Monocular Occlusion Research Articles

Visual Hierarchical Processing and Lateralization of Cognitive Functions through Domestic Chicks' Eyes

Hierarchical stimuli have proven effective for investigating principles of visual organization in humans. A large body of evidence suggests that the analysis of the global forms precedes the analysis of the local forms in our species. Studies on lateralization also indicate that analytic and holistic encoding strategies are separated between the two hemispheres of the brain. This raises the question of whether precedence effects may reflect the activation of lateralized functions within the brain. Non-human animals have perceptual organization and functional lateralization that are comparable to that of humans. Here we trained the domestic chick in a concurrent discrimination task involving hierarchical stimuli. Then, we evaluated the animals for analytic and holistic encoding strategies in a series of transformational tests by relying on a monocular occlusion technique. A local precedence emerged in both the left and the right hemisphere, adding further evidence in favour of analytic processing in non-human animals.

Binocular disturbance after glaucoma drainage device implantation.

Binocular vision disturbance is a well-described complication of glaucoma drainage device (GDD) implantation. The pathophysiology is not well-understood, but may involve bulk effects from the implant and surrounding bleb, as well as modulation of muscle function due to surgical trauma and post-operative inflammation, resulting in a combined resection/posterior fixation effect. Retrospective studies have found the risks of motility disorder and diplopia vary widely, estimated to be 56%-86% and 57%-75%, respectively. More recently, cross-sectional studies and prospective trials estimate post-GDD incidence to be approximately 1%-44%, with the incidence in newer generation of implants designed to limit bleb size likely lower at 1%-5%. Suggested methods of management strategies include prismatic spectacles, monocular occlusion, extreme monovision, and strabismus surgery.

The blindside: Impact of monocular occlusion on spatial attention

Monocular occlusion has been posited to reduce activation of the contralateral hemisphere (“Sprague effect”), thus inducing a contralateral spatial bias (toward the viewing eye). Healthy right-handed participants bisected horizontal lines during monocular eye viewing. Although subjects tended to deviate away from the viewing eye, only left-eye viewing deviated significantly right of midline. These results suggest that eye patching may induce an attentional compensation similar to that in hemianopic patients. Alternatively, increased activation of higher cortical regions mediating spatial attention in contralateral hemispace may be an adaptive response to decreased activation of its ipsilateral superior colliculus induced by contralateral eye patching.

How to deal with diplopia

Diplopia is a frequent neuro-ophthalmologic symptom with diverse etiologies. This article describes elementary diagnostic tests and frequent causes of diplopia. Monocular diplopia persists when the other eye is closed and usually disappears when the patient looks through a pinhole. It is usually caused by errors in the optical media of the eye and has to be differentiated from spectacle-induced side effect and non-organic disorders. A sign of non-organic etiology is absence of change in image position when the head is tilted. Binocular diplopia disappears regardless of which eye is closed. Binocular diplopia occurs when the images of both eyes cannot be fused. The most frequent direct cause of diplopia is acquired strabismus. Knowledge of several specific types of strabismus enables efficient patient management. Congenital and decompensating strabismus like accommodative esotropia, pathophoria, strabismus surso- and deorsoadductorius, retraction syndrome, Brown's syndrome and esotropia in high myopia only need ophthalmologic treatment. Orbital injury, orbital tumor, ocular myositis, Graves orbitopathy and vascular disease usually require multidisciplinary management. Neurogenic paresis, superior oblique myokymia, ocular neuromyotonia, myasthenia, chronic progressive external ophthalmoplegia (CPEO), internuclear ophthalmoplegia (INO) and skew deviation require specific neurologic examination. Treatment of diplopia includes treatment of the fundamental disorder, monocular occlusion, prisms and strabismus surgery.

