Simulating binocular visual field status in glaucoma

AIMS—To simulate the central binocular visual field using results from merged left and right monocular Humphrey fields. To assess the agreement between the simulation and the binocular Humphrey Esterman visual field test (EVFT).
METHOD—59 consecutive patients with bilateral glaucoma each recorded Humphrey 24-2 fields for both eyes and binocular EVFT on the same visit. EVFT results were used to identify patients exhibiting at least one defect (<10 dB) within the central 20° of the binocular field. This criterion is relevant to a patient''s legal fitness to drive in the UK. Individual sensitivity values from monocular fields are merged to generate a simulated central binocular field. Results are displayed as a grey scale and as symbols representing defects at the <10 dB level. Agreement between patients failing the criterion using the simulation and the EVFT was evaluated.
RESULTS—Substantial agreement was observed between the methods in classifying patients with at least one defect (<10 dB) within the central binocular field (kappa 0.81; SE 0.09). Patients failing this criterion using the EVFT results were identified by the binocular simulation with high levels of sensitivity (100%) and specificity (86%).
CONCLUSIONS—Excellent agreement exists between the simulated binocular results and EVFT in classifying glaucomatous patients with central binocular defects. A rapid estimate of a patient''s central binocular field and visual functional capacity can be ascertained without extra perimetric examination.

     

Effect of stimulus field size and localization on the binocular pattern reversal visual evoked response

The role of the central and peripheral stimulus fields on monocular and binocular amplitude and binocular summation of the pattern reversal visual evoked response were investigated. When the central stimulus field size was smaller than 2.4 °, there was no significant difference between the amplitude of the monocular and the binocular responses, but when it was equal to or larger than 3.2 ° × 3.2 °, the binocular amplitude was significantly larger than the monocular. The value of binocular summation was highest at the central stimulus field of 4.0 ° × 4.0 °; at larger sizes, there were no significant changes in the value. Use of a central stimulus field size larger than 3.2 ° × 3.2 ° was therefore considered a prerequisite for the effective assessment of visual function, especially binocular function, by means of the pattern reversal visual evoked response.With regard to the role of peripheral stimulus field on pattern reversal response, both the monocular and binocular responses, but particularly the latter, were found to be sensitive to a scotoma produced by covering the center of a full-field stimulus. The value of the binocular summation showed a significant reduction with a small central scotoma. We concluded that the pattern reversal visual evoked response is very sensitive to a central scotoma and that binocular function is mediated mainly through the central stimulus field.     

单眼视野损伤程度对青光眼患者双眼视野的影响

目的：探讨单眼视野丢失严重程度对原发性闭角型青光眼、原发性开角型青光眼和正常眼压性青光眼患者双眼视野缺损的影响。

方法：根据双眼单眼视野缺损的阶段,将120例青光眼患者和30例健康参与者分为正常、早期、中度或重度四个阶段。通过整合视野和Esterman双眼视野评估确定双眼视野。在组内和组间比较单眼和双眼视野参数。

结果：对于一只眼睛处于正常或早期阶段而另一只眼睛处于严重阶段的患者,双眼综合视野平均偏差分别为-2.8±1.1、-5.5±1.9dB,以及Esterman的平均得分分别为99.1%±1.7%和95.6%±4.7%。当双眼发展为中度或重度损伤(中度/中度,中度/重度或重度/重度)时,双眼综合视野平均偏差低于-6dB,中度/中度和中度/严重损伤组Esterman的平均得分分别为94.2%±6.0%、94.3%±4.9%,但当双眼处于重度损伤阶段时,Esterman的平均得分迅速从大于90%下降到68.4%±26.3%。

结论：如果一只眼睛处于正常或早期阶段,双眼视野可以保持相对完整。当双眼进展到中度或重度阶段时,通过双眼综合视野平均偏差测量的双眼视野缺损是显著的,并且仅当双眼进入严重阶段时才检测到显著的Esterman双眼视野缺损。     

Dynamic visual fields of one-eyed observers.

