Biomedical subjects

Zoi Kapoula

Publications and source records attributed to Zoi Kapoula.

5 recordsLinked to original sources

PubMed2005

Latency of saccades, vergence, and combined movements in children with early onset convergent or divergent strabismus.

The goal of this study was to examine latency of horizontal eye movements in the natural space (saccades, vergence, and combined saccade-vergence movements) in children with early onset convergent or divergent strabismus. Ten children were tested (8-11 years old): three with divergent strabismus, seven with convergent strabismus. A paradigm was used to elicit pure lateral saccades at far and near distance, pure vergence (convergence and divergence) and saccades combined with vergence movements. Horizontal eye movements from both eyes were recorded simultaneously by a photoelectric device (Oculometer, Dr. Bouis). The latency of saccades (at far and near distance), of vergence (convergence and divergence), and of combined movements greatly varies among subjects and has tendency to be longer than that observed in normal children of matched age, however, these differences reach significance in only a few cases. Children with divergent strabismus and residual gross binocular vision show abnormally longer vergence latencies than children with convergent strabismus without binocular vision. The initiation of combined movements does not show a dominant pattern, such as preceding vergence, as is found in normal children. Finally, strabismus surgery has no major effect on latencies. We conclude that there is no overall deficiency in latencies of eye movements in 3D space in children with early onset strabismus. Most likely, monocular visual input can be efficient as normal binocular vision for vergence movements. In a few subjects with divergent strabismus and fragile, intermittent binocular vision, latencies can be abnormally long, just because of the fragile binocular input and/or attention effort needs to use it. The absence of a pattern of initiation similar to normal children could be due to attention and fixation capabilities.

Case-Control Studies↗

PubMed2004

EEG activity related to preparation and suppression of eye movements in three-dimensional space.

Eight normal subjects made visually guided eye movements to four LED targets placed at two different distances (20 and 70 cm) and on either side (+/-10 degrees ) at 70 cm. Four types of eye movements were elicited: pure saccades, convergence, divergence, and combined (divergent saccades). EEG activity was recorded from 62 electrodes and was aligned to stimulus onset. A negativity peaked after 140 ms and was modulated according to the location of the stimulus in space and the type of movement prepared, mainly in central and posterior cortex. For saccade targets, we confirmed a stimulus-related negativity in the posterior and central cortical area, contralateral to target direction. For convergence and divergence targets, this negativity was bilaterally distributed; convergence targets activated a rather extended cortical network in the central and posterior area, while divergence targets activated a more confined posterior area, spreading ventrally from the occipital cortex. Cortical activity for combined targets was lateralised contralaterally to stimulus direction but its topography resembled more closely that after the divergence stimulus. When observers suppressed the relevant eye movement to the stimulus, EEG activity was enhanced on the right hemisphere, showing the more pronounced effect on the right occipital-temporal and central-parietal electrode sites.

Adult↗

PubMed2004

Monocular versus binocular vision in postural control.

OBJECTIVE: In previous studies about the control of posture there have been controversial findings. Our aim was to examine the role of monocular and binocular vision in controlling posture in quiet stance. METHODS: Twenty-eight normal subjects were tested. We used a force platform in measuring postural stability. In main experiment, postural stability was measured in four conditions: both eyes open (BEO), dominant eye open (DEO) non-dominant eye open (NDEO), and both eyes closed (BEC). In a further experiment, 11 subjects were tested in conditions where a vertical prism was placed in front of dominant eye. Prism was strong enough to cause diplopia. Our interest was to see, if diplopia affected the balance. RESULTS: In main experiment, at level of group the body-sway in any of the three ocular (viewing) conditions did not differ from each other. At level of individuals, binocular vision was more effective on controlling posture in only half of subjects. In prism experiment, relative to normal binocular viewing the postural stability was modified in both prism conditions, but there was no difference between monocular and binocular viewing with prism. CONCLUSION: In quiet stance and in subjects with perfect binocular vision and stereopsis, the benefit out of binocular viewing in postural stability is subject-dependent. At the level of group, monocular vision provides equally good postural stability as binocular vision.

Adult↗

PubMed2004

Eye movements in reading isolated words: evidence for strong biases towards the center of the screen.

Three experiments were conducted that compared the eye movement pattern to a peripheral word or letter string as a function of the position of an initial fixation stimulus relative to the center of the screen and the straight-ahead position. Results revealed a strong bias of the eye behavior towards the center of the screen, but not towards the straight-ahead position. Saccades were greater in length, and landed closer to the center of words/strings when launched from a position left of center than when launched from either center or right part of the screen. In addition, the initial saccade launch site was deviated to the right, or to the left of the initial fixation stimulus depending on where relative to the center of the screen the fixation stimulus was displayed. Data were interpreted with the assumption that saccades are programmed in a visual reference framework, with saccade amplitude being computed in relative coordinates. Further research will determine whether the observed bias generalizes to text reading.

Adult↗

PubMed2003

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

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.

Adult↗