Binocular interactions in normal and anomalous binocular vision

Binocular interactions for grating patterns were investigated in humans with normal binocular vision and in humans with abnormal binocular visual experience due to strabismus and/or amblyopia via 1) comparison of monocular and binocular contrast thresholds; 2) interocular transfer of the threshold elevation aftereffect; and 3) dichoptic masking. Whereas the normal observers showed improved binocular over monocular contrast sensitivity (i.e., binocular summation) and substantial interocular transfer of the threshold elevation aftereffect, the abnormal observers showed an absence of binocular summation and no significant interocular transfer. The dichoptic masking experiments showed that a suprathreshold masking grating presented to one eye elevated the contrast threshold for gratings presented to the fellow eye, within a narrow range of spatial frequencies (about 1 octave wide at half height) and orientations, centered about the spatial frequency and orientation of the mask. The magnitude and bandwidth of this masking effect was similar in subjects with normal and abnormal binocular vision, occurring even when the masking grating was presented to the amblyopic eye. These effects depend upon the contrast of the masking grating. In individuals with normal binocular vision, a grating with subthreshold contrast presented to one eye reduces the contrast threshold for detection of gratings of similar spatial frequency and orientation presented to the fellow eye. No such subthreshold summation is evident in the amblyopic observers. We conclude that while strabismus and/or amblyopia disrupted the normal excitatory interactions between the two eyes, cortical inhibitory binocular connections were not disrupted.     

Binocular interactions in normal and anomalous binocular vision: effects of flicker.

Temporal modulation thresholds were determined for monocular viewing and for binocular viewing of stimuli presented in phase or in counterphase to each eye of observers with normal binocular vision and those lacking stereopsis. The results showed that in individuals with normal binocular vision sensitivity was much greater for in-phase than for counterphase stimulation at low temporal frequencies, but that this superiority declined at higher temporal frequencies. Averaged across frequencies, binocular sensitivity for in-phase stimulation was 40-50% higher than monocular sensitivity. In contrast, in the observers lacking stereopsis the ratios of binocular in-phase/monocular sensitivity averaged 1.02, and there were no significant differences in sensitivity to in-phase and counterphase stimulation. This failure of binocular integration at threshold does not result from differences in transmission time between the 2 eyes. However, while individuals lacking stereopsis showed an absence of binocular interaction for uniform-field flicker at threshold, they showed suprathreshold dichoptic temporal frequency masking which was similar to that found in normal persons.     

正常人双眼视觉的多焦视觉诱发电位研究

目的　研究正常人mVEPs双眼总和特征 ,对mVEPs在双眼视觉研究中的应用价值作一初步探讨。方法　应用VERIS视觉电生理仪对 1 0例正常受检者双眼及单眼mVEPs反应进行检测 ,对上下半侧视野、 1 /4象限视野及半环形视野mVEPs反应总和波进行双眼与单眼反应振幅的对比研究。结果　上下半侧视野、 1 /4象限视野mVEPs反应总和波的双眼反应振幅比单眼反应振幅明显增大 ,表明存在mVEPs双眼总和。半环区域mVEPs反应分析 ,中央区存在mVEPs双眼总和 ,上方中心外围区域双眼总和现象不明显。结论　正常人存在mVEPs双眼总和 ,视野中央区 5°较周边区双眼总和似乎更显著 ,提示黄斑区对双眼视觉起更重要作用。mVEPs用于双眼视觉研究是一个有价值的工具 ,可以提供比传统P -VEP更详细的信息。     

Fourier analysis of steady-state visual evoked potentials in subjects with normal and defective stereo vision

The purpose of this work was to study the second harmonic in the steady state pattern visual evoked potential (ssVEP) to various stimulus frequencies in subjects with normal and defective binocularity. ssVEPs were elicited by 4 c/deg sinusoidal gratings, with temporal frequencies ranging from 5 to 20 Hz (exp. 1) and 15 to 27.5 Hz (exp. 2). Responses were Fourier analysed and power and phase of the second harmonic to stimulus frequency were measured. For power, binocular enhancement in a bimodal fashion was found both in normals and in subjects with defective binocularity. The power with binocular stimulation was significantly higher in the normal group in the high frequency domain. Latency, estimated from the phase-frequency function, was longer in the group with defective binocularity, but this was statistically significant only for the high frequency domain. The results suggest that a visual system with normal binocular function can follow a stimulus with high temporal frequency more accurately than a system with disturbed binocularity.     

