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Results for “Vision, Monocular”

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PubMed1987

Plasticity of monocular and binocular vision following cerebral blindness: evoked potential evidence.

Using monocular and dynamic random dot correlogram (DRDC) stimuli, sequential visual evoked potentials changes were demonstrated in 2 patients following cerebral blindness. The recovery of binocular vision was delayed in comparison to the recovery of monocular vision. The results are not due to simple acuity impairment or convergence deficiency, and thus provide evidence for the vulnerability of postsynaptic cortical mechanisms of human binocular vision.

Adult↗

PubMed2003

Visual field defects in albino ferrets (Mustela putorius furo).

The extent of the horizontal visual field was determined behaviourally in 4 pigmented and 5 albino ferrets (Mustela putorius furo, Carnivora, Mammalia) using perimetry. During binocular vision, all pigmented and three albino ferrets responded equally well to stimuli presented anywhere along the horizontal perimeter in the central 180 degrees of the visual field. The remaining two albinos had a visual field defect in the right hemifield (>30 degrees eccentricity). During monocular vision, a significant difference between the visual fields of pigmented and albino ferrets became apparent. In pigmented ferrets, the visual field of each eye included the ipsilateral (temporal) and a substantial portion of the contralateral (nasal) hemifield. In albinos, the visual field of each eye was limited to the ipsilateral hemifield and reactions to visual stimuli abruptly declined directly beyond the vertical meridian.

Albinism, Ocular↗

PubMed1986

Vision function recovery during orthoptic therapy in an adult esotropic amblyope.

Orthoptic therapy was instituted in a 29-year-old patient having moderate amblyopia, constant small-angle esotropia, and large and steady eccentric fixation. This combination of factors, especially the age, pointed toward a poor prognosis for attainment of markedly improved vision function. Rate of recovery of several monocular vision functions was monitored during one year of orthoptic therapy. Results showed substantial improvement in most areas, thus providing evidence of neural plasticity at multiple sites in the visual pathways in this adult amblyope.

Accommodation, Ocular↗

PubMed2003

Effect of firefighter masks on monocular and binocular peripheral vision.

Peripheral vision can impact essential job functions of firefighters and other workers who use Self-Contained Breathing Apparatus and other full face masks. It is important for physicians to know how these masks alter peripheral vision. Also, one must understand the effect of monocular vision on peripheral vision. Using the Goldman Perimeter Machine we measured peripheral vision in the monocular and binocular state, with and without two different types of masks. The results show that monocularity causes an average loss of 23 degrees in the nasal meridian. The use of the masks did not affect this difference. Also, the masks caused an average loss of 28 degrees of peripheral vision in the inferior meridian. How these losses affect the ability of the users of the masks to perform their essential job functions still needs to be researched.

Adult↗

PubMed2000

Reaching measures of monocular distance perception: forward versus side-to-side head movements and haptic feedback.

We investigated whether forward or side-to-side head movements yielded more accurate and precise monocular egocentric distance information, as shown by performance in a reaching task. Observers wore a head-mounted camera and display to isolate the optic flow generated by their head movements and had to reach to align a stylus directly under a target surface. Performance in the two head movement conditions was also tested with normal monocular vision. We tested performance in the two head movement conditions when the observers were given haptic feedback and compared performance when haptic feedback was removed. Performance was both more accurate and more precise in the forward head movement condition than in the side-to-side head movement condition. Performance in the side-to-side condition also deteriorated more after the removal of haptic feedback than did performance in the forward head movement condition. In the normal monocular condition, performance was comparable for the two head movement conditions. The implications for enucleated patients are discussed.

Distance Perception↗

PubMed1995

Are retinal or mesencephalic dopaminergic systems involved in monocular optokinetic nystagmus asymmetry in frog?

In monocular vision, frogs display a unidirectional optokinetic horizontal nystagmus (H-OKN) reacting only to temporal-nasal (T-N) stimulation. The N-T component is almost absent. The analysis of search coil recordings after administration of dopamine into the viewing eye, the occluded eye or directly into the pretectum, hardly modifies the H-OKN triggered by the viewing eye irrespective of the concentration used. Conversely, administration of Piribedil, a strong D2 dopamine agonist, provokes the appearance of a N-T component, suppressing the monocular H-OKN asymmetry, whether the drug is injected by intravitreal or intrapretectal route. It is suggested that Piribedil could also bind with receptors other than dopamine's.

