Ocular prevalence versus ocular dominance

Ocular dominance in cataract surgery: research status and progress

Ocular dominance (OD), a commonly used concept in clinical practice, plays an important role in optometry and refractive surgery. With the development of refractive cataract surgery, the refractive function of the intraocular lens determines the achievement of the postoperative full range of vision based on the retinal defocus blur suppression and binocular monovision principle. Therefore, OD plays an important role in cataract surgery. OD is related to the visual formation of the cerebral cortex, and its plasticity suggests that visual experience can influence the visual system. Cataract surgery changes the visual experience and transforms the dominant eye, which confirms the plasticity of the visual system. Based on the concept and mechanism of OD, this review summarizes the application of OD in cataract surgery.

Can children measure their own vision? A comparison of three new contrast sensitivity tests

PURPOSE

To investigate the feasibility of children measuring their own contrast sensitivity using a range of tablet- and paper-based tests.

METHODS

Forty children aged 5-15 years with amblyopia (N = 10), bilateral vision impairment (N = 10) or good vision (N = 20) measured their own vision on a screen-based optotype test (Manifold), a gamified vision test (PopCSF) and a paper-based test (Spotchecks) in a laboratory with minimal supervision. Completion rate, test-retest repeatability, test duration and participants' preferences were recorded for each test.

RESULTS

Most participants (36/40) were able to perform all three tests. All tests were correlated with clinically measured visual acuity and contrast sensitivity (p < 0.001). The 95% coefficient of repeatability was 0.30 dB for Manifold, 0.29 dB for PopCSF and 0.13 dB for Spotchecks. All tests differentiated between children with reduced contrast sensitivity and control participants. PopCSF and Spotchecks were also able to differentiate between children with amblyopia and those with good vision. Median test time was 152, 130 and 202 s for Manifold, PopCSF and Spotchecks, respectively. Twenty-two participants preferred the PopCSF test, 10 preferred Spotchecks and 6 preferred Manifold. Thirty-nine out of the 40 children (98%) said they would measure their own vision at home using at least one of these tests every month.

CONCLUSIONS

Children and young people can test their own contrast sensitivity with repeatable results. Of these three tests, the most repeatable was Spotchecks, the quickest was PopCSF and participants' favourite was PopCSF. Nearly all of the participants said they would be willing to use at least one of the three tests at home.

Achromatopsia-Visual Cortex Stability and Plasticity in the Absence of Functional Cones

Purpose

Achromatopsia is a rare inherited disorder rendering retinal cone photoreceptors nonfunctional. As a consequence, the sizable foveal representation in the visual cortex is congenitally deprived of visual input, which prompts a fundamental question: is the cortical representation of the central visual field in patients with achromatopsia remapped to take up processing of paracentral inputs? Such remapping might interfere with gene therapeutic treatments aimed at restoring cone function.

Methods

We conducted a multicenter study to explore the nature and plasticity of vision in the absence of functional cones in a cohort of 17 individuals affected by autosomal recessive achromatopsia and confirmed biallelic disease-causing CNGA3 or CNGB3 mutations. Specifically, we tested the hypothesis of foveal remapping in human achromatopsia. For this purpose, we applied two independent functional magnetic resonance imaging (fMRI)-based mapping approaches, i.e. conventional phase-encoded eccentricity and population receptive field mapping, to separate data sets.

Results

Both fMRI approaches produced the same result in the group comparison of achromatopsia versus healthy controls: sizable remapping of the representation of the central visual field in the primary visual cortex was not apparent.

Conclusions

Remapping of the cortical representation of the central visual field is not a general feature in achromatopsia. It is concluded that plasticity of the human primary visual cortex is less pronounced than previously assumed. A pretherapeutic imaging workup is proposed to optimize interventions.

Small temporal asynchronies between the two eyes in binocular reading: Crosslinguistic data and the implications for ocular prevalence

We investigated small temporal nonalignments between the two eyes’ fixations in the reading of English and Chinese. We define nine different patterns of asynchrony and report their spatial distribution across the screen of text. We interpret them in terms of their implications for ocular prevalence—prioritizing the input from one eye over the input from the other eye in higher perception/cognition, even when binocular fusion has occurred. The data are strikingly similar across the two very different orthographies. Asynchronies, in which one eye begins the fixation earlier and/or ends it later, occur most frequently in the hemifield corresponding to that eye. We propose that such small asynchronies cue higher processing to prioritize the input from that eye, during and after binocular fusion.

Detection of Epstein-Barr Virus in 130 Cases of Eyelid Sebaceous Gland Carcinoma Using In Situ Hybridization

Purpose

In this study, we aimed to investigate the presence of Epstein–Barr virus (EBV) in the eyelid sebaceous gland carcinoma (SGC) and its association with the clinicopathologic features.

