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PubMed1999

Complex spike activity of Purkinje cells in the ventral uvula and nodulus of pigeons in response to translational optic flow.

The complex spike (CS) activity of Purkinje cells in the ventral uvula and nodulus of the vestibulocerebellum was recorded from anesthetized pigeons in response to translational optic flow. Translational optic flow was produced using a "translator" projector: a mechanical device that projected a translational optic flowfield onto the walls, ceiling, and floor of the room and encompassed the entire binocular visual field. CS activity was broadly tuned but maximally modulated in response to translational optic flow along a "best" axis. Each neuron was assigned a vector representing the direction in which the animal would need to translate to produce the optic flowfield that resulted in maximal excitation. The vector is described with reference to a standard right-handed coordinate system, where the vectors, +x, +y, and +z represent, rightward, upward, and forward translation of the animal, respectively. Neurons could be grouped into four response types based on the vector of maximal excitation. +y neurons were modulated maximally in response to a translational optic flowfield that results from self-motion upward along the vertical (y) axis. -y neurons also responded best to translational optic flow along the vertical axis but showed the opposite direction preference. The two remaining groups responded best to translational optic flow along horizontal axes: -x + z neurons and -x-z neurons. In summary, our results suggest that the olivocerebellar system dedicated to the analysis of translational optic flow is organized according to a reference frame consisting of three approximately orthogonal axes: the vertical axis, and two horizontal axes oriented 45 degrees to either side the midline. Previous research has shown that the rotational optic flow system, the eye muscles, the vestibular semicircular canals and the postural control system all share a similar spatial frame of reference.

Animals↗
PubMed1998

Selective intra-arterial fibrinolysis of acute central retinal artery occlusion.

BACKGROUND AND PURPOSE: Occlusion of the central retinal artery (CRAO) causes a sudden decrease of monocular vision. Because early restoration of blood flow may improve outcome, we attempted to treat CRAO with selective intra-arterial fibrinolysis. METHODS: Intra-arterial fibrinolysis was performed within 6 hours after symptom onset in 17 patients with thromboembolic CRAO. Symptoms were painless, acute and severe decrease of vision. Urokinase (100 000 to 900 000 IU) was given through a microcatheter into the ophthalmic artery over 10 to 90 minutes. For comparison, the history and visual outcome of 15 control patients who did not receive fibrinolytics were evaluated. In both groups some of the patients underwent paracentesis and/or received carboanhydrase inhibitors. RESULTS: Patients who underwent fibrinolysis fared better than control patients (P=0.01). Three patients (17.6%) recovered completely after fibrinolysis and regained visual acuity of 20/20 (n=2) to 25/20 (n=1). Two additional patients (11.8%) showed a marked improvement to a visual acuity of 20/30. In 6 patients (35. 3%) vision improved slightly. They were able to count fingers, detect hand movements, or perceive light. In 6 patients (35.3%), fibrinolytic treatment was without effect. Among control patients, 1 patient (6.7%) showed partial, 4 patients (26.7%) minimal, and 10 (66.7%) no improvement of vision. CONCLUSIONS: A complete or marked improvement of visual acuity was achieved in one third of intra-arterial fibrinolysis patients but in none of the control patients. Intra-arterial fibrinolysis seems to have the potential to "lighten" the spontaneously poor outcome of CRAO.

Acute Disease↗
PubMed1997

Brightness fading during Ganzfeld adaptation.

The time course and extent of brightness fading in a Ganzfeld were determined for adapting luminances ranging from 0.01 to 100 cd/m2. Magnitude estimation and interocular brightness matching were used. During Ganzfeld adaptation, perceived brightness decreased slowly and leveled off, on average, after 5-7 min (adapting time increasing with luminance). On average, the total brightness loss was equivalent to a 1.2 log unit reduction in luminance, independent of adapting luminance. The residual brightness perceived at the final plateau was generally higher than the brightness of the Eigengrau, suggesting a partially sustained luminance channel.

Adaptation, Physiological↗
PubMed1980

Relationship between perceptual stability, and sighting dominance.