Animals↗

PubMed1988

Visual information and skill level in time-to-collision estimation.

Previous studies on the visual origin of time-to-collision (Tc) information have demonstrated that Tc estimates can be based solely on the processing of target expansion rate (optic variable tau). But in the simulated situations used (film clips), there was little reliable information on speed (owing to reduced peripheral vision) and distance (owing to the absence of binocular distance cues) available. In order to determine whether these kinds of information are also taken into account, it is necessary to take an approach where the subject receives a more complete visual input. Thus, an experiment conducted on a circuit under actual driving conditions is reported. Experienced drivers and beginners, who were passengers in a car, had to indicate the moment they expected a collision with a stationary obstacle to take place. Subjects were blindfolded after a viewing time of 3 s. The conditions for speed evaluation (normal versus restricted visual field) and distance evaluation (binocular versus monocular vision) by subjects were varied. The approach speed (30 and 90 km h-1) and actual Tc (3 and 6 s) were also varied. The results show that accuracy of Tc estimation increased with (i) normal visual field, (ii) binocular vision, (iii) higher speeds, and (iv) driving experience. These findings have been interpreted as indicating that both speed and distance information are taken into account in Tc estimation. They suggest furthermore that these two kinds of information may be used differently depending on the skill level of the subject. The results are discussed in terms of the complementarity of the various potentially usable visual means of obtaining Tc information.

Acceleration↗

PubMed1996

The effect of pupil and observation distance on the contrast sensitivity function.

Measuring the contrast sensitivity function (CSF) is becoming more frequent in the analyses that are routinely done in optometric practice. This measurement is generally done in far vision, and the observation distance and its effects are not considered to significantly alter this function. Among these effects we should point out the accommodation of the visual optical system to the stimulus and the errors in accommodation associated with this, changes in pupil diameter and therefore in retinal illumination when the observation distance changes, the different level of aberrations (spherical aberration, astigmatism) for different cases, and so on. All of these factors contribute to the fact that the contrast sensitivity of a visual system varies according to the accommodative stimulus. In this study we attempt to clarify the influence of these different parameters by evaluating the CSF for three observation distances. The study was done in monocular vision, with a natural pupil and with a 3 mm artificial pupil that made it possible to maintain the same level of retinal illumination for all distances.

Accommodation, Ocular↗

PubMedDate not supplied

Affect changes observed with right versus left lateral visual field stimulation in psychotherapy patients: possible physiological, psychological, and therapeutic implications.

Seventy psychotherapy patients were given two pairs of goggles each taped over to allow vision from only the left or the right lateral visual field (LVF and RVF). Sixty percent reported at least a one-point difference between visual fields on a five-point anxiety scale; 23% reported at least a two-point difference. Among 21 patients with major depression, 11 reported greater anxiety through the LVF, four reported greater anxiety through the RVF, and six reported no difference. Among 18 with posttraumatic stress disorder (PTSD), 10 reported greater anxiety from the RVF and four from the LVF, and four reported no difference. The absolute difference in anxiety ratings was significantly greater (P < .001) between the two pairs of experimental goggles than between two pairs of control goggles allowing monocular vision among 40 patients in whom the four pairs were tested. During a subsequent psychiatric interview, 40 of 49 patients who were responsive while using the experimental goggles manifested an intensification of their usual symptoms on one side and an alleviation on the other. The possible physiological, psychological, and therapeutic implications of these findings are discussed.

Adolescent↗

PubMed2005

The impact of visual field loss on driving performance: evidence from on-road driving assessments.

PURPOSE: The purpose of this study was to investigate the relationship between visual field loss and driving performance as determined by on-road driving assessments. METHODS: We reviewed the files of 1350 patients enrolled in a rehabilitation program at the Bloorview MacMillan Rehabilitation Centre, Toronto, Canada. We identified 131 patients with visual field loss who had undergone an on-road driving assessment. These patients had a primary diagnosis of visual impairment or a primary diagnosis of cerebral vascular accident (CVA) with a secondary diagnosis of visual impairment. None of these patients had documentation of neglect, substantial motor or cognitive deficits. We report the data obtained from 13 hemianopics, 7 quadrantanopics, 25 patients with monocular vision, 10 patients with moderate peripheral losses (<135 degrees of horizontal visual field measured at the midline), and 76 patients with mild peripheral losses (between 135 degrees and 186 degrees of horizontal visual field). The on-road assessment consisted of driving in the area surrounding the rehabilitation center, and the outcome was based on performance on a number of tasks commonly encountered in daily driving. For the purposes of this study, the assessment outcomes were classified as safe, unknown, or unsafe. RESULTS: Overall, the extent of visual field loss did not have a significant impact on driving performance (chi2 = 4.37, p = 0.358). However, hemianopia tended to have a worse impact on driving performance than quadrantanopia with a marginally significant result (chi2 = 3.33, p = 0.068). Overall, the location of the visual loss was not significantly related to driving fitness (chi2 = 1.05, p = 0.30). However, localized defects in the left hemifield (chi2 = 9.561, p = 0.002) and diffuse visual loss in the right hemifield (chi2 = 10.395, p = 0.001) seemed to be associated with driving impairments. A large proportion of monocular drivers were safe drivers and the location of their deficit had no significant impact. CONCLUSIONS: Although the extent of visual field defects appears to be related to driving performance as determined by an on-road driving assessment, large individual differences were observed. This highlights the need for individualized on-road assessments for patients with visual field defects.

Automobile Driving↗

PubMed2006

Cortical effects of brief daily periods of unrestricted vision during early monocular form deprivation.

Experiencing daily brief periods of unrestricted vision during early monocular form deprivation prevents or reduces the degree of resulting amblyopia. To gain insight into the neural basis for these "protective" effects, we analyzed the monocular and binocular response properties of individual neurons in the primary visual cortex (V1) of macaque monkeys that received intermittent unrestricted vision. Microelectrode-recording experiments revealed significant decreases in the proportion of units that were dominated by the treated eyes, and the magnitude of this ocular dominance imbalance was correlated with the degree of amblyopia. The sensitivity of V1 neurons to interocular spatial phase disparity was significantly reduced in all treated monkeys compared with normal adults. With unrestricted vision, however, there was a small but significant increase in overall disparity sensitivity. Binocular suppression was prevalent in monkeys with constant form deprivation but significantly reduced by the daily periods of unrestricted vision. If neurons exhibited consistent responses to stimulation of the treated eye, monocular response properties obtained by stimulation of the two eyes were similar. These results suggest that the observed protective effects of brief periods of unrestricted vision are closely associated with the ability of V1 neurons to maintain their functional connections from the deprived eye and that interocular suppression in V1 may play an important role in regulating synaptic plasticity of these monkeys.

Animals↗

PubMedDate not supplied

Effects of superior colliculus inhibition on three-dimensional visual motion processing in the lateral suprasylvian visual area of the cat.

PURPOSE: To determine whether visual inputs from the tectothalamocortical pathway influence three-dimensional motion processing within the lateral suprasylvian (LS) area of the cat. METHODS: Tungsten microelectrodes were used for recording visual-evoked potentials (VEPs) from the LS area of 4 cats. Random dot stereograms were used as visual stimuli. Three-dimensional, motion-triggered VEPs were recorded from the LS area. Each motion sequence consisted of an abrupt onset of motion disparity with a 2 degrees amplitude followed by an abrupt offset and a stationary phase of 900 ms. The velocity of the motion disparity was varied in eight steps from 10 degrees to 400 degrees per second. The onset of motion disparity was used as the trigger for recording the VEPs. Single or multiple injections (two to three) of muscimol were made mainly into the rostral superior colliculus (SC). The amplitudes of the VEPs before and after the muscimol injection were compared. RESULTS: A large negative wave ( N1) with an implicit time of 92.7 +/- 13.5 ms (mean +/- SD, n = 98) was recorded consistently. The amplitude of N1 was significantly larger on stereovision of motion disparity than on either binocular vision of two-dimensional lateral motion or monocular vision, indicating that N1 contains neurons sensitive to motion disparity. The amplitude of N1 was not altered by muscimol injection into the SC at velocities < or =50 degrees/s. On the other hand, the amplitude of N1 was reduced to 66-71% of that observed before muscimol injection at velocities > or =75 degrees/s. CONCLUSIONS: These findings suggest that the LS area processes three-dimensional motion inputs via two parallel pathways, the geniculostriate pathway and the tectothalamocortical pathway, at velocities of motion disparity > or =75 degrees/s, while the three-dimensional motion inputs project to the LS area only via the geniculostriate pathway at velocities of motion disparity < or = 50 degrees/s.

Animals↗

PubMed1994

Minimal angle of resolution in monocular, single-colour vision and the TAIS model.

The mathematical model TAIS simulates visual perception of single-colour or black-and-white, non-moving objects. It makes an analysis of the luminance spatial distribution in an optional direction and describes it in linguistic terms. The model comprises three modules that successively convolve the luminance distribution with a spatial filter (a normalized Gaussian function), calculate the second derivative of the convolution and, with use of context-free and context-sensitive grammars, generate a string of symbols. The string of symbols contains the information, simplified in form and rectified from visual noise, about perceived spatial changes of brightness. The model simulates various visual phenomena, e.g. edge detection and spatial resolution, and it predicts the resolving power dependence on the light source size. The model-generated dependence of minimal angle of resolution on the light source width fits the experimental data with linear correlation coefficients in the range 0.70-0.94. The diagram consists of decreasing and constant parts, its shape adjusted to experimental data through selection of the Gaussian filter parameter and second derivative threshold.

Adaptation, Ocular↗

PubMed1981

Recovery from monocular deprivation in the monkey. III. Reversal of anatomical effects in the visual cortex.

Transneuronal autoradiography was used to study the effects of visual deprivation on the ocular dominance stripes in layer IVc of the striated cortex of Erythrocebus patas (Old World) monkeys. The animals were studied after: (a) 21-28 days of monocular deprivation starting at, or within, a few days of birth; (b) the same treatment followed by a further 3, 6, 15 or 126 days of monocular vision through both eyes (reopening). One other monkey was monocularly deprived from birth to 1890 days. In most cases the behaviour of the ocular dominance stripes formed by the initially closed eye was studied. After 24 days of monocular deprivation from birth, the input from the normal eye was distributed uniformly within layer IVc, with no periodicity evident. After 21 days of deprivation, the deprived eye's input formed narrow stripes occupying about 38% of layer IVc in the operculum. Seven months of monocular deprivation reduced this to about 29%. Opening the closed eye after the deprivation produced no change in the area innervated: when periods of 15 or 96 days of binocular vision followed the deprivation, the areas innervated by the initially deprived eye were 26 and 30% respectively. However, in both cases the deprived eye's input formed blobs and spots, rather than uniformly narrow stripes. In contrast to reopening, reverse suturing increased the fraction of layer IVc occupied by input form the initially deprived eye. In the operculum, the effects of reverse suturing appeared to be fully developed after only 6 days of reversal: the initially deprived eye's stripes having expanded to occupy about 50% of layer IVc. A further 9 days' reversal produced little change in this. In the visual cortex in the calcarine fissure, the effect of the initial deprivation ws more severe, and the expansion induced by reverse suturing more pronounced. The initial deprivation caused the stripes to shrink to occupy 24% of layer IVc; after 6 days of reverse sulture the proportion increased to 52%, while after 15 days of reverse suture about 88% of IVc was occupied. These results show that reverse suturing can cause fresh growth of afferent axons in regions of layer IVc from which they had been at least partially removed, either by the normal process of segregation, or as a consequence of monocular deprivation. Taken in conjuction with the findings of the accompanying two papers (Blackemore et al...

Animals↗

PubMed2003

An evaluation of the lag of accommodation using photorefraction.

