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Diplopia (double vision) in strabismus is prevented by suppression of the image emanating from one eye. In a recent study conducted in two macaques raised with exotropia (an outward ocular deviation) but having normal acuity in each eye, simultaneous display of stimuli to each eye did not induce suppression in V1 neurons. Puzzled by this negative result, we have modified our protocol to display stimuli in a staggered sequence, rather than simultaneously. Additional recordings were made in the same two macaques, following two paradigms. In trial type 1, the receptive field in one eye was stimulated with a sine-wave grating while the other eye was occluded. After 5 s, the occluder was removed and the neuron was stimulated for another 5 s. The effect of uncovering the eye, which potentially exposed the animal to diplopia, was quantified by the peripheral retinal interaction index (PRII). In trial type 2, the receptive field in the fixating eye was stimulated with a grating during binocular viewing. After 5 s, a second grating appeared in the receptive field of the nonfixating eye. The impact of the second grating, which had the potential to generate visual confusion, was quantified by the receptive field interaction index (RFII). For 82 units, the mean PRII was 0.48 ± 0.05 (0.50 = no suppression) and the mean RFII was 0.46 ± 0.08 (0.50 = no suppression). These values suggest mild suppression, but the modest decline in spike rate registered during the second epoch of visual stimulation might have been due to neuronal adaptation, rather than interocular suppression. In a few instances neurons showed unequivocal suppression, but overall, these recordings did not support the contention that staggered stimulus presentation is more effective than simultaneous stimulus presentation at evoking interocular suppression in V1 neurons. NEW & NOTEWORTHY In strabismus, double vision is prevented by interocular suppression. It has been reported that inhibition of neuronal firing in the primary visual cortex occurs only when stimuli are presented sequentially, rather than simultaneously. However, these recordings in alert macaques raised with exotropia showed, with rare exceptions, little evidence to support the concept that staggered stimulus presentation is more effective at inducing interocular suppression of V1 neurons.

People with strabismus acquired during childhood do not experience diplopia (double vision). To investigate how perception of the duplicate image is suppressed, we raised two male monkeys with alternating exotropia by disinserting the medial rectus muscle in each eye at age four weeks. Once the animals were mature, they were brought to the laboratory and trained to fixate a small spot while recordings were made in primary visual cortex (V1). Drifting gratings were presented to the receptive fields of 500 single neurons for eight interleaved conditions: (1) right eye monocular; (2) left eye monocular; (3) right eye9s field, right eye fixating; (4) right eye9s field, left eye fixating; (5) left eye9s field, right eye fixating; (6) left eye9s field, left eye fixating; (7) both eyes9 fields, right eye fixating; (8) both eyes9 fields, left eye fixating. As expected, ocular dominance histograms showed a monocular bias compared with normal animals, but many cells could still be driven via both eyes. Overall, neuronal responses were not affected by switches in ocular fixation. Individual neurons exhibited binocular interactions, but mean population indices indicated no net interocular suppression or facilitation. Even neurons located in cortex with reduced cytochrome oxidase (CO) activity, representing portions of the nasal visual field where perception is suppressed during binocular viewing, showed no net inhibition. These data indicate that V1 neurons do not appear to reflect strabismic suppression and therefore the elimination of diplopia is likely to be mediated at a higher cortical level. SIGNIFICANCE STATEMENT In patients with strabismus, images fall on non-corresponding points in the two retinas. Only one image is perceived, because signals emanating from the other eye that convey the duplicate image are suppressed. The benefit is that diplopia is prevented, but the penalty is that the visual feedback required to adjust eye muscle tone to realign the globes is eliminated. Here, we report the first electrophysiological recordings from the primary visual cortex (V1) in awake monkeys raised with strabismus. The experiments were designed to reveal how perception of double images is avoided.

Microtropia describes a primary ocular deviation of less than 10 prism diopters associated with harmonious anomalous retinal correspondence and reduced stereopsis. It is routinely accepted that children with microtropia are less likely to achieve equal vision following occlusion therapy than those with bifoveal fixation. The most commonly used methods of diagnosing a microtropia are the 4 diopter prism test (4∆PT) and assessment of ocular fixation. This study examines the agreement between the two tests. One hundred and twelve typically developing children without a manifest strabismus who were able to undertake a linear visual acuity test and had two or more lines of anisoacuity following refractive adaption to their full cycloplegic correction underwent assessment of the 4∆PT and ocular fixation along with their routine orthoptic examination. One hundred and twelve children (46 boys and 66 girls) attending the Orthoptic department who fitted the above criteria were included in the analysis. The mean age at examination was 6 years. 80.3% had anisometropia of at least 1.25 diopters. The 4∆PT indicated a microtropia in 74 cases, whereas assessment of fixation indicated a microtropia in 68 cases. In 88 cases (78.6%), the results of the two tests agreed. Analysis found only moderate agreement between the two tests (k = 0.540 (CI 0.379-0.700)). Logistic regression analysis comparing those children where the two tests agreed with those where they disagreed found no difference in the level of anisoacuity (p = 0.7823), degree of anisometropia (p = 0.9385), the vision in the worst eye (p = 0.5260), the refractive error in the "worst" eye (p = 0.865), or the age at the time of testing (p = 0.4485) between the two groups. When assessing for a microtropia, it was found that not all children who elicit a central suppression response on the 4∆PT are found to be fixing eccentrically and vice versa. This could potentially have implications for the treatment of their amblyopia. It is important not to rely on just one test at one time to make the diagnosis of microtropia. Rather, if one or other test indicates a microtropia the first time they are attempted, this should be reassessed regularly as treatment progresses and certainly before treatment is stopped and suboptimal visual acuity is accepted.