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

Outcomes of cataract extraction in functionally monocular patients. Case-control study

PURPOSE: To compare the ocular comorbidities, visual outcomes, and surgical complications between a series of functionally monocular patients who had phacoemulsification and intraocular lens (IOL) implantation and a control group of age- and sex-matched binocular patients. SETTING: Jules Stein Eye Institute and the Department of Ophthalmology, UCLA School of Medicine, Los Angeles, California, USA. METHODS: The records of a consecutive series of 100 functionally monocular patients who had phacoemulsification and IOL implantation were reviewed. The records of a control group of binocularly sighted patients who were matched to the monocular patients by age, sex, and date of surgery were also reviewed. RESULTS: Thirteen patients in the monocular group were monocular because of surgical complications. The remaining patients (87%) were monocular from medical conditions. Monocular patients had significantly more ocular comorbidity than binocular control patients (P <.0001). Age-related macular degeneration, diabetic retinopathy, and open-angle glaucoma were the most common reasons for monocular status and the most common ocular comorbidities in study eyes. The median preoperative best corrected visual acuity (BCVA) was 20/50 in the monocular group and 20/40 in the binocular group. The median postoperative BCVA was 20/25 and 20/20, respectively. A final BCVA of 20/40 or worse was the result of preexisting macular pathology or glaucoma in every instance. Surgical complications (P =.096) and the number of postoperative procedures (P =.724) were similar between the 2 groups. CONCLUSIONS: Ocular comorbidity was significantly more prevalent in the eyes of monocular patients. Monocular and binocular patients experienced a 3-line improvement in BCVA after cataract surgery; however, the final median acuity was 20/25 in the monocular group and 20/20 in the binocular group. The 2 groups had a similar complication rate.     

弱视儿童双眼总和视觉诱发电位变化的研究

目的探讨弱视儿童双眼视功能及总和图形视觉诱发电位（P-VEP）反应的特点,评估总和P-VEP反应对双眼视觉功能检测的意义。方法选取80名正常儿童和在南昌大学附属第二医院儿童眼科确诊的远视性弱视儿童151例,进行双眼总和P-VEP检查,分析总和P-VEP反应的特点。正常儿童与弱视儿童的人口基线学特征经统计学分析差异无统计学意义。P-VEP检查方法和刺激条件的选择参照吴乐正等的方法,记录电极的放置按照视觉电生理国际标准化的要求。视力检查采用国际标准视力表,双眼视觉功能检查采用Titmus立体图、同视机三级画片。P-VEP检测结果以双眼反应/单眼反应（B/M）比值作为评价指标。结果弱视组儿童总和P-VEP反应低于正常对照组（t=10.75,P〈0.01）;不同程度弱视组的B/M值随弱视的严重程度明显减低（F=10.93,P〈0.01）;无同时视者总和P-VEP与有同时视者比较,差异有统计学意义（t=7.835,P〈0.01）。结论总和P-VEP反应作为一种客观指标,可以反映弱视儿童的双眼视功能状况,对其双眼视功能的评价具有一定的价值。     

Comparative monocular brightness contributions in normal binocular observers

In order to find out whether equal monocular light stimuli result in equal monocular brightness sensations in normal binocular observers, one-half of a bipartite field presented to one eye was matched to the other half seen by the opposite eye while a binocular surrounding field maintained constant adaptation. Ratios of monocular luminances required for brightness matches showed an overall average mismatch of 2% (SD = 2) in 12 subjects. This value is significant at the 0.01 level, and only one subject showed a mismatch greater than 6% (more than 2 SD from the mean). It is concluded that about two-thirds of normal binocular observers would be expected to show monocular contributions to brightness that match each other within 4% or better.     

