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PubMed1975

Cats raised in a one-directional world: effects on receptive fields in visual cortex and superior colliculus.

Cats were reared in a visual environment in which irregularly-shaped patches of luminescent paint moved constantly leftward. The distribution of preferred directions and orientations of cortical neurons in these cats was examined. Most cortical neurons encountered had leftward components in their preferred directions, and although no anisotropy of orientation was present in the rearing environment, most cortical neurons responded optimally to stimuli oriented at or near vertical. Variations in the strength of the induced bias of direction and orientation were noted among the different subclasses of cortical neurons. Preferred velocities of cortical neurons did not appear matched to the velocity of stimuli in the rearing environment. The ocular dominance distribution among cortical neurons in the unidirectional cats was skewed toward the contralateral eye relative to normal cats. The distribution of preferred directions in collicular neurons was largely unaltered by the rearing procedures employed. As in normal cats, units in the left colliculus more frequently responded best to rightward stimulus movement while those in the right colliculus preferred leftward movement. The ocular dominance distribution among collicular units was somewhat skewed toward the contralateral eye.

Animals↗
PubMed1994

Voluntary saccadic oscillations, resembling ocular flutter and opsoclonus.

Two human subjects, who had no signs of other neurologic disorders, produced large amplitude, to-and-fro saccadic oscillations. One subject generated these oscillations intentionally. Eye movement recordings by DC electro-oculography and/or magnetic scleral search coil showed that the movements were bursts of conjugate saccades in opposing directions with no intersaccadic intervals. They were multidirectional (horizontal, vertical, or oblique), had amplitudes up to 40 degrees and had linear or curvilinear trajectories. These characteristics are similar to those of ocular flutter and opsoclonus in patients with brainstem and/or cerebellar disorders. Our observations show that fixation instabilities resembling ocular flutter and opsoclonus can be produced voluntarily.

Electrooculography↗
PubMed2001

Ocular responses to head rotations during mirror viewing.

The gain of the human vestibuloocular reflex (VOR) is influenced by the proximity of the object of regard. In six human subjects, we measured the eye rotations induced by passive, sinusoidal, horizontal head rotations at 2.0 Hz during binocular fixation of a stationary far target at 7 m; a stationary target close to the subject's near point of fixation (<15 cm); and the bridge of the subject's own nose, viewed through a mirror positioned so that, for each subject, the angle of vergence was similar to that during viewing of the near target. The median gain of compensatory eye movements for the group of subjects during far viewing was 0.99 (range 0.80-1.04), during near viewing was 1.21 (range 0.88-1.47), and during mirror viewing was 0.85 (range 0.71-1.01). The gain during near and mirror viewing was significantly different for each subject (P < 0.001) even though the vergence angles were similar. The lower gain values during mirror viewing can be attributed to the geometric relationship between the head rotation, the position of the eyes in the head, and the movement of the subject's virtual image in the mirror. To determine whether visually mediated eye movements were responsible for the observed gain values, we conducted a control experiment in which subjects were rotated using a sum-of-sines stimulus that minimized the effects of predictive visual tracking; differences of gain values between near- and mirror-viewing conditions were similar to those during rotation at 2 Hz. We conclude that, in these experiments, target proximity and vergence angle were not the key determinants of gain of the visuo-vestibular response during head rotation while viewing a near target but that contextual cues from motion vision were more important in generating the appropriate response.

Adult↗
PubMed1998

Vision and vestibular adaptation.