In humans, extrastriate visual areas are strongly activated by symmetry. However, perfect symmetry is rare in natural visual images. Recent findings showed that when parts of a symmetric shape are presented at different points in time the process relies on a perceptual memory buffer. Does this temporal integration need a retinotopic reference frame? For the first time we tested integration of parts both in the temporal and spatial domain, using a non-retinotopic frame of reference. In Experiment 1, an irregular polygonal shape (either symmetric or asymmetric) was partly occluded by a rectangle for 500 ms (T1). The rectangle moved to the opposite side to reveal the other half of the shape, whilst occluding the previously visible half (T2). The reference frame for the object was static: the two parts stimulated retinotopically corresponding receptive fields (revealed over time). A symmetry-specific ERP response from ~300 ms after T2 was observed. In Experiment 2 dynamic occlusion was combined with an additional step at T2: the new half-shape and occluder were rotated by 90°. Therefore, there was a moving frame of reference and the retinal correspondence between the two parts was disrupted. A weaker but significant symmetry-specific response was recorded. This result extends previous findings: global symmetry representation can be achieved in extrastriate areas non-retinotopically, through integration in both temporal and spatial domain.

Objective: To evaluate if there are any Binocular Vision (BV) modifications after refractive surgery in patients with hyperopia or hyperopic astigmatism. Methods: Prospective study of patients with hyperopia or hyperopic astigmatism operated of refractive surgery between May 1999 and February 2002. There were 31 patients, aged between 18 and 59, who suffered a Refractive surgery with the Lasik technique. The preoperative study included: Best corrected visual acuity, cycloplegic refraction, motility evaluation, binocular vision examination, (Polarized Vectografic study, retinal correspondence and fusion amplitude with the Synoptophore, TNO Estereopsis). We re-evaluate the patients with the same protocol at 3, 6 and 12 months of follow up after surgery. Results: 1. Postoperative BV was similar or better than the preoperative data in 76% of the cases. 2. The modifications were not homogeneous in all the tests 3. There is a tendency to the endoforia after surgery. 4. Patients without strabismus had a situation similar or better than the preoperative status in 71,42% of the cases but only one had esoforia with transitory asthenopia. 5. In the group of patients with strabismus there was a small progression towards endophoria in an important number of cases (10/14), 2 of them aggravated mildly their strabismus. 3 patients with accommodative strabismus were compensated after refractive surgery, although one need them for reading. Conclusions: After refractive surgery we have found modifications of BV or Ocular motility in an important number of cases (24%), but most of them are not symptomatic after 12 months of follow-up. We suggest to evaluate preoperatively Binocularity with a completely Orthoptic Protocol.

To determine whether late surgical correction provides fusion in adults who have constant strabismus beginning in early childhood. Materials and Methods: This was a prospective study that included 34 consecutive adults with a history of early onset strabismus who had not previously undergone surgery. They were tested with the Bagolini striated glasses (BSG), Worth four-dot (W4D) test, cover test, and four-prism diopter (4-PD) test, preoperatively, and 6 weeks after surgery. Results: The mean age was 23.8 years, 17 patients had esotropia and 17 patients had exotropia. Preoperatively, all patients demonstrated a manifest horizontal deviation ranging from 30∆ to 60∆ and had suppression. At 6 weeks postoperatively, 33 patients had a horizontal manifest deviation of

A recent study shows that retinal direction selectivity influences a subset of cells in primary visual cortex which respond to the optic flow associated with forward motion, while other cortical direction selective cells perform this computation independently.

Purpose: Accurate measurement of strabismus is vital to proper diagnosis and treatment. Objective and subjective measurement techniques can be used. The authors hypothesized that subjective measurement techniques would measure larger deviations than objective ones. Methods: Adults with strabismus, visual acuity greater than 20/50 in each eye, and normal retinal correspondence were measured in primary gaze at distance and near using the alternate prism and cover test and the red glass test. Results: Seventy-three patients were prospectively enrolled. Objective mean deviations were 9.1 (distance horizontal), 5.1 (distance vertical), 10.0 (near horizontal), and 2.6 (near vertical) prism diopters (PD). Subjective mean deviations were 10.2 (distance horizontal), 6.8 (distance vertical), 12.2 (near horizontal), and 3.2 (near vertical) PD. Subjective measurements were larger by a statistically significant margin and were more likely to show the presence of a vertical deviation not measured objectively (19 occurrences vs 2 at near, P = .008; 15 occurrences vs 0 at distance, P = .004). The measured deviations were within 5 PD horizontally and 3 PD vertically most of the time (range: 66.7% to 83.6%). Conclusions: The red glass test was more likely to measure a larger deviation at distance and near and to identify a vertical deviation not seen objectively at both distance and near. The mean difference between the tests was usually not large enough to affect surgical treatment, but could potentially result in different amounts of prescribed prism for patients treated optically. [ J Pediatr Ophthalmol Strabismus. 2017;54(4):216–220.]

Purpose: The objective of the present study was to identify the differences in real responses to prism stimulation in patients with exophoria. Methods: The present study involved 25 participants with exophoria who did not have any eye disease and had best correct visual acuity of 20/20 or better. A synoptophore was used to measure the subjective and objective deviation angles, as well as the angle of anomaly. Moreover, responses to prism stimulation were identified using afterimage transfer test with the synoptophore. Results: Among the total of 25 participants, 16(64%) showed anormalous retinal correspondence (ARC), with 5(20%) and 11(44%) having harmonious and unharmonious ARC, respectively. Prevalence of ARC was higher than normal retinal correspondence(NRC) in both groups divided according to amount of deviation angle. However, both NRC and ARC were found to have low correlations with amount of deviation angle(p=0.25, p=0.53, p=0.38). In the afterimage transfer test, position of the initial afterimage had a statistically significant correlation with angle of anomaly(p

Binocular vision means both binocular single vision and vision in both eyes recognized as monovision, and visual acuity, anisometropia, and ocular deviation are involved in binocular vision. Therefore, binocular function test should be performed during the diagnosis and treatment of the strabismus, amblyopia, and aniseikonia. The binocular function test examines the stereopsis, fusion and suppression, and abnormality of retinal correspondence, to assess whether and how much the two eyes are integrated into single vision. Because the degree of dissociation of the two eyes differs according to the individual test, careful interpretation is required.

