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PubMed2005

Oculomotor studies of cerebellar function in autism.

Histopathological, neuroimaging and genetic findings indicate cerebellar abnormalities in autism, but the extent of neurophysiological dysfunction associated with those findings has not been systematically examined. Suppression of intrusive saccades (square wave jerks) and the ability to sustain eccentric gaze, two phenomena requiring intact cerebellar function, were examined in 52 high-functioning individuals with autism and 52 age- and IQ-matched healthy subjects during visual fixation of static central and peripheral targets. Rates of intrusive saccades were not increased in autism during visual fixation, and foveopetal ocular drift was also not increased when subjects held an eccentric gaze. The absence of gross disturbances of visual fixation associated with cerebellar disease in individuals with autism, such as increased square wave jerk rates and foveopetal drift when holding eccentric gaze, indicates that the functional integrity of cerebellar--brainstem networks devoted to oculomotor control is preserved in autism despite reported anatomic variations. However, increased amplitude of intrusive saccades and reduced latency of target refixation after intrusive saccades were observed in individuals with autism, especially when subjects maintained fixation of remembered target locations without sensory guidance. The atypical metrics of intrusive saccades that were observed may be attributable to faulty functional connectivity in cortico-cerebellar networks.

Adolescent↗
PubMed1978

Aetiological factors in dyslexia: II. ocular-motor programming.

A study is presented in which the preprogramming of saccadic eye movements is examined in normal (16 boys, 4 girls) and dyslexic subjects (19 boys, 1 girl), as well as the patterning of occular-motor differences between subjects, which is consistent with the previous study in which no differences in saccadic control are demonstrated between groups of subjects.

Child↗
PubMed2006

How active gaze informs the hand in sequential pointing movements.

Visual information is vital for fast and accurate hand movements. It has been demonstrated that allowing free eye movements results in greater accuracy than when the eyes maintain centrally fixed. Three explanations as to why free gaze improves accuracy are: shifting gaze to a target allows visual feedback in guiding the hand to the target (feedback loop), shifting gaze generates ocular-proprioception which can be used to update a movement (feedback-feedforward), or efference copy could be used to direct hand movements (feedforward). In this experiment we used a double-step task and manipulated the utility of ocular-proprioceptive feedback from eye to head position by removing the second target during the saccade. We confirm the advantage of free gaze for sequential movements with a double-step pointing task and document eye-hand lead times of approximately 200 ms for both initial movements and secondary movements. The observation that participants move gaze well ahead of the current hand target dismisses foveal feedback as a major contribution. We argue for a feedforward model based on eye movement efference as the major factor in enabling accurate hand movements. The results with the double-step target task also suggest the need for some buffering of efference and ocular-proprioceptive signals to cope with the situation where the eye has moved to a location ahead of the current target for the hand movement. We estimate that this buffer period may range between 120 and 200 ms without significant impact on hand movement accuracy.

Adult↗
PubMed1988

Long-term visual results after pars plicata lensectomy-vitrectomy for congenital cataracts.

We performed a pars plicata lensectomy-vitrectomy on 32 patients (47 eyes) with congenital cataracts. Ocular abnormalities, mainly nystagmus, strabismus, and microphthalmia, were present in 29 patients. No complications occurred intraoperatively or postoperatively in 39 eyes with up to 8 1/2 years' follow-up (average 2.2 years). The pars plicata approach is a good surgical technique for the management of congenital cataracts.

Adolescent↗
PubMed1997

Torsional eye movements in patients with skew deviation and spasmodic torticollis: responses to static and dynamic head roll.

We measured torsional eye movements induced by sinusoidal rotation or static tilt, of the head in roll while viewing a far or near target in 4 patients with skew deviation due to brainstem lesions, 4 patients with spasmodic torticollis (ST), 2 patients with unilateral eighth nerve section (VIIIS), and 10 normal subjects. Torsional nystagmus was present in all 4 patients with skew deviation. In subjects and patients, responses to both sinusoidal and static roll were larger while viewing the far target, consistent with factors dictated by geometry. Response gains to sinusoidal roll were abnormal in 3 patients with skew (increased in one, decreased in two), abnormal in 3 with ST (increased in 1, decreased in 2), and in abnormal both VIIIS patients (decreased). Greater abnormalities were evident in 3 skew patients while rolling away from the side of their brainstem lesions and in both VIIIS patients while rolling toward their lesioned ears. There were similar but less pronounced changes during static head roll. We conclude that patients with skew, ST, and VIIIS may all have abnormal ocular counter-rolling that is more evident during dynamic testing while viewing a far target. Such abnormalities endure because of the limited influence exerted by vision on torsional eye movements.