A study was made of perceptual stability (in binocular, right and left monocular vision) and sighting dominance. 47 female psychology students served as subjects. The intention was to verify: (1) the hypothesis of asymmetry between the two eyes in the duration of the retinal image, which is indicative of sensory dominance; (2) the existence of a relationship between the two forms of dominance. The results seem to confirm the first hypothesis. Other relationships between sighting dominance and stability of image emerged. There was a positive correlation between sighting dominance and perceptual stability in binocular vision. There appear to be significant differences in perceptual stability depending on whether subjects show right, left, or no dominance.

Adult↗
PubMed1987

Depth on a flat screen.

The hypothesis was tested that the coupling of parallax shifts between objects depicted on a monitor screen around a fixation point with the head movements of an observer viewing this screen monocularly around a point coinciding with the fixation point is sufficient to create a convincing depth impression and to enable the observer to make reliable estimations of depth. The estimates were based on monocular vision and involved the aligning of wedges. The investigation consisted of two analogous experiments carried out simultaneously, one on depth estimations virtually in the screen and one on depth estimations virtually in front of the screen. In each experiment three conditions were compared: an active condition in which the coupling of parallax shifts and observer's head movements operated, a passive condition in which it did not, and a real-life set-up to measure the maximum reliability in depth estimation. The hypothesis is confirmed: in the active condition the variances in the alignments are significantly smaller than in the passive condition and approach those in the real-life set-up. This holds not only for estimates in the screen but also for estimates in front of the screen, that is, we can make a thing apparently leap out of the screen towards the observer. Results are interpreted against the background of the debate between the direct and the indirect theories of perception.

Cues↗
PubMed1994

3-D vision and figure-ground separation by visual cortex.

A neural network theory of three-dimensional (3-D) vision, called FACADE theory, is described. The theory proposes a solution of the classical figure-ground problem for biological vision. It does so by suggesting how boundary representations and surface representations are formed within a boundary contour system (BCS) and a feature contour system (FCS). The BCS and FCS interact reciprocally to form 3-D boundary and surface representations that are mutually consistent. Their interactions generate 3-D percepts wherein occluding and occluded object parts are separated, completed, and grouped. The theory clarifies how preattentive processes of 3-D perception and figure-ground separation interact reciprocally with attentive processes of spatial localization, object recognition, and visual search. A new theory of stereopsis is proposed that predicts how cells sensitive to multiple spatial frequencies, disparities, and orientations are combined by context-sensitive filtering, competition, and cooperation to form coherent BCS boundary segmentations. Several factors contribute to figure-ground pop-out, including: boundary contrast between spatially contiguous boundaries, whether due to scenic differences in luminance, color, spatial frequency, or disparity; partially ordered interactions from larger spatial scales and disparities to smaller scales and disparities; and surface filling-in restricted to regions surrounded by a connected boundary. Phenomena such as 3-D pop-out from a 2-D picture, Da Vinci stereopsis, 3-D neon color spreading, completion of partially occluded objects, and figure-ground reversals are analyzed. The BCS and FCS subsystems model aspects of how the two parvocellular cortical processing streams that join the lateral geniculate nucleus to prestriate cortical area V4 interact to generate a multiplexed representation of Form-And-Color-And-DEpth, or FACADE, within area V4. Area V4 is suggested to support figure-ground separation and to interact with cortical mechanisms of spatial attention, attentive object learning, and visual search. Adaptive resonance theory (ART) mechanisms model aspects of how prestriate visual cortex interacts reciprocally with a visual object recognition system in inferotemporal (IT) cortex for purposes of attentive object learning and categorization. Object attention mechanisms of the What cortical processing stream through IT cortex are distinguished from spatial attention mechanisms of the Where cortical processing stream through parietal cortex. Parvocellular BCS and FCS signals interact with the model What stream. Parvocellular FCS and magnocellular motion BCS signals interact with the model Where stream.(ABSTRACT TRUNCATED AT 400 WORDS)

Depth Perception↗
PubMed2000

Structured long-range connections can provide a scaffold for orientation maps.