Most research on texture density has utilized textures rendered as two-dimensional (2D) planar surfaces, consistent with the conventional definition of density as the number of texture elements per unit area. How the brain represents texture density information in the three-dimensional (3D) world is not yet clear. Here we tested whether binocular information affects density processing using simultaneous density contrast (SDC), in which the perceived density of a texture region is changed by a surround of different density. We considered the effect on SDC of two types of binocular information: the stereoscopic depth relationships and the interocular relationships between the center and surround textures. Observers compared the perceived density of two random dot patterns, one with a surround (test stimulus) and one without (match), using a 2AFC staircase procedure. In Experiment 1 we manipulated the stereo-depth of the surround plane systematically from near to far, relative to the center plane. SDC was reduced when the difference in stereo-depth between test center and surround increased. In Experiment 2 we spread the surround dots randomly across a stereo-depth volume from small to large volume sizes, and found that SDC was slightly reduced with volume size. The decrease of SDC in both experiments was observed with dense surrounds only, but not with sparse surrounds. In the last experiment we presented center and surround in the same depth plane but dichopticly, monopticly, and binocularly. A strong interocular transfer of SDC was found in the dichoptic condition. Together these results show that texture density processing is sensitive to binocularity.

The misalignment of visual input in strabismus disrupts positional judgments. We measured positional accuracy in the extrafoveal visual field (1°-7° eccentricity) of a large group of strabismic subjects and a normal control group to identify positional distortions associated with the direction of strabismus. Subjects performed a free localization task in which targets were matched in opposite hemifields whilst fixating on a central cross. The constant horizontal error of each response was taken as a measure of accuracy, in addition to radial and angular error. In monocular conditions, all stimuli were viewed by one eye; thus, the error reflected spatial bias. In dichoptic conditions, the targets were seen by separate eyes; thus, the error reflected the perceived stimulus shift produced by ocular misalignment in addition to spatial bias. In both viewing conditions, both groups showed reliable over- and underestimations of visual field position, here termed a compression of response coordinates. The normal group showed compression in the left periphery, regardless of eye of stimulation. The strabismic group showed a visual field-specific compression that was clearly associated with direction of strabismus. The variation in perceived shift of strabismic subjects was largely accounted for by the biases present in monocular viewing, suggesting that binocular correspondence was uniform in the tested region. The asymmetric strabismic compression could not be reproduced in normal subjects through prism viewing, and its presence across viewing conditions suggests a hemifield-specific change in spatial coding induced by long-standing ocular misalignment.

In subjects with alternating strabismus, either eye can be used to saccade to visual targets. The brain must calculate the correct vector for each saccade, which will depend on the eye chosen to make it. The superior colliculus, a major midbrain center for saccade generation, was examined to determine whether the maps serving each eye were shifted to compensate for strabismus. Alternating exotropia was induced in two male macaques at age 1 month by sectioning the tendons of the medial recti. Once the animals grew to maturity, they were trained to fixate targets with either eye. Receptive fields were mapped in the superior colliculus using a sparse noise stimulus while the monkeys alternated fixation. For some neurons, sparse noise was presented dichoptically to probe for anomalous retinal correspondence. After recordings, microstimulation was applied to compare sensory and motor maps. The data showed that receptive fields were offset in position by the ocular deviation, but otherwise remained aligned. In one animal, the left eye's coordinates were rotated ∼20° clockwise with respect to those of the right eye. This was explained by a corresponding cyclorotation of the ocular fundi, which produced an A-pattern deviation. Microstimulation drove the eyes accurately to the site of receptive fields, as in normal animals. Single-cell recordings uncovered no evidence for anomalous retinal correspondence. Despite strabismus, neurons remained responsive to stimulation of either eye. Misalignment of the eyes early in life does not alter the organization of topographic maps or disrupt binocular convergence in the superior colliculus.SIGNIFICANCE STATEMENTPatients with strabismus are able to make rapid eye movements, known as saccades, toward visual targets almost as gracefully as subjects with normal binocular alignment. They can even exercise the option of using the right eye or the left eye. It is unknown how the brain measures the degree of ocular misalignment and uses it to compute the appropriate saccade for either eye. The obvious place to investigate is the superior colliculus, a midbrain oculomotor center responsible for the generation of saccades. Here, we report the first experiments in the superior colliculus of awake primates with strabismus using a combination of single-cell recordings and microstimulation to explore the organization of its topographic maps.

PURPOSE: A head-centric disparity model of anomalous binocular correspondence (ABC) in strabismus provides a framework that captures several associated perceptual-motor characteristics that are unexplained by the retino-centric model (anomalous retinal correspondence) of Von Graefe and Burian. The head-centric model elaborates on the anomalous-projection model of Verhoeff and Brock, originally described by Wells, late in the 18th century, which proposes that three-dimensional space perception is based on information obtained separately from the two eyes in ABC, without binocular retinal correspondence. Binocular parallax angles formed by the two eyes' monocular head-centric directions provide sufficient information to estimate distance but not enough to stimulate diplopia without a reference for zero disparity. METHODS (MODEL DESCRIPTION): The retino-centric model computes binocular disparity from differences between retino-centric directions specified by the two eyes, with each eye's direction referenced to its own primary visual direction. The head-centric analog to retinal disparity is binocular parallax that could provide distance information but not a stimulus for diplopia. Diplopia is computed from differences between binocular parallax angles subtended by object points and a reference for zero disparity, that is, the head-centric Horopter, which adjusts for viewing distance, independently of convergence of the eyes. RESULTS (CLINICAL OBSERVATIONS): Several perceptual-motor phenomena associated with anomalous correspondence demonstrate two sensory fusion mechanisms in ABC that involve registered vergence signals and changes in the horopter, independent of vergence. CONCLUSIONS: In ABC, the subjective-squint angle is unaffected by registered vergence movements. Binocular sensory fusion is obtained via the head-centric model by adjusting the diameter of the head-centric horopter, independent of the vergence angle, from the fixation distance to the distance of another reference point. By altering the reference viewing distance for zero disparity, the sign and magnitude of disparity stimuli for fusion and diplopia are changed, thereby enabling the perception of a fused fixation target and the appreciation of physiological diplopia in strabismus. Language: en