Methods

One hundred and thirty paraffin-embedded SGC specimens were retrieved from the Clinical Pathology Department of Zhongshan Ophthalmic Center. Epstein–Barr virus-encoded RNA (EBER) was detected with in situ hybridization (ISH) using the Leica BOND system autostainer. The age and gender distributions of all patients were analyzed and compared with earlier reports. Pearson's χ² and Fisher's exact tests were used to determine the association between clinicopathological features such as age, gender, laterality eye, tumor basal dimension, degree of tumor differentiation, and EBER positivity. Likewise, the relationship between the grade and tumor basal dimension in EBER-positive SGC of the eyelid was analyzed.

Results

Thirty-four out of one hundred and thirty (26.2%) eyelid SGC specimens were positively stained for EBER. The age range of highest incidence was 46–75 years, and the female to male ratio was 1 : 0.9. No significant correlation was found between EBER-positivity and age (p = 0.5370), gender (p = 0.4758), and degree of tumor differentiation (p = 0.7787). However, EBV positivity was strongly correlated with the right eye (p = 0.0287), the tumor basal dimension (p = 0.0001). EBV positivity grade presented statistically associated with tumor size (p = 0.0329).

Conclusion

We conclude that ISH is a sensitive method to identify EBV in SGC of the eyelid. A possible causal association of EBV in SGC patients is suggested by high frequency of EBER-ISH positivity and its association with the clinicopathologic features.

The Dominant Eye: Dominant for Parvo- But Not for Magno-Biased Stimuli?

Eye dominance is often defined as a preference for the visual input of one eye to the other. Implicit in this definition is the dominant eye has better visual function. Several studies have investigated the effect of visual direction or defocus on ocular dominance, but there is less evidence connecting ocular dominance and monocular visual thresholds. We used the classic “hole in card” method to determine the dominant eye for 28 adult observers (11 males and 17 females). We then compared contrast thresholds between the dominant and non-dominant eyes using grating stimuli biased to be processed more strongly either by the magnocellular (MC) or parvocellular (PC) pathway. Using non-parametric mean rank tests, the dominant eye was more sensitive overall than the non-dominant eye to both stimuli (z = −2.54, p = 0.01). The dominant eye was also more sensitive to the PC-biased stimulus (z = −2.22, p = 0.03) but not the MC-biased stimulus (z = −1.16, p = 0.25). We discuss the clinical relevance of these results as well as the implications for parallel visual pathways.

The Stereoacuity-Dependent Concordance between Preferred Fixating Eye and Sighting Dominant Eye in Paediatric Intermittent Exotropia

Objective: To investigate if the concordance between sighting dominance and fixation preference depends on stereoacuity in children with intermittent exotropia (IXT). Methods: A total of 160 children (aged 7.24 ± 2.14 years, range 4-13 years) with the basic type of IXT at distance participated in the study. Binocular fusion and vergence were evaluated with synoptophore. Stereoacuity was assessed using the Titmus stereo test. The hole-in-the-card test was used to determine sighting dominance, while the eye of fixation preference was determined by the cover-uncover test. The chi-squared test was used to evaluate whether a distribution was different from the chance distribution. The Kappa value was computed to quantify the concordance between fixation preference and sighting dominance. Results: The mean deviations were 19 ± 4.58 prism diopters (PD) and 18.9 ± 4.47 PD for at distance and near, respectively. The mean amplitude of divergence was 5.34 ± 1.89 PD, and the mean amplitude of convergence was 14.08 ± 4.96 PD. Subjects were categorized as having either good (40-60 seconds of arc, n = 41), moderate (80-140 seconds of arc, n = 46), poor (≥ 200 seconds of arc, n = 45), or having no measurable stereoacuity (n = 28). The concordance between sighting dominance and fixation preference was high in subjects with good (Kappa = 0.858) or moderate (kappa = 0.812) stereoacuity, but it decreased quickly in subjects with poor stereoacuity (kappa = 0.496) or no stereopsis (kappa = 0.563). Conclusions: In pediatric patients with IXT, the concordance between sighting dominance and fixation preference depends on stereoacuity. The results from these two tests become increasingly incongruent as stereoacuity deteriorated.

Single cell transcriptome profiling of retinal ganglion cells identifies cellular subtypes

Retinal ganglion cells (RGCs) convey the major output of information collected from the eye to the brain. Thirty subtypes of RGCs have been identified to date. Here, we analyze 6225 RGCs (average of 5000 genes per cell) from right and left eyes by single-cell RNA-seq and classify them into 40 subtypes using clustering algorithms. We identify additional subtypes and markers, as well as transcription factors predicted to cooperate in specifying RGC subtypes. Zic1, a marker of the right eye-enriched subtype, is validated by immunostaining in situ. Runx1 and Fst, the markers of other subtypes, are validated in purified RGCs by fluorescent in situ hybridization (FISH) and immunostaining. We show the extent of gene expression variability needed for subtype segregation, and we show a hierarchy in diversification from a cell-type population to subtypes. Finally, we present a website for comparing the gene expression of RGC subtypes.

