https://repub.eur.nl/pub/73200/1-s2.0-0042698995001385-main-1-.pdf

Unequal amplitude saccades produced by aniseikonic patterns: effects of viewing distance.

The goal of the study was to test the quality of binocular coordination of saccades in children and adults, and its dependency upon the viewing distance. Fourteen normal children (4.5-12 years old) and 10 normal adults (22-44 years old) participated. Two distances were studied: far (150 cm) and close (20 cm). Horizontal saccades from both eyes were recorded simultaneously by a photoelectric device. The results show (i) poor binocular coordination of saccades in children is distance dependent: coordination is particularly poor at near and could compromise single binocular vision; and (ii) post-saccadic drift analysis indicates that stability of the eyes after the saccade as well as the quality of binocular alignment during fixation are poor in children, regardless of the viewing distance. The results provide a reference for the normal development of binocular motor control and have important implications for reading in young children. Language: en

Binocular coordination of saccades at far and at near in children and in adults.

Purpose To examine the quality of binocular coordination of saccades in children with various types of strabismus and the effect of strabismus surgery. Methods Eight subjects were tested (5-15 years old): five with convergent strabismus, three with divergent strabismus. A standard saccade paradigm was used to elicit horizontal saccades to target LEDs (5 degrees to 15 degrees ). Saccades from both eyes were recorded simultaneously with the photograph-electric Skalar IRIS device (Delft, The Netherlands). This task was run before and about 3 weeks after strabismus surgery. Results Before surgery, the difference in the amplitude of the saccade between the left eye and the right eye was larger (15% of the saccade size) than in normal children of similar age. After strabismus surgery for all subjects the squint angle was reduced, and the amplitude of the disconjugacy of saccades decreased significantly, dropping to normal values (6%). As in normal children, postsaccadic eye drift (both its conjugate and its disconjugate components) was small in amplitude. The difference compared with normal subjects was that disconjugate drift did not restore the disconjugacy of the saccade itself (e.g., in normal subjects drift is convergent when saccade disconjugacy is divergent and vice versa). Rather, disconjugate drift tended to drive the eyes toward static eye misalignment (e.g., the drift was mostly convergent for convergent strabismics and divergent for divergent strabismics). Surgery had no significant effect on either component of the drift. Conclusions The improvement of the binocular coordination of the saccades could be due, at least partially, to central adaptive mechanisms rendered possible by surgical realignment of the eyes. Separate mechanisms control the binocular coordination of saccades and the alignment of the eyes during the postsaccadic fixation period.

Binocular coordination of saccades in children with strabismus before and after surgery.

Aging does not affect the accuracy of vertical saccades nor the quality of their binocular coordination: A study of a special elderly group

We sought to determine if perceived depth can elicit vergence eye movements independent of binocular disparity. A flat surface in the frontal plane appears slanted about a vertical axis when the image in one eye is vertically compressed relative to the image in the other eye: the induced size effect (Ogle, 1938). We show that vergence eye movements accompany horizontal gaze shifts across such surfaces, consistent with the direction of the perceived slant, despite the absence of a horizontal disparity gradient. All images were extinguished during the gaze shifts so that eye movements were executed open-loop. We also used vertical compression of one eye's image to null the perceived slant resulting from prior horizontal compression of that image, and show that this reduces the vergence accompanying horizontal gaze shifts across the surface, even though the horizontal disparity is unchanged. When this last experiment was repeated using vertical expansions in place of the vertical compressions, the perceived slant was increased and so too was the vergence accompanying horizontal gaze shifts, although the horizontal disparity again remained unchanged. We estimate that the perceived depth accounted, on average, for 15-41% of the vergence in our experiments depending on the conditions.

http://lsr-web.net/Assets/NEIPages/FredMiles/pdfs/SheligaMiles03.pdf

Perception can influence the vergence responses associated with open-loop gaze shifts in 3D