IntroductionDissociated tests of strabismus provide valuable information for diagnosis and monitoring of ocular misalignment in patients with normal retinal correspondence. However, they are vulnerable to operator error and rely on a fixed head position. Virtual reality headsets obviate the need for head fixation, while providing other clear theoretical advantages, including complete control over the illumination and targets presented for the patient's interaction.PurposeWe compared the performance of a virtual reality-based test of ocular misalignment to that of the traditional Lees screen, to establish the feasibility of using virtual reality technology in ophthalmic settings in the future.MethodsThree patients underwent a traditional Lees screen test, and a virtual reality headset-based test of ocular motility. The virtual reality headset-based programme consisted of an initial test to measure horizontal and vertical deviation, followed by a test for torsion.ResultsThe pattern of deviation obtained using the virtual reality-based test showed agreement with that obtained from the Lees screen for patients with a fourth nerve palsy, comitant esotropia, and restrictive thyroid eye disease.ConclusionsThis study reports the first use of a virtual reality headset in assessing ocular misalignment, and demonstrates that it is a feasible dissociative test of strabismus.

We describe a unique case in which a retinal slippage fold after right retinal detachment surgery resulted in a contralateral monocular scotoma. The scotoma in the left visual field matched the right retinal fold in visual space. This previously undescribed phenomenon could be explained by a lack of response from visual cortical neurons receiving inputs from the redundant folded retina. This may represent a top-down plasticity in the cortical retinotopic map.

© 2014 the authors. In strabismus, potentially either eye can inform the brain about the location of a target so that an accurate saccade can be made. Sixteen human subjects with alternating exotropia were tested dichoptically while viewing stimuli on a tangent screen. Each trial began with a fixation cross visible to only one eye. After the subject fixated the cross, a peripheral target visible to only one eye flashed briefly. The subject’s task was to look at it. As a rule, the eye to which the target was presented was the eye that acquired the target. However, when stimuli were presented in the far nasal visual field, subjects occasionally performed a “crossover” saccade by placing the other eye on the target. This strategy avoided the need to make a large adducting saccade. In such cases, information about target location was obtained by one eye and used to program a saccade for the other eye, with a corresponding latency increase. In 10/16 subjects, targets were presented on some trials to both eyes. Binocular sensory maps were also compiled to delineate the portions of the visual scene perceived with each eye. These maps were compared with subjects’ pattern of eye choice for target acquisition. There was a correspondence between suppression scotoma maps and the eye used to acquire peripheral targets. In other words, targets were fixated by the eye used to perceive them. These studies reveal how patients with alternating strabismus, despite eye misalignment, manage to localize and capture visual targets in their environment.

Bitemporal hemianopic visual field impairment frequently leads to binocular vision difficulties. Patients with bitemporal hemianopia with pre-existing exophoria complain of horizontal diplopia, sometimes combined with vertical deviation (with pre-existing hyperphoria). The symptoms are a result of the phoria decompensating into a tropia (hemi-slide) due to the lack of retinal correspondence between the remaining nasal fields of both eyes. We measured these effects using a dichoptic perimeter. We showed that aligning the eyes with prisms could prevent diplopia if the bitemporal hemianopia is incomplete. We also describe the successful use of a novel fusion aid – the ‘stereo-typoscope’ – that utilizes midline stereopsis to prevent diplopia resulting from hemi-sliding in patients with complete bitemporal hemianopia.

Exploratory research to investigate the monocular change in visual acuity due to type of occlusion of the fellow eye (interocular effect) in amblyopes and nonamblyopes.The study design was a prospective convenience sampling of consecutive eye clinic patients with amblyopia/amblyogenic factors and visually normal volunteers. Participants were divided into two main groups based on entry-level visual acuity using clinical methods: amblyopes (≥2 lines interocular difference) and nonamblyopes. Ocular alignment, refractive error, stereoacuity, fixation status, and retinal correspondence were determined. The change in acuity of the nondominant eye based on two types of dominant eye occlusion (translucent, lightproof) was derived from a computer-generated acuity test using staircase methodology.Some participants in each main group had an interocular effect of up to 0.15 logMAR. However, both overall group means did not show an improved visual acuity with one type of occlusion compared to the other. Subgroup analysis revealed a significant increase in the magnitude of interocular effect with esodeviations and abnormal retinal correspondence. Ansiometropic and strabismic amblyopes differed, showing monocular improvements with lightproof and translucent occlusion, respectively.Interocular effect related to the amount of light transmission allowed by the type of occlusion over the dominant eye may differ in amblyopia subtypes and increased magnitude of effect is related to the presence of esotropia and abnormal retinal correspondence.

Purpose People with reduced visual acuity are permitted to drive with the aid of bioptic telescopes in the USA, the Netherlands, and Canada. When viewing through a monocular bioptic telescope, suppression of the deviating eye in strabismus may reduce the ability of the non-telescope eye to detect objects whose images fall in the ring scotoma area of the telescope eye, which could impair detection of traffic-relevant events. This ability to detect stimuli in the ring scotoma area was compared for strabismic and non-strabismic patients. Methods Ten strabismic and six non-strabismic patients with bilaterally reduced visual acuity (0.30–1.0 logMAR, 6/12 to 6/60) participated. A dichoptic perimeter presented stimuli to the fellow (non telescope) eye in the area of the ring scotoma under binocular viewing. Fellow-eye detection rates were determined with and without a bioptic, on uniform and patterned backgrounds, while performing passive (viewing a cross) and active (reading letters) fixation tasks. Results All strabismic patients were found to have anomalous retinal correspondence. Both non-strabismic and strabismic patients had lower fellow-eye detection rates on patterned than on uniform backgrounds, and while performing the active task. In addition, strabismic patients had lower detection with than without the bioptic on the patterned background. They also had a larger decrease in detection from the uniform to the patterned background than non-strabismic patients (26% vs 8%). Depending on the angle and direction of the deviation relative to the stimulus side, strabismus either increased or decreased fellow-eye stimulus eccentricity on the retina. Larger detection rate reductions between the uniform and patterned backgrounds were associated with more eccentric stimulus locations (ρ = 0.61, p = 0.013). Conclusions Both strabismic patients and non-strabismic patients were able to detect stimuli with the fellow eye in the ring scotoma area, demonstrating successful bi-ocular multiplexing. However, strabismic patients generally had a greater reduction in detection performance from the uniform to the patterned background than non-strabismic patients, which was accounted for in part by differences in stimulus eccentricities on the retina (that varied with the angle and direction of the strabismus). However, a study with a larger sample, including participants with strabismus and normal retinal correspondence, is needed before our findings can be generalized.