Evaluation of Sensory Dominance Using Binocular Rivalry as Related to Ocular Deviations

INTRODUCTION AND PURPOSE

To investigate the relationship between sensory dominance and ocular deviations.

PATIENTS AND METHODS

Sixty-three patients were evaluated with a new device for the measurement of exclusive visibility during binocular rivalry. The patients were consisted of twenty-three with exotropia (XT), twenty with intermittent exotropia [X(T)], twenty with exophoria (XP), respectively. Device is composed of two retinometers, their holders in which angle and position can be adjustable and a PC for data storage and analysis. In each of eyes, exclusive visibility of one stimulus during binocular rivalry was measured for 60 sec, and the strength of ocular dominance was evaluated by the difference of exclusive visibility between dominant and nondominant eye.

RESULTS

The difference of exclusive visibility time between dominant and nondominant eye were 9.8±3.7 sec in the XT group, 6.1±4.1 sec in the X(T) group and 2.2±1.5 sec in the XP group, respectively. There were significant differences between XT and X(T) (P<0.01) as well as between XT and XP (P<0.001).

CONCLUSIONS

The present result indicates that sensory dominance was obviously influenced by ocular deviations since exclusive visibility of dominant eye was prolonged with decreasing the opportunity of normal binocular vision such as XT or X(T).

Lateral preference in Williams-Beuren syndrome is associated with cognition and language

Williams-Beuren syndrome (WBS) is a genetically defined neurodevelopmental disorder presenting with intellectual disability associated with a specific neurocognitive profile characterized by anxiety, hypersociability, poor visuospatial skills and relatively preserved language. We have defined the lateral preference in 69 individuals (40 males and 29 females, age range 5-47 years) with WBS confirmed by molecular testing, and explored its correlation with cognition, behavior problems, the main aspects of the behavioral phenotype, and specific molecular variants (parental origin and size of the 7q11.23 deletion). Lateral preference (hand, foot, eye and ear) and neurobehavioral features [intelligence quotient (IQ), sociability, visuospatial construction, narrative skills and behavior] were assessed by a battery of tests and parental interviews. A large proportion of WBS individuals showed either left or mixed handedness (26 and 19%, respectively). Hand, foot and ear lateral preference showed significant association with IQ, with individuals with mixed lateral preference presenting lower general IQ, especially verbal IQ, with respect to subjects with well-defined laterality. Approachability, visuospatial ability, behavior problems or molecular variants were not associated with lateral preference. Our results indicate that, as in other neurodevelopmental disorders, laterality is poorly defined in a significant proportion of WBS individuals, and reinforces the idea that a correct definition of lateral preference is important for cognition and language.

The role of sensory ocular dominance on through-focus visual performance in monovision presbyopia corrections

Monovision presbyopia interventions exploit the binocular nature of the visual system by independently manipulating the optical properties of the two eyes. It is unclear, however, how individual variations in ocular dominance affect visual function in monovision corrections. Here, we examined the impact of sensory ocular dominance on visual performance in both traditional and modified monovision presbyopic corrections. We recently developed a binocular adaptive optics vision simulator to correct subjects' native aberrations and induce either modified monovision (1.5 D anisometropia, spherical aberration of +0.1 and -0.4 μm in distance and near eyes, respectively, over 4 mm pupils) or traditional monovision (1.5 D anisometropia). To quantify both the sign and the degree of ocular dominance, we utilized binocular rivalry to estimate stimulus contrast ratios that yield balanced dominance durations for the two eyes. Through-focus visual acuity and contrast sensitivity were measured under two conditions: (a) assigning dominant and nondominant eye to distance and near, respectively, and (b) vice versa. The results revealed that through-focus visual acuity was unaffected by ocular dominance. Contrast sensitivity, however, was significantly improved when the dominant eye coincided with superior optical quality. We hypothesize that a potential mechanism behind this observation is an interaction between ocular dominance and binocular contrast summation, and thus, assignment of the dominant eye to distance or near may be an important factor to optimize contrast threshold performance at different object distances in both modified and traditional monovision.

Comparison of conventional versus crossed monovision in pseudophakia

AIMS

To compare the visual performances and patient satisfactions of conventional monovision, which corrects the dominant eye for distance vision, and crossed monovision, which corrects the non-dominant eye for distance vision in patients with pseudophakia.

METHODS

This prospective randomised study was conducted in 59 patients who underwent implantation of different targets of monofocal intraocular lens for each eye at Konkuk University Medical Center between November 2009 and August 2012. The following were examined before bilateral cataract surgery and 2 months after the surgery: refractive error, binocular uncorrected distance visual acuity (UCDVA), uncorrected near visual acuity (UCNVA), best corrected visual acuity (BCVA) and stereopsis. Questionnaires to evaluate postoperative spectacle dependence and patient satisfaction were completed by all patients.

