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Aim The aim of this study was to evaluate an interdisciplinary visual assessment for multiply challenged children diagnosed with cerebral palsy (CP). Method A comprehensive ophthalmological assessment together with a visual classification scale (VCS) and a questionnaire evaluating daily visual function were completed regarding 77 children (41 females, 36 males; age range 3–20y; mean age 8y 3mo [SD 4y 3mo]; Gross Motor Function Classification System [GMFCS] level V; Manual Ability Classification System level V) who were diagnosed with CP (79.2% spastic quadriplegia, 6.5% athetoid quadriplegia, 10.4% mixed type, 3.9% hemiplegia). All participants had severe to profound motor and intellectual disability and an inability to communicate consistently through either verbal or assisted communication. The interrater and test–retest reliability of the questionnaire and its validity in comparison with the VCS were examined. In addition, the contribution of ophthalmological testing in predicting daily visual function was assessed. Results The ophthalmological examination revealed three diagnostic subgroups: a group with cerebral visual impairment (CVI), a group with optic atrophy, and a group without visual impairment. The questionnaire was found to have high values of interrater reliability (interclass correlation coefficient [ICC]=0.873; 95% confidence interval [CI] 0.762–0.935) and test–retest reliability (ICC=0.988; 95% CI 0.964–0.996). Validity was established for the questionnaire factors: task-orientated visual function (r=0.802; 95% CI 0.669–0.885) and basic visual skills (r=0.691; 95% CI 0.504–0.816). The questionnaire provided information about daily visual performance not available from one-time ophthalmological testing, particularly for participants diagnosed with CVI. The visual performance scale significantly predicted daily visual function for all groups. Interpretation This study highlights the benefits of implementing a diagnostic performance scale as well as a reliable functional questionnaire to achieve a precise visual assessment of children with severe neurological impairment.

Purpose A primary task of the eye care professional is determining the refraction, or optical correction, of a patient. The duochrome red-green test is a standard tool for verification of the final refraction. Traditionally, it is recommended for use both prior to and subsequent to determining the cylindrical or astigmatic component of the refraction. In order for it to be effective when used before correcting the cylinder it is necessary that the COLC (Circle of Least Confusion) be on the retina. This study examined whether it is necessarily true that the duochrome response in uncorrected astigmatism will be as trust-worthy as it is with corrected cylinders. Methods The red-green examination was performed monocularly under the following three conditions: a. fully corrected refraction for the subgroup of eyes that had spherical refractions and for the subgroup of eyes with sphero-cylindrical refractions. b. best sphere-only correction without cylinder correction in sphero-cylindrical eyes c. an induced cylinder error in spherical eyes. The interval between the last “red” response and the first “green” response for the right eyes as a group and separately for the physiological cylinder and induced cylinder correction sub-groups was calculated and compared using a paired, two-tailed t-test. Results The intervals between “red” and “green” responses were not significantly different in the population as a whole and in the uncorrected physiological cylinder and induced cylinder subgroups examined. Conclusion Based on the finding that the interval of red-green equality with fully corrected cylinder and without the cylindrical correction are not significantly different, the red-green duochrome test can indeed be used both before and after cylindrical correction.

The visual system uses the pattern of motion on the retina to analyze the motion of objects in the world, and the motion of the observer him/herself. Distinguishing between retinal motion evoked by movement of the retina in space and retinal motion evoked by movement of objects in the environment is computationally difficult, and the human visual system frequently misinterprets the meaning of retinal motion. In this study, we demonstrate that the visual system of the Rhesus monkey also misinterprets retinal motion. We show that monkeys erroneously report the trajectories of pursuit targets or their own pursuit eye movements during an epoch of smooth pursuit across an orthogonally moving background. Furthermore, when they make saccades to the spatial location of stimuli that flashed early in an epoch of smooth pursuit or fixation, they make large errors that appear to take into account the erroneous smooth eye movement that they report in the first experiment, and not the eye movement that they actually make.

