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At least 19 recordsLinked to original sources
PubMed1991

Trochlear unit activity during ocular convergence.

1. Ocular convergence is usually accompanied by excyclotorsion of the eyes. Furthermore, the magnitude of cyclotorsion is dependent on the elevation of the eyes. The reason for this excyclotorsion during convergence is not understood. 2. Excyclotorsion could be produced by either increased activity in the inferior oblique muscle or decreased activity in the superior oblique muscle. An earlier study indicated that convergence may also be accompanied by a temporal (lateral) translation of the eye. This observation is more consistent with a relaxation of the superior oblique than contraction of the inferior oblique. 3. This hypothesis was tested by recording the activity of 31 neurons in the trochlear nucleus, which contains the superior oblique motoneurons. This was done in alert monkeys that were trained to make both versional and vergence eye movements. In addition, the cyclotorsion associated with convergence was measured in one of these monkeys. 4. A consistent excyclotorsion associated with convergence was observed. Trochlear unit activity decreased during convergence in all cells tested. The magnitude of this decrease was significantly greater than that seen with conjugate adduction. Furthermore, the size of the decrease varied systematically with ocular elevation in a manner that was consistent with earlier measures of cyclotorsion during convergence. 5. These results suggest that the excyclotorsion seen during convergence, and perhaps the lateral translation of the eye, are due to a relaxation of the superior oblique muscle. This relaxation during convergence is greater than that which accompanies similar conjugate movements of the eyes. We hypothesize that this peculiar pattern of muscle innervation has a motor rather than sensory function.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Extrastriate cortical neurons correlated with ocular convergence in the cat.

Responses of neurons in the lateral suprasylvian area to visual stimulation in association with ocular convergence were studied in eight alert cats trained to track a visual target moving in depth. Activities of 18 (3%) of 659 cells were related to ocular convergence. These 18 neurons were divided into two groups: activities of seven neurons (40%) correlated with peak velocities of convergence eye movement at both fast and slow target speeds (group I), while those of five neurons (30%) correlated with them only at faster target speed (group II). Activities of six other neurons correlated with peak velocity of ocular convergence at faster target speed but were not tested at slower speed. Activities of four group-I neurons (60%) did not or only weakly correlate with lens accommodation, while those of four group-II neurons (80%) correlated with peak velocity or amplitude of lens accommodation. It can therefore be concluded that the four group-I neurons are primarily related to ocular convergence. Other cells were either convergence-related, lens accommodation-related or both. It is suggested that these different types of neurons contribute in combination to optimal control of convergence eye movement.

Accommodation, Ocular↗
PubMed2002

Missing lateral rectus force and absence of medial rectus co-contraction in ocular convergence.

For a given position of the eye in the orbit, most abducens motoneurons (LRMNs) fire at higher rates in converged gaze than when convergence is relaxed, implying that lateral rectus (LR) muscle force will be higher for a given eye position in convergence. If medial rectus (MR) muscle force balances LR force, it too would be higher in convergence, that is, LRMN recording studies predict horizontal rectus co-contraction in convergence. Three trained rhesus monkeys with binocular eye coils and custom muscle force transducers (MFTs) on LR and MR of one eye alternately fixated near (approximately 7 cm) and far (200 cm) targets with vergence movements of 20-30 degrees. Tonic muscle forces were also measured during conjugate fixation of far targets over a 30 x 30 degrees field. MFT characteristics and effects on oculomotility were assessed. Contrary to predictions, we found small (<1 g) decreases in both LR and MR forces in convergence, for those gaze positions that were used in the brain stem recording studies. This missing LR force paradox (higher LRMN firing rates in convergence but lower LR forces) suggests that motoneurons or muscle fibers contribute differently to oculorotary forces in converged and unconverged states, violating the final common path hypothesis. The absence of MR co-contraction is consistent with, and supports, the missing LR force finding. Resolution of the missing LR force paradox might involve nonlinear interactions among muscle fibers, mechanical specialization of muscle fibers and other articulations of the peripheral oculomotor apparatus, or extranuclear contributions to muscle innervation.