The saccadic system has been traditionally regarded as two-dimensional (horizontal, vertical) and basically conjugate in the two eyes. However, saccades to disparate targets (e.g., targets in real three-dimensional space that are located in different directions and at different distances) are naturally disconjugate. We report here that memory-guided saccades to a disparate target flashed 1 s earlier become disconjugate following repeated trials. After 15 min of repetition, the disconjugacy persists even when the target to be remembered is no longer disparate. This suggests fast memory-based learning. Learning, however, fails to occur if, during the repetition trials, the memory delay is 2 s. These findings suggest that the saccadic system has access to a 3D representation of targets and is gifted with 3D short-term memory and learning capacity.

Disconjugate memory-guided saccades to disparate targets: evidence for 3D sensitivity

Fast disconjugate adaptations of saccades in microstrabismic subjects

This study examines squint change and the binocular coordination of horizontal and vertical saccades in an adult subject with incomitant strabismus (20 or 40 prism diopters) strongly depending on the eye used for fixating. The patient had no binocular vision and was diagnosed ‘horror fusionis’ since her childhood. We found the angle of horizontal squint to be smaller when the patient was fixating with the preferred eye than with the nonpreferred eye. The squint was smaller when both eyes viewed and one eye fixated attentionally than when the nonfixating eye was closed. This suggests the importance of binocular visual stimulation. We found no significant changes in the amplitude of the disconjugacy of the saccades. However, when the preferred, left eye fixated attentionally (under binocular viewing) or monocularly, the pattern of the disconjugacy changed: the majority of the saccades showed divergent disconjugacy. This pattern is qualitatively similar to that seen in normal subjects. In this patient, diver...

Role of attention and eye preference in the binocular coordination of saccades in strabismus

In normal subjects, saccade amplitude inequality can be induced almost immediately when the image is made larger for one eye. This disconjugacy allows binocular fusion at the point of regard despite the image size inequality. It persists under subsequent monocular viewing which suggests a fast adaptive mechanism. This study tests whether such disconjugacy can be induced in subjects with microstrabismus who do not have foveal fusion. Three microstrabismic subjects viewed a random dot pattern the size of which was 10% larger in one eye. Within 40 sec horizontal saccades became larger in the eye viewing the larger image by 4-10%; the induced disconjugacy persisted under subsequent monocular viewing. Thus, fast disconjugate adaptation is possible in microstrabismus demonstrating that foveal fusion is not necessary to achieve it.

Fast Disconjugate Adaptations Microstrabismic Subjects

Binocular saccades in response to briefly flashed, memorized disparate targets (different for the two eyes) become disconjugate following repeated trials. After 15 min of such training, the disconjugacy persists, even when the target to memorize is no longer disparate. This study examines the hypothesis that disparity memorization has a motor basis. We report here three experiments in which subjects were trained for 15-min periods. In experiment 1, subjects made no saccade after target presentation (static training); in experiment 2 subjects intended to make a saccade, but they actually made a saccade in only 10% or 20% of the trials; in experiment 3 subjects made anti-saccades. For all three experiments, the flashed target was disparate and the memory delay for each trial was 1 s. To examine the effects of learning for all three experiments, before and after training, we recorded memory-guided saccades to non-disparate targets (monocular viewing). Experiments 1 and 2 produced inconsistent (before/after training) changes in the disconjugacy of saccades. Thus, the disparity of potential saccade targets had no lasting effect on the disconjugacy of saccades if a saccade was not made. In contrast, the anti-saccades in experiment 3 developed a disconjugacy opposite to the disparity of the remembered target. These findings indicate that the execution of the saccade is necessary to memorize disparity of the target.

F. Zamfirescu

Papers

Disconjugate memory-guided saccades to disparate targets: evidence for 3D sensitivity

Fast disconjugate adaptations of saccades in microstrabismic subjects

Role of attention and eye preference in the binocular coordination of saccades in strabismus

Fast Disconjugate Adaptations Microstrabismic Subjects

Motor execution is necessary to memorize disparity.