Design of a noninvasive face mask for ocular occlusion in rats and assessment in a visual discrimination paradigm

The rat visual system is structured such that the large (>90 %) majority of retinal ganglion axons reach the contralateral lateral geniculate nucleus (LGN) and visual cortex (V1). This anatomical design allows for the relatively selective activation of one cerebral hemisphere under monocular viewing conditions. Here, we describe the design of a harness and face mask allowing simple and noninvasive monocular occlusion in rats. The harness is constructed from synthetic fiber (shoelace-type material) and fits around the girth region and neck, allowing for easy adjustments to fit rats of various weights. The face mask consists of soft rubber material that is attached to the harness by Velcro strips. Eyeholes in the mask can be covered by additional Velcro patches to occlude either one or both eyes. Rats readily adapt to wearing the device, allowing behavioral testing under different types of viewing conditions. We show that rats successfully acquire a water-maze-based visual discrimination task under monocular viewing conditions. Following task acquisition, interocular transfer was assessed. Performance with the previously occluded, "untrained" eye was impaired, suggesting that training effects were partially confined to one cerebral hemisphere. The method described herein provides a simple and noninvasive means to restrict visual input for studies of visual processing and learning in various rodent species.

Evidence that convergence rather than accommodation controls intermittent distance exotropia

This study considered whether vergence drives accommodation or accommodation drives vergence during the control of distance exotropia for near fixation. High accommodative convergence to accommodation (AC/A) ratios are often used to explain this control, but the role of convergence to drive accommodation (the CA/C relationship) is rarely considered. Atypical CA/C characteristics could equally, or better, explain common clinical findings. Nineteen distance exotropes, aged 4-11 years, were compared while controlling their deviation with 27 non-exotropic controls aged 5-9 years. Simultaneous vergence and accommodation responses were measured to a range of targets incorporating different combinations of blur, disparity and looming cues at four fixation distances between 2 m and 33 cm. Stimulus and response AC/A and CA/C ratios were calculated. Accommodation responses for near targets (p = 0.017) and response gains (p = 0.026) were greater in the exotropes than in the controls. Despite higher clinical stimulus AC/A ratios, the distance exotropes showed lower laboratory response AC/A ratios (p = 0.02), but significantly higher CA/C ratios (p = 0.02). All the exotropes, whether the angle changed most with lenses ('controlled by accommodation') or on occlusion ('controlled by fusion'), used binocular disparity not blur as their main cue to target distance. Increased vergence demand to control intermittent distance exotropia for near also drives significantly more accommodation. Minus lens therapy is more likely to act by correcting overaccommodation driven by controlling convergence, rather than by inducing blur-driven vergence. The use of convergence as a major drive to accommodation explains many clinical characteristics of distance exotropia, including apparently high near stimulus AC/A ratios.

Selective Rapid Eye Movement Sleep Deprivation Affects Cell Size and Number in Kitten Locus Coeruleus

Cells in the locus coeruleus (LC) constitute the sole source of norepinephrine (NE) in the brain and change their discharge rates according to vigilance state. In addition to its well established role in vigilance, NE affects synaptic plasticity in the postnatal critical period (CP) of development. One form of CP synaptic plasticity affected by NE results from monocular occlusion, which leads to physiological and cytoarchitectural alterations in central visual areas. Selective suppression of rapid eye movement sleep (REMS) in the CP kitten enhances the central effects of monocular occlusion. The mechanisms responsible for heightened cortical plasticity following REMS deprivation (REMSD) remain undetermined. One possible mediator of an increase in plasticity is continuous NE outflow, which presumably persists during extended periods of REMSD. Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the synthesis of NE and serves as a marker for NE-producing cells. We selectively suppressed REMS in kittens for 1 week during the CP. The number and size of LC cells expressing immunoreactivity to tyrosine hydroxylase (TH-ir) was assessed in age-matched REMS-deprived (RD)-, treatment–control (TXC)-, and home cage-reared (HCC) animals. Sleep amounts and slow wave activity (SWA) were also examined relative to baseline. Time spent in REMS during the study was lower in RD compared to TXC animals, and RD kittens increased SWA delta power in the latter half of the REMSD period. The estimated total number of TH-ir cells in LC was significantly lower in the RD than in the TXC kittens and numerically lower than in the HCC animals. The size of LC cells expressing TH-ir was greatest in the HCC group. HCC cells were significantly larger than TH-ir cells in the RD kittens. These data are consistent with presumed reduction in NE in forebrain areas, including visual cortex, caused by 1 week of REMSD.