Gaze-evoked blinks are contractions of the orbicularis oculi (OO)—the lid closing muscle—occurring during rapid movements of the head and eyes and result from a common drive to the gaze and blink motor systems. However, blinks occurring during shifts of gaze are often suppressed when the gaze shift is made to an important visual stimulus, suggesting that the visual system can modulate the occurrence of these blinks. In head-stabilized, human subjects, we tested the hypothesis that the presence of a visual stimulus was sufficient, but not necessary, to modulate OO EMG (OOemg) activity during saccadic eye movements. Rapid, reorienting movements of the eyes (saccades) were made to visual targets that remained illuminated (visually guided trials) or were briefly flashed (memory-guided trials) at different amplitudes along the horizontal meridian. We measured OOemg activity and found that the magnitude and probability of OOemg activity occurrence was reduced when a saccade was made to the memory of the spatial location as well as to the actual visual stimulus. The reduced OOemg activity occurred only when the location of the target was previously cued. OOemg activity occurred reliably with spontaneous saccades that were made to locations with no explicit visual stimulus, generally, back to the fixation location. Thus the modulation of gaze-evoked OOemg activity does not depend on the presence of visual information per se, but rather, results from an extraretinal signal.

The pro and anti-saccade task (PAT) is a widely used tool in the study of overt and covert attention with promising potential role in neurocognitive and psychiatric assessment. However, specific PAT protocols can vary significantly between labs, potentially resulting in large variations in findings across studies. In light of recent calls towards a standardization of PAT the current study's objective was to systematically and purposely evaluate the effects of block vs. interleaved administration—a fundamental consideration—on PAT measures in a within subject design. Additionally, this study evaluated whether measures of a Posner-type cueing paradigm parallels measures of the PAT paradigm. As hypothesized, results indicate that PAT performance is highly susceptible to administration mode. Interleaved mode resulted in larger error rates not only for anti (blocks: M = 22%; interleaved: M = 42%) but also for pro-saccades (blocks: M = 5%; interleaved: M = 12%). This difference between block and interleaved administration was significantly larger in anti-saccades compared to pro-saccades and cannot be attributed to a 'speed/accuracy tradeoff'. Interleaved mode produced larger pro and anti-saccade differences in error rates while block administration produced larger latency differences. Results question the reflexive nature of pro-saccades, suggesting they are not purely reflexive. These results were further discussed and compared to previous studies that included within subject data of blocks and interleaved trials.

There are presently several ongoing clinical trials to provide usable sight to profoundly visually impaired patients by means of electrical stimulation of the retina. Some of the blind patients implanted with retinal prosthesis reported un-patterned perception and yet benefit from the device in many activities of daily living, seemingly because they adopt active scanning strategies. The aim of the present work is to evaluate if and under what conditions a measured visual acuity level is truly an indication that the brain perceived a patterned image from the electrical stimulation of the visual prosthesis. Sighted subjects used a pixelized simulator in which they perceived either a low resolution sub-sampling of the original image (“normal mode” – patterned vision) or an image that was solely a function of the brightness and size of the original image (“brightness mode” – no patterned vision). Results show that subjects were able to adopt a head scanning strategy that enabled acuity beyond the resolution set by a static view of the stimulus. In brightness mode, i.e. without patterned vision, most subjects achieved a measurable acuity level better than the limit set by the geometrical resolution of the entire array but worse than the limit set by the distance between neighboring simulated pixels. In normal mode all subject achieved acuity level that is better than the geometrical resolution of the simulated pixels. Thus, visual acuity levels comparable with the electrodes/pixels resolution implies that the patient perceives an image with spatial patterns.