Adult↗
PubMed2003

Ocular scanning and perceptual size distortion in hemispatial neglect: effects of prism adaptation and sequential stimulus presentation.

When asked to compare two lateralized shapes for horizontal size, neglect patients often indicate the left stimulus to be smaller. Gainotti and Tiacci (1971) hypothesized that this phenomenon might be related to a rightward bias in the patients' gaze. This study aimed to assess the relation between this size underestimation and oculomotor asymmetries. Eye movements were recorded while three neglect patients judged the horizontal extent of two rectangles. Two experimental manipulations were performed to increase the likelihood of symmetrical scanning of the stimulus display. The first manipulation entailed a sequential, rather than simultaneous presentation of the two rectangles. The second required adaptation to rightward displacing prisms, which is known to reduce many manifestations of neglect. All patients consistently underestimated the left rectangle, but the pattern of verbal responses and eye movements suggested different underlying causes. These include a distortion of space perception without ocular asymmetry, a failure to view the full leftward extent of the left stimulus, and a high-level response bias. Sequential presentation of the rectangles and prism adaptation reduced ocular asymmetries without affecting size underestimation. Overall, the results suggest that leftward size underestimation in neglect can arise for a number of different reasons. Incomplete leftward scanning may perhaps be sufficient to induce perceptual size distortion, but it is not a necessary prerequisite.

Adaptation, Physiological↗
PubMed1987

Oculomotor and skeletal motor systems share one map of visual space.

Previous research has shown that cognitive and motor visual systems have separate maps of visual space because spatial values in them can be manipulated independently. Here we ask whether the motor map in turn can be divided into separate representations of space. Forty large saccadic eye movements in darkness resulted in significant ocular undershoot of a remembered eccentric target location, and a comparable amount of undershoot with manual pointing to the same remembered target. Saccadic and manual measures were also highly correlated within sessions as well as between sessions. Because pointing could be changed by manipulating only saccades, we conclude that the two systems share a single map of space.

Eye Movements↗
PubMed1978

Abnormal head positions due to ocular problems.

This paper involves the research of 30 patients, all of whom exhibited a head tilt, turn, or a combination of the two. We report the sensory aspects of 8 of these individuals and demonstrate the fusional ability of each patient. In the majority of the cases, the results were positive. It was found that most abnormal head positions were developed to maintain fusion.

Adolescent↗
PubMed1982

Neuro-otology of the lateral medullary infarct syndrome.

Nine patients had a lateral medullary infarction. Examination during the acute phase of the lesion to determine oculomotor and oculovestibular functions showed that all patients had hypermetric saccades and increased gain of the vestibulo-ocular reflex (VOR) to the side of the lesion and hypometric saccades and decreased gain of the VOR to the side opposite the lesion. These abnormalities may be the consequence of the isolation of the vestibular nuclei from the flocculus, with loss of saccadic and vestibular gains by the cerebellum.

Adult↗
PubMed1982

Non-linear interaction of the vestibular and the eye tracking system in man.

Oculomotor control in man was investigated during passive, sinusoidal, whole-body rotation under a conflict between the vestibulo-ocular reflex (VOR) and the eye tracking system (ETS), as to the appropriate direction of compensatory eye movements. ETS predominated at stimulus frequencies below 0.8 Hz, and VOR above 1.5 Hz. In the intermediate frequency range the dominance repeatedly flipped between ETS and VOR, suggesting that the interaction of the two systems is not linear, but rather governed by a switch.

Eye Movements↗
PubMed2001

Abnormal vestibular control of gaze and posture in a strain of a waltzing rat.