In the visual cortex of the cat and ferret, it is established that maturation of orientation selectivity is shaped by experience-dependent plasticity. However, recent experiments indicate that orientation maps are remarkably stable and experience-independent. We present a model to account for these seemingly paradoxical results. In this model, a scaffold consisting of non-isotropic lateral connections is laid down in horizontal circuitry before visual experience. These lateral connections provide an experience-independent framework for the developing orientation maps by inducing a broad orientation tuning bias in the model neurons. Experience-dependent plasticity of the thalamocortical connections sharpens the tuning while the preferred orientation of the neurons remains unchanged. This model is verified by computer simulations in which the scaffolds are generated both artificially and inferred from experimental optical imaging data. The plasticity is modeled by the BCM synaptic plasticity rule, and the input environment consists of natural images. We use this model to provide a possible explanation of the recent observation in which two eyes without common visual experience develop similar orientation maps. Finally, we propose an experiment involving the disruption of lateral connections to distinguish this model from models proposed by others.

Animals↗
PubMed2001

Aphakic hydrogel contact lens fitting on a monocular canine: a case report.

BACKGROUND: Though plano bandage contact lenses used for therapeutic purposes are not uncommon for dogs, no literature regarding contact lenses to correct aphakic canines currently exists. CASE REPORT: Oliver, a 7-year-old terrier mix, was aphakic in his left eye and essentially blind in his right eye as the result of a large retinal detachment. Surgical complications and endothelium damage contraindicated an intraocular lens implant in his left eye. While co-managed with his veterinary ophthalmologist, Oliver was prescribed an aphakic hydrogel contact lens to improve his monocular vision. CONCLUSION: Oliver was successful (by clinical criteria) with his contact lens. Although it is difficult to quantify his vision without a visual evoked potential, Oliver appeared more attentive and confident with the contact lens. This case report demonstrates a successful canine aphakic contact lens fit through the efforts of his owners, co-managing veterinary ophthalmologist, and optometrist.

Animals↗
PubMedDate not supplied

Ocular prosthesis in children--clinical report.

Children and adolescents are particularly susceptible to injuries because of their fearless manner of play and their athletic immaturity due to which irreparable trauma to the eye is very commonly seen. Glaucoma is another common cause for eye loss in children. The loss of an eye causes disfigurement of the face due to which the children become emotionally weak and conscious and avoid taking part in social events, which in turn causes anxiety, stress and depression at an early age in life. Recovery after the loss of an eye requires an adjustment to monocular vision and improvement of the appearance with the use of artificial eyes carefully prepared to match the remaining natural eye. The custom made ocular prostheses are very comfortable and help children improve their appearances, which in turn, encourages them to build up their self-confidence to return back to their social life.

Adolescent↗
PubMedDate not supplied

Effects of sighting and sensory dominance on monovision high and low contrast visual acuity.

We investigated the relationship between ocular dominance and monovision visual performance in 15 presbyopic subjects. Ocular dominance was determined using sighting (hole-in-the-card and mirror tests) and sensory (anisometropic blur suppression test) methods. Correcting the dominant sighting eye for a given viewing distance was found to be an unreliable method of optimizing blur suppression or binocular high/low contrast visual acuity at that distance. If there is any advantage to a particular strategy for selecting the distance monovision eye, it must be realized in vision performance areas other than visual acuity.

Adult↗
PubMed1990

[The influence of aging and different type of targets on eye accommodation].

The influence of aging and a couple of external and internal targets on eye accommodation under monocular vision using an infrared optometer were studied. The subjects were 11 healthy adults aged 20-40. In comparison with using internal targets, the amount of accommodative response, tension velocity for accommodation and relaxation velocity for accommodation showed a tendency to increase when using an external target. In particular, these tendencies showed a predominantly in middle-aged subjects. It is suggested that external targets gives some more precise information concerning eye accommodation. In using internal targets, instrument myopia and psycho-physiological factors might bring about a disturbance of reproducibility during eye accommodation.