Eye movements were recorded from three subjects as they initiated tracking of a small circle (“target”) moving leftward or rightward, above or below the horizontal meridian, either alone or in the presence of a small square (“distractor”) moving leftward or rightward on the other side of the horizontal meridian. At the start of each trial, subjects were provided with either a “form” cue (always centrally positioned and having the circular shape and color of the upcoming moving target) or a “location” cue (a small white square positioned where the upcoming target would appear). The latency of pursuit increased in the presence of an oppositely moving distractor when subjects were provided the form cues but not when they were provided the location cues. The latency of saccades showed similar, but smaller, increases when subjects were given the form cues. On many trials with the form cues, pursuit started in the direction of the distractor and then reversed to follow the target. On these trials, the initial saccade often, but not always, also followed the distractor. These results indicate that the mechanisms of target selection for pursuit and saccades are tightly coordinated but not strictly yoked. The shared effects of the distractor on the latencies of pursuit and saccades probably reflect the common role of visual attention in filtering the inputs that guide these two types of eye movements. The differences in the details of the effects on pursuit and saccades suggest that the neural mechanisms that trigger these two movements can be independently regulated.

We compared the accuracy of oblique, memory-guided saccades if the eye is stationary or moves horizontally during the memory period. We studied 11 patients with cerebellar disease and 11 age-matched control subjects. Normal subjects showed similar accuracy of saccades for both conditions. In contrast, all patients showed greater errors if the eye moved horizontally during the memory period; however, errors of both vertical and horizontal components of memory-guided saccades were similar. Thus, inaccuracy of memory-guided saccades could not be simply attributed to failure to internally monitor change in horizontal gaze during the memory period. Instead, we propose that the greater saccadic errors which occurred when gaze changed during the memory period reflected a disruption of predictive mechanisms governing eye movements.

Rottach, Klaus G., Vallabh E. Das, Walter Wohlgemuth, Ari Z. Zivotofsky, and R. John Leigh. Properties of horizontal saccades accompanied by blinks. J. Neurophysiol. 79: 2895–2902, 1998. Using the magnetic search coil technique to record eye and lid movements, we investigated the effect of voluntary blinks on horizontal saccades in five normal human subjects. The main goal of the study was to determine whether changes in the dynamics of saccades with blinks could be accounted for by a superposition of the eye movements induced by blinks as subjects fixated a stationary target and saccadic movements made without a blink. First, subjects made voluntary blinks as they fixed on stationary targets located straight ahead or 20° to the right or left. They then made saccades between two continuously visible targets 20 or 40° apart, while either attempting not to blink, or voluntarily blinking, with each saccade. During fixation of a target located straight ahead, blinks induced brief downward and nasalward deflections of eye position. When subjects looked at targets located at right or left 20°, similar initial movements were made by four of the subjects, but the amplitude of the adducted eye was reduced by 65% and was followed by a larger temporalward movement. Blinks caused substantial changes in the dynamic properties of saccades. For 20° saccades made with blinks, peak velocity and peak acceleration were decreased by ∼20% in all subjects compared with saccades made without blinks. Blinks caused the duration of 20° saccades to increase, on average, by 36%. On the other hand, blinks had only small effects on the gain of saccades. Blinks had little influence on the relative velocities of centrifugal versus centripetal saccades, and abducting versus adducting saccades. Three of five subjects showed a significantly increased incidence of dynamic overshoot in saccades accompanied by blinks, especially for 20° movements. Taken with other evidence, this finding suggests that saccadic omnipause neurons are inhibited by blinks, which have longer duration than the saccades that company them. In conclusion, the changes in dynamic properties of saccades brought about by blinks cannot be accounted for simply by a summation of gaze perturbations produced by blinks during fixation and saccadic eye movements made without blinks. Our findings, especially the appearance of dynamic overshoots, suggest that blinks affect the central programming of saccades. These effects of blinks need to be taken into account during studies of the dynamic properties of saccades.

We measured the eye movements of three sisters with Niemann-Pick type C disease who had a selective defect of vertical saccades, which were slow and hypometric. Horizontal saccades, and horizontal and vertical pursuit and vestibular eye movements were similar to control subjects. The initial movement of oblique saccades was mainly horizontal and most of the vertical component occurred after the horizontal component ended; this resulted in strongly curved trajectories. After completion of the horizontal component of an oblique saccade, the eyes oscillated horizontally at 10–20 Hz until the vertical component ended. These findings are best explained by models that incorporate separate feedback loops for horizontal and vertical burst neurons, and in which the disease selectively affects vertical burst neurons.

