Temporal dynamics of ocular aberrations: monocular vs binocular vision

The temporal dynamics of ocular aberrations are important for the evaluation of, e.g. the accuracy of aberration estimates, the correlation to visual performance, and the requirements for real-time correction with adaptive optics. Traditionally, studies on the eye's dynamic behavior have been performed monocularly, which might have affected the results. In this study we measured aberrations and their temporal dynamics both monocularly and binocularly in the relaxed and accommodated state for six healthy subjects. Temporal frequencies up to 100 Hz were measured with a fast-acquisition Hartmann–Shack wavefront sensor having an open field-of-view configuration which allowed fixation to real targets. Wavefront aberrations were collected in temporal series of 5 s duration during binocular and monocular vision with fixation targets at 5 m and 25 cm distance. As expected, a larger temporal variability was found in the root-mean-square wavefront error when the eye accommodated, mainly for frequencies lower than 30 Hz. A statistically-significant difference in temporal behavior between monocular and binocular viewing conditions was found. However, on average it was too small to be of practical importance, although some subjects showed a notably higher variability for the monocular case during near vision. We did find differences in pupil size with mono- and binocular vision but the pupil size temporal dynamics did not behave in the same way as the aberrations' dynamics.     

Individual differences in binocular coordination are uncovered by directly comparing monocular and binocular reading conditions

Purpose. We evaluated systematically binocular coordination during a reading task by comparing binocular and monocular reading, and considering the potential effects of individual heterophoria and eye dominance. Methods. A total of 13 participants (aged 19-29 years, refractive errors -0.5 to 0.125 diopters [D]) read single sentences in a haploscope while eye movements were measured with an EyeLinkII eyetracker. Results. When reading monocularly, saccade amplitudes increased by 0.04 degrees and first fixation durations became longer by approximately 10 ms. Furthermore, saccade disconjugacies increased, and compensatory vergence drifts during fixation turned into a divergent drift relative to the viewing distance. The vergence angle adjusted for the actual viewing distance became less convergent during monocular reading by 0.5 degrees. Moreover, in participants who were almost orthophoric, only the first fixation duration became longer (by 20 ms) when the reading conditions changed from binocular to monocular. For exophoric participants, all parameters of binocular coordination changed, and first fixation duration decreased by 20 ms. When reading monocularly, no differences between the dominant right eye and the nondominant left eye were found. Conclusions. Because of obvious differences in binocular coordination between monocular and binocular reading, some vergence adjustments are driven actively by fusional processes. Furthermore, higher demands on these binocular fusional processes can be uncovered only by a detailed evaluation of monocular reading conditions.     

Quantitative measurement of ocular dominance using binocular rivalry induced by retinometers

PURPOSE: To develop a new method using binocular rivalry and retinometers to quantitatively examine ocular dominance and to investigate the magnitude of ocular dominance in cataract patients preoperatively and postoperatively. SETTING: Eye Clinic, Kitasato University School of Medicine Hospital, Sagamihara, Kanagawa, Japan. METHODS: The duration of exclusive visibility of the dominant and nondominant eye target in binocular rivalry were measured in 60 healthy volunteers (study 1) and preoperatively and postoperatively in 10 cataract patients (study 2). Rivalry targets were presented directly to the retina of each eye using 2 retinometers. Subjects reported the exclusive visibility of 1 eye target, and the total duration of exclusive visibility for each eye in dominant and nondominant eye trials was evaluated. RESULTS: In study 1, the magnitude of ocular dominance was quantitatively assessed with 4 grades based on differences in total duration of exclusive visibility between dominant and nondominant eyes. In study 2, magnitude of ocular dominance could be evaluated in all cataract patients regardless of refractive and cataract conditions. Magnitude of ocular dominance displayed significant correlations between preoperative and postoperative conditions (simple regression, P<.001). CONCLUSIONS: Ocular dominance can be quantitatively evaluated using this new method based on binocular rivalry and retinometers, particularly in cataract patients. Magnitude of ocular dominance may indicate preoperatively whether a patient with cataracts will have sufficient ocular dominance to adjust to monovision correction.     

Maximum reading speed and binocular summation in patients with central vision loss

Objective

Visual acuity is a poor predictor of the maximum reading speed of patients with central vision loss. This study examines the effects of binocular summation of acuity on the maximum reading speed of these patients.

Design

Prospective, observational case series.

Participants

Twenty patients with central vision loss participated.