A psychophysical study of human binocular interactions in normal and amblyopic visual systems

During infancy and childhood, spatial contrast sensitivity and alignment sensitivity undergo maturation, and during this period the visual system has considerable plasticity. The purpose of this study was to compare the nature of interocular interactions of these spatial functions in normally sighted children and adults, and to study the extent to which interocular interactions are impaired in anisometropic amblyopia. Spatial functions were measured under three viewing conditions: monocular (fellow eye occluded), dichoptic (uniform stimulus presented to the fellow eye but with a peripheral fusion lock), and binocular. Measurements were made in each eye during monocular and dichoptic viewing. In the contrast sensitivity task, Gabor stimuli were presented in one of two temporal intervals. For the alignment task, a three-element Gabor stimulus was used. The task of the subject was to indicate the direction of displacement of the middle patch with respect to the outer patches. The findings indicate that in children, binocular contrast sensitivity was better than monocular (binocular summation) but so too was dichoptic sensitivity (dichoptic summation). The magnitude of binocular/dichoptic summation was significantly greater in children than in normally sighted adults for contrast sensitivity, but not for alignment sensitivity. In anisometropic amblyopes, however, we find that for the group as a whole the amblyopic eye does not benefit when the fellow eye views a dichoptic stimulus, compared to dark occlusion of that eye. In addition, we found considerable inter-individual variation within the amblyopic group. Implications of these findings for techniques used in vision therapy are discussed.     

Stereoacuity development in children with normal binocular single vision.

We made 344 stereoacuity determinations (Titmus Stereotest) on 321 children, ages 1 1/2 to 13 years, who had normal binocular single vision tested by other factors. The data showed a gradual improvement in stereoacuity scores with increasing age--up to age 9--when a normal stereoacuity of 40 seconds of arc was consistently found. The lower limits of stereoacuity compatible with normal binocular single vision were 3 1/2 years, 3,000 seconds; 5 years, 140 seconds: 5 1/2 years, 100 seconds; 6 years, 80 seconds; 7 years, 60 seconds; and 9 years, 40 seconds.     

Eye position stability in amblyopia and in normal binocular vision

Purpose. We investigated whether the sensory impairments of amblyopia are associated with a decrease in eye position stability (PS). Methods. The positions of both eyes were recorded simultaneously in three viewing conditions: binocular, monocular fellow eye viewing (right eye for controls), and monocular amblyopic eye viewing (left eye for controls). For monocular conditions, movements of the covered eye were also recorded (open-loop testing). Bivariate contour ellipses (BCEAs), representing the region over which eye positions were found 68.2% of the time, were calculated and normalized by log transformation. Results. For controls, there were no differences between eyes. Binocular PS (log(10)BCEA = -0.88) was better than monocular PS (log(10)BCEA = -0.59) indicating binocular summation, and the PS of the viewing eye was better than that of the covered eye (log(10)BCEA = -0.33). For patients, the amblyopic eye exhibited a significant decrease in PS during amblyopic eye (log(10)BCEA = -0.20), fellow eye (log(10)BCEA = 0.0004), and binocular (log(10)BCEA = -0.44) viewing. The PS of the fellow eye depended on viewing condition: it was comparable to controls during binocular (log(10)BCEA = -0.77) and fellow eye viewing (log(10)BCEA = -0.52), but it decreased during amblyopic eye viewing (log(10)BCEA = 0.08). Patients exhibited binocular summation during fellow eye viewing, but not during amblyopic eye viewing. Decrease in PS in patients was mainly due to slow eye drifts. Conclusions. Deficits in spatiotemporal vision in amblyopia are associated with poor PS. PS of amblyopic and fellow eyes is differentially affected depending on viewing condition.     

Further followup: (Part IV) A case of acute loss of binocular vision and stereoscopic depth perception

(Combined case report followup) This is a continuation of a personal report by a knowledgeable vision scientist, of the loss of binocular vision due to a major vitreous hemorrhage. Please see the initial report for further details. (Romano PE. A case of acute loss of binocular vision and stereoscopic depth perception. (The misery of acute monovision, having been binocular for 68 years) Binocul Vis Strabismus Q 2003; 18:51-55; and followup Binocul Vis Strabismus Q 2003; 18:101-103, Binocul Vis Strabismus Q 2003; 18:174-175. This report covers months nine and ten following the hemorrhage. In the two months since the last report, Visual acuity continues to improve to 20/20 with correction, one line less than the fellow eye. Residual ring shaped floaters only occasionally interfere with visual function which is normal now for virtually all extents and purposes. The previously reported observation that binocular ocular sighting dominance is gaze dependent is confirmed by prior recently published research: Khan AZ, Crawford JD. Ocular dominance reverses as a function of horizontal gaze angle. Vision Research 2001; 41:1743-1748.     

The effect of binocular and monocular distractors on saccades in participants with normal binocular vision

We tested the effect of visual distractors presented monocularly and binocularly on saccade latency and accuracy to determine whether differences occur in saccadic planning with binocular or monocular visual input. For five participants with normal binocular single vision (BSV), saccade latency and accuracy were compared with distractors presented to the dominant eye, non-dominant eye or to both eyes. Eye movements of the dominant eye were recorded using a Skalar infra-red recorder. In the presence of normal BSV, the effect of distractors is significantly larger for saccade latency and accuracy with binocular distractor presentation than for monocular presentations, with no difference between distrators presented to the dominant or non-dominant eye. The implications of these results are discussed with regard to saccade programming.     