RESULTS

The conventional monovision group and the crossed monovision group were composed of 28 and 31 patients, respectively. There were no significant differences in postoperative UCDVA, UCNVA, BCVA and stereopsis between the two groups. In addition, patient satisfaction with near and distant vision and spectacle dependence were not significantly different in the two groups.

CONCLUSIONS

The clinical results of the crossed monovision were not significantly different from the results of conventional monovision. Therefore, crossed monovision can also be a valuable option for correcting postoperative presbyopia in patients considering bilateral cataract surgery.

TRIAL REGISTRATION NUMBER

KCT0001065.

Extrastriate projections in human optic radiation revealed by fMRI-informed tractography

The human optic radiation (OR) is the main pathway for conveying visual input to occipital cortex, but it is unclear whether it projects beyond primary visual cortex (V1). In this study, we used functional MRI mapping to delineate early visual areas in 30 healthy volunteers and determined the termination area of the OR as reconstructed with diffusion tractography. Direct thalamo-cortical projections to areas V2 and V3 were found in all hemispheres tested, with a distinct anatomical arrangement of superior–inferior fiber placement for dorsal and ventral projections, respectively, and a medio-lateral nesting arrangement for projections to V1, V2 and V3. Finally, segment-specific microstructure was examined, revealing sub-fascicular information. This is to date the first in vivo demonstration of direct extrastriate projections of the OR in humans.

Laterality does not affect the depth perception, but interpupillary distance

In this study, which investigates the relationship between the levels of stereopsis with eye and hand dominance or interpupillary distance, 120 healthy young volunteers were investigated. Eye dominance was determined by modified Miles technique following a complete eye examination. Handedness was assessed with the Edinburgh handedness inventory. Interpupillary distance was measured with millimetric ruler. Stereoacuity was measured in both contour (Titmus test) and random dot (TNO test) stereograms. The stereopsis scores were evaluated in terms of hand or eye dominance. The correlation between stereopsis score and interpupillary distance was assessed. Main outcome measures were stereopsis scores according to hand and eye dominance. As a result, right- and left-handed individuals showed no differences in terms of stereopsis. No differences were found in stereopsis scores between right- and left-eye dominant people. There was a correlation between interpupillary distance and the depth of stereopsis (r = −0.248, P < 0.05). Contrary to the expectation, the left and right dominant individuals did not differ in levels of stereopsis. Interpupillary distance has a positive effect on stereopsis.

A new method for quantifying ocular dominance using the balancing technique

INTRODUCTION AND PURPOSE

To develop a chart for the clinical setting that can quantify ocular dominance by using the modified balancing technique, a method based on binocular rivalry.

METHODS

In 100 healthy young volunteers, rightward-tilted and leftward-tilted square-wave gratings were presented to the right and left eye, respectively. A newly designed chart employing balancing techniques based on binocular rivalry was used in conjunction with a viewer. Target contrast in the nondominant eyes was fixed at 100%, while in the dominant eyes it was varied from 100% to 10% during ten steps that used a square-wave grating of 2 cycles per degree and which were 4° in size. By varying the contrast of the dominant eye, a "reversal point," which is where the exclusive visibility time or the conscious perception frequency of the nondominant eye exceeds the dominant eye, is revealed. This can be used to assess the magnitude of the ocular dominance.

RESULTS

Ocular dominance magnitude results indicated there was a good correlation between the modified and original balancing techniques. The modified balancing technique also showed high measurement repeatability.

CONCLUSIONS

A chart that uses the modified balancing technique for ocular dominance examinations can be used as a simple test to quantify ocular dominance within clinical settings.

Bagolini glasses: do they affect the horizontal prism fusion amplitude?

PURPOSE

Bagolini striated glasses (BSG) can be used while performing the prism fusion amplitude to verify the maintenance of binocularity. The aim of this clinical study was to evaluate whether these glasses affect the prism fusion amplitude.

METHODS

Fifty-six subjects were examined at the Eye Care Clinic at the University of Applied Sciences Utrecht. The positive and negative prism fusion amplitudes were measured, incorporating the BSG at random, for both near and distance, with right and left eye fixating.

RESULTS

Fifty-two normal subjects with a mean age of 21 years (range 17-28) were recruited. The median prism fusion amplitude at near was 10 BI to 33 BO with the BSG and 13 BI to 38 BO without (p < 0.001). At distance the median amplitude was 8 BI to 33 BO both with and without these glasses (p = 0.104).

CONCLUSION

Although BSG are useful to verify whether binocularity is maintained, significantly smaller fusional ranges were obtained during measurements at near. In clinical terms, fusional ranges can vary significantly when using the BSG.