The waltzing behavior is usually attributed to vestibular dysfunction. However, the vestibular control of gaze and posture has not yet been measured quantitatively in any waltzing mutant. Therefore, this study was aimed at investigating the relationship between inner-ear morphology, the circling behavior, and the vestibular control of gaze and posture in a new strain of waltzing rats. Light- and electron-microscopy studies of these mutants did not reveal any structural abnormalities of the vestibular neural epithelia. In addition, the expression of Calretinin and 200-kD phosphorylated and non-phosphorylated neurofilaments was also found to be normal in the vestibular neural epithelia and ganglion cells. In contrast, the mutants showed severe dysfunctions of the vestibular control of gaze and posture. The skeletal geometry of the alert unrestrained animals was studied using cineradiography. At rest, waltzing rats held their heads tilted down: the horizontal semicircular-canal's plane was near the earth-horizontal's plane, instead of being tilted up as in Long Evans control rats. In addition, their cervical column was pitched more forward (33.6 degrees) than in the control group (6.9 degrees). The circling behavior was observed frequently, and the rats had episodes of circling in both directions. The episodes of circling amounted to an average of 17 turns, and the average angular velocity of the circling was 645 degrees/s. Unilateral labyrinthectomy induced the same postural and oculomotor syndromes in the waltzing and control groups. This indicates that the mutant vestibular nerve had a significant resting discharge before the lesion. Eye movements were recorded using acutely implanted search coils. Although waltzing rats were able to perform normal spontaneous eye movements, they showed a complete deficit of the horizontal vestibulo-ocular reflex (HVOR) and an impairment of the maculo-ocular reflex (MOR) during constant velocity, off-vertical axis rotation (OVAR). These results show, for the first time, that deficient transduction and/or processing of the horizontal-canal- and macular-related information can be causally related to the circling behavior and abnormal posture, respectively.

Animals↗
PubMed1999

Ocular tracking: behavior and neurophysiology.

'Ocular tracking' refers to visually driven, slow eye movements that stabilize moving images on the retina, thereby facilitating high acuity vision. Recent behavioral studies have shown that the primate brain produces several kinds of ocular tracking responses that operate precisely and consistently, with ultra-short latencies. Electrophysiological studies indicate that these tracking responses are mediated by a pathway that includes the medial superior temporal area of the cerebral cortex. Responses of neurons in this pathway are consistent with the short latencies and complex visual properties observed in behavioral studies of the tracking response.

Animals↗
PubMed1974

Vestibulo-ocular and optokinetic reactions to rotation and their interaction in the rabbit.

1. Compensatory eye movements due to sinusoidal yaw movements on a torsion swing were measured in alert rabbits. A range of combinations of frequencies (0.048-1.8 Hz) and amplitudes (1-25 degrees ) were used. Gain (cumulative slow phase eye movement amplitude/swing amplitude) and phase (eye position vs. swing position - 180 degrees ) were calculated from averaged records.2. Eyes were either closed (canal-ocular reactions only), open in earth-fixed visual surroundings (natural interaction of vestibular and optokinetic reactions), or looking at platform-fixed surroundings, which rotated with the animal (conflict situation). In some rabbits, the same stimulus programme was applied a month after bilateral destruction of the labyrinths (optokinetic reactions only).3. For canal-ocular reactions, no true threshold was found. Yet the system showed a small but systematic non-linearity which is tentatively explained by an acceleration-dependence of gain. For the higher frequencies (0.40-1.8 Hz) used, gain was 0.55-0.75, with a decrease at the lower frequencies, down to 0.16-0.33 at 0.048 Hz. The response showed a phase-lead of about 45 degrees at 0.048 Hz and was nearly in phase at 1-1.8 Hz. The long time constant of the cupula-endolymph system was estimated at about 3.3 sec.4. With earth-fixed visual surroundings a frequency-independent gain (range 0.55-0.82) with negligible phase error was found for the entire stimulus range tested. This natural combination of canal-ocular and optokinetic systems appears to function very efficiently, with mutual correction of the defects of the systems apart.5. With platform-fixed visual surroundings the canal-ocular system was severely inhibited and its non-linearities were markedly enhanced by the optokinetic system, especially when the torsion swing moved slowly.6. The general shape of input-output relations of optokinetic reactions after labyrinthectomy were similar to those found earlier in normal animals, but gain was subnormal for the entire stimulus range tested.

Animals↗
PubMedDate not supplied

Tonic downward and inward ocular deviation ipsilateral to pontine tegmental hemorrhage.

A 61-year-old man presented with coma and left hemiparesis. He was found to have tonic downward and inward deviation of the right eye, and a right lateral gaze palsy. He also had occasional downward bobbing movements of the right eye, and a partial bilateral upgaze paresis. CT showed a right pontine tegmental hemorrhage extending to the ipsilateral midbrain. Tonic ocular downward and inward deviation associated with pontine tegmental hemorrhage may be due to irritation of mesencephalic downgaze and convergence centers by rostral extension of the hematoma. Although 'eyes seeming to peer at the tip of the nose' is characteristic of thalamic hemorrhage, it may also be seen secondary to pontine tegmental hemorrhage.