Characteristics of divergence excess type intermittent exotropia in Asian children

Exotropia is twice as common as esotropia in Asian children, with divergence excess intermittent exotropia contributing more than one half of exotropia cases. In this study, distance-near relationships and ratios of accommodative convergence to accommodation (AC/A) are compared using different measurement methods in Asian children with divergence excess intermittent exotropia. Children with intermittent exotropia and a distance deviation exceeding the near by at least 10(Δ) were consecutively recruited. After prism cover test measurements at 6 m and 33 cm, AC/A ratios were calculated using the heterophoria method and the gradient method with -2.0 D and +3.0 D lenses at 6 m and 33 cm, respectively. AC/A ratios were recalculated after 1 hour of monocular patching. A total of 42 children (mean age, 6.9 years; range, 3-16 years) were included. The mean difference between distance and near deviation was 22(Δ) before occlusion and 14(Δ) after (P < 0.001). Approximately one third had a distance-near difference <10(Δ) after occlusion. With the heterophoria method, 100% of patients had high AC/A ratios before occlusion, with 71% continuing to have high AC/A ratios after. With the gradient method, 52% of patients had high AC/A ratios before occlusion, with 68% of this subgroup continuing to have high AC/A ratios after. Pseudo-divergence excess was found in one third of the subjects. More children were diagnosed with high AC/A ratios using the heterophoria method than with the gradient method. Without monocular occlusion, approximately one third of the children with normal AC/A ratios may be mistaken to have high AC/A ratios when measured with either method. Identification of high AC/A ratio exotropic patients is critical due to the risk of developing consecutive esotropia at near after strabismus surgery.

A multisensory visuotactile illusion induced by monocular occlusion with a black contact lens does not depend on touch signals on the face: Evidence from behavioural and modelling studies

A multisensory visuotactile illusion induced by monocular occlusion with a black contact lens does not depend on touch signals on the face: Evidence from behavioural and modelling studies

Cells in the supraoculomotor area in monkeys with strabismus show activity related to the strabismus angle

We have earlier shown that monkeys reared with daily alternating monocular occlusion for the first few months of life develop large horizontal strabismus, A/V patterns, dissociated vertical deviation (DVD), and dissociated horizontal deviation (DHD). Here, we present results from neurophysiological experiments that show that neuronal activity of cells within the supraoculomotor area (SOA) of juvenile strabismic monkeys is correlated with the angle of strabismus. There was no modulation of SOA cell activity with conjugate eye position as tested during horizontal smooth pursuit. Comparison of SOA population activity in these strabismic animals and normal monkeys (described in the literature) suggests that both vergence (misalignment in the case of the strabismic animals) thresholds and vergence position sensitivities are different in the strabismic animals compared to the normals. Our data suggest that activity within the SOA cells is important in determining the state of horizontal strabismus possibly by altering vergence tone in extraocular muscle.