The horizontal dark oculomotor rest position

BACKGROUND

This study sought to investigate whether eye dominance and age are related to the stimulus-free oculomotor resting state described via the dark disconjugate position (near or far), the dark conjugate position (left to right), and the near dissociated phoria.

METHODS

Nineteen non-presbyopes and 25 presbyopes with normal binocular vision participated in two identical sessions. The left-eye and the right-eye positions were recorded using a video-based infrared eye tracker while the subjects were in total darkness. Dark disconjugate responses and dark conjugate responses were calculated by computing the difference and the average of the left-eye and the right-eye response, respectively. The right-eye decaying to the phoria level was recorded for 15 s.

RESULTS

A one-way ANOVA assessed statistical differences in dark conjugate and dark disconjugate positions, comparing 1) the right-eye and the left-eye sensory and/or motor dominant groups and 2) the non-presbyope and presbyope groups. The test-retests of the dark disconjugate position, the dark conjugate position and the near dissociated heterophoria were high between sessions (r > 0.85; p < 0.00001). For non-presbyopes the right-eye (left-eye) motor and sensory dominant subjects showed a rightward (leftward) dark conjugate position (p < 0.01). The dark disconjugate position was receded in presbyopes compared to non-presbyopes (p < 0.0001).

CONCLUSION

The data support that the left-eye, or the right-eye, motor and sensory dominance predicts the direction of the dark conjugate position. Future studies could investigate the underlying neural substrates that may, in part, contribute to the resting state of the oculomotor system in a stimulus-free environment. Knowledge of the brain-behavior governing visual-field preference has implications for understanding the natural aging process of the visual system.

[Decline of monocular contrast sensitivity during binocular fixation]

To investigate binocular single vision, we examined monocular contrast sensitivity during binocular fixation by changing the intervals between the beginning of fixation and a probe stimulus, within 10 seconds. Monocular contrast sensitivities were quite stable within 1s of the interval delay in both eyes, but they were reduced in either eye if the interval delay was more than 1s (Experiment 1). In Experiment 2, a similar stimulus was monocularly presented. In this case, decline of contrast sensitivity was not observed in either eye. In Experiment 3, when the stimulus was interrupted briefly before the probe presentation, the contrast sensitivity was recovered. These results suggest that after prolonged viewing the binocular system does not sustain either eye sensitivity equally unless there is interruption of the binocular stimulation.

Looking at eye dominance from a different angle: is sighting strength related to hand preference?

Sighting dominance (the behavioural preference for one eye over the other under monocular viewing conditions) has traditionally been thought of as a robust individual trait. However, Khan and Crawford (2001) have shown that, under certain viewing conditions, eye preference reverses as a function of horizontal gaze angle. Remarkably, the reversal of sighting from one eye to the other depends on which hand is used to reach out and grasp the target. Their procedure provides an ideal way to measure the strength of monocular preference for sighting, which may be related to other indicators of hemispheric specialisation for speech, language and motor function. Therefore, we hypothesised that individuals with consistent side preferences (e.g., right hand, right eye) should have more robust sighting dominance than those with crossed lateral preferences. To test this idea, we compared strength of eye dominance in individuals who are consistently right or left sided for hand and foot preference with those who are not. We also modified their procedure in order to minimise a potential image size confound, suggested by Banks et al. (2004) as an explanation of Khan and Crawford's results. We found that the sighting dominance switch occurred at similar eccentricities when we controlled for effects of hand occlusion and target size differences. We also found that sighting dominance thresholds change predictably with the hand used. However, we found no evidence for relationships between strength of hand preference as assessed by questionnaire or by pegboard performance and strength of sighting dominance. Similarly, participants with consistent hand and foot preferences did not show stronger eye preference as assessed using the Khan and Crawford procedure. These data are discussed in terms of indirect relationships between sighting dominance, hand preference and cerebral specialisation for language and motor control.

Sighting versus sensory ocular dominance

Purpose

An indication of the laterality of ocular dominance (OD) informs the clinical decision making process when considering certain ophthalmic refractive and surgical interventions. Can predictive reliance be assured regardless of OD technique or is the indication of a dominant eye method-dependent?

Methods

Two alternative OD test formats were administered to a group of 72 emmetropic healthy young adult subjects: the ‘hole-in-card’ test for sighting dominance and the ‘+1.50D blur’ test for sensory dominance. Both techniques were chosen as being likely familiar to the majority of ophthalmic clinicians; to promote and expedite application during the examination routine neither test required specialist training nor equipment.

Results

Right eye dominance was indicated in 71% of cases by the sighting test but in only 54% of subjects using the sensory test. The laterality of OD indicated for the individual subject by each technique was in agreement on only 50% of occasions.