Reduced surround suppression in monocular motion perception

Motion discrimination of large stimuli is impaired at high contrast and short durations. This psychophysical result has been linked with the center-surround suppression found in neurons of area MT. Recent physiology results have shown that most frontoparallel MT cells respond more strongly to binocular than to monocular stimulation. Here we measured the surround suppression strength under binocular and monocular viewing. Thirty-nine participants took part in two experiments: (a) where the nonstimulated eye viewed a blank field of the same luminance (n = 8) and (b) where it was occluded with a patch (n = 31). In both experiments, we measured duration thresholds for small (1 deg diameter) and large (7 deg) drifting gratings of 1 cpd with 85% contrast. For each subject, a Motion Suppression Index (MSI) was computed by subtracting the duration thresholds in logarithmic units of the large minus the small stimulus. Results were similar in both experiments. Combining the MSI of both experiments, we found that the strength of suppression for binocular condition (MSI_binocular = 0.249 ± 0.126 log₁₀ (ms)) is 1.79 times higher than under monocular viewing (MSI_monocular = 0.139 ± 0.137 log₁₀ (ms)). This increase is too high to be explained by the higher perceived contrast of binocular stimuli and offers a new way of testing whether MT neurons account for surround suppression. Potentially, differences in surround suppression reported in clinical populations may reflect altered binocular processing.     

Correlation of the binocular visual field with patient assessment of vision

PURPOSE: To determine which measures of the binocular visual field correlate best with the patient's assessment of vision. METHODS: Esterman binocular visual field testing and four other binocular visual field tests (designated peripheral 20 dB [p20], peripheral 22 dB [p22], central 24 dB [c24] and central 26 dB [c26]) were performed in 101 patients with glaucoma or suspected glaucoma. Scores from these five tests, as well as binocular visual field scores calculated from monocular testing (best-location summation and probability summation), were correlated with performance on the National Eye Institute's Visual Function Questionnaire (VFQ)-25 and Short-Form (SF)-36 quality of life instruments, as well as with the linear rating scale utility test. RESULTS: The mean percentage of correct responses was 87%, 69%, 59%, 78%, and 71% for the Esterman, p20, p22, c24, and c26 tests, respectively. The distribution of scores was much broader for the p20 and p22 tests than for the Esterman test. The mean decibels for the binocular visual fields calculated from the monocular visual fields were 21.5 +/- 7.7 dB for the best-location algorithm and 25.1 +/- 6.7 dB for the probability-summation algorithm. The binocular visual field score calculated with the best-location algorithm correlated better with the overall, general vision, distance activities, and peripheral vision domains of theVFQ-25 (partial correlation coefficients of 0.48, 0.48, 0.49, and 0.51, respectively) than did the probability-summation algorithm and all five binocular visual field tests. The best-location algorithm also had the strongest correlation with the linear rating scale utility test (partial correlation coefficient, 0.40). CONCLUSIONS: In this sample of clinic-based patients with glaucoma or suspected glaucoma, a global score derived from a combination of two monocular fields correlated better with patient assessment of vision than did the Esterman and four novel binocular visual field tests.     

双眼视野总合现象及发生机制的探讨

目的:观察视野正常及异常者双眼视野总合现象,探讨最佳眼法、双眼平均法、最佳点法、双眼总合法等四种双眼视野形成学说的有效性。方法:用OCTOPUS 101型计算机视野计对15例视野正常者及58例各种眼病视野异常者的单、双眼视野进行了测定。结果:无论单眼视野正常与否,双眼视野均存在有总合现象,即双眼视野的视网膜平均光敏感度(mean sensitivity,MS)高于单眼。视野正常组与视野异常组的双眼视野总合现象发生率(总合率),分别为93.00％、和93.10％,差异无显著性(P>0.05)。双眼视野MS较单眼MS升高幅度(总合幅度),在视野正常组平均为7.05％,视野异常组总合幅度变异较大。通过双眼视野MS实测值与四种双眼视野形成学说的估算值比较发现,无论在视野正常组及视野异常组,四种学说中以最佳点法预测的双眼视野MS值与实测值差异最小。结论:双眼视野总合是一种普遍存在的视觉现象,四种双眼视野形成学说中以最佳点法最能揭示双眼视野总合现象。眼科学报 2002;18:253-258.     