Cerebral Hemorrhage↗
PubMed2005

Effect of angular acceleration on the localization performance of a remembered target.

Both the influence of a remembered "earth-fixed" target (RT) on the vestibulo-ocular reflex and the effect of "unilateral cold caloric vestibular stimulation" on the localization of a RT have previously been proved. As "unilateral caloric stimulation" is not a physiological stimulus, the aim of the present study was to analyze whether even physiological "bilateral vestibular stimulation" (rotation) is able to affect the RT position. The pointing error (PE) towards an RT both without and following angular acceleration was investigated in 24 healthy volunteers. Postrotatory nystagmus response was recorded by electronystagmography. Evaluation parameters were "nystagmus frequency", "total amplitude" and "velocity of the slow phase"; the horizontal and vertical PE. The fixation of an RT led to a significant reduction of about 28% in nystagmus amplitude compared to the test condition in darkness. "After rotatory stimulation" a systematic horizontal PE in the direction of the fast phase of the postrotatory nystagmus (direction of "illusory self-rotation") occurred and the magnitude of this PE increased significantly compared to the test situation "without vestibular stimulation", but showed only a non-uniform negative correlation with two of the nystagmus parameters. It has to be concluded that "after rotatory stimulation", in contrast to "unilateral cold caloric vestibular stimulation", the subjective sense of "illusory self-motion" leads to a horizontal PE in the direction of the nystagmus fast phases.

Acceleration↗
PubMed1998

Strabismus in premature infants in the first year of life. Cryotherapy for Retinopathy of Prematurity Cooperative Group.

OBJECTIVES: To present the 3- and 12-month strabismus data from 3030 premature infants with birth weights less than 1251 g enrolled in the Multicenter Trial of Cryotherapy for Retinopathy of Prematurity. DESIGN: Data from the 3- and 12-month examinations conducted at 23 regional study centers were tabulated for all infants. The main outcome measure, ocular motility, was compared with baseline demographic variables and retinopathy of prematurity severity for the worse eye. Findings at 3 months were compared with the incidence of strabismus at 12 months. RESULTS: At 3 months, 200 (6.6%) of the 3030 infants were strabismic. In the 2449 infants examined at both time points, 289 (11.8%) were found to have strabismus at 12 months. Retinopathy of prematurity was significant for strabismus at both 3 and 12 months (P<.001). The presence of strabismus at 3 months was found to be a highly significant predictor of strabismus at 12 months. Anisometropia, abnormal fixation, and unfavorable retinal structure also were significant predictors of strabismus at 1 year. The total prevalence of strabismus in the first year of life was 14.7%. CONCLUSION: The presence of acute-phase retinopathy of prematurity places the premature infant at increased risk for strabismus.

Cryotherapy↗
PubMed1990

Light-gazing by visually impaired children.

This study assessed the prevalence and characteristics of light-gazing by all visually impaired children referred during a 2 1/2-year period. Light-gazing (compulsive staring into lights) is one of the many clinical signs of cortical visual impairment (CVI), and in the present study it occurred in 60 per cent of children with CVI. The authors believe that light-gazing by any child with ocular lesions indicates some degree of CNS involvement. Visually impaired children who flicker their fingers in front of their eyes against a light source demonstrate an extension of this compulsive behaviour. This and other studies suggest that blind mannerisms have specific neuropathological substrata and therefore are useful clinical signs.

Blindness↗
PubMedDate not supplied

Ophthalmologic manifestations of Alzheimer's disease.

Alzheimer's disease is a progressive neurologic disorder which may present with visual disturbance before the diagnosis is clearly established. Central acuity and visual field are initially normal. Alzheimer patients may show anomalies of color vision, spatial contrast sensitivity, susceptibility to visual masks, fundus examination, ocular motility, higher cortical visual function, visual evoked potential, and pattern electroretinogram. Pathologic analysis has shown abnormalities at all levels of the visual axis from retinal ganglion cell to associative visual cortex. Correlations between the visual abnormalities of Alzheimer's disease and corresponding neuroanatomic substrates are discussed.

Adult↗