Purpose The purpose of the current research is to understand if the different eye movement abnormalities in patients with the same neurologic disease are related to varied disease processes or, alternately, do different patients adopt different strategies to overcome a singular brain deficiency. Methods Using a magnetic search coil, we measured saccade dynamics, that is position and velocity waveforms, for patients diagnosed with spinocerebellar ataxia type 3 (SCA-3), also known as Machado-Joseph disease (MJD). Results We observed that the saccadic waveform of the majority of the SCA-3 patients (7 of 10) exhibited dynamic overshoot, with the eye passing the desired endpoint and making a rapid correction before coming to rest. Patients with normal waveforms, that is with no dynamic overshoot, had saccades with relatively low peak velocity. Conclusions Velocity feedback in a closed loop control system is essential for providing a fast response without overshoot. Lack of a velocity feedback or an imbalance between position and velocity gains yields a tradeoff between response time and overshoot. While the goal of a saccade is to get to the desired position, models based on animal research suggest that the saccadic control also incorporates a velocity feedback. Results presented here indicated that all SCA-3 patients had deviations in the saccadic waveform, albeit of two types, either slow saccades or dynamic overshooting saccades. Using saccadic models based on animal research can explain how a single deficit, that is a mismatched velocity control of the motor error due to the disease, can yield these two different abnormalities in human patients.

Objective: The aim of this study was to test whether elderly individuals underestimate the time that it will take them to cross a street by comparing estimated with actual road-crossing time. Background: In many developed countries, elderly people are overrepresented among pedestrian fatalities from motor vehicle accidents. There is surely more than one contributing factor to this phenomenon, and many have been offered. We propose that one additional factor may be that although older people are consciously aware that they no longer walk at the same pace as they once did, they do not take this fact into consideration when planning a street crossing. Method: We compared the ability of young and old pedestrians to estimate the time that it will take them to cross a street, using both prospective and retrospective time estimation. Results: A significant interaction was found between age group and crossing time. Among elderly participants, actual crossing times were significantly longer than both their precrossing estimation and their postcrossing estimation, which did not significantly differ from each other. In contrast, the undergraduate group’s crossing times did not display a significant difference across measurements. Conclusion: This study implies that even if older pedestrians correctly evaluate the road situation, they may nonetheless endanger themselves by underestimating the time that it will take them to cross the street. We suggest that minimizing this effect could be accomplished by educating seniors to the fact that they are not as fast as they once were and that this fact needs to be factored in to street-crossing decisions.

The aim of this study was to evaluate an interdisciplinary visual assessment for multiply challenged children diagnosed with cerebral palsy (CP).A comprehensive ophthalmological assessment together with a visual classification scale (VCS) and a questionnaire evaluating daily visual function were completed regarding 77 children (41 females, 36 males; age range 3-20y; mean age 8 y 3 mo [SD 4 y 3 mo]; Gross Motor Function Classification System [GMFCS] level V; Manual Ability Classification System level V) who were diagnosed with CP (79.2% spastic quadriplegia, 6.5% athetoid quadriplegia, 10.4% mixed type, 3.9% hemiplegia). All participants had severe to profound motor and intellectual disability and an inability to communicate consistently through either verbal or assisted communication. The interrater and test-retest reliability of the questionnaire and its validity in comparison with the VCS were examined. In addition, the contribution of ophthalmological testing in predicting daily visual function was assessed.The ophthalmological examination revealed three diagnostic subgroups: a group with cerebral visual impairment (CVI), a group with optic atrophy, and a group without visual impairment. The questionnaire was found to have high values of interrater reliability (interclass correlation coefficient [ICC]=0.873; 95% confidence interval [CI] 0.762-0.935) and test-retest reliability (ICC=0.988; 95% CI 0.964-0.996). Validity was established for the questionnaire factors: task-orientated visual function (r=0.802; 95% CI 0.669-0.885) and basic visual skills (r=0.691; 95% CI 0.504-0.816). The questionnaire provided information about daily visual performance not available from one-time ophthalmological testing, particularly for participants diagnosed with CVI. The visual performance scale significantly predicted daily visual function for all groups.This study highlights the benefits of implementing a diagnostic performance scale as well as a reliable functional questionnaire to achieve a precise visual assessment of children with severe neurological impairment.