Objective evaluation of binocular function with pattern reversal VER. III. Effect of stimulus size and localization

The effect of central and peripheral stimulus field on monocular and binocular amplitude and binocular summation of the pattern reversal VER were investigated. When the central stimulus field size was smaller than 2.0 degrees X 2.0 degrees, there was no significant difference between the amplitudes of the monocular and binocular VER, but when it was equal to or larger than 2.4 degrees, the binocular VER amplitude was significantly larger than the monocular. The value of the binocular summation was highest at the central stimulus field size of 4.0 degrees X 4.0 degrees; at larger sizes, there were no significant changes in the value. Use of a central stimulus field size larger than 2.4 degrees X 2.4 degrees was therefore considered a prerequisite for the effective assessment of visual function, especially binocular function using the pattern reversal VER. Regarding the effect of peripheral stimulus field, both the monocular and binocular VER, but particularly the latter, were found to be sensitive to the central scotoma produced by covering the center of the full-field stimulus. The value of the binocular summation showed a significant reduction with the small central scotoma. We concluded that the pattern reversal VER is very sensitive to a central scotoma and that binocular function is mediated mainly through the central part of the stimulus field.     

Five-year forecasts of the Visual Field Index (VFI) with binocular and monocular visual fields

Background

In clinical care, visual field (VF) damage is assessed using monocular VF testing, yet patients perceive the world binocularly. This study was conducted to compare 5-year forecasts for the Visual Field Index (VFI) generated from series of binocular and monocular VFs.

Methods

Series of ten consecutive VFs (Humphrey 24–2 Full-threshold) spanning on average 3.7 (SD: ±0.8) years from 60 eyes of 30 glaucomatous patients were retrospectively examined. The VFs of both eyes were merged to produce the integrated VF and its VFI score (Binocular VFI) was estimated. Forecasts of binocular and monocular VFIs were calculated for each patient by projecting the fitted linear regression 5 years ahead from the last VF following the method on the Humphrey Guided Progression Analysis (GPA) print-out. The precisions of the forecasts were calculated as the width of the 95 % prediction limit (PL).

Results

The mean 5 year forecast for binocular VFIs was 92 % (SD: 11 %), which was significantly higher than forecasts from right and left eyes (79 % [SD: 19 %] and 82 % [SD: 16 %] respectively; P?<?0.05). The width of the 95 % PL for 5-year predictions with monocular VFIs (mean right eye: 29 % [SD: 19 %] and mean left eye: 27 % [SD: 16 %]) were significantly larger than that of the binocular VFI (mean: 12 % [SD: 7 %]; P?<?0.05).

Conclusions

Five year forecasted VFI values using binocular measures return significantly better values, and can be made with greater confidence than those based on monocular measures. In turn, forecasts of a patient’s binocular VFI might be more relevant to estimating the patient’s future functional VF.     

The effects of blur and size on monocular and stereoscopic localization

Monocular localization of non-abutting stimuli and stereoscopic localization of the same second-order targets are performed with the same precision (Wilcox, L.M. & Hess, R.F. (1996) Is the site of non-linear filtering in stereopsis before or after binocular combination? Vision Research, 36, 391-399). Further, both tasks show a similar dependence on the scale of the stimulus. Since prior studies used Gaussian-enveloped stimuli, modifications of stimulus scale produced concurrent changes in edge blur. The experiments reported here assess the relative contributions of size and blur to the observed dependence on envelope scale for both monocular localization and stereoacuity. Stereoacuity for first-order targets was found to be an order of magnitude better than stereoacuity for second-order targets and monocular acuity for both first- and second-order targets. Further, while first-order stereopsis was found to depend solely on blur, second-order stereoacuity and monocular acuity were affected by both size and blur. These results suggest that while stereoacuity for first-order stimuli may be determined by a correlative process limited by early additive noise, stereoacuity for second-order stimuli and monocular acuity for non-abutting targets are more likely limited by stimulus-dependent spatial subsampling.     

Preference for binocular concordant visual input in early postnatal development remains despite prior monocular deprivation

Short daily periods of binocular vision, if concordant and continuous, have been shown to outweigh or protect against much longer daily periods of monocular deprivation to allow the development of normal visual acuity in both eyes of kittens. The greater weight placed on binocular visual input could arise because of an inherent bias for binocular input within the visual pathway at all times during development (Binocular model), or else from a more passive process that follows from its match to a highly binocular template at the time mixed daily visual input began (Template model). To distinguish between the predictions of these two models, kittens were monocularly deprived from normal eye-opening until either 4, 5, or 6 weeks of age at which time they received mixed daily visual input for 4 weeks. According to the Template model, the preferred input for these animals would be monocular exposure (ME) because of its match to the monocular template produced by a period of preceding monocular deprivation. However, instead of short daily period of ME offsetting much longer periods of binocular exposure (BE) to perpetuate the dire effects of the prior deprivation, short daily periods of BE promoted significant recovery of vision in the deprived eye. The fit to the Binocular model implies the existence of a robust substrate for binocular vision that is highly resistant to disruption and which could form the substrate for binocular approaches to treatment of amblyopia.     