Intermittent exotropia is a common oculomotor anomaly where one eye intermittently deviates outwards. Patients with this type of strabismus are often not aware of the exodeviation and do not usually experience diplopia. In this review, we discuss what is known about the cortical mechanisms which achieve single vision during exodeviation in this condition, and highlight some outstanding questions.

Purpose:- Disparity sensitivity may be explained by interocular positional differences of the receptive fields (RF) of visual cortical cells or by interocular shifts of the On and Off RF subregions. Since this latter model assumes shifts are orthogonal to the orientation of the RF, cells with disparity sensitivity should be oriented. The objective of the present study is to test this assumption.Methods:- Single unit recordings were performed in areas V1 and V2 of two Macaca mulatta. For assessing disparity sensitivity, we generated dynamic random dot stereograms. A stereofigure was flashed over the cell RF with different horizontal disparities. To assess orientation sensitivity we used a flashing bar with eight orientations, in several positions over the cell RF in a pseudorandom manner.Results:- We found no relationship between sensitivity to horizontal disparity and orientation preference in V1 and V2 cells.Conclusions:- Our data indicate that horizontal disparity sensitivity and orientation preference are unrelated properties. This favors the notion that sensitivity to horizontal disparity is mostly based on RF interocular horizontal positional differences. © 2010 The Authors. Ophthalmic and Physiological Optics © 2010 The College of Optometrists.

Purpose: Fixation disparity, i.e. the vergence error for stationary fusion stimuli, can be measured objectively with eye trackers and subjectively with nonius lines. Between these two measures, previous studies found differences that tended to be proportional to the amount of forced vergence, i.e. the discrepancy between vergence and accommodative stimulus. We investigate whether objective and subjective fixation disparity might be similar without forced vergence. Method: We simultaneously measured fixation disparity with the EyeLink II system and with flashed dichoptic nonius lines in 17 subjects who observed targets at a vergence stimulus of 6 deg in an haploscope with 60 cm viewing distance. Results: We found individual differences in objective fixation disparity in a range of about 20 (eso) to −60 (exo) min arc which was considerably larger than the range of subjective fixation disparity. Results were similar for long fixation periods (about 15 s) and short fixation periods (about 1.5 s) between 5 deg saccadic gaze shifts. Further, objective fixation disparity was correlated with objective heterophoria, i.e. the vergence state without a fusion stimulus (r = 0.8, p

The retinal correspondence was measured at several points of the binocular visual field in a case of anomalous correspondence. It was found that the anomalous correspondence was not limited to the foveae, but that there were pairs of peripheral anomalously corresponding points. The angle of anomaly was not constant over the binocular field. The correspondence was reciprocal at some points, non-reciprocal at others. A comparison was made between normal and anomalous correspondence and the learning of anomalous correspondence was discussed.

Prolonged viewing of an unchanging pattern causes adaptation, which can be demonstrated by visual aftereffects such as the tilt and waterfall illusions. In normal observers, these typically exhibit interocular transfer (IOT), being observed when the adapting and test stimuli are shown to different eyes. Convergence of inputs from both eyes upon binocular neurons only occurs in the primary visual cortex (V1), and adaptation is substantially a cortical phenomenon. However, little is known about a physiological substrate of IOT in V1 and how it relates to the binocularity of neurons and local ocular dominance (OD) column architecture. We employed optical imaging to obtain OD maps in cat V1 and recorded from single neurons at targeted penetration sites to quantify their adaptation by drifting gratings when adapter and test stimulus were presented either to the same or to the opposite eyes. In contrast to earlier reports, clear IOT of adaptation was observed for binocular as well as monocular neurons; at population level, its strength amounted to 55%. Moreover, the position of the cells with respect to OD column borders had no significant effect on the strength of IOT. IOT does not appear to strongly depend on conventional binocularity of neurons.