Responses of Medial Rectus Motoneurons in Monkeys with Strabismus

Monkeys reared under conditions of alternating monocular occlusion during their first few months of life show large horizontal strabismus, "A" patterns, and dissociated vertical deviation. "A" patterns manifest as an inappropriate horizontal component in the deviated eye during vertical eye movements (cross-axis movement). The objective of this study was to investigate response properties of medial rectus motoneurons (MRMNs) in relation to strabismus properties. Burst-tonic activity of 21 MRMNs in the oculomotor nucleus were recorded from two monkeys with exotropia as they performed horizontal and vertical smooth pursuit (0.2 Hz, ±10°) under monocular viewing conditions. Neuronal responses and horizontal component of eye movements were used to identify regression coefficients in a first-order model for each tracking condition. Comparison of position, velocity, and constant parameter coefficients, estimated from horizontal tracking data with either eye viewing, showed no significant differences (P > 0.07), indicating that neuronal activity could account for the horizontal misalignment. Comparison of the position, velocity, and constant parameter coefficients estimated from horizontal tracking and the cross-axis condition showed no significant differences (P > 0.07), suggesting that motoneuron activity could account for most of the inappropriate horizontal cross-axis movement observed in the covered eye during vertical smooth pursuit. These data suggest that, in animals with sensory-induced strabismus, central innervation to extraocular muscles is responsible for setting the state of strabismus. Mechanical factors such as muscle length adaptation (for horizontal misalignment) and pulley heterotopy or static torsion (for "A" patterns) likely do not play a major role in determining properties in a sensory-induced strabismus.

Disparity biasing in depth from monocular occlusions

Monocular occlusions have been shown to play an important role in stereopsis. Among other contributions to binocular depth perception, monocular occlusions can create percepts of illusory occluding surfaces. It has been argued that the precise location in depth of these illusory occluders is based on the constraints imposed by occlusion geometry. Tsirlin et al. (2010) proposed that when these constraints are weak, the depth of the illusory occluder can be biased by a neighboring disparity-defined feature. In the present work we test this hypothesis using a variety of stimuli. We show that when monocular occlusions provide only partial constraints on the magnitude of depth of the illusory occluders, the perceived depth of the occluders can be biased by disparity-defined features in the direction unrestricted by the occlusion geometry. Using this disparity bias phenomenon we also show that in illusory occluder stimuli where disparity information is present, but weak, most observers rely on disparity while some use occlusion information instead to specify the depth of the illusory occluder. Taken together our experiments demonstrate that in binocular depth perception disparity and monocular occlusion cues interact in complex ways to resolve perceptual ambiguity.

Comparison of a monocular pupillometer and the pupillometry function of a binocular free-viewing autorefractor

To compare a binocular free-viewing autorefractor pupillometer (WAM 5500 Binocular Accommodation Instrument) and a monocular occlusion pupillometer (Neuroptics pupillometer). Department of Ophthalmology and Visual Sciences, Texas Tech University Health Sciences Center, Lubbock, Texas, USA. Evaluation of diagnostic test or technology. Normal subjects were tested under 1 lux and 7 lux ambient illumination with controlled distance fixation. The monocular occlusion pupillometer and free-viewing autorefractor pupillometer test order and eye test order were randomized. Devices were compared using Bland-Altman plots. Effects of eye test order and device test order were analyzed. The number of outliers (ie, difference ≥ 0.5 mm between devices) was tabulated. The mean device difference (monocular pupillometer minus binocular pupillometer) was +0.51 mm ± 0.36 (SD) (range -0.20 to +1.50 mm) in right eyes and +0.27 ± 0.31 mm (SD) (range -0.30 to +1.00 mm) in left eyes at 1 lux and +0.26 ± 0.28 mm (range -0.30 to +0.90 mm) and +0.21 ± 0.24 mm (range -0.80 to +0.40 mm), respectively, at 7 lux. The outlier frequency (N = 49) at 1 lux was 23 (47%) in right eyes and 7 (14%) in left eyes and at 7 lux, 11 (22%) and 10 (20%), respectively. At all age decades, the free-viewing autorefractor underestimated dark-adapted pupil diameter. Eye test order and device order did not cause unidirectional bias. The free-viewing pupillometer frequently disagreed with the monocular occlusion pupillometer by more than 0.5 mm. Testing the first eye with the monocular pupillometer did not induce sustained pupillary constriction that might bias results in the second eye.