Conclusions

Reasons are considered for the poor intra-individual agreement between OD tests, along with an item of procedural advice for the clinician.

Binocular balance in normal vision and its modulation by mean luminance

PURPOSE

To better understand the neural basis of sensory dominance in the normal population, we applied a recently established test designed to quantify the degree of suppression in amblyopia to participants with normal binocular vision.

METHODS

This test quantifies the degree of dichoptic imbalance in coherent motion sensitivity by manipulating the contrast of stimuli seen by the two eyes. The contrast at which balanced dichoptic motion sensitivity occurs is referred to as the "balance point" and is an estimate of the degree of suppression. We apply the same logic to the measurement of sensory dominance by measuring the distribution of "balance points" within the normal population.

RESULTS

We show that although most subjects are balanced or only weakly imbalanced, a minority is strongly imbalanced. To ascertain the site of sensory dominance, we assessed the degree to which normal sensory balance can be modulated by changing the interocular mean luminance. We found that mismatches in mean luminance between the two eyes had a pronounced effect on the balance point determination.

CONCLUSIONS

Because cells in the lateral geniculate nucleus exhibit a strong modulation to sustained changes in the mean light level, this may suggests that the inhibitory circuits underlying sensory eye dominance are located at a precortical site.

Surface edges mitigate the disparity gradient constraint on binocular fusion and visual direction

One function of the visual system is to combine the different views of the two eyes so that each object appears in a single direction. Using pairs of isolated dots, previous studies have found that binocular fusion gives way to diplopia if the disparity gradient between the dots is steep. This paper evaluates whether fusion is possible in the presence of steep disparity gradients if those gradients occur between the edges of two surfaces, not isolated dots. Two target squares with a steep disparity gradient were presented alone, or were incorporated into separate surfaces - one foreground, the other background. The addition of surfaces, or support texture, restored fusion, overcoming the disparity gradient constraint on fusion. Visual direction was the average of the monocular views in the presence of support texture, indicating that single vision arose from fusion rather than a local suppression of one eye's view. The results suggest a close relationship between the disparity gradient constraint on fusion and the mitigating influence of support texture, because both effects decline dramatically over the same small range of element separations and both effects are reduced by differences in contrast polarity.

A new interocular suppression technique for measuring sensory eye dominance

PURPOSE

Recently devised tests have implemented forms of interocular suppression (e.g., binocular rivalry) to assess eye dominance. In an effort to combine the strengths of these tests, the authors introduce a new technique for quantifying the magnitude of interocular suppression by using an easily administered psychophysical test.

METHODS

Eighty-eight observers participated in the interocular suppression test, which involved dichoptic presentation of dynamic noise to one eye and a target stimulus to the other. Observers made a form-discrimination judgment once the target emerged from suppression. The authors reasoned that the dominant eye is less susceptible to interocular suppression and as a result, perception and thus, form discrimination would be faster when the target is presented to the dominant eye as opposed to the nondominant eye. Observers' sighting dominance, acuity, contrast sensitivity, and test-retest reliability were also assessed.

RESULTS

There were significant interocular differences in mean reaction times within and across observers. Of the observers, 68% and 32% observers were categorized as right eye dominant and left eye dominant, respectively, according to the test. Moreover, 38% of observers showed strong eye dominance. Observers' discrimination accuracy (98%) and test-retest reliability (r = 0.52-0.67) were high. Consistent with results in previous studies, statistical correlations were weak between the sighting dominance test, acuity scores, contrast sensitivity measures, and the interocular suppression test.

CONCLUSIONS

This interocular suppression technique offers an efficient, reliable, quantitative method of evaluating eye dominance and may be useful in making decisions about differential refractive correction of the two eyes.

Ocular prevalence: difference between crossed and uncrossed disparities of stereo objects

BACKGROUND

Many observers perceive a horizontal offset between a stereoscopically viewed object and a reference object in the fixation plane, although both objects are presented along a single line that projects through the midpoint between both eyes. These observers weigh one eye more than the other when determining the visual directions of stereo objects. This unequal weighting has been called ocular prevalence. We considered that ocular prevalence might be asymmetric, that is, different for crossed and uncrossed stereo disparities.

METHODS

We examined 11 subjects with normal eyes and a stereo resolution of less than 100 sec arc. A vertical line was dichoptically presented for 100 ms at crossed or uncrossed stereo disparities of 1, 2, 3, 4, 5, 6, or 7 min arc; this stereo object was judged in relation to a reference line in the fixation plane.

RESULTS

Ten of the 11 subjects had ocular prevalence, but only 3 of the 10 showed a significant difference between crossed and uncrossed disparities.

CONCLUSIONS

Ocular prevalence occurs frequently among observers with normal binocular vision, but only a minority of these observers show a difference between crossed and uncrossed disparities of the stereo object. It is unclear whether this difference bears clinical importance.