This article summarizes six recent degree-of-freedom studies of visual-vestibular interaction during natural activities and relates the findings to canal-otolith interactions evaluated during eccentric axis rotations. Magnetic search coils were used to measure angular eye and head movements of young and elderly subjects. A flux gate magnetometer was used to measure three-dimensional head translation. Three activities were studied: standing quietly, walking in place, and running in place. Each activity was evaluated with three viewing conditions: a visible target viewed normally, a remembered target in darkness, and a visible target viewed with x2 binocular telescopic spectacles. Canal-otolith interaction was assessed with passive, whole-body, transient, and steady-state rotations in pitch and yaw at multiple frequencies about axes that were either oculocentric or eccentric to the eyes. For each rotational axis, subjects regarded visible and remembered targets located at various distances. Horizontal and vertical angular vestibulo-ocular reflexes were demonstrable in all subjects during standing, walking, and running. When only angular gains were considered, gains in both darkness and during normal vision were less than 1.0 and were generally lower in elderly than in young subjects. Magnified vision with x2 telescopic spectacles produced only small gain increases as compared with normal vision. During walking and running all subjects exhibited significant mediolateral and dorsoventral head translations that were antiphase locked to yaw and pitch head movements, respectively. These head translations and rotations have mutually compensating effects on gaze in a target plane for typical viewing distances and allow angular vestibulo-ocular reflex gains of less than 1.0 to be optimal for gaze stabilization during natural activities. During passive, whole-body eccentric pitch and yaw head rotations, vestibulo-ocular reflex gain was modulated as appropriate to stabilize gaze on targets at the distances used. This modulation was evident within the first 80 msec of onset of head movement, too early to be caused by immediate visual tracking. Modeling suggests a linear interaction between canal signals and otolith signals scaled by the inverse of target distance. Vestibulo-ocular reflex performance appears to be adapted to stabilize gaze during translational and rotational perturbations that occur during natural activities, as is appropriate for relevant target distances. Although immediate visual tracking contributes little to gaze stabilization during natural activities, visual requirements determine the performance of vestibulo-ocular reflexes arising from both canals and otoliths.

Adaptation, Physiological↗
PubMed2006

Current concepts of mechanical and neural factors in ocular motility.

PURPOSE OF REVIEW: The oculomotor periphery was classically regarded as a simple mechanism executing complex behaviors specified explicitly by neural commands. A competing view has emerged that many important aspects of ocular motility are properties of the extraocular muscles and their associated connective tissue pulleys. This review considers current concepts regarding aspects of ocular motility that are mechanically determined versus those that are specified explicitly as innervation. RECENT FINDINGS: While it was established several years ago that the rectus extraocular muscles have connective tissue pulleys, recent functional imaging and histology has suggested that the rectus pulley array constitutes an inner mechanism, analogous to a gimbal, that is rotated torsionally around the orbital axis by an outer mechanism driven by the oblique extraocular muscles. This arrangement may account mechanically for several commutative aspects of ocular motor control, including Listing's Law, yet permits implementation of non-commutative motility. Recent human behavioral studies, as well as neurophysiology in monkeys, are consistent with implementation of Listing's Law in the oculomotor periphery, rather than centrally. SUMMARY: Varied evidence now strongly supports the conclusion that Listing's Law and other important ocular kinematics are mechanically determined. This finding implies more limited possibilities for neural adaptation to some ocular motor pathologies, but indicates possibilities for surgical treatments.

Animals↗
PubMed2006

Ocular prevalence and stereoacuity.

BACKGROUND: Most people attribute a higher weight to the input from one eye than to that from the other eye when they have to align stereodisparate objects in the same visual direction. This preference for visual directions has been termed 'ocular prevalence', according to the Latin praevalentia = superior power. QUESTIONS: (1) Is ocular prevalence of one eye (or its correlate, partial suppression of the other eye in the prevalence task) restricted to large stereodisparities, close to Panum's limit, or does it occur also at small stereodisparities, near the stereoscopic threshold? (2) Is ocular prevalence a handicap for stereoacuity? METHODS: Six non-strabismic observers with equal visual acuity of their two eyes were examined. To determine their ocular prevalence, they were presented with vertical vernier lines at stereodisparities ranging between 30 and 430 arcsec. They had to judge whether the lower, anterior line was located on the right- or left-hand side of the upper, posterior line. Their stereoscopic threshold was measured with an adaptive staircase procedure, using the Freiburg Stereoacuity Test. RESULTS: All six observers exhibited some ocular prevalence. It changed considerably on repeated measurements. In three observers, it even switched from one eye to the other. Ocular prevalence occurred not only at large stereodisparities, close to Panum's limit, but also at small stereodisparities. The stereoscopic threshold of the six observers ranged between 1.7 and 12.3 arcsec. CONCLUSION: Ocular prevalence is common, intra-individually variable and occurs even at small stereodisparities close to the stereoscopic threshold. It is compatible with 'optimal' stereoacuity. Hence, ocular prevalence appears to be a harmless feature of normal binocular vision.