Experience-Independent Development of the Hamster Circadian Visual System

Experience-dependent functional plasticity is a hallmark of the primary visual system, but it is not known if analogous mechanisms govern development of the circadian visual system. Here we investigated molecular, anatomical, and behavioral consequences of complete monocular light deprivation during extended intervals of postnatal development in Syrian hamsters. Hamsters were raised in constant darkness and opaque contact lenses were applied shortly after eye opening and prior to the introduction of a light-dark cycle. In adulthood, previously-occluded eyes were challenged with visual stimuli. Whereas image-formation and motion-detection were markedly impaired by monocular occlusion, neither entrainment to a light-dark cycle, nor phase-resetting responses to shifts in the light-dark cycle were affected by prior monocular deprivation. Cholera toxin-b subunit fluorescent tract-tracing revealed that in monocularly-deprived hamsters the density of fibers projecting from the retina to the suprachiasmatic nucleus (SCN) was comparable regardless of whether such fibers originated from occluded or exposed eyes. In addition, long-term monocular deprivation did not attenuate light-induced c-Fos expression in the SCN. Thus, in contrast to the thalamocortical projections of the primary visual system, retinohypothalamic projections terminating in the SCN develop into normal adult patterns and mediate circadian responses to light largely independent of light experience during development. The data identify a categorical difference in the requirement for light input during postnatal development between circadian and non-circadian visual systems.

Surgical Outcomes in Convergence Insufficiency-Type Exotropia

To determine the efficacy of different types of strabismus surgeries in patients with convergence insufficiency (CI)-type exotropia, according to their response to diagnostic monocular occlusion. Retrospective cohort study. Sixty-five patients with CI-type exotropia with near-distance differences of ≥10 prism diopters (PD) who underwent strabismus surgery. Patients were divided into 3 groups according to their response to monocular occlusion: (1) true-CI group: near-distance differences ≥10 PD before and after occlusion; (2) masked-CI group: near-distance differences <10 PD before occlusion and ≥10 PD after occlusion; and (3) pseudo-CI group: near-distance differences ≥10 PD before occlusion and <10 PD after occlusion. Either bilateral lateral rectus recession based on near measurements with 1 mm augmentation (BLR) or unilateral medial rectus resection based on the near deviation with lateral rectus recession based on the distant deviation (RR) was performed. Cumulative probabilities of success, near-distance differences of exodeviation, rate of recurrence per person-year, and risk factors of recurrence. There were 24 children in the true-CI group, 19 children in the masked-CI group, and 22 children in the pseudo-CI group. The cumulative probabilities of success at 2 years after BLR versus RR were 61% versus 100% in the true-CI group, 58% versus 100% in the masked-CI group, and 77% versus 71% in the pseudo-CI group. The RR procedure was significantly more successful than the BLR procedure in the true-CI and masked-CI groups. Successful outcome in CI-type exotropia was closely related to the patients' response to monocular occlusion. In patients with CI-type exotropia maintained after monocular occlusion, unilateral resection-recession based on near-distance measurements is recommended. Proprietary or commercial disclosure may be found after the references.

Convergence Excess Esotropia: A Proposed New Classification and the Effect of Monocular Occlusion on the Ac/A Ratio

Convergence excess esotropia defines an esotropia on accommodation at near fixation with binocular single vision and motor fusion at distance fixation associated with a high accommodative convergence: accommodation (Ac/A) ratio. The effect of occlusion on exotropia has been well described and is known to alter the Ac/A ratio. This study examines the effect of monocular occlusion on convergence excess esotropia. The Ac/A ratio was measured using the gradient method at 1/3 and 6 m in 10 patients with convergence excess esotropia immediately prior to and following a 30-minute period of monocular occlusion. Clinically and statistically significant differences to the angle of deviation and the Ac/A ratio were found in some patients following occlusion. Ac/A ratio measurement in convergence excess esotropia is influenced by fusional tenacity. Disrupting this fusion with a period of monocular occlusion results in changes to the angle of deviation in some patients, suggesting subcategorization of this condition into true and simulated convergence excess esotropia. Measurements of the Ac/A ratio are influenced by fixation distance.