Methods

Maximum reading speed was measured binocularly using the MNREAD acuity charts. Monocular and binocular acuities were measured with the Early Treatment Diabetic Retinopathy Study (ETDRS) chart. Binocular summation was evaluated with a binocular ratio (BR) calculated as the ratio between the acuity of the better eye to binocular acuity. Fixation stability and preferred retinal locus (PRL) distance from the former fovea were evaluated with the MP-1 microperimetre.

Results

Six patients experienced acuity summation (BR > 1.05), 5 experienced acuity inhibition (BR < 0.95), and 9 showed equality (BR = 1 ± 0.05). There were no differences in the mean acuity of the better eye, fixation stability, or PRL distance from the fovea of the 3 groups. Maximum reading speed was significantly slower (p < 0.05) for patients who experienced binocular inhibition (mean 42 ± 27 words/min [wpm], median 40 wpm) than for those who experienced binocular summation (mean 107 ± 39 wpm, median 108 wpm) or equality (mean 111 ± 62 wpm, median 90 wpm). BR correlated with the maximum reading speed for the overall sample (r[18] = 0.49, p = 0.03). BR together with PRL distance from the former fovea in the better eye explained 45% of the variance in maximum reading speed.

Conclusions

Binocular summation of acuity rather than visual acuity alone affects maximum reading speed of patients with central vision loss. Patients with binocular inhibition read significantly slower than those with binocular summation or equality. Assessment of binocular summation is important when devising reading rehabilitation techniques.     

Absence of binocular summation, eye dominance, and learning effects in color discrimination

We evaluated binocular summation, eye dominance, and learning in the Trivector and Ellipses procedures of the Cambridge Colour Test (CCT). Subjects (n = 36, 18-30 years old) were recruited among students and staff from the University of S?o Paulo. Inclusion criteria were absence of ophthalmological complaints and best-corrected Snellen VA 20/20 or better. The subjects were tested in three randomly selected eye conditions: binocular, monocular dominant eye, and nondominant eye. Results obtained in the binocular and monocular conditions did not differ statistically for thresholds measured along the protan, deutan, and tritan confusion axes (ANOVA, P > 0.05). No statistical difference was detected among discrimination ellipses obtained in binocular or monocular conditions (ANOVA, P > 0.05), suggesting absence of binocular summation or of an effect of eye dominance. Possible effects of learning were examined by comparing successive thresholds obtained in the three testing conditions. There was no evidence of improvement as a function of testing order (ANCOVA, P > 0.05). We conclude that CCT thresholds are not affected by binocularity, eye dominance, or learning. Our results differ from those found by Verriest et al. (1982) using the Farnsworth-Munsell 100 Hue test and Hovis et al. (2004) using the Farnsworth-Munsell panel D-15 test.     

Suppressive processes in binocular vision: ocular dominance and amblyopia.

Recent suggestsions linking suppression observed in amblyopia ex anopsia with that manifested in normal ocular dominance coordinations were experimentally tested. Training procedures which normally alleviate functional amblyopic suppression were shown to have similar results in alleviating the suppression of the nondominant eye in visually normal observers. Methodological and theoretical implications of these results are discussed.     

Effects on stereopsis of monocular versus binocular degradation of image contrast

Stereoacuity on a number of common clinical tests was reduced twice as much by degradation of the contrast of one eye's image as by an equal reduction of contrast of the image in both eyes. This finding, in conjunction with related clinical and animal study results, emphasizes the need for early detection of conditions causing interocular contrast asymmetry in infants and children, if normal binocular visual development is to be achieved. It also raises question about the effect of monocular occlusion therapy on the binocular potential of amblyopic patients.     

长期单眼配戴角膜塑形镜对眼表的影响

目的：探讨持续单眼配戴角膜塑形镜对眼表的影响。

方法：回顾性研究2013-01/2015-12在无锡市101医院眼科门诊就诊的单眼近视眼(对侧眼为正视眼)持续配戴角膜塑形镜6mo以上的患者。观察戴镜眼和非戴镜眼在戴镜前和戴镜后各时间点(1wk,1、3、6mo)的泪膜破裂时间、泪液基础分泌量、角膜中央厚度、角膜内皮细胞密度、结膜充血、角膜上皮荧光素染色的情况。

