Ocular prevalence versus ocular dominance

Ocular dominance manifests itself in tests that contain stereo-objects with a disparity beyond Panum's area, e.g. in pointing a finger. These tests force subjects to decide in favour of one or the other eye. In contrast, ocular prevalence is determined using stereo-targets imaged within Panum's areas. These tests allow a graded quantification of the balance between the eyes. Here we present the computer-based Freiburg Ocular Prevalence Test in which stereo-disparate targets have to be aligned, and compare it with the Haase Stereo-balance Test that requires an estimation of the horizontal distance between stationary stereo-disparate objects. In addition, we compare ocular prevalence with ocular dominance. METHODS: (1) We measured the influence of a neutral-grey filter in front of one eye to assess the suitability of the Freiburg and the Haase Tests in revealing graded amounts of ocular prevalence. (2) About 20 subjects with equal vision of their two eyes underwent the Freiburg and the Haase Tests for ocular prevalence, and Parson's Monoptoscope Test for ocular dominance. RESULTS: (1) In both the Freiburg and the Haase Tests, the neutral-grey filter shifted ocular prevalence by about 50%. (2) An ocular prevalence of more than 10% occurred in 13 of the 20 subjects using the Freiburg, and in 14 using the Haase Test. On average, the ocular prevalence was 24.1+/-3.8% in the Freiburg and 32.0+/-8.2% in the Haase Test. The dominant eye coincided with the prevalent eye in 15 of the 20 subjects. DISCUSSION: The effect of the neutral-grey filter indicated that both the Freiburg and the Haase Tests can be used to measure fractions of ocular prevalence, although the Freiburg Test carries a higher reproducibility. Spontaneous ocular prevalence occurs frequently in persons with equal vision of their two eyes. This suggests that ocular prevalence does not represent a condition that requires treatment. Rather, partial suppression of one eye, the correlate of ocular prevalence, may play a physiological role in that it helps to disregard double images at stereo-disparities close to the limits of Panum's area.     

Contradictory influence of context on predominance during binocular rivalry

Background: Binocular rivalry is a complex process characterised by alternations in perceptual suppression and dominance that result when two different images are presented simultaneously to the left and right eyes. It has been reported recently that the addition of contextual cues will promote the predominance of the context consistent rivalry target. In contrast to Levelt' second proposition (1965), this effect has been found to result exclusively from an increase in the dominance phase duration, while the suppression phase duration remains unaffected. Methods: Human subjects were simultaneously presented with a small disc consisting of gratings (four cycles per degree) of different orientations to the two eyes. Four experiments were conducted to ascertain the effects of background gratings and contextual colour information on target predominance and phase duration. For each of the four experimental conditions, the orientation and colour of the target gratings and surrounding contextual background were systematically manipulated. Results: In this study, we report an effect opposite to that of Levelt. Contradictory contextual information increases target predominance and phase duration during binocular rivalry. Our results demonstrate that it is possible to promote the dominance of the context contradictory percept with co‐linearity, cochromaticity and orientation cues. In line with previous studies involving context, we find that this effect on predominance is due to an increase in the duration of the dominance rather than the suppression phase. Discussion: We discuss our findings in respect to those from previous studies and consider high‐ and low‐level processes that may be responsible for these apparently ‘contradictory’ roles of context on binocular rivalry. In addition, we discuss how the apparent ‘anti‐Levelt’ effect of context can be reinterpreted in a manner that brings it back in line with Levelt's second proposition and raises the question of whether ‘suppressability’ plays a disproportionately large role in determining the duration of perceptual phases in binocular rivalry.     

Eye movements and stereopsis during dichoptic viewing of moving random-dot stereograms

The dynamic properties of the version and vergence system were studied in relation to stereopsis for movements of the whole visual scene. Large random-dot stereograms (30 X 30 deg arc), moving laterally, were viewed dichoptically by human subjects without a fixed visual frame of reference. Sinusoidal movements in counterphase of the two half-images constituting the stereogram induced sinusoidal ocular vergence movements. The gain of vergence depended on the frequency as well as the amplitude of stimulus movement, while the phase lag depended only on the frequency. Fusion and stereopsis were retained up to a maximal velocity of change in relative position of the two half-images between 6 and 13.5 deg/sec. Sinusoidal movement of one half-image while the other one remained stationary induced sinusoidal ocular version as well as vergence movements. For version gains were higher and phase lags were smaller than for vergence. At the retinal level, residual overall binocular disparities between the two half-images up to 2 deg arc were tolerated without loss of stereopsis. The presence of sinusoidally varying overall binocular disparities and ocular vergence movements without perception of motion in depth suggests that these variables are not adequate cues for perception of (change in) depth.     

外伤性白内障人工晶体植入后双眼单视的探讨

目的探讨单眼白内障摘除后植入后房型人工晶体能否恢复双眼单视及立体视。方法将３６例外伤性白内障摘除后分一期和二期植入后房型人工晶体。术后分别观察其裸眼及矫正视力、双眼屈光状态，并用同视机、线状镜、障碍阅读及Ｔｉｔｍｕｓ立体视觉检查图检查双眼视及立体视的状态。结果３６例术后视力均显著提高，３个月后矫正视力４．９５以上者２４例（６６．７％），４．８以上者３０例（８３．３％）。其中２６例检查双眼视及立体视，２１例恢复良好。结论单眼白内障尤其是儿童，应提倡早期植入人工晶体，以促进双眼单视及立体视觉的恢复和发育。     

Modulatory effects of binocular disparity and aging upon the perception of speed

Two experiments investigated modulatory effects of a surround upon the perceived speed of a moving central region. Both the surround’s depth and velocity (relative to the center) were manipulated. The abilities of younger observers (mean age was 23.1 years) were evaluated in Experiment 1, while Experiment 2 was devoted to older participants (mean age was 71.3 years). The results of Experiment 1 revealed that changes in the perceived depth of a surround (in this case caused by changes in binocular disparity) significantly influence the perceived speed of a central target. In particular, the center’s motion was perceived as fastest when the surround possessed uncrossed binocular disparity relative to the central target. This effect, that targets that are closer than their background are perceived to be faster, only occurred when the center and surround moved in the same directions (and did not occur when center and surround moved in opposite directions). The results of Experiment 2 showed that the perceived speeds of older adults are different: older observers generally perceive nearer targets as faster both when center and surround move in the same direction and when they move in opposite directions. In addition, the older observers’ judgments of speed were less precise. These age-related changes in the perception of speed are broadly consistent with the results of recent neurophysiological investigations that find age-related changes in the functionality of cortical area MT.     

Extra-retinal signals support the estimation of 3D motion

In natural settings, our eyes tend to track approaching objects. To estimate motion, the brain should thus take account of eye movements, perhaps using retinal cues (retinal slip of static objects) or extra-retinal signals (motor commands). Previous work suggests that extra-retinal ocular vergence signals do not support the perceptual judgments. Here, we re-evaluate this conclusion, studying motion judgments based on retinal slip and extra-retinal signals. We find that (1) each cue can be sufficient, and, (2) retinal and extra-retinal signