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At least 343 records · Page 19Linked to original sources
PubMed2003

Developmental plasticity of mouse visual acuity.

Monocular deprivation in mice between postnatal days 19 and 32 has been reported to significantly shift ocular dominance within the binocular region of primary visual cortex; however, it is not known whether visual deprivation in mice during this physiologically defined critical period also results in amblyopia, as it does in other mammals. We addressed this uncertainty by psychophysically assessing in adulthood (postnatal day 70 or older) the grating acuity of normal and monocularly deprived mice, using the Visual Water Task. The visual acuity of mice tested with their nondeprived eyes was equivalent to that of normal mice ( approximately 0.5 cycles/degree); however, acuity measured with eyes monocularly deprived of vision transiently between postnatal days 19 and 32 was reduced by over 30% ( approximately 0.31 cycles/degree). Identical binocular deprivation produced a significant, but smaller, decrease in acuity ( approximately 0.38 cycles/degree). The effects of monocular and binocular deprivation were long lasting and occurred only if visual deprivation occurred between postnatal days 19 and 32. These data indicate that the deleterious effects of early visual deprivation on visual acuity in mice are similar to those reported in other mammals, and together with electrophysiological evidence of ocular dominance plasticity, suggest that the mechanisms of mouse visual plasticity are fundamentally the same as that in other mammals. Therefore, the mouse is probably a good model for investigating the basic cellular and molecular mechanisms underlying visual developmental plasticity and amblyopia.

Age Factors↗
PubMed2004

Both monocular and binocular signals contribute to motion rivalry.

There is an ongoing debate on whether binocular rivalry involves competition among monocular cells or binocular cells. We investigated this issue psychophysically with two specially designed test stimuli. One test stimulus contained monocular motion signals but greatly reduced binocular motion signals, while the other contained binocular motion signals but no monocular motion signals. For comparison, we also employed a normal rivalrous control containing both monocular and binocular motion signals, and a non-rivalrous flicker-noise control with neither monocular nor binocular motion signals. We found that binocular rivalry for the two test stimuli was significantly reduced compared with the normal rivalrous control, but not completely eliminated compared with the non-rivalrous control. Therefore, both monocular and binocular motion signals appear to contribute to motion rivalry, suggesting that motion rivalry must involve competition among both monocular and binocular cells.

Differential Threshold↗
PubMed1997

A theory of illusory lightness and transparency in monocular and binocular images: the role of contour junctions.

A theory of illusory transparency and lightness is described for monocular and binocular images containing X-, T- and I-contour junctions. This theory asserts that the geometric and luminance relationships of contour junctions induce illusory transparency and lightness percepts by causing a phenomenal scission of a homogenous luminance into multiple contributions. Specifically, it is argued that a discontinuous change in contrast along aligned contours that preserve contrast polarity induces a scission of the lower contrast region into a near-transparent surface or an illumination change, and a more distant surface that continues behind behind this near layer. This scission is assumed to cause changes in perceived lightness and/or surface opacity. Discontinuous changes in contrast along contours also are assumed to induce end-cut illusory contours that run roughly perpendicular to the inducing orientation of the contour, both monocularly and binocularly. Binocular illusory contours are shown to be caused by the presence of unmatchable contour terminators. It is argued that the presented theory can provide a unified account of a variety of monocular and binocular illusions that induce uniform transformations in perceived lightness, including neon-color spreading, the Munker-White illusion, Benary's illusion, and illusory monocular and binocular transparency.

Contrast Sensitivity↗
PubMed1992

[Interactions between GABAergic and cholinergic mechanisms involved in monocular optokinetic nystagmus in frogs].

The systemic administration of atropine, a muscarinic cholinergic antagonist, was found to suppress the Nasal-Temporal (N-T) component of the frog monocular optokinetic nystagmus (OKN), which had appeared following a prior injection of bicuculline and which does not exist in the normal animal. On the contrary, the administration of a nicotinic cholinergic antagonist (D-TC, alpha-BGT, Hexamethonium) following that of bicuculline has prolonged the duration of the induced N-T component. Thus, ACh was shown to attenuate or to reinforce the GABAergic inhibition of the N-T component through muscarinic receptors or nicotinic receptors respectively. These data point to the existence of strong interactions between these two neurotransmission systems involved in frog monocular OKN.

Animals↗
PubMed2005

Dynamic visual fields of one-eyed observers.

BACKGROUND: The horizontal binocular visual field can extend to more than 200 degrees, while a monocular field is limited to 160 degrees. Additionally, the nose and other facial structures may block the monocular field further during certain eye movements. The purpose of this study was to compare the monocular against the binocular visual field and determine if head and eye movements can functionally overcome any measured deficit. METHODS: In Experiment 1, visual fields were measured monocularly with a bowl perimeter using 5 fixation positions. Binocular visual fields were calculated by combining the monocular visual field with its mirror image. In Experiment 2, subjects were allowed to make head, eye, and body movements to search for flashing lights 360 degrees around them, spaced every 45 degrees. The numbers of lights identified were compared for the subjects performing monocularly versus binocularly. RESULTS: The size of the overall monocular visual field was found to vary between 48% and 76% of the binocular visual field, depending on eye position. For the flashing light experiment, head and eye movements could not overcome the entire visual-field deficit with monocular viewing. Monocular performance remained 11.4% less than binocular performance. CONCLUSIONS: The visual-field deficit seen with monocular viewing is greatest with nasal fixation, and head and eye movements cannot totally compensate for this deficit when viewing time is limited. Vision standards that require full visual fields in each eye are more appropriate for occupations in which peripheral visual targets must be identified and visual search time is limited.

Adult↗
PubMed1995

Accommodation in humans with juvenile macular degeneration.

Accommodation, or the change in refractive power of the eye to focus objects at different distances, is driven by many stimuli including defocus blur, the awareness of target distance or proximal cues, and through the vergence crosslink (convergence accommodation). The effectiveness of defocus blur as an accommodative stimulus is decreased in normally-sighted subjects as visual acuity is experimentally reduced and as the target is imaged at increasing eccentricities from the fovea. Since subjects with central retinal abnormalities have reduced visual acuity and typically fixate eccentrically, one would predict that defocus blur would not be an effective accommodative stimulus for them. Using an infrared optometer, steady-state accommodative responses of six subjects with juvenile macular degeneration (JMD) and of three normally-sighted controls were measured. The effectiveness of defocus blur in stimulating accommodation varied across the subjects and was related to visual acuity, with those subjects having worse acuity showing less accurate accommodative responses. When provided with additional cues to accommodative demand (i.e. proximal and/or binocular cues), subjects with JMD showed more accurate accommodative responses. In general, those subjects who did not modulate accommodative response with changing defocus blur cues showed the most accurate accommodation under binocular viewing. In contrast, those subjects who did change accommodative response with changing defocus blur cues showed the most accurate accommodation under monocular viewing.

Accommodation, Ocular↗
PubMed2001

Monocular blindness as a complication of trigeminal radiofrequency rhizotomy.

PURPOSE: To raise the awareness of the rare complication of monocular blindness resulting from radiofrequency rhizotomy for trigeminal neuralgia. METHODS: Case series from tertiary referral centers. Patients were referred after complaint of loss of vision. RESULTS: We report three patients who had trigeminal neuralgia and underwent treatment by radiofrequency rhizotomy. Each developed complete loss of vision in one eye immediately after the procedure. One patient died of an unrelated cause, and pathologic analysis revealed changes compatible with acute trauma to the right optic nerve. CONCLUSION: Our third case confirms the hypothesis that traumatic optic neuropathy after trigeminal radiofrequency rhizotomy results from malpositioning of the rhizotomy needle through the inferior orbital fissure into the orbital apex rather than the foramen ovale.

Aged↗
PubMedDate not supplied

[500 visual acuity tests in infants with Teller acuity cards].

Assessment of visual resolution with Teller Acuity Cards is now routine procedure in infant visual check-up. A grating is printed on one end of a card on an homogeneous background of the same mean luminance. A series of spatial frequencies at an interval of one half octave covers the range of infant acuity. Binocular and monocular acuities have been measured on 517 infants between 100 and 399 days of age. The cards can be used from a few weeks of age up to 18 months at least. Then it gets more chancy to keep the child attentive. Binocular and two monocular tests take 6 minutes with a normal child. Binocular grating acuity normally reaches 6.5 cycles/degree at 4 months of age, and 12 c/deg at 12 months. Monocular acuity is one half octave lower. From the level of acuity obtained and observation of the behaviour, amblyopia can be detected and low vision can be estimated easily in infants.

Equipment Design↗
PubMedDate not supplied

[Fechner's paradox: clinical symptomatology].

The Fechner's paradox is a visual phenomenon characterized by the fact that the monocular luminosity seems greater than the binocular luminosity. It's a simple and non-dissociating method for the clinical study of the binocular vision. In pathology, the Fechner's paradox may be abolished, or inverse, or may exist spontaneously. The abnormalities were induced by strabismus, or by some others ocular diseases disturbing the binocular vision (unilateral cataract, retinal lesions).

Humans↗
PubMed2002

Binocular information in the control of prehensile movements in multiple-object scenes.

Recent evidence suggests that the visual control of prehension may be less dependent on binocular information than has previously been thought. Studies investigating this question, however, have generally only examined reaches to single objects presented in isolation, even though natural prehensile movements are typically directed at objects in cluttered scenes which contain many objects. The present study was designed, therefore, to assess the contribution of binocular information to the control of prehensile movements in multiple-object scenes. Subjects reached for and grasped objects presented either in isolation or in the presence of one, two or four additional 'flanking' objects, under binocular and monocular viewing conditions. So that the role of binocular information could be clearly determined, subjects made reaches both in the absence of a visible scene around the target objects (self-illuminated objects presented in the dark) and under normal ambient lighting conditions. Analysis of kinematic parameters indicated that the removal of binocular information did not significantly affect many of the major indices of the transport component, including peak wrist velocity. However, peak grip apertures increased and subjects spent more time in the final slow phase of movement, prior to grasping the object, during monocularly guided reaches. The dissociation between effects of binocular versus monocular viewing on transport and grasp parameters was observed irrespective of the presence of flanking objects. These results therefore further question the view that binocular vision is pre-eminent in the control of natural prehensile movements.

Adult↗
PubMed2000

Regional blood flow in the myopic chick eye during and after form deprivation: a study with radioactively-labelled microspheres.

The purpose of the present study was to determine the regional blood flow in the myopic chick eye during and after short-term monocular form deprivation. Chicks were monocularly form-deprived by covering one eye with a translucent occluder for 7-10 days. The anterior chamber-lens distance, the vitreous chamber length and the axial length of the eye were measured by ultrasonography, the equatorial diameter was measured with calipers and the size of the eye was estimated by weighing. The regional blood flow in the eye was determined with radioactively-labelled microspheres in three groups of animals: a group of chicks wearing an occluder (n = 10), a group of chicks in which the occluder was removed 7 or 24 hr prior to the blood flow determination (n = 9), and a group of age-matched control chicks without occluder (n = 9). Monocular form deprivation increased the axial length 0.64 +/- 0.06 and 0.56 +/- 0.09 mm compared to the contralateral control eye in the two groups of chicks wearing an occluder (P < 0.001). Both the equatorial diameter and the weight of the eye increased significantly (P < 0.001). Removal of the occluder tended to reduce the difference in the vitreous chamber length during the first 24 hr. There was no statistically significant difference in the blood flow of the anterior uvea, choroid, pecten or the sclera between the form-deprived and contralateral control eyes (P > 0.05, n = 10), but when comparing to the control group, the blood flow was significantly (P < 0.05) reduced in the choroid of the occluded eye. A similar tendency was found in the anterior uvea. When the blood flow was measured 7-24 hr after the removal of the occluder, a marked increase was found in the blood flow of the choroid of both eyes compared to the situation during occlusion (P < 0.001), and to the control group (P < 0.05). In the pecten a significant (P < 0.05) increase of the blood flow in comparison to the situation during occlusion and the control group was detected after removal of the occluder, and a similar change was found in the contralateral control eye, but it did not reach statistical significance. In the anterior uvea and sclera the blood flow was also significantly (P < 0.05) or almost significantly increased after removal of the occluder in both eyes. The arterial blood pressure was 79 +/- 2, 88 +/- 2 and 99 +/- 5 mmHg in the control group, the group with monocular occlusion, and the group in which the occluder was removed, respectively.Thus, monocular form deprivation in the chick reduced the choroidal blood flow, and a similar tendency was found in the anterior uvea. However, there was no statistically significant difference in blood flow between the form-deprived and contralateral control eyes. Removal of the occluder increased the blood flow in all tissues, notably the choroid and pecten. Generally the changes in blood flow seemed to be bilateral, despite monocular occlusion.

Animals↗
PubMed1999

Visual perception of the Moiré effect.

The perception of Moiré fringes is studied with two different tests for binocular and monocular conditions. The results are negative for binocular conditions, and positive for the monocular case when afterimages are used.

Adult↗
PubMed1997

Comparison of the monocular occlusion and a direct method for objective measurement of fixation disparity.

PURPOSE: Previous studies have measured objective fixation disparity using a monocular occlusion method, by which the monocular components of misalignment are revealed by measuring the shift in the position of the fixating eye after occlusion of the other eye. METHODS: We assessed the use of the monocular occlusion method by comparing it to direct measurements of binocular vergence. RESULTS: The direct method required precise calibration, but was found to be reliable. Several problems were discovered with the monocular occlusion method: (1) when using a central fusion stimulus, fixation was difficult to control accurately enough to measure the small monocular shifts in eye position expected at lower vergence demands; (2) with a peripheral fusion target, objective fixation disparity could not be measured directly; and (3) upon occlusion, a variable saccade occurred in the fixating eye. CONCLUSION: Objective measurement of fixation disparity with the direct method is quicker and more reliable than with the monocular occlusion method.

Adult↗
PubMed1991

Critical flicker frequency under monocular and binocular conditions.

Critical flicker frequency of 40 undergraduate students, 20 men and 20 women whose mean age was 19.3 yr., was measured under monocular and binocular viewing conditions, using the Lafayette Visual Perception Control with Display Unit. Half of the subjects received monocular treatment first and binocular treatment second, and the other half received the treatments in the reversed order. A 2-min. rest was allowed between these treatments. Analysis shows that mean CFF under the monocular condition was significantly lower than that under binocular conditions. The findings were discussed in terms of visual constraint and eye strain and fatigue under the monocular viewing condition.

Adult↗