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Practical Neurology Oct 2018Ocular neuromyotonia is a rare, albeit treatable, ocular motor disorder, characterised by recurrent brief episodes of diplopia due to tonic extraocular muscle...
Ocular neuromyotonia is a rare, albeit treatable, ocular motor disorder, characterised by recurrent brief episodes of diplopia due to tonic extraocular muscle contraction. Ephaptic transmission in a chronically damaged ocular motor nerve is the possible underlying mechanism. It usually improves with carbamazepine. A 53-year-old woman presented with a 4-month history of recurrent episodes of binocular vertical diplopia (up to 40/day), either spontaneously or after sustained downward gaze. Between episodes she had a mild left fourth nerve palsy. Sustained downward gaze consistently triggered downward left eye tonic deviation, lasting around 1 min. MR scan of the brain was normal. She improved on starting carbamazepine but developed a rash that necessitated stopping the drug. Switching to lacosamide controlled her symptoms.
Topics: Female; Fixation, Ocular; Humans; Isaacs Syndrome; Middle Aged; Ocular Motility Disorders
PubMed: 29467180
DOI: 10.1136/practneurol-2017-001866 -
Journal of Autism and Developmental... May 2016We examined the factors that influence ocular fixation control in adults with autism spectrum disorder (ASD) including sensory information, individuals' motor...
We examined the factors that influence ocular fixation control in adults with autism spectrum disorder (ASD) including sensory information, individuals' motor characteristics, and inhibitory control. The ASD group showed difficulty in maintaining fixation especially when there was no fixation target. The fixational eye movement characteristics of individuals were consistent regardless of the presence or absence of a fixation target in the controls, but not in the ASD group. Additionally, fixation stability did not correlate with an ability to suppress reflexive saccades measured by an antisaccade task. These findings suggest that ASD adults have deficits in converting alternative sensory information, such as retinal signals in the peripheral visual field or extraretinal signals, to motor commands when the foveal information is unavailable.
Topics: Adult; Autism Spectrum Disorder; Female; Fixation, Ocular; Humans; Male; Ocular Motility Disorders; Photic Stimulation; Saccades; Visual Fields
PubMed: 26739354
DOI: 10.1007/s10803-015-2688-y -
Acta Oto-rhino-laryngologica Belgica 1998Ocular fixation test and ocular fixation index (OFI) never have been interpreted in terms of mathematical models, despite their widespread diffusion. However, ocular... (Review)
Review
Ocular fixation test and ocular fixation index (OFI) never have been interpreted in terms of mathematical models, despite their widespread diffusion. However, ocular fixation is a typical case of visual-vestibular interaction, and mathematical models have proven very helpful in interpreting some mechanisms of this interaction, e.g. those of the optokinetic-vestibular interaction. In the present paper, a first attempt is proposed toward a model interpretation of OFI. By using very simple mathematical models, the hypothesis is tested that visual suppression of vestibular nystagmus results from direct action of smooth pursuit system (SPS). The aim is to draw consequences and recognize possible limits of this hypothesis. Dependence of OFI on SPS performance is examined. Although the available experimental data are insufficient for comprehensive validation of the model, the results agree with the current interpretations. In particular, quantitative support is given to the sensitivity of OFI to central vestibular diseases. Although the interpretation of visual suppression and OFI in terms of mathematical models is still at a very preliminary stage, models may provide a theoretical reference framework for the interpretation of new experimental results and/or suggest new test protocols.
Topics: Fixation, Ocular; Humans; Models, Theoretical; Reflex, Vestibulo-Ocular
PubMed: 9581191
DOI: No ID Found -
Experimental Brain Research Feb 2002The macaque lateral intraparietal area (LIP) has been implicated in visuospatial attention and saccade planning. Since area LIP also contains a representation of the...
The macaque lateral intraparietal area (LIP) has been implicated in visuospatial attention and saccade planning. Since area LIP also contains a representation of the central visual field, we investigated its possible role in fixation and foveal attention in a visual fixation task with gap (momentary disappearance of fixation point). In addition to the expected visual neurons ( n=119), two main categories were identified: (1) cells responding tonically both during the presence and momentary absence of the fixation stimulus( n=47); a subset of these neurons studied in a saccade task showed perisaccadic inhibition in half of the cases (14/27). The timing of this inhibition, however, is only loosely related to saccade timing; (2) cells responding mainly to the absence of the fixation stimulus, with either abrupt or gradual onset of activity during the gap ( n=62). During saccades, these neurons showed presaccadic buildup and/or postsaccadic activity, which was spatially tuned in about half of the tested cells (28/53). Ninety-one percent of the cells in the first category and 59% of the cells in the second category were located in the dorsal portion of area LIP (LIPd). These results are consistent with the hypothesis of an oculomotor-attentional network contributing to fixation engagement and disengagement in a subregion of LIP.