Properties of receptive field on binocular fusion stimulation in the central visual field

BACKGROUND: Visual information projected onto corresponding points on the right and left retinas converges on the binocular cells in the visual cortex. The aim of this study is to investigative the characteristics of the receptive field for binocular stimulation in the central visual field of normal-sighted human subjects. METHODS: We investigated the receptive field for binocular stimulation under fusion conditions by combining the Octopus 201 with the space synoptophore. We measured binocular and monocular sensitivities while the fusion patterns were projected onto the Octopus 201 cupola, using the space synoptophore. We designed a new program to test 37 points in the central 6 degrees visual field. Six target sizes were tested: the white-spot targets of 0.054 degrees, 0.108 degrees, 0.216 degrees, 0.431 degrees, 0.862 degrees and 1.724 degrees projected diameters. RESULTS: The threshold energy necessary for binocular stimulation was lower than that for the monocular stimulation in all subjects. This difference was more obvious on the test points that were more distant from the fovea when target sizes of 0.054 degrees and 0.108 degrees were used. The amount of binocular summation ratio was highest for target size 0.054 degrees in each stimulus area in the central 6 degrees of the visual field. When we measured binocular summation using target sizes larger than 0.108 degrees, the result was the constant summation. CONCLUSIONS: The size of the receptive field for binocular stimulation is smaller than monocular stimulation under the same fusion condition. The amount of binocular summation varies as a function of target size.     

Cataract surgery takes longer in functionally monocular patients.

BACKGROUND AND OBJECTIVES: To determine differences in the amount of work involved in caring for functionally monocular patients who undergo cataract surgery compared with binocularly sighted patients. PATIENTS AND METHODS: This was a retrospective study that included 100 consecutive functionally monocular patients and 100 binocularly sighted control patients matched by age (+/-5 years) and date of surgery ( +/-1 year). Office records were reviewed to determine several measures of office and operating room work effort. RESULTS: There was no difference between groups in preoperative telephone calls (P = .136), postoperative telephone calls (P = .580), preoperative office visits (P = .875), postoperative office visits (P = .601), or the number of times surgery was scheduled (P = 1.00). Monocular patients required more time for surgery (37.4 minutes) than binocular patients (32.4 minutes) (P= .010). CONCLUSIONS: It takes longer to perform cataract surgery on functionally monocular patients than on binocularly sighted patients.     

Comparison of the monocular Humphrey visual field and the binocular Humphrey esterman visual field test for driver licensing in glaucoma subjects in Sweden

ABSTRACT: BACKGROUND: The purpose of the study was to compare the monocular Humphrey Visual Field (HVF) with the binocular Humphrey Esterman Visual Field (HEVF) for determining whether subjects suffering from glaucoma fulfill the new medical requirements for possession of a Swedish driver's license. METHODS: HVF SITA Fast 24-2 full threshold (monocularly) and HEVF (binocularly) tests were performed consecutively on the same day on 40 subjects with glaucomatous damage of varying degrees in both eyes. Assessment of results was constituted as either "passing" or "failing" score, according to the new medical requirements put into effect September 1, 2010 by the Swedish Transport Agency. RESULTS: Forty subjects were recruited and participated in the study. Sixteen subjects passed both tests, and sixteen subjects failed both tests. Eight subjects passed the HEFV but failed the HVF. There was a significant difference between HEVF and HVF (chi2, p=0.004). There were no subjects who passed the HVF, but failed the HEVF. CONCLUSIONS: The monocular visual field test (HVF) gave more specific information about the location and depth of the defects, and therefore is the overwhelming method of choice for use in diagnostics. The binocular visual field test (HEVF) seems not be as efficient as the HVF in finding visual field defects in glaucoma patients, and is therefore of doubtful use in evaluating visual capabilities in traffic situations.     