Adult↗
PubMed2001

Retinal pigment epithelium translocation and central visual function in age related macular degeneration: preliminary results.

PURPOSE: To test the feasibility of a new surgical technique, and to assess visual function over the translocated retinal pigment epithelium (RPE) cells in patients operated upon for subfoveal choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD). MATERIALS AND METHODS: Six patients presenting previously untreated exudative AMD underwent surgical excision of the subfoveal CNV with RPE translocation and were followed from 1 to 10.5 months. The surgery consisted of a standard three port pars plana vitrectomy (TPPPV), excision of the CNV and RPE translocation. Pre and post-operative ocular examination included best-corrected visual acuity measurement, fundus color stereo photography and fundus fluorescein angiography. Optical coherence tomography (OCT) and confocal laser scanning ophthalmoscopy (cLSO) were performed post-operatively. A cross fixation target and a single-point flashing light were projected on different areas of the posterior pole using a cLSO. Photopic 10-2 perimetry, photopic fine matrix mapping, cLSO microperimetry were also performed pre and post-operatively in four patients. OCT cross-sectional scans and cLSO RPE autofluorescence were recorded to detect the presence of viable translocated RPE. Visual acuity, fixation, photopic 10-2 perimetry, photopic fine matrix mapping and cLSO microperimetry were tested for the presence of central visual function. RESULTS: RPE could be effectively translocated at the time of CNV removal from the edge of the RPE defect to a subfoveal location. OCT showed the translocated RPE as an area of increased optical reflectivity with optical shadowing external to it. cLSO showed autofluorescence of the translocated RPE. The cross fixation target was seen when projected on the translocated RPE. During eccentric fixation, the patients could see a flashing point-target projected on the translocated RPE. Photopic 10-2 perimetry, photopic fine matrix mapping and cLSO microperimetry showed presence of central visual function. CONCLUSIONS: The authors propose that translocation of RPE at the time of CNV removal, from the edge of the RPE defect to a subfoveal location, may have a role in the surgical management of AMD.

Aged↗
PubMed1985

Visual depth illusion and falls in the elderly.

This article investigates the relation of vision and the effects of age on the maintenance of posture. This relationship in the elderly is explored within the context of visual depth illusions induced by repeating patterns that occur on escalator treads and elsewhere in the environment. Age does not appear to reduce the susceptibility of the elderly to visual depth illusions. However, if age is coupled with declines in motor control and strength, the elderly are probably more susceptible to falls.

Accidents↗
PubMed1984

Human visual development over the first 6 months of life. A review and a hypothesis.

The behavioural changes that occur in visual development in the first 6 months of human life are discussed in relation to the possible underlying changes in neurophysiological mechanisms, with inter-species comparisons being made when appropriate. Recent data on the developing infant's changing capacity to discriminate various stimulus attributes is considered. It appears that orientation discrimination and cortically related visual evoked potentials are present at, or soon after, birth. However, data on colour discrimination, field differences in detection tasks and control of visual attention suggest a subcortical site for control of behaviour for the first month of life. The improvements in spatial and temporal resolution depend on maturation of both peripheral and central structures in the visual pathway and so do not provide a clear distinction between cortical and subcortical function. There is clear evidence that binocular function in the cortex does not emerge until three months postnatally. A hypothesis is proposed that maturation of a number of pathways between cortex and subcortical structures underlies the observed behavioural changes starting at around 2 months of age. The initial immaturity of connections between cortex and pretectum may give rise to asymmetrical monocular OKN. Maturation of pathways from cortex to colliculus could account for improvements in convergence, allowing development of cortical binocularity, and for the developing ability to control shifts of visual attention.

Accommodation, Ocular↗