Animals↗
PubMed1989

Abducens internuclear neurons carry an inappropriate signal for ocular convergence.

1. Single-unit recording studies in alert Rhesus monkeys characterized the vergence signal carried by abducens internuclear neurons. These cells were identified by antidromic activation and the collision of spontaneous with antidromic action potentials. The behavior of abducens internuclear neurons during vergence was compared with that of horizontal burst-tonic fibers in the medial longitudinal fasciculus (MLF) and to that of a large sample of unidentified abducens cells (presumably both motoneurons and internuclear neurons). 2. The results indicate that abducens internuclear neurons and lateral rectus motoneurons behave similarly during vergence eye movements: the majority of both groups of cells decrease their firing rate for convergence eye movements: a minority show no change for vergence. This finding is strongly supported by recordings of horizontal burst-tonic fibers in the MLF, the majority of which decrease their activity significantly for convergence eye movements. 3. These findings indicate that a net inappropriate vergence signal is sent to medial rectus motoneurons via the abducens internuclear pathway. Because medial rectus motoneurons increase their activity appropriately during symmetrical convergence, this inappropriate MLF signal must be overcome by a more potent direct vergence input. 4. Overall, both abducens internuclear neurons and lateral rectus motoneurons decrease their activity for convergence less than would be expected based on their conjugate gain. This implies that some degree of co-contraction of the lateral and medial rectus muscles occurs during convergence eye movements. 5. Some horizontal burst-tonic MLF fibers decrease their activity more for convergence than any recorded abducens neuron. These fibers may arise from cells in the nucleus prepositus hypoglossi or vestibular nuclei.

Abducens Nerve↗
PubMedDate not supplied

Eye position signals in the abducens and oculomotor nuclei of monkeys during ocular convergence.

Many neurons in oculomotor pathways encode signals related to eye position. For example, motoneurons in the third, fourth, and sixth cranial nuclei discharge at highly regular rates during fixation intervals. During fixations of far targets, their tonic discharge is linearly related to conjugate eye position. Previous studies provided evidence that premotor cells in brainstem pathways also encoded conjugate eye position. McConville et al. (this volume), however, measured eye movements during binocular fixations when the eyes were converged and concluded that the position signal encoded by premotor position-vestibular-pause (PVP) cells in the vestibular nuclei is related to monocular (right or left) eye position rather than to conjugate eye position. This surprising relationship would not have been noticed in earlier studies that measured the movements of only one eye (using a single eye coil) or that measured only the conjugate movements of the two eyes (using bitemporal EOG electrodes). How general a feature of oculomotor signal processing is this finding? In this paper, we re-examine the eye position signal in abducens and oculomotor neurons when the movements of the two eyes are conjugate and when they are disjunctive and therefore disassociated. The data suggest that abducens neurons (AMNs and AINs) and oculomotor neurons (putative medial rectus motoneurons), unlike PVP cells, are not monocular but encode mixtures of right and left eye position signals.

Abducens Nerve↗
PubMed2004

Relationship between mandibular deviation and ocular convergence.

Recent studies have confirmed the relationship between head posture, mandibular position and visual focusing. A case-controlled study was conducted to assess the occurrence of ocular convergence defects between subjects with functional mandibular latero-deviation and healthy subjects in pediatric age. Sixty subjects (the study group) presented mandibular latero-deviation classified as functional according to the use of a clinical examination and frontal and basal tele-radiography. Sixty subjects without functional mandibular laterodeviation (control group) were selected randomly from all subjects seeking pediatric dental care and matched by gender and age to study group. All one hundred and twenty subjects were submitted to orthoptic tests performed by the same operator. These results seemed to confirm that in mandibular latero-deviation subjects ocular convergence defects occurred in greater frequency than in controls underlining the importance of role of pediatric dentistry among interdisciplinary cooperation.