Accommodation, Ocular↗
PubMed1989

The effect of prolonged monocular occlusion on latent nystagmus in the treatment of amblyopia.

We recorded eye movements in 8 patients with latent nystagmus (LN) before and after 2 days of occlusion of the better eye. The slow-phase speed of the nystagmus (SPS) during fixation with the worse eye became lower after 2 days of occlusion of the better eye. However, the SPS during fixation with the better eye became higher after 2 days of occlusion of the better eye. The sum of SPS during fixation with the better eye and SPS during fixation with the worse eye remained the same. Oscillopsia complaints gradually disappeared over days during the occlusion. It seems likely that the alteration of the LN during prolonged monocular vision is caused by a slow-velocity bias of the neural integrator, a compensatory drift, generated by the flocculus using retinal-slip information. The difference between SPS during fixation with the better eye and SPS during fixation with the amblyopic eye in LN patients with amblyopia is probably also caused by this compensatory drift. As the compensatory drift changes its direction and magnitude slowly over days, it seems advisable to occlude the better eye in children with amblyopia and LN during days per week, and not during hours per day.

Adaptation, Ocular↗
PubMed1989

Clinical observations on occlusion myopia.

The authors studied the refractive errors and axial lengths on thirty patients. A retrospective analysis suggests some degree of monocular vision deprivation early in life. Axial myopia was found in most of the cases, indicating that emmetropization is a vision-dependent phenomenon. But, some exceptions were found, supporting the concept that multiple factors are involved in the pathogenesis of myopia.

Adolescent↗
PubMed1988

Initial acquisition of visual discriminations following selective cortical lesions in cats.

Split-brain adult cats with various visual cortex lesions were tested for their ability to acquire several pattern discriminations using monocular vision. Different lesions were made in the two hemispheres to control for possible individual differences in learning speed due to factors other than the lesion. Results indicated that removal of either areas 17, 17 + 18, 18 + 19, or 19 did not abolish the ability to learn pattern discriminations. However, when compared to control animals, lesioned animals learned more slowly the various discriminations, especially subjects having lesions in 18 + 19. These results tend to confirm the hypothesis that the integrity of individual visual cortical areas for the perception and discrimination of simple patterns is important but not essential.

Animals↗
PubMed1985

The eye of the venomous marine teleost Trachinus vipera with special reference to the structure and ultrastructure of visual cells and pigment epithelium.

The benthic Trachinus vipera occurs to a depth of 50 m and migrates inshore during the summer. It lies buried in the sand with the top of its head exposed. The benthic habitat and predatory behaviour, tuned to function in twilight, are reflected in the structure and ultrastructure of the eye. The eye is well camouflaged by an iridescent cornea and a differentially coloured spectacle. The spontaneous eye movements are either coordinated, for binocularity, or independent, for monocular vision. The latter is aided by the reduction of the blind spot to a thin streak. Consequently the optic nerve is flattened. When leaving the eyeball it becomes folded, which may allow for lengthening. The cones of the duplex retina are arranged in a square mosaic, with a central single cone and identical twin cones. The square mosaic is stabilized by an intricate framework of so-called "fins", and the twin cones do not "twist" into a row pattern in the dark as observed in the diurnal guppy. The twin cones do not extend sclerally in the dark, while the single cones, rods and pigment epithelial processes undergo retinomotor movements. Regional differences are observed: The sensitivity of the dorsal retina is enhanced by a great number of rods, bundled as in deep-sea fish. The lipid granules in the dorsal pigment epithelium may act as a tapetum lucidum, reflecting light back through the retina. A cluster of triple cones in the dorso-temporal region may represent a site for increased sensitivity and/or acute vision. An unusual inclusion body, with a dense core similar to a lipid droplet, and surrounded by membranes, is observed in the dorsal pigment epithelium. The membranes are seen to be continuous with the smooth endoplasmic reticulum, nuclear membrane and myeloid bodies. This body changes diurnally and may be a type of phagosome.

Adaptation, Ocular↗