结果：单眼持续配戴角膜塑形镜患者共53例,年龄10.43±1.70岁,等效球镜度-3.37±1.50D。戴镜眼戴镜1wk泪膜破裂时间缩短,戴镜后1wk与戴镜后1、3、6mo泪膜破裂时间相比,差异无统计学意义(P>0.05); 非戴镜眼泪膜破裂时间各时间点无明显差异(P>0.05)。戴镜眼和非戴镜眼戴镜后各时间点泪液基础分泌量与戴镜前相比,差异均不明显(P>0.05)。戴镜后各时间点角膜中央厚度和角膜内皮细胞密度与戴镜前比较,差异均无统计学意义(P>0.05)。戴镜眼角膜上皮染色主要为Ⅰ级点染,Ⅰ级点染在戴镜后1wk,1、3、6mo分别为10眼(19%)、6眼(11%)、8眼(15%)、6眼(11%),Ⅱ级点染分别为1眼(2%)、0眼、0眼、1眼(2%)。10例患者戴镜后会出现结膜充血(评分1分)。所有病例在及时停戴、使用抗生素及角膜修复剂后,角膜上皮点状染色均消失,结膜充血消退。非戴镜眼观察期内未见明显结膜充血,角膜上皮染色均为0级。

结论：持续配戴角膜塑形镜会引起泪膜稳定性的下降,结膜、角膜上皮会出现不同程度的影响,但对泪液分泌、角膜厚度和角膜内皮细胞无明显影响。非戴镜眼无明显眼表损害。     

Better perception of global motion after monocular than after binocular deprivation.

We used random-dot kinematograms to compare the effects of early monocular versus early binocular deprivation on the development of the perception of the direction of global motion. Patients had been visually deprived by a cataract in one or both eyes from birth or later after a history of normal visual experience. The discrimination of direction of global motion was significantly impaired after early visual deprivation. Surprisingly, impairments were significantly worse after early binocular deprivation than after early monocular deprivation, and the sensitive period was very short. The unexpectedly good results after monocular deprivation suggest that the higher centers involved in the integration of global motion profit from input to the nondeprived eye. These findings suggest that beyond the primary visual cortex, competitive interactions between the eyes can give way to collaborative interactions that enable a relative sparing of some visual functions after monocular deprivation.     

The effect of wavelength on binocular summation

Binocular (dichoptic) summation was studied for identical wavelengths (monochromatic combinations) and dissimilar wavelengths (bichromatic combinations) presented to each eye. For comparison, monocular summation data were obtained from the same subjects. Dichoptic bichromatic additivity failures were found to be qualitatively similar to, but more pronounced than, corresponding bichromatic monoptic additivity failures. Also, for color normals, dichoptic monochromatic summation was greatest for saturated spectral hues and least for less saturated hues.     

The dazzle reflex: electrophysiological signals from ocular muscles reveal strong binocular summation effects

Under dark adapted or dim conditions the mammalian visual system is carefully programmed to respond rapidly to the sudden onset of bright lights. This response, called the dazzle reflex, is controlled from sub-cortical structures of the brain. It is known anecdotally that exposure to a bright light when dark adapted induces an instinctive closure of one eye to reduce the pain associated with dazzle. This binocular summation of the dazzle response has not previously been reported. The dazzle reflex can be measured in human subjects by recording the electrical activity from surface electrodes located near the muscles around the eye. In this paper we report an investigation of the apparent binocular summation of the dazzle reflex using this technique. The data reveal a clear difference between monocular and binocular stimulation, with the binocular response being much larger than the monocular response. Furthermore this monocular/binocular difference arises only if the stimulus duration is longer than approximately 1 s. These observations are interpreted in terms of the known physiology of blink mechanisms.     

Effect of higher-order wavefront aberrations on binocular summation

PURPOSE: To determine the effect of individual Zernike wavefront aberrations on binocular summation and binocular visual acuity. METHODS: A 0.25-microm wavefront aberration of second, third and fourth order Zernike modes were introduced into a set of log minimum angle of resolution unit (logMAR) visual acuity charts convolved by CTView. Subjects were dilated and fitted with an artificial pupil of 3 mm. For each set of charts, right eye, left eye, and binocular acuity was measured. The gain in binocular visual acuity over monocular visual acuity was defined as binocular summation. The visual acuity lost binocularly reading aberrated charts was normalized for each subject and defined as the aberration induced loss in acuity. RESULTS: Binocular summation was 10.0% (95% limits of agreement 8.8 to 11.1%) in the unaberrated state and ranged from 17.3 to 3.4% in the Zernike modes studied. Binocular summation was greatest in defocus followed by coma and astigmatism. The aberration induced loss in monocular and binocular acuity was higher for Zernike modes with low angular frequency compared to those with high angular frequency. Linear regression showed a significant relationship between aberration-induced loss of visual acuity and binocular summation. CONCLUSIONS: A fixed amount of root mean square (RMS) aberration has a varied effect on binocular vision depending on the angular frequency and radial order of Zernike mode. Binocular vision has a positive effect in reducing the visual impact of aberrations as Zernike modes that suffer from the most loss of visual acuity also experience the greatest amounts of binocular summation.     