In early acquired strabismus the visual system typically develops sensory adaptations to avoid the symptoms of diplopia and visual confusion (Pickwell, 1984), often reported as “double vision”. If these adaptations did not develop, the patient would experience diplopia, as the image of an object seen with the fovea of the nondeviated eye would also be seen with a peripheral retinal area of the deviated eye (retinal images would not fall on corresponding points); and visual confusion, as the fovea of the deviated eye would receive an image different to that falling on the fovea of the non-deviated eye (two corresponding points would receive different images which would appear superimposed, in the same direction). These phenomena are usually reported, when they occur in central retina, by patients who develop strabismus as adults (at an age when they typically do not develop adaptations). While diplopia and visual confusion occur only under binocular viewing conditions (as a consequence of strabismus), the resultant adapting mechanisms may function under either binocular viewing conditions or may persist under monocular conditions. The sensory adaptive changes that may occur during binocular vision are suppression and abnormal retinal correspondence (ARC) (Von Noorden, 1969; Pickwell, 1984). A suppression scotoma may appear in the central retina of the deviated eye to avoid visual confusion and may extend (nasally in ET) to avoid diplopia (Pickwell, 1984). ARC is a binocular adaptation of the visual direction system, measurable only under binocular conditions, where objects are perceived as localized in the same direction in spite of their images falling on normally non-corresponding retinal locations (Pickwell, 1984). These adaptation mechanisms may persist monocularly in the form of amblyopia or eccentric fixation. Amblyopia is the developmental impaired vision (of no organic cause) typified by reduced visual acuity, distorted space perception and incorrect localization of objects in space (Bedell et al., 1985; Skottun et al., 1986; Fronius et al., 2004). It may be a consequence of long term binocular suppression that remains under monocular conditions - although some advocate that it may precede the strabismus (Schor, 1978). Strabismic amblyopia is most commonly associated with constant ET (Quah et al., 1991). Eccentric fixation refers to abnormal monocular visual fixation with an area other than the fovea (Von Noorden, 1970; Kirschen and Flom, 1978; Pickwell, 1984). The eccentric fixation locus typically occurs within 5deg (~10Δ) from the fovea (Flom et al., 1980; Pickwell, 1981; Bedell et al., 1990; Matilla et al., 1995; Cleary and Thompson, 2001) and it may be stable or unstable. The perceived direction of an object in space is determined by the retinal location it stimulates in conjunction with extraretinal information (e.g. eye position in orbit). Each retinal locus has a retinal visual direction associated with it. In a normal eye, the fovea has the principal visual direction (PVD) that is associated with the straight-ahead egocentric visual direction when the eye is in the primary position of gaze. Likewise, each retinal locus has a motor value, which means that it induces a fixed magnitude eye movement (saccadic) during the fixation reflex that brings the fovea to the direction of the object that stimulated that retinal location. The zero retinomotor value (ZRMV) (normally at the fovea) is the retinal point to which the eye makes a reflex saccadic re-fixation movement when presented with a peripheral stimulus (Ciuffreda, 1991; Steinman et al., 2000). Usually the new monocular fixation locus in eccentric fixation becomes associated with the PVD and the ZRMV (Von Noorden, 1970; Ciuffreda et al., 1979; Bedell and Flom, 1981), although some authors argue that the PVD may remain unchanged (Pickwell, 1984). ET with an angle of deviation of about 15deg (~28Δ) is not rare (Swan, 1948; De Muelenaere and Hambresin, 1956; Guzzinati, 1956; Prizner, 1975; Olivier and Von Noorden, 1981; Birch et al., 2004). In these cases, the fovea of the deviated eye is directed at an object whose image falls within the physiological blind spot of the non-deviated eye and vice versa. It has been suggested that this phenomenon may be a mechanism to avoid diplopia (Swan, 1947) and visual confusion. Swan (1948) defined the Blind Spot Syndrome as a type of adaptation to ET with angle of deviation of about 15deg, with occasional diplopia, normal retinal correspondence, and normal visual acuity. Others have reported cases of Blind Spot Syndromes (De Muelenaere and Hambresin, 1956; Guzzinati, 1956; Uemura, 1964; McKenzie et al., 1970; Prizner, 1975; Harrer, 1984). However, controversy surrounds the nature of these cases. The case we report here is not a case of Blind Spot Syndrome (see Discussion section). We have documented, using an objective method of assessing visual direction, a case of left ET wherein (under left monocular viewing) the left PVD and ZRMV are located within the left physiological blind spot.

Background Prism overcorrection is a complementary procedure to reduce the residual postoperative esotropia caused by anomalous retinal correspondence (ARC) after surgery for esotropia. We have investigated the results of this treatment. Patients and methods For Group 1, the files of 63 patients treated with postoperative prism overcorrection in the Department of Ophthalmology, University of Giessen, were evaluated regarding the pre-and postoperative squint angles (SPCT, simultaneous and APCT, alternate prism and cover test) and the angle of ARC, determined by the red filter test and by the increase of esotropia after neutralisation of the squint angle (APCT). Postoperatively, squint angles had been measured immediately (APCT) after removal of the eye patch and 10 minutes to 2 hours later (SPCT and APCT). Subsequently, prism overcorrection was performed with a Fresnel prism foil (40 PD basis temporally) in front of the fellow eye for a maximum of 3 months. After 3 months, SPCT and APCT were performed. For Group 2, the files of 28 patients with a preoperative angle of ARC of 5 degrees or more, treated in the Department of Ophthalmology, University of Heidelberg, were evaluated. These patients had not been treated with prism overcorrection. The squint angles had been measured (SPCT and APCT) on the preoperative day, on the first postoperative day, a few hours after removing the eye patch, and after three months. Results For Group 1, at surgery, the patients were 4 to 12 years old (median: 6.2 years). The preoperative squint angle ranged from + 5 degrees to + 27 degrees (median: + 12 degrees) in the SPCT and from + 7 degrees to + 27 degrees (median: + 14 degrees) in the APCT. The angle of ARC was between + 4 degrees and + 15 degrees (median: + 7 degrees). Both combined recess and resect surgery (with or without additional oblique muscle surgery) or bilateral retroequatorial medial rectus myopexy, in part depending on the squint angle pattern with medial rectus recession, were performed. Immediately after removing the patch, the squint angle (APCT) was between - 10 degrees and + 5 degrees (median: + 1 degrees). Ten minutes to 2 hours later, the manifest squint angle ranged from 0 to + 12 degrees (median: + 7 degrees). The angle had decreased significantly to - 6 to + 12 degrees (median: + 5 degrees) after 3 months. For Group 2, the patients' ages were between 5 and 12 years (median: 6.5 years). The squint angles ranged from + 11.5 degrees to + 35 degrees (median: + 20 degrees) in the SPCT and APCT. The angle of ARC was between + 5 degrees and + 17 degrees (median: + 8 degrees). Combined recess and resect surgery or bilateral recession of the medial rectus (with or without oblique muscle surgery both) were performed. The SPCT several hours after removal of the patch showed angles of - 4 degrees to + 14 degrees (median: + 4.25 degrees). Three months later the manifest squint angles ranged from - 5 degrees to + 14 degrees (median: + 3 degrees). Discussion After prism overcorrection (Group 1), there was a significant reduction of the residual esotropia. Without this additional treatment (Group 2), there was no significant change in the postoperative squint angle. However, neither the positive outcome in Group 1 nor the difference to Group 2 do unequivocally prove that there is a beneficial effect of prism overcorrection, since preoperative conditions were different and the sample size in Group 2 was small, especially after matching for equal preoperative conditions. A spontaneous reduction of the postoperative esotropia cannot be excluded. Further studies are necessary in order to investigate the specific effect of prism overcorrection.