The inattentive eye often will not notice it, but synchronization among human walking partners is quite common. In this first investigation of this phenomenon, we studied its frequency and the mechanisms that contribute to this form of "entrainment." Specifically, by modifying the available communication links between two walking partners, we isolated the feedback mechanisms that enable couples to synchronize their stepping pattern when they walk side-by-side. Although subjects were unaware of the research aims and were not specifically asked to walk in synchrony, we observed synchronized walking in almost 50% of the walking trials, among couples who do not usually walk together. The strongest in-phase synchrony occurred in the presence of tactile feedback (i.e., handholding), perhaps because of lower and upper extremity coupling driven in part by arm swing. Interestingly, however, even in the absence of visual or auditory communication, couples also frequently walked in synchrony while 180 degrees out-of-phase, likely using different feedback mechanisms. These findings may partially explain how patients with certain gait disorders and disturbed rhythm enhance their gait when they walk with a partner and suggest alternative interventions that might improve the stepping pattern. Further, this preliminary investigation highlights the relatively ubiquitous nature of an interesting phenomenon that has not previously been studied and suggests that further work is needed to better understand the mechanisms that entrain the gait of two walking partners and allows couples to walk in synchrony with minimal or no conscious effort.

Developmental dyslexia is a language-based learning disability with frequently associated non-linguistic sensory deficits that have been the basis of various perception-based theories. It remains an open question whether the underlying deficit in dyslexia is a low level impairment that causes speech and orthographic perception deficits that in turn impedes higher phonological and reading processes, or a high level impairment that affects both perceptual and reading related skills.We investigated by means of contrast detection thresholds two low-level theories of developmental dyslexia, the magnocellular and the fast temporal processing hypotheses, as well as a more recent suggestion that dyslexics have difficulties in sequential comparison tasks that can be attributed to a higher-order deficit. It was found that dyslexics had significantly higher thresholds only on a sequential, but not a spatial, detection task, and that this impairment was found to be independent of the inter-stimulus interval. We also found that the poor performance of dyslexics on the temporal task was dependent on the size of the required memory trace of the image rather than on the number of images. Our findings do not support the magnocellular theory and challenge the fast temporal deficit hypothesis. We suggest that dyslexics may have a higher order, dual mechanism impairment. We also discuss the clinical implications of our findings.

Eye movements during fixation of a stationary target prevent the adaptation of the photoreceptors to continuous illumination and inhibit fading of the image. These random, involuntary, small, movements are restricted at long time scales so as to keep the target at the center of the field of view. Here we use the Detrended Fluctuation Analysis (DFA) in order to study the properties of fixational eye movements at different time scales. Results show different scaling behavior between horizontal and vertical movements. When the small ballistics movements, i.e. micro-saccades, are removed, the scaling exponents in both directions become similar. Our findings suggest that micro-saccades enhance the persistence at short time scales mostly in the horizontal component and much less in the vertical component. This difference may be due to the need of continuously moving the eyes in the horizontal plane, in order to match the stereoscopic image for different viewing distance., Comment: 5 pages, 4 figures

We compared horizontal and vertical smooth pursuit eye movements in five healthy human subjects. When maintenance of pursuit was tested using predictable waveforms (sinusoidal or triangular target motion), the gain of horizontal pursuit was greater, in all subjects, than that of vertical pursuit; this was also the case for the horizontal and vertical components of diagonal and circular tracking. When initiation of pursuit was tested, four subjects tended to show larger eye accelerations for vertical as opposed to horizontal pursuit; this trend became a consistent finding during diagonal tracking. These findings support the view that different mechanisms govern the onset of smooth pursuit, and its subsequent maintenance when the target moves in a predictable waveform. Since the properties of these two aspects of pursuit differ for horizontal and vertical movements, our findings also point to separate control of horizontal and vertical pursuit. Copyright © 1996 Elsevier Science Ltd.

