Biomedical subjects

Zoï Kapoula

Publications and source records attributed to Zoï Kapoula.

25 records · Page 2Linked to original sources

PubMed2003

Gap effects on saccade and vergence latency.

To explore visual space, we make saccades, vergence, and, most frequently, combined saccade-vergence eye movements. The initiation of saccades is well studied, while that of vergence is less explored. Saccade latency is influenced by the fixation task: when the target appears simultaneously with the offset of the fixation point, latencies tend to be regular, whereas the introduction of a gap period before target onset causes the emergence of express latencies (80- to 120-ms). This study examines in ten normal adults whether the gap paradigm has a similar effect on the latency of vergence and combined eye movements. The second goal is to identify contextual factors that favor the emergence of short latencies, by comparing a condition in which gap and simultaneous trials were performed in separate blocks (pure blocks) with a condition in which the two types of trials were interleaved randomly (mixed blocks). The results are: (1) the gap paradigm reduced similarly (by approximately -30 ms) the mean latency of saccades, convergence, divergence, and both the saccadic and vergence components of combined eye movements; (2) the gap paradigm was responsible for the emergence of 80- to 120-ms latencies for saccades and divergence (pure or combined), but rarely for convergence; (3) inspection of the latency distributions showed that such short latencies formed a clearly distinct population, different from anticipatory responses or regular latencies, for saccades (pure or combined) but not for pure vergence; importantly, distinct express latencies were found also for the convergence and divergence components of combined eye movements; (4) no difference was found for the group of subjects between pure and mixed blocks, but the latter yielded shorter latencies for some subjects, suggesting an idiosyncratic phenomenon. We suggest that distinct express latencies are specific to saccades and could correspond to a specific mode of saccade initiation. Interestingly, the express mode of triggering can be transferred to the vergence component in the ecological condition in which saccade is combined with vergence.

Adolescent↗

PubMed2003

Oculomotor consequences of feeble image size inequality at near reading distance.

Reading and working with a computer screen are activities of everyday life that take place at near vision. This study examines whether at such a near distance, normal subjects are capable of modifying the natural conjugacy of their saccades when exposed to a feeble image size inequality of 2%; similar inequality exists for persons who wear spectacles of slightly different power for the two eyes. Subjects were seated at 40 cm in front of a screen where a random dot pattern was projected. They were asked to make saccades of 7.5 degrees and 15 degrees along the horizontal and vertical principal meridians and horizontal saccades between secondary and tertiary positions in the upper and lower field. Five subjects performed the experiment with a 2% overall reduction lens inserted over their dominant eye; three subjects participated in a second experiment with an overall magnification lens of 2% also inserted in front of the dominant eye. The results showed a persistent decrease or increase in the size of the saccade of the dominant eye that was subject dependent for horizontal saccades, but consistent over subjects for vertical saccades. Persistent disconjugacy, at least for vertical saccades, is interpreted as evidence of learning.

Analysis of Variance↗

PubMed2003

Saccades, vergence and combined eye movements in a young subject with Congenital Central Hypoventilation Syndrome (CCHS).

PURPOSE: To study saccades, vergence and combined eye movements in a case of Congenital Central Hypoventilation Syndrome. METHODS: A 16-year-old girl with congenital partial third cranial nerve palsy, with ptosis and divergent strabismus dependent on viewing distance, participated in this study. A first operation for her ptosis was done seven years ago and an operation for her strabismus was done four years ago. The day of our oculomotor test, the patient had a residual exotropia of 12 prism diopters, mild amblyopia of the left eye and no binocular vision. LEDs on a table placed at eye level were used to stimulate saccades, pure vergence along the median plane and combined saccade-vergence movements. Horizontal eye movements from both eyes were recorded simultaneously with a photoelectric device (Bouis Oculometer). RESULTS: The binocular coordination of saccades in this subject was unstable and more variable than normal, and there was divergent post-saccadic drift, i.e., in the direction of her residual deviation. The patient had difficulty making movements in space, particularly vergence eye movements. Pure saccades and combined movements showed abnormally long latencies and marked hypometrias. The velocity of pure saccades was normal. In contrast, the velocity of saccades in the combined movements was abnormally slow. CONCLUSION: The long latency and the low accuracy of the eye movements in natural space indicate a general deficit in the central circuitry that controls the initiation and programming of all these types of eye movements. The absence of pure vergence and the slowness of the saccades in the combined movements could be due to a brainstem deficit specific to the vergence oculomotor system.