Case-Control Studies↗
PubMed1998

Judging distance from ocular convergence.

Subjects misjudge distances considerably when forced to rely on extra-retinal information. Nevertheless, they can reproducibly set a target to the same distance as a reference, or to double or half that distance, even when they have to look back and forth between them because they are prevented from seeing one when looking at the other. Our explanation for this apparent discrepancy is that people have access to reasonably accurate extra-retinal information on changes in ocular convergence, but can only use this information to judge distances if they had reliable information about the orientation of the eyes before the convergence changed.

Convergence, Ocular↗
PubMed2003

[Asthenopic complaints and ocular convergence at the computer workstation: new test procedures for practice and research].

BACKGROUND: The present paper summarizes a series of ergonomic studies on the relation between asthenopic complaints and binocular vision at the computer workstation. In particular, the paper reports on measurements of the accuracy of ocular convergence during fixation of central fusion stimuli (i. e. fixation disparity) as a function of viewing distance. METHODS: Different versions of subjective tests for fixation disparity (using dichoptic nonius lines) are presented, including a computer-controlled procedure (the eye-test PC). RESULTS: These new tests suggest that non-presbyopic subjects with normal binocular vision may suffer from asthenopic complaints if they have - in near vision - an exo fixation disparity larger than average. CONCLUSION: In these cases, the stress exercised on the convergence system can be reduced by using a longer viewing distance at the workplace.

Accommodation, Ocular↗
PubMed1992

Ocular convergence-related neuronal responses in the lateral suprasylvian area of alert cats.

Neuronal spike discharges were recorded from the lateral suprasylvian (LS) area while ocular convergence was elicited in five alert cats. Ocular convergence was elicited by presenting a visual target moving in depth. Cats were rewarded for convergence eye movement. In 9 out of 426 cells sampled in the caudal postero-medial LS area, the number of spikes was positively correlated with the peak eye velocities during ocular convergence. Significant correlation was found mostly within 400 ms preceding the moment at which the maximum velocity of ocular convergence was obtained. The result favors the hypothesis that the LS area plays an important role in the integrative control of ocular convergence.

Animals↗
PubMed1996

Roles of the lateral suprasylvian cortex in convergence eye movement in cats.

Ocular convergence and lens accomodation were evoked by microstimulation in the lateral suprasylvian area (LS cortex) in the parieto-occipital cortex in the cat. Electrolytic lesions in LS cortex reduced the amplitude and velocity of ocular convergence. Neurons in LS cortex discharged in relation to ocular convergence and/or lens accommodation. These results support the hypothesis that the LS cortex plays an important role in controlling ocular convergence The LS cortex receives visual inputs from cortical visual areas 17, 18 and 19, and in addition from the superior colliculus through the LP nucleus of the thalamus. Electrophysiological recordings have revealed that these visual inputs, which include cues about 3-dimensional target motion, are integrated in the LS cortex. The integrated output from LS cortex may provide the brainstem motor centers with the neural signals that facilitate eye movements, especially when the target is moving at high speeds. Outputs from the LS cortex travel directly to brainstem structures including the superior colliculus and pretectum. Evidence from monkey suggests that information may also travel to the mesencephalic reticular formation, where neurons have been recorded that are related to ocular convergence, lens accomodation or both. Although comparable data is lacking in the cat, it is suggested that the efferent circuit from the LS cortex to the motor nuclei in the brainstem included both the superior colliculus and the mesencephalic reticular formation. It is also suggested that this pathway is rather short, given that the mean latency of the early component of evoked disjunctive eye movements was approximately 60 ms.

Animals↗
PubMed1996

Changes in oculomotor functions before and after loading of a 3-D visually-guided task by using a head-mounted display.