Two to five percent of all children are affected by developmental strabismus, a disorder in which the normal development of binocular vision is disrupted and the eyes become permanently misaligned.1–3 The misalignment of the two eyes can cause diplopia (double vision) and visual confusion. In diplopia, an object is projected to the fovea of one eye as well as to the peripheral retina of the deviated eye, and visual confusion occurs due to the projection of different objects in the environment to the foveae of the two eyes.4 However, patients with developmental strabismus do not experience diplopia and visual confusion because of two adaptive mechanisms adopted by the brain: visual suppression and anomalous retinal correspondence.4–6 Visual suppression of the images from one eye (deviated eye) results in temporary blind fields in the retina, known as scotomas, that are present in binocular viewing conditions but not in monocular viewing conditions. It could be that the fovea of the deviated eye is suppressed to avoid visual confusion, and that portions of temporal hemiretina in exotropes and nasal hemiretina in esotropes are suppressed to prevent diplopia.1,6–8 However, Economides et al.9 mapped areas of visual suppression in exotropic human subjects by using a color discrimination task and found that the fovea and portions of the temporal retina immediately adjacent to the fovea in the deviated eye are not suppressed in exotropes. They also showed that visual confusion is avoided by anomalous retinal correspondence (ARC), in which the fovea of the viewing eye is paired with a noncorresponding location in the deviated eye. Strabismic patients with relatively little amblyopia can switch the eye of fixation spontaneously depending on the location of the object they want to fixate, and this fixation-switch feature of strabismus is likely the result of visual suppression of portions of each eye's retina.7,10–12 Studies from our lab have replicated fixation-switch behavior in a monkey model for strabismus, and analyzing the spatial patterns of fixation switch in strabismic monkeys has provided insight into how visual information from the two eyes is processed and converted into action in strabismus.13,14 Fundamentally our results supported the idea that fixation-switch behavior follows from suppression of a portion of temporal retina in exotropes and a portion of nasal retina in esotropes. However, the fovea and portions of the temporal retina immediately adjacent to the fovea (portions of the nasal retina adjacent to the fovea in esotropes) were apparently not suppressed because the animals switched fixation when the target appeared in these retinal locations, thereby in agreement with the suppression maps of Economides et al.9 A novel finding was that the transition zone between preference for right eye fixation and preference for left eye fixation was “fuzzy” in that the animals could choose either eye to fixate the target appearing at certain spatial locations, suggesting that visual suppression can be partial. Agaoglu and colleagues13 proposed a framework for fixation-switch behavior wherein the oculomotor system has retinal error information from both eyes, and the choice of fixating eye is made according to the strength of retinal error representations from each eye. Economides et al.15 also examined fixation-switch behavior in human exotropes and showed a coupling between perceptual state and spatial patterns of fixation-switch behavior. The overall motivation for the current study was to continue to investigate the nature of the visual information available to the brain from the two eyes that it can use to drive eye movements. Specifically, we asked whether motion information available only to the deviated eye could be used by the oculomotor system to drive eye movements. Similar to studies that employed dichoptically presented drifting grating stimuli with motion in opposite directions to assess eye dominance or interocular suppression from optokinetic motor responses,16–22 our strategy was to present an optokinetic stimulus (a drifting grating) only to the deviated eye of the strabismic monkeys and determine whether it was sufficient to generate an optokinetic nystagmus (OKN). Our investigation suggests that optokinetic oculomotor responses can indeed be generated by a stimulus that falls on/around the fovea of the deviated eye, supporting the overall hypothesis that the oculomotor system has retinal information available from both eyes in strabismus. Some of these data have been presented before (Agaoglu S, et al. IOVS 2014;55:ARVO E-Abstract 2573).

Purpose We present a new method for identifying the absolute location (i.e., relative to the optic disc) of the preferred retinal location (PRL) simultaneously for the two eyes of patients with central vision loss. For this, we used a binocular eye-tracking system that determines the pupillary axes of both eyes without a user calibration routine. Methods During monocular viewing, we measured the pupillary axis and the angle between it and the visual axis (angle Kappa) for 10 eyes with normal vision. We also determined their fovea location relative to the middle of the optic disc with the MP-1 microperimeter. Then, we created a transformation between the eye-tracking and microperimeter measurements. We used this transformation to predict the absolute location of the monocular and binocular PRLs of nine patients with central vision loss. The accuracy of the monocular prediction was evaluated with the microperimeter. The binocular PRLs were checked for retinal correspondence and functionality by placing them on fundus photographs. Results The transformation yielded an average error for the monocular measures of 0.2 (95% confidence interval, 1.0 to -0.6 degrees) horizontally and 0.5 (95% confidence interval, 1.1 to -0.1 degrees) vertically. The predicted binocular measures showed that the PRLs were generally in corresponding locations in the two eyes. One patient whose PRLs were not in corresponding positions complained about diplopia. For all patients, at least one PRL fell onto functional retina during binocular viewing. Conclusions This study shows that measurements of the location of the binocular PRLs relative to the pupillary axes can be transformed into absolute locations.

Patients with retinal degeneration lose sight due to the gradual demise of photoreceptors. Electrical stimulation of surviving retinal neurons provides an alternative route for the delivery of visual information. We demonstrate that subretinal implants with 70-μm-wide photovoltaic pixels provide highly localized stimulation of retinal neurons in rats. The electrical receptive fields recorded in retinal ganglion cells were similar in size to the natural visual receptive fields. Similarly to normal vision, the retinal response to prosthetic stimulation exhibited flicker fusion at high frequencies, adaptation to static images and nonlinear spatial summation. In rats with retinal degeneration, these photovoltaic arrays elicited retinal responses with a spatial resolution of 64 ± 11 μm, corresponding to half of the normal visual acuity in healthy rats. The ease of implantation of these wireless and modular arrays, combined with their high resolution, opens the door to the functional restoration of sight in patients blinded by retinal degeneration.