Effects of ocular dominance on the vertical vergence induced by a 2-diopter vertical prism during standing

This study examined the eye movement responses to vertical disparity induced by a 2-diopter vertical prism base down while in standing position. Vertical vergence movements are known to be small requiring accurate measurement with the head stabilized, and was done with the EyeLink 2. The 2-diopter vertical prism, base down, was inserted in front of either the non-dominant eye (NDE) or dominant eye (DE) at 40 and 200 cm. The results showed that vertical vergence was stronger and excessive relative to the required value (i.e. 1.14 degrees ) when the prism was on the NDE for both distances, but more appropriate when the prism was on the DE. The results suggest that sensory disparity process and vertical vergence responses are modulated by eye dominance.

Monovision: a review

In presbyopia, patients can no longer obtain clear vision at distance and near. Monovision is a method of correcting presbyopia where one eye is focussed for distance vision and the other for near. Monovision is a fairly common method of correcting presbyopia with contact lenses and has received renewed interest with the increase in refractive surgery. The present paper is a review of the literature on monovision. The success rate of monovision in adapted contact lens wearers is 59-67%. The main limitations are problems with suppressing the blurred image when driving at night and the need for a third focal length, for example with computer screens at intermediate distances. Stereopsis is impaired in monovision, but most patients do not seem to notice this. These limitations highlight the need to take account of occupational factors. Monovision could cause a binocular vision anomaly to decompensate, so the pre-fitting screening should include an assessment of orthoptic function. Various methods have been used to determine which eye should be given the distance vision contact lens and the literature on tests of ocular dominance is reviewed. It is concluded that tests of blur suppression are most likely to be relevant, but that ocular dominance is not fixed but is rather a fluid, adaptive, phenomenon in most patients. Suitable patients can often be given trial lenses that allow them to experiment with monovision in real world situations and this can be a useful way of revealing the preferred eye for each distance. Of course, no patient should drive or operate machinery until successfully adapted to monovision. Surgically induced monovision is less easily reversed than contact lens-induced monovision, and is only appropriate after a successful trial of monovision with contact lenses.

Ocular dominance diagnosis and its influence in monovision

PURPOSE

To analyze the response of normal emmetropic subjects to different ocular dominance tests and to analyze the influence of this response in surgically induced monovision.

DESIGN

A prospective study of diagnostic accuracy was carried out to analyze the different tests to determine ocular dominance, without a gold standard test.

METHODS

Nine different tests were carried out in a group of 51 emmetropic subjects to determine both motor and sensory ocular dominance. For analysis, patients were divided into two groups according to age. Normal ophthalmologic examination results were the inclusion requirement, with normal binocular vision and good stereoacuity.

RESULTS

A significant percentage of uncertain or ambiguous results in all tests performed was found, except in the hole-in-card and kaleidoscope tests. When the tests were compared, two by two, the correlation or equivalence found was low and was much lower if tests were compared three by three.

CONCLUSIONS

No clear ocular dominance was found in most studied subjects; instead, there must be a constant alternating balance between both eyes in most emmetropic persons, but not in those with pathologic features. This fact would explain the great variability both between and within different kinds of tests. Also, it would establish that the monovision technique is well tolerated in most patients, with unsuccessful results only in those patients with strong or clear dominance. Consequently, it seems appropriate to evaluate patient's dominance before monovision surgery to exclude those individuals with clear dominance.

Distance impairs postural stability only under binocular viewing

Prior studies indicate that postural stability under binocular viewing is not better than under monocular viewing. This was tested at the distances of 145 cm [Fox, C.R. (1990). Some visual influences on human postural equilibrium: binocular versus monocular fixation. Perception and Psychophysics, 47 (5), 409-422] and 90 cm [Isotalo, E., Kapoula, Z., Feret, P.H., Gauchon, K., Zamfirescu, F., & Gagey, P.M. (2004). Monocular versus binocular vision in postural control. Auris Nasus Larynx, 31 (1), 11-17]. On the other hand, postural stability is known to decrease with distance increase. We re-examined the effect of binocular versus monocular viewing on postural stability at near and far distances (40 and 200 cm), and for both young (25.7+/-2.7 years), and old subjects (61.2+/-4.6 years). For both groups of subjects, proximity decreased the area of CoP, the standard deviation of antero-posterior sway (SDy) and the variance of speed. The group of elderly presented increased variance of speed at far distance in comparison with young subjects. The novel finding is the interaction between distance and viewing condition. Under binocular viewing, the area of CoP was significantly higher at far distance than at near; in contrast, monocular viewing produced similar CoP values at both distances. Increased instability at far distance when both eyes are viewing is attributed to decreased sensitivity to binocular disparity cues and to visual motion in depth resulting from body sway. Monocular viewing would provide similar stability at far and at near distance, because sensitivity to lateral visual motion, detected monocularly, decreases less with distance than sensitivity to binocularly detected motion in depth. Alternatively, such monocular viewing could increase subject's attention and lead to tighter postural control regardless of the distance.

