizontal vergence responses. This suggests separate horizontal and vertical vergence centers with different dynamics. There is also scant evidence, however, for an interaction of the two systems.6 Another important issue is whether the command signals that generate these vergence eye movements are entirely driven by binocular disparity or also depend on monocular input, that is, eyeof-origin information. Recent electrophysiological evidence suggests that eye movement commands are encoded monocularly for each eye in premotor pathways.7,8 Here we provide behavioral evidence by using different combinations of horizontal and vertical vergence steps for an eye-dependent interaction between horizontal and vertical vergence signals in humans.