BACKGROUND: Patients suffering from pituitary adenomas and diseases of the chiasma typically show a bitemporal hemianopia. The residual undisturbed nasal visual fields of both eyes should have an extension of (at least) 120 degrees and are according to the actual German traffic rules (FeVAndV) for cars of the classes A, B, M, L and T. The intact half fields fit geometrically to one virtual normal field, that seems to correspond in the centre of a normal field. Reports on this problem often do not address correctly the questions of suitability for participation in road traffic. PATIENTS: The case of a patient with typical bitemporal hemianopia illustrates the sensorial peculiarities: the functioning temporal retinal halves do not correspond. This patient suffered additionally from disturbing diplopia due to a small-angle exotropia. The extent of the performed eye muscle surgery was selected to induce a slight overcorrection, i. e., resulting in 3 to 5 degrees esotropia. This eliminated the diplopia, but resulted in a vertical scotoma of the extension of the esotropia. CONCLUSIONS: In bitemporal hemianopia the undisturbed nasal visual half fields do not add up to a "nearly normal field of one eye". Moreover, either diplopia or--much more dangerous in traffic--a central vertical scotoma is the result. The explanation for this is a sliding of the hemifields of each eye without stabilisation by corresponding areas of the retinas of the right and left eyes. The peripheral extension of the visual field is not the key to the problem to imagine how a patient with typical bitemporal hemianopia will visualise daily life and traffic. In bitemporal hemianopia there is substantially no eligibility for driving a car or motor bicycle in road traffic. Language: de

Background: An unequal weighting of the eyes in the directional perception ofstereodisparate objects, is referred to as ocular prevalence of the right or left eye, respectively. Between 1962 and 1964 H.-J. Haase developed a valence test for the prismatic correction of heterophoria. He suggested that there would be less prevalence for stereo images presented in front of or behind a reference plane, and that this asymmetry of prevalence may be related to the direction of the associated heterophoria (eso- or exophoria). According to H.-J. Haase, the asymmetry may indicate a fixation disparity with a corresponding shift in retinal correspondence. Hence, the valence test could be an indicator for the prismatic correction of heterophoria. Methods: Prevalence was tested in 37 subjects, using three methods: The subjects were asked to describe their perception (1), to make a paper drawing of their perception (2), and to align the position of the stereo images to the central fusion target with a computer-controlled device (3). Methods 2 and 3 were used to reduce a possible suggestive influence on part of the investigator. The associated heterophoria was determined with the cross test by H.-J. Haase. Results: Depending on whether the triangular stereo images were presented behind or in front of the reference plane, more or less prevalence was measured (mean values) in the group with exophoria than in the group with esophoria. These results were confirmed with all three methods. The asymmetry of prevalence was correlated with the direction of the associated heterophoria with r=0.5. Conclusion: Statistically, these results confirm Haase's hypothesis of a relation between the asymmetry of ocular prevalence and the direction (eso- or exophoria) of the associated heterophoria. Since this relation holds true only for the group mean value, but not for each individual, the valence test cannot be generally recommended as an adjunct for the prismatic correction of heterophoria.

Background and Objective: Acute acquired concomitant esotropia is a rare form of strabismus that usually presents during infancy or early childhood with diplopia and minimal refractive error. The aim of this study was to evaluate the response to the prism adaptation test in a group of normosensorial patients with acute acquired concomitant esotropia and to determine its predictive value for surgical outcome. Patients and Methods: Six patients (median age, 11.5 years) with acute acquired concomitant esotropia underwent the prism adaptation test by applications of Fresnel press-on and prismatic lenses. The sensorial condition of each patient had been evaluated with the TNO stereopsis test, the Irvine test, Bagolini striated glasses, and the Worth four-dot test during the prism adaptation test, when maximum compensation angle was achieved, and after surgery. In all patients, surgery was performed based on the angle of the squint after the prism adaptation test. Patients were observed 1 day, 3 months, 6 months, and 1 year after surgery. Results: An increase in the angle of the squint occurred in all patients during prism adaptation. The maximum value was obtained in the same amount of time whether with prisms of increasing power or by direct application of the final value of the prisms. The final prismatic value (target angle) was always the same. Conclusions: The accuracy of the patients' selection confirmed the existence of highly reproducible compensational movements to the prismatic correction in not only patients with anomalous retinal correspondence but also normosensorial patients. Prism adaptation test results were useful in these patients because of their high predictive value for the surgical treatment. J Pediatr Ophthalmol Strabismus 2005;42:342–348.

This paper compares monocular versus binocular viewing in AMD patients during fixation and the potential of binocular function. Twenty-seven patients with bilateral AMD were recruited. A scanning laser ophthalmoscope was used to identify PRLs and map retinal scotomas monocularly. An infrared eye tracker was used to evaluate gaze position changes (and indirectly retinal locus changes) between monocular and binocular fixation. Through their combined use the retinal loci used for fixation under binocular viewing conditions were identified. Binocular function was tested with Bagolini striated glasses and fusion at the PRLs was tested with a computer-driven display. It was found that only five patients used the same PRL to fixate under monocular and binocular conditions for both eyes. 44.4% of the patients with symmetrical scotomas but only one patient with asymmetrical scotomas showed no shift in gaze position. However, there was no difference between them (chi-square, p = 0.03). Binocular PRLs fell on retinal areas that could be fused in 85.1% of the patients. Still, in 25.9% of the patients binocular PRLs fell within the scotoma in the worse eye. All patients exhibited fusion when tested with the Bagolini glasses, but only 33% showed evidence of fusion near the PRL. These results demonstrate that AMD patients could use a different PRL when viewing binocularly versus monocularly. Although retinal correspondence of binocularly used fixation locus is retained, fusion near the PRL seems impaired in the majority of the cases. These results provide an insight into how people with bilateral scotomas operate in the real world.