Ocular prevalence and stereoacuity1

BACKGROUND

Most people attribute a higher weight to the input from one eye than to that from the other eye when they have to align stereodisparate objects in the same visual direction. This preference for visual directions has been termed 'ocular prevalence', according to the Latin praevalentia = superior power.

QUESTIONS

(1) Is ocular prevalence of one eye (or its correlate, partial suppression of the other eye in the prevalence task) restricted to large stereodisparities, close to Panum's limit, or does it occur also at small stereodisparities, near the stereoscopic threshold? (2) Is ocular prevalence a handicap for stereoacuity?

METHODS

Six non-strabismic observers with equal visual acuity of their two eyes were examined. To determine their ocular prevalence, they were presented with vertical vernier lines at stereodisparities ranging between 30 and 430 arcsec. They had to judge whether the lower, anterior line was located on the right- or left-hand side of the upper, posterior line. Their stereoscopic threshold was measured with an adaptive staircase procedure, using the Freiburg Stereoacuity Test.

RESULTS

All six observers exhibited some ocular prevalence. It changed considerably on repeated measurements. In three observers, it even switched from one eye to the other. Ocular prevalence occurred not only at large stereodisparities, close to Panum's limit, but also at small stereodisparities. The stereoscopic threshold of the six observers ranged between 1.7 and 12.3 arcsec.

CONCLUSION

Ocular prevalence is common, intra-individually variable and occurs even at small stereodisparities close to the stereoscopic threshold. It is compatible with 'optimal' stereoacuity. Hence, ocular prevalence appears to be a harmless feature of normal binocular vision.

Vernier acuity for stereodisparate objects and ocular prevalence

QUESTION

How precisely can objects, located in different depth planes, be aligned to the same visual direction?

METHODS

Twenty normal observers were presented with vertical Vernier lines at various stereodisparities. They had to judge whether the lower, anterior line was located on the right- or left-hand side of the upper, posterior line.

RESULTS

Over a stereodisparity range from zero to 62'', the threshold for detecting a lateral offset between the Vernier lines remained at the "hyperacuity" level of about 7''. With larger stereodisparities, the threshold increased about fourfold, probably due to a mutual, partial suppression of the position signals from the right and left eyes. The reference point from which the observers judged the relative visual directions between stereodisparate objects was not located midway between the eyes; rather, it was often decentred towards the right or the left eye, meaning that the observers had an "ocular prevalence". Their ocular prevalence was, however, not strong enough to have an effect on the Vernier acuity for stereodisparate objects. (Under pathological conditions like strabismic amblyopia, one should expect a 100% prevalence of the good eye, implying that the Vernier acuity reaches the monocular level, irrespective of any depth difference between objects.)

CONCLUSION

Vernier acuity decreases with increasing stereodisparity. Ocular prevalence, occurring frequently among persons with normal eyes, has no effect on Vernier acuity for stereodisparate objects. For a typical everyday viewing condition, the reduced Vernier acuity beyond a stereodisparity of 62'' means that, from a viewing distance of 40 cm, precision mechanics have to guide their instrument as close as 0.4mm to a workpiece, until they can utilise their best position acuity.

Eye preference within the context of binocular functions

BACKGROUND

Eye preference refers to an asymmetric use of the two eyes, but it does not imply a unitary asymmetry between the eyes. Many different methods are used to assess eye preference, including eyedness questionnaires and sighting tasks that require binocular and monocular alignment of a target through a hole in the middle of a card or funnel. The results of these coarse accounts of eye preference are useful as a first screening, but do not allow for graded quantification of the manifested asymmetry in binocular vision. Moreover, they often concern only a rather selective range of binocular functions. The aim of the present study was to further differentiate eye preference within the context of other binocular functions as measured in standard optometric tests, and to validate their relation to questionnaire data of eyedness.

METHODS

Conventional accounts of eye preference (German adaptation of Coren's questionnaire and a sighting task) were compared with various optometric tests of binocular function within a sample of 103 subjects. Examination included visual acuity and accommodation in each eye, stereoscopic prevalence, suppression due to binocular rivalry, fixation disparity (Mallett test).

RESULTS

Sighting dominance was leftward in 32% and rightward in 68% of the cases and was highly correlated (Kendall's tau(b)=0.70) with eyedness. Further significant associations were restricted to stereoscopic prevalence which correlated with sighting dominance (tau(b)=0.55), eyedness (tau(b)=0.50), and rivalry dominance (tau(b)=0.28).

CONCLUSION

Eye preference seems to be essentially reflected by eyedness, sighting dominance, and stereoscopic prevalence, but largely unrelated to fixation disparity, accommodation, and visual acuity.