弱视患儿双眼视功能训练前后双眼总和VEP反应的变化

目的探讨双眼视功能训练在弱视治疗中的作用。方法对综合治疗后双眼视力≥0.6的69例双眼视功障碍患儿进行双眼视功能训练,并对其中27例患儿作双眼总和VEP反应检测。结果双眼视功能训练后,患儿的弱视眼基本痊愈率、立体视锐度正常率、双眼总和VEP反应结果均明显提高,与训练前有显著性差异(P<0.01)。结论双眼总和VEP反应检测能够反映弱视眼双眼视功能的作用。     

Effect of stimulus size on binocular summation within the binocular visual field

PURPOSE: To study the influence of stimulus sizes on binocular summation using the modified Octopus 201 combined with a space synoptophore. METHODS: Four normal subjects, aged 21 to 26 were tested. Using the SARGON program, we designed a new program to test 37 points in the central 6 degrees visual field. Sensitivity of the central 6 degrees visual field under monocular and binocular conditions was measured while the fusion patterns were displayed on the space synoptophore. The visual fields were measured at stimulus sizes 1, 3, and 5. RESULTS: The visual sensitivity under binocular conditions was higher than under monocular conditions for all the stimulus sizes. Binocular summation for stimulus size 1 was present in a flat form, for stimulus size 3 in a convex form, and for stimulus size 5 in a concave form in the central 6 degrees visual field. CONCLUSION: Binocular summation differed in stimulus size and retinal eccentricity. Binocular summation for stimulus size 3 increased in the fovea and it increased for stimulus size 5 in the peripheral area in the central 6 degrees visual field.     

Effect of monocular deprivation on NMDAR1 immunostaining in ocular dominance columns of the marmoset Callithrix jacchus

We previously showed that immunoreactivity to N-Methyl-D-aspartate (NMDA) receptors in primary visual cortex of Callithrix jacchus is regulated by visual activity during the second and third postnatal months (Fonta et al., 1997). The purpose of the present study was to show that the columnar pattern of high and low NMDAR1 immunoreactivity observed in monocularly deprived animals corresponds to ocular dominance columns linked to the nondeprived and deprived eye, respectively. We compared cortical distribution of NMDAR1 receptors and the projection zones of thalamic afferents, revealed by transneuronal transport of tritiated proline, in 2-month-old, either monocularly deprived or control, marmosets. The data show that ocular dominance columns exist in 2-month-old marmosets and that a 2-week monocular deprivation by means of eyelid suture leads to a modification of the thalamo-cortical afferents organization. Experiments of neuronal tracing and immunohistochemistry performed on the same animals demonstrated that cortical domains with decreased NMDAR1 level correspond to the deprived eye columns. These investigations, coupled to the previous results, strongly suggest that the NMDA receptors, regulated by visual activity, are involved in the refining of ocular dominance columns in the primary visual cortex of juvenile marmoset.     

The separation of monocular and binocular contrast

The contrast asynchrony is a stimulus configuration that illustrates the visual system’s separable responses to luminance and luminance contrast information (Shapiro, 2008, Shapiro et al., 2004). When two disks, whose luminances modulate in phase with each other, are each surrounded by a disk, one light and one dark, observers can see both the in-phase brightness signals and the antiphase contrast signals and can separate the two. Here we present the results of experiments in which observers viewed a similar stimulus dichoptically. We report that no asynchrony is perceived when one eye is presented with modulating disks and the other eye is presented with the black and white surround rings, nor is an asynchrony perceived in gradient versions of the contrast asynchrony. We also explore the “window shade illusion” (Shapiro, Charles, & Shear-Heyman, 2005) dichoptically and find that when a modulating disk is presented to one eye and a horizontally split black/white annulus is presented to the other, observers perceive a “shading” motion up and down the disk. This shading can be seen in either direction in the binocular condition, but it is almost always seen as moving towards low contrast in the monocular condition. These findings indicate the presence of separable retinal and cortical networks for contrast processing at different temporal and spatial scales.     

The effect of monocular defocus on binocular contrast sensitivity

The monocular contrast sensitivity loss with defocus is well known. We measured binocular contrast sensitivity of sinewave gratings of 6 c/deg in the presence of different levels of monocular defocus. In the absence of defocus, the binocular sensitivity was about 42% higher than monocular. With increasing monocular defocus, the binocular sensitivity decreased steadily until it reached a level below the monocular, showing binocular inhibition. The clinical implications of binocular inhibition with monocular defocus are discussed.