Topics: Animals; Fixation, Ocular; Macaca fascicularis; Macaca mulatta; Neurons; Parietal Lobe; Photic Stimulation; Visual Acuity
PubMed: 11845247
DOI: 10.1007/s00221-001-0954-z -
Journal of Pediatric Ophthalmology and... 2022
Topics: Humans; Fixation, Ocular
PubMed: 35611827
DOI: 10.3928/01913913-20220314-03 -
Ophthalmic & Physiological Optics : the... Oct 1992A-scan readings must be taken along the visual axis for accurate axial length measurement. Various fixation targets, which ideally should not induce accommodation, are... (Comparative Study)
Comparative Study
A-scan readings must be taken along the visual axis for accurate axial length measurement. Various fixation targets, which ideally should not induce accommodation, are used to limit eye movements. In this study results using the Humphrey biometer under different fixation conditions were compared to establish the most suitable target. We also investigated corneal applanation effects by comparing optical and ultrasonic measurements of anterior chamber depth. We examined 12 randomly selected normal eyes of 12 young subjects. Three A-scans were recorded for each of five fixation conditions: spotlight at 6 m; Snellen letter at 6 m; solid probe's built-in green fixation target; Snellen letter at 6 m viewed through a -4.00 DS lens; spotlight at 6 m under cycloplegia (the comparison condition). Variability 'within' each fixation condition, estimated by the standard deviation for each subject, was equal throughout the 12 subjects for each fixation condition. Also variation was independent of size of the ocular dimension. The good agreement between the comparison condition and optical anterior chamber depth measurements indicated that the solid probe produced little applanation. Differences 'between' fixation conditions were investigated. It was concluded that a spotlight or letter at 6 m provides a suitable fixation target for biometry. Built-in fixation targets can produce significant errors.
Topics: Adult; Anterior Chamber; Biometry; Eye; Female; Fixation, Ocular; Humans; Male; Reproducibility of Results; Ultrasonography
PubMed: 1293540
DOI: No ID Found -
American Journal of Ophthalmology Dec 1976A mirror is the ideal fixation device for an ophthalmoscopic examination: it is the essense of simplicity, and there is nothing the patient would rather watch than...
A mirror is the ideal fixation device for an ophthalmoscopic examination: it is the essense of simplicity, and there is nothing the patient would rather watch than himself.
Topics: Fixation, Ocular; Humans; Methods; Ophthalmoscopy
PubMed: 998709
DOI: 10.1016/0002-9394(76)90076-3 -
Current Opinion in Neurology Feb 2001Our detailed understanding of the physiology and anatomy of the ocular motor system allows an accurate differential diagnosis of pathological eye movement patterns. This... (Review)
Review
Our detailed understanding of the physiology and anatomy of the ocular motor system allows an accurate differential diagnosis of pathological eye movement patterns. This review covers important clinical studies and studies in basic research relevant for the neurologist published during the past year.
Topics: Animals; Fixation, Ocular; Humans; Muscular Diseases; Oculomotor Muscles; Pursuit, Smooth; Reflex, Vestibulo-Ocular; Saccades; Vision, Binocular
PubMed: 11176211
DOI: 10.1097/00019052-200102000-00002 -
Aviation, Space, and Environmental... Oct 2002This experiment had two purposes. The first purpose was to compare ocular fixation during eye tracking, head tracking, and head tracking with a visual cue to head...
PURPOSE
This experiment had two purposes. The first purpose was to compare ocular fixation during eye tracking, head tracking, and head tracking with a visual cue to head position. The second purpose was to compare head tracking with and without a visual cue to head position.
METHODS
Eleven subjects tracked a pseudo-random laser target in three conditions. In one condition (Condition 1), subjects tracked the target primarily with the eyes. In a second condition (Condition HT), subjects tracked the target with the head but no visual cue to head position was provided. In the final condition, subjects tracked the target with the head and were given a visual cue to head position (Condition HR).
RESULTS
On average, ocular fixation was worst in Condition HR and similar in Condition 1 and Condition HT. Mismatches in target and head velocity greater than 60 degrees x sec(-1) occurred more frequently in Condition HR than in Condition HT.
CONCLUSIONS
Ocular tracking of a pseudo-random target is adversely affected in a minor way by head movement, but tracking declines significantly when head tracking is performed with a visual cue to head position. In terms of velocity matching, head tracking is also adversely affected by a head position cue.
Topics: Adult; Aerospace Medicine; Cues; Eye Movements; Female; Fixation, Ocular; Head Movements; Humans; Male
PubMed: 12398268
DOI: No ID Found -
Advances in Neurology 1998FOS is a relatively recently described specific mode of precipitation of seizures and paroxysmal EEG abnormalities. Elimination of central vision and fixation, even in... (Review)
Review
FOS is a relatively recently described specific mode of precipitation of seizures and paroxysmal EEG abnormalities. Elimination of central vision and fixation, even in the presence of light, induces high-amplitude occipital or generalized paroxysmal discharges. FOS is suggested on routine EEG by abnormalities that consistently occur as long as the patient's eyes are closed but not when the eyes are open. The model example of FOS is early-onset and late-onset BCEOP. Idiopathic and cryptogenic generalized epilepsies with FOS have been described. Scotosensitive epilepsy implies seizures and EEG abnormalities induced by the complete elimination of retinal light stimulation, and most cases described as scotosensitive are probably FOS. FOS has characteristics opposite to those of photosensitive epilepsies, but conversion from one to the other or co-existence may rarely occur. The underlying mechanisms of FOS are not known, but they may be related to an abnormality of the alpha-rhythm generators.
Topics: Animals; Electroencephalography; Epilepsy; Fixation, Ocular; Humans; Photic Stimulation
PubMed: 9385419
DOI: No ID Found