PURPOSE. Dyslexia is a language-based learning disability characterized by difficulties with reading, spelling, and writing. Persons with dyslexia often have deficits in processing rapid temporal sensory information. There is also evidence of sensorimotor deficits in persons with dyslexia. Whether these deficits include ocular motor problems is still an open question. Some previous studies have shown an increased saccadic latency in dyslexics, whereas others have not reproduced this finding. The purpose of the present study was to investigate saccadic latency in young adults with dyslexia during the double-step paradigm, a task that requires rapid sequential visual information processing and saccade generation. The study hypothesis was that dyslexics have a longer saccadic latency in the second orthogonal saccade, a task that nondyslexics parallel process and perform rapidly. METHODS. Eight students with dyslexia and eight age-matched control subjects participated in the study. Their eye movements were monitored with the scleral search coil technique in simple saccade trials and in the double-step paradigm. The second saccade was either orthogonal or colinear to the first. Intersaccadic interval and latency were calculated for the second saccade. RESULTS. No difference in saccadic latency was found for colinear second saccades; however, dyslexics had significantly longer latencies for orthogonal second saccades. This included a subset of subjects who had longer latencies for orthogonal than for colinear saccades. CONCLUSIONS. The findings indicate that under certain conditions, when the demand for rapid visual information processing is high and a rapid saccade sequence is required, some persons with dyslexia show ocular motor deficits manifested by longer saccadic latencies.

PURPOSE. The Duncker illusion, also known as induced motion, is the illusory component of an object's motion that results from background movement. The origins of this robust phenomenon are still subject to debate. The goal of this study was to examine the role eye movements play in its generation. METHODS. The Duncker illusion was generated by rear-projecting an LED target and a random-dot background onto a semi-translucent screen. Each moved under independent control of mirror galvanometers. The background was either stationary or moved vertically, whereas the target moved horizontally with various degrees of a vertical component. Using a two-alternative, forced-choice cancellation paradigm involving multiple interleaved staircases, seven human subjects quantified the illusion under a variety of conditions. These conditions included varying the exposure time from 50 to 200 ms. RESULTS. The strength of the illusion did not decrease, even when exposures too brief to generate eye movement were used. Four of the subjects showed no difference between long and short exposures (P > 0.12). In two the illusion was stronger for short exposures (P < 0.05), and in one the illusion was not quantifiable. There was little intrasubject variability across trial types, yet there was a large intersubject variability in the strength of the illusion. CONCLUSIONS. The illusion is robust in that it is perceived under a wide variety of conditions by all observers. By varying the parameters, it was possible to demonstrate that eye movements do not play a role in generating the illusion and that this robust illusion is most likely caused by the visual system attributing relative motion between target and background to target motion and ignoring any true background movement. The mechanism by which this occurs varies in degree between individuals.

In 10 human subjects, we measured the accuracy of saccades to remembered locations of targets that were flashed on a 20 × 30 deg random dot display, while they tracked a spot of light that stepped between three vertical locations. The background was either stationary or stepping horizontally in synchrony with vertical motion of the spot of light, a condition that induced a strong illusion of diagonal target motion. Memory-guided saccades were less accurate horizontally, but not vertically, when the background moved compared with when it was stationary. The horizontal component of memory-guided saccades correlated better with the position of the background when the target was flashed than with the position of the background at the end of the memory period. We conclude that the visual illusion corrupted the working memory of target location, but had a lesser effect on the estimate of gaze at the end of the memory period, which seemed to depend more on extraretinal signals.