Changes in visual and oculomotor functions were tested in eight young volunteer subjects after performing a 3-D visually-guided task for 25 min. The visual stimuli were given by using a head-mounted display. No significant change was detected in the AC/A ratio and the stereo acuity. Changes were found in refraction and ocular convergence. Slight but significant hyperopic changes were detected in refraction after the task. The mean amplitude of convergence eye movement elicited by test stimuli after the task was significantly changed in the pooled data. They were significantly reduced when the subjects were tested by the disparity step of 0.7 degrees, but significantly increased when tested by the step of 6 degrees. The mean amplitudes were not significantly changed after the task when the subjects were tested by the intermediate disparity steps of 1.5 and 3 degrees. In data obtained for each subject, the amplitude of ocular convergence evoked by test stimuli after the task was reduced significantly in most subjects. In the majority of subjects, however, the results were not consistently significant when they were tested by step stimuli with different disparities. In only a few subjects, the changes were consistently significant except when the largest disparity was tested. On the other hand, the mean peak velocities of ocular convergence after the task were not significantly changed in the pooled data. In individual subjects, the changes of velocities of ocular convergence evoked by test stimuli after the task were more variable: they increased in some subjects but decreased in other subjects. Consequently, in only one subject, both amplitudes and peak velocities of ocular convergence tested by the disparity steps of 0.7, 1.5 and 3 degrees were consistently reduced after the task. The changes in refraction or ocular convergence found in this study were relatively small, and were not in the pathological range. The significance of these data are discussed. The results of the present study provide the basis for the more detailed analyses of the human factor in the head-mounted display.

Adult↗
PubMed2003

Convergence defects in patients with temporomandibular disorders.

The aim of this study is to show the presence of a correlation between ocular convergence defects (OCD) and temporomandibular disorders (TMD) among a group of adult subjects. The group studied was made up of 48 subjects (12 males and 36 females). The average age was 35 with a range of 19-45 years of age. The subjects presented with TMD and muscular pain and/or dysfunction. Forty-eight subjects with TMD for the case study were matched by gender and age to 48 control subjects seeking routine dental care (control group). All the subjects were examined by the same orthoptist who classified the ocular convergence degree using two tests. The first test evaluated the distances (in centimeters) of the convergence near point (3-4 cm: normal; 5-7 cm: sufficient; > 7 cm: insufficient). The second test assessed the fusional convergence using a Berens prism test (> 25 diopters: normal; between 18-25: sufficient; < 18 diopters: insufficient). In the TMD group, 36 subjects (75%) showed a compromise of convergence: 13 (36%) were classified in the 5-7 degree range and 23 (48%) in the > 7 cm degree range. The Berens test showed ten subjects (28%) in the group < 18D and 26 (72%) in the group 18-25D. The control-group presented ten (21%) subjects with compromise of convergence: three classified in the group < 18D and seven in the group 18-25D. The TMD subjects presented a higher statistical percentage (p < 0.0001) of ocular convergence defects. The TMD patients also reported a strong association referred to specific signs and symptoms, i.e., limited maximal opening or myofascial pain. There were some subjective reports also of headaches and torcicollis (neck stiffness) which appeared significantly more frequently in subjects with a compromise of convergence. The study showed a much higher prevalence of ocular convergence defects in patients with head, neck, and shoulder pain.

Adult↗
PubMed2001

Distance perception within near visual space.

We investigated the perception of distance of visual targets with constant size and luminance presented between 20 and 120 cm from subjects' eyes. When retinal disparity cues were present, the subjects could reproduce very accurately the distance of a seen reference in this area. When only extraretinal information was available, distance perception was still correct for distances of 40 cm or less. However, distances beyond 60 cm were underestimated. When forced to evaluate the distance between a reference and themselves, e.g. when evaluating the absolute distance or half the distance or twice the distance of a reference, subjects used an egocentric plane of reference located on average 10.4 cm in front of their eyes. Measurements of binocular eye movements indicated a clear relationship between vergence angle and target distance. The egocentric plane of reference at 10.4 cm also corresponds to the maximum achievable vergence. These results suggest that ocular convergence can be used as a reliable cue for distance within the arm's reaching space.

Adult↗