OBJECTIVE: The lag of accommodation which occurs in most human subjects during reading has been proposed to explain the association between reading and myopia. However, the measured lags are variable among different published studies and current knowledge on its magnitude rests largely on measurements with the Canon R-1 autorefractor. Therefore, we have measured it with another technique, eccentric infrared photorefraction (the PowerRefractor), and studied how it can be modified. METHODS: Particular care was taken to ensure correct calibration of the instrument. Ten young adult subjects were refracted both in the fixation axis of the right eye and from the midline between both eyes, while they read text both monocularly and binocularly at 1.5, 2, 3, 4 and 5 D distance ("group 1"). A second group of 10 subjects ("group 2"), measured from the midline between both eyes, was studied to analyze the effects of binocular vs monocular vision, addition of +1 or +2 D lenses, and of letter size. Spherical equivalents (SE) were analyzed in all cases. RESULTS: The lag of accommodation was variable among subjects (standard deviations among groups and viewing distances ranging from 0.18 to 1.07 D) but was significant when the measurements were done in the fixation axis (0.35 D at 3 D target distance to 0.60 D at 5 D with binocular vision; p<0.01 or better all cases). Refracting from the midline between both eyes tended to underestimate the lag of accommodation although this was significant only at 5 D (ANOVA: p<0.0001, post hoc t-test: p<0.05). There was a small improvement in accommodation precision with binocular compared to monocular viewing but significance was reached only for the 5 D reading target (group 1--lags for a 3/4/5 D target: 0.35 vs 0.41 D/0.48 vs 0.47 D/0.60 vs 0.66 D, ANOVA: p<0.0001, post hoc t-test: p<0.05; group 2--0.29 vs 0.12 D, 0.33 vs 0.16 D, 0.23 vs -0.31 D, ANOVA: p<0.0001, post hoc t-test: p<0.05). Adjusting the letter height for constant angular subtense (0.2 deg) induced scarcely more accommodation than keeping letter size constantly at 3.5 mm (ANOVA: p<0.0001, post hoc t-test: n.s.). Positive trial lenses reduced the lag of accommodation under monocular viewing conditions and even reversed it with binocular vision. CONCLUSIONS: After consideration of possible sources of measurement error, the lag of accommodation measured with photorefraction at 3 D (0.41 D SE monocular and 0.35 D SE binocular) was in the range of published values from the Canon R-1 autorefractor. With the measured lag, simulations of the retinal images for a diffraction limited eye suggest surprisingly poor letter contrast on the retina.

Accommodation, Ocular↗

PubMedDate not supplied

Vision impairment and driving.

Driving is the primary mode of travel in many countries. It facilitates the performance of routine daily activities and is thus integral with the concept of quality of life. Vision is inarguably a fundamental component of safe driving. Drivers with certain eye conditions reduce their driving exposure and restrict their driving to the safest times, yet there is preliminary evidence that some eye conditions increase the risk of crashes. Visual acuity is only weakly related to crash involvement, whereas peripheral vision appears to play a more critical role. Color vision deficiency by itself is not a threat to safe driving. Based on the current literature, it is unclear whether other types of visual sensory impairment have a significant impact on driving safety and performance. Tests of visual attention and processing speed show great promise as methods of identifying high-risk drivers. There is a serious need for well-designed studies in key practical areas, such as the safety of low-vision drivers who use bioptic telescopes, the impact of monocular vision impairment on safety, and the effectiveness of vision rescreening policies after initial licensure. For ophthalmologists to guide patients about driving fitness, valid and reliable assessment tools must be developed and made widely available.

Accidents, Traffic↗

PubMed1997

Evidence Supporting the Importance of Peripheral Visual Information for the Directional Control of Aiming Movement.

The focus of the present study was on determining whether the high level of directional accuracy found in aiming studies in which the subjects can see their hand in the visual periphery supports the existence of a kinetic visual channel or, rather, the advantage of binocular over monocular vision for movement directional control. The limits of this kinetic visual channel were also explored. The results of the 1st experiment indicated that seeing one's hand in the visual periphery is sufficient to ensure optimal directional aiming accuracy. Further, no differences in aiming accuracy were noted between monocular and binocular vision. These results supported the existence of a visual kinetic channel. In the 2nd experiment, whether this kinetic visual channel would operate with movements slower (55°/s) than those usually used in studies that had proved its existence (over 110°/s) was determined. The results indicated that this visual kinetic channel was operative even at relatively slow movement velocities. Central vision of the hand seemed to be used for on-line directional control of relatively slow movements.

binocular vision↗

PubMed2001

Peripheral oculomotor palsy affects orienting of visuospatial attention.

Patients affected by VI cranial nerve palsy were required to orient their attention in monocular vision and to detect a stimulus appearing either in attended or in unattended locations. Results showed that while during non-paretic eye vision stimulus detection in the attended location was faster than that in the unattended one, during paretic eye vision no difference in detection speed was present. However, in this latter condition, detection speed in both attended and un attended locations were as fast as that measured during non-paretic eye vision in attended location. Demonstration that peripheral oculomotor impairment influences monocular covert orienting of visuospatial attention strongly support the idea that visuospatial attention and oculomotor mechanisms share similar cortical networks.

Abducens Nerve Diseases↗