Stereoacuity degradation by experimental and real monocular and binocular amblyopia

Fourteen normal adult volunteers with normal binocular single vision and normal stereoacuity submitted to monocular and binocular degradation of their stereoacuity by cycloplegia and fogging with spherical lenses. Stereoacuity (SA) was reduced as soon as visual acuity (VA), both monocular and binocular, was reduced. There was a marked similarity in the degree of SA reduction produced by monocular and binocular amblyopia. The degree of SA reduction was slightly more marked with monocular decrements than with binocular at VAs between 20/25 and 20/50. Significant intersubject variation was noted. The majority of subjects maintained gross SA at 20/200 monocular or binocular. One subject was reduced to gross stereopsis at 20/30 monocular and 20/50 binocular VAs. Two subjects were able to retain 40 sec of SA until vision was degraded to 20/50. Conversely, 40 sec of SA was not achieved by any subject at monocular or binocular vision less than 20/40 (test for malingering). Thirteen patients with real monocular and binocular organic or functional amblyopia were then compared with the experimental group. On the whole, patients scored somewhat better than normals but their scores fell within the range of responses found in the normal group.     

The accuracy of metric judgements: Perception of surface normal

Observers adjusted a probe (a short rod) to appear normal to a planar surface slanted in depth. In Experiment 1, observers (N = 12) performed this metric task in two conditions: with reduced cues to calibration of binocular viewing parameters and with full cues. The results provided evidence for the use of an internal working metric in metric tasks because they confirm predictions that (i) errors should be largely systematic and accounted for by assuming an inaccurate working metric and (ii) this metric should be consistent with miscalibration of relevant viewing parameters. The data support the prediction that performance errors decrease in a manner consistent with improved binocular calibration, when better cues to relevant viewing parameters are provided. We performed two additional control experiments as further tests of the binocular miscalibration account, to determine whether performance in Experiment 1 could be explained instead by the use of monocular cues. We found that monocular performance was significantly poorer than binocular performance in reduced-cue conditions (Experiment 2) and full-cue conditions (Experiment 3). These control experiments provide confirmation that binocular cues contribute to performance in the full-cue conditions of Experiment 1, and that disparity was the only effective cue to slant in reduced-cue conditions.     

Pattern reversal VER as a tool for evaluating unbalanced visual inputs between the two eyes

We studied the effects of unequal or unbalanced visual inputs on the binocular system of normal subjects by measuring the amplitudes of the binocularly and the monocularly recorded VER and determining the value of binocular summation. The stimuli used were patterns that were either fused or not fused, of unequal luminosity and of unequal image size. When identical patterns were delivered to each eye and the patterns were fused, the binocular VER demonstrated a larger amplitude than the monocular VER, resulting in a binocular summation that was prominent in the low-contrast stimulus pattern. With stimulus patterns of higher contrast, the amplitudes of the binocular and the monocular VER did not differ greatly, and the value of binocular summation was significantly decreased. When fusion was disturbed with a base-in prism, the binocular VER displayed smaller amplitudes than the monocular VER, indicating binocular interaction or inhibition. With a small interocular luminosity difference, the binocular VER exhibited a larger amplitude than the monocular VER (binocular summation), but as the difference exceeded a certain level (0.6 to 0.8 log units), the binocular VER amplitudes were smaller than those of the monocular VER (binocular inhibition). With very large luminosity differences, the binocular VER amplitudes were almost similar to those of the monocular VER (suppression). When the perceived image size of the retina was altered with an aniseikonic lens, the binocular VER displayed larger amplitudes than those of the monocular VER (binocular summation) in aniseikonia equal to or less than 3.0%. At 5.0% aniseikonia, the binocular VER amplitudes were almost equal to the monocular VER (zero summation). At aniseikonia equal to or larger than 8.0%, the binocular VER amplitudes were significantly smaller than those of the monocular VER (binocular inhibition or interaction).