Binocular beats: psychophysical studies of binocular interaction in normal and stereoblind humans

We describe a psychophysical method for assessing binocular integration using dichoptically-presented uniform fields. By temporally modulating uniform field luminances at different frequencies between the eyes, a rhythmic beat is produced--a visual percept characterized by undulations in luminance at a frequency equal to the arithmetic difference between the two monocular stimulus frequencies. Using a signal detection paradigm, we studied the beat as a function of modulation depth in normal and binocularly deficient subjects. Normal subjects easily detected the beat, even at low modulation depths, while stereoblind subjects (with stereoacuity worse than 2000 sec arc) failed to detect beats at any modulation depth or with any combination of stimulus frequencies tested. The beat provides evidence for the confluence of monocular signals into binocular integrating mechanisms. Our results therefore suggest that the status of functioning binocular mechanisms is related to the detectability of the beat. This uniform-field stimulus does not require accurate accommodation, fixation, vergence or high spatial resolution, thus making this technique particularly attractive for the study of binocular interaction in developing infants and in binocularly deficient adults.     

间歇性外斜视术后双眼视功能重建的临床研究

目的：了解间歇性外斜视术后双眼视功能重建的临床规律。方法：对１００例术后建立双眼视觉的患者分成４组,对术前后双眼视觉进行分析比较。结果：（１）１００例中术前有不同程度的近立体视觉者６７例,术后增加至９３例,术后近立体视觉重建有明显改善（Ｐ〈０．０５）。（２）术前有同视机Ｉ组功能者５１例,术后增加至８２例,术后同视机Ｉ组功能重建有显著改善（Ｐ〈０．０５）。（３）术前有同视机ＩＩ级功能者４０例,术后增     

Co-development of VEP motion response and binocular vision in normal infants and infantile esotropes

PURPOSE: To determine the maturational course of nasotemporal asymmetry in infantile esotropia and to define the relationships among the symmetry of the motion visual evoked potential (MVEP), eye alignment, fusion, and stereopsis. METHODS: Sixty healthy term infants and 34 infants with esotropia participated. Nasotemporal MVEP asymmetry was assessed by the presence of a significant F1 response component with an interocular phase difference of approximately 180 degrees and by an amplitude "asymmetry index." Fusion was evaluated using the 4 p.d. base out prism test. Random dot stereoacuity was assessed in infants with forced-choice preferential looking (FPL) using the Infant Random Dot Stereocards. Eye alignment was assessed by the alternate prism and cover or the modified Krimsky test. RESULTS: Normal infants 2 to 3 months of age exhibited marked nasotemporal MVEP asymmetry, which rapidly diminished by 6 to 8 months. Neonates did not exhibit MVEP asymmetry. There was good concordance between fusion and MVEP symmetry and between stereopsis and MVEP symmetry; the concordance between MVEP symmetry and orthoposition of the visual axes was significantly poorer. The same proportion of normal and young esotropic infants showed symmetrical MVEPs. Regardless of the age at surgery, most patients with infantile esotropia had asymmetrical MVEPs after surgery. CONCLUSIONS: These data support a strong link between fusion and MVEP symmetry during both normal maturation and in infantile esotropia. Furthermore, the finding that the youngest infants with esotropia do not differ significantly from normal suggests that the nasotemporal asymmetry found in older patients with infantile esotropia does not represent an arrest of maturation but, rather, a pathologic change of the motion pathways.     

A comparison of stereopsis testing between red/green targets and polarized targets in children with normal binocular vision.

BACKGROUND: Measurement of stereopsis is important in assessing a patient's binocular status. Several measurement methods are available, most commonly using polarized targets. Recently, less expensive red/green targets have become available. In this study, we compare polarized versus red/green methods, using random dot and contour targets. METHODS: Sixty children with no strabismus, amblyopia, or high refractive error and normal ocular health were recruited. Stereopsis measurements were taken using the red/green and polarized versions of the Random Dot Letter "E"/RDE Test, Random Dot Butterfly/Stereo Butterfly Test, Stereo Circles/Wirt Circles, Stereo Numbers, and Stereo Animals tests. Observed agreement was used to assess agreement between results. Wilcoxon signed-rank tests were used to compare an individual's response with both targets. RESULTS: There was greater than 95% agreement using any of the Random Dot-based tests and the Stereo Animals tests. However, agreement was less than 60% with the Stereo Numbers test and less than 35% with the Stereo Circles/Wirt Circles test. CONCLUSION: The red/green versions of the Random Dot-based tests and the Stereo Animals test appear to be a cost-effective alternative to their polarized equivalents. Our data, however, show that the red/green versions tend to underestimate the level of stereopsis when using the Stereo Numbers and Stereo Circles/Wirt Circles tests compared to their polarized equivalents.     

Vertical disparity and binocular vision in the praying mantis.

We have investigated how the binocular control of prey capture in the praying mantis is affected by abnormally large vertical disparities, which were introduced by prisms placed in front of the eyes. The position of a target on the two retinae determines both the magnitude of head saccades made to fixate a target and its perceived distance. Over the whole range of vertical disparities tested (up to at least 30 deg), the frequency of fixating saccades is normal while the amplitude of their vertical component is a compromise between the saccades specified by each eye individually. Distance measurements are not affected by imposed vertical disparities. But the larger the vertical disparity, the more reluctant the mantid is to strike at the target until disparities exceed 15 deg when no strikes are elicited at all.