Adolescent↗

PubMed2003

Effects of TMS over the right prefrontal cortex on latency of saccades and convergence.

PURPOSE: The prefrontal cortex (PFC) is known to inhibit unwanted saccades through its connections to the superior colliculus (SC). Indeed, transcranial magnetic stimulation (TMS) of the PFC decreases saccade latency by increasing the rate of express saccades. This study examined whether a similar phenomenon exists for vergence. METHODS: In a gap paradigm, six healthy subjects were asked to look at LEDs placed in a horizontal plane and to make lateral saccades, pure convergence along the median plane, and combined eye movements. Eye movements were recorded binocularly. TMS was applied over the right (r)PFC synchronously with the onset of the target. In a control condition, TMS was applied over the motor cortex (MC). RESULTS: TMS over the MC had no effect on the latency of any type of eye movements. In contrast, TMS over the rPFC (1) decreased significantly (P = 0.00367) the latency of contralateral pure saccades, (2) had no effect on the latency of pure convergence, (3) and caused a mild decrease in the latency of both the saccadic and the convergence components of combined eye movements, and the effect was bilateral. Decreased latencies were mainly due to an increase of the rate of express movements. CONCLUSIONS: The inhibition exerted by PFC over SC and preventing express movements from occurring is presumably a saccade-specific mechanism. When the saccade is combined with convergence, the express triggering can be transferred to a certain extent to the convergence.

Adult↗

PubMed2002

EEG cortical potentials preceding vergence and combined saccade-vergence eye movements.

Previous event-related potential (ERP) studies of eye movements were restricted to saccades, the rapid conjugate movements used to change direction of fixation. Our study explored ERP activity for vergence eye movements used for the adjustment of the angle of the visual axes to the distance of the object. These movements are essential when exploring the natural 3D world. Subjects made the following visually guided movements to LED targets: pure convergence or divergence along the median plane, pure lateral saccades within the same distance, and combined movements (lateral and divergent or convergent). ERPs were recorded from 14 surface electrodes and were analyzed for 200 ms prior to the onset of the eye movement. The highest activation was observed prior to vergence. Activation was diffused and peaked at 50 ms prior to the onset of vergence. Combined vergence and sacccadic movements revealed a composite pattern of ERP activity from both saccades and pure vergence. These findings suggest a cortical substrate for vergence eye movements in humans that is engaged in the natural exploration of visual space.

Adult↗

PubMed2002

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

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.

Adolescent↗

PubMed2002

The latency of saccades, vergence, and combined eye movements in children and in adults.

PURPOSE: To examine the latency of eye movements in three-dimensional space (saccade, vergence, and combined saccade-vergence) in children and adults. METHODS: Fifteen normal children (4.5-12 years of age) and 15 normal adults (22-44 years of age) were tested. A standard paradigm was used to elicit pure lateral saccades at far and close viewing distance, pure vergence (convergence and divergence), and saccade combined with vergence movements. Horizontal eye movements from both eyes were recorded simultaneously by the oculometer, a photoelectric device. RESULTS: The mean latency in saccades, vergence, and combined eye movements was longer in children than in adults; the variability of such latency values was also larger in children. There was a progressive decrease with age in mean latency. All latencies approached or reached adult levels at approximately 10 to 12 years of age. Latency of saccades at close viewing distance was shorter than that at far in both adults and children. Convergence latency was longer than divergence latency in adults and most of the children. Latency of components of combined movements was longer than that of corresponding pure movements. Children initiated combined movements by triggering the vergence component first, whereas adults did not show a dominant pattern. The percentage of synchronous start of the two components was significantly higher in adults. CONCLUSIONS: Saccade- and vergence-triggering mechanisms are distinct and mature progressively and in parallel with age. The capacity for synchronization of the two components of combined eye movements develops more slowly and remains below adult level, even at the age of 12 years.

Adult↗