Changes to Control of Adaptive Gait in Individuals with Long-standing Reduced Stereoacuity

Gait during obstacle negotiation is adapted in visually normal subjects whose vision is temporarily and unilaterally blurred or occluded. This study was conducted to examine whether gait parameters in individuals with long-standing deficient stereopsis are similarly adapted. Twelve visually normal subjects and 16 individuals with deficient stereopsis due to amblyopia and/or its associated conditions negotiated floor-based obstacles of different heights (7-22 cm). Trials were conducted during binocular viewing and monocular occlusion. Analyses focused on foot placement before the obstacle and toe clearance over it. Across all viewing conditions, there were significant group-by-obstacle height interactions for toe clearance (P < 0.001), walking velocity (P = 0.003), and penultimate step length (P = 0.022). Toe clearance decreased (approximately 0.7 cm) with increasing obstacle height in visually normal subjects, but it increased (approximately 1.5 cm) with increasing obstacle height in the stereo-deficient group. Walking velocity and penultimate step length decreased with increasing obstacle height in both groups, but the reduction was more pronounced in stereo-deficient individuals. Post hoc analyses indicated group differences in toe clearance and penultimate step length when negotiating the highest obstacle (P < 0.05). Occlusion of either eye caused significant and similar gait changes in both groups, suggesting that in stereo-deficient individuals, as in visually normal subjects, both eyes contribute usefully to the execution of adaptive gait. Under monocular and binocular viewing, obstacle-crossing performance in stereo-deficient individuals was more cautious when compared with that of visually normal subjects, but this difference became evident only when the subjects were negotiating higher obstacles; suggesting that such individuals may be at greater risk of tripping or falling during everyday locomotion.

Depth ordering in natural stereoscopic images: The role of monocular occlusion

Depth ordering in natural stereoscopic images: The role of monocular occlusion

Changes of Deviation After the Patch and +3.00 Diopter Spherical Lens Test in Basic Intermittent Exotropia

Purpose: To assess the change of deviation angle after the patch test and +3.00 diopter (D) spherical lens test in basic intermittent exotropia. Methods: The present study included 57 patients diagnosed with basic intermittent exotropia. The deviation angles at near and far before and after monocular occlusion of 40 minutes or more were measured. Afterward, change of deviation was also measured by placing +3.00 D spherical lenses at near. Results: Results from the study revealed pre-occlusion mean deviation angles of 23.1 7.41 prism diopters (PD) at near, and 23.9 6.56 PD at far. After the patch test, the mean deviation angles were increased to 28.3 6.50 PD (p 6.40 PD (p 7.53 PD (p 1.19 PD/D. Conclusions: Both the patch test and +3.00 D spherical lens test significantly increased the deviation angles at near and far, they helped to find the maximum deviation angle in patients with basic intermittent exotropia.

Visual Targeting of Forelimbs in Ladder-Walking Locusts

Accurate limb placement helps animals and robots to walk on substrates that are uneven or contain gaps. Visual information is important in controlling limb placement in walking mammals but has received little attention in insects. We investigated whether desert locusts walking along a horizontal ladder use vision to control limb placement. High-speed video analysis showed that locusts targeted their front legs to specific rungs in the absence of any previous contact, suggesting that visual information alone is sufficient for targeting single steps. Comparison between the proportions of missed steps before and after monocular occlusion showed that monocular visual information was used to place the ipsilateral but not the contralateral front leg. Accurate placement also depended upon mechanosensory inputs from the antennae and proprioceptive feedback from the ipsilateral but not the contralateral forelimb. Locusts also compensated for the loss of inputs to one eye by altering their stepping pattern. Changing the rung position after initiation of a step showed that targeting of the front leg depends on visual information acquired before but not during a step. The trajectory was only modified after missing the rung. Our data show that locusts walking in environments where footholds are limited use visual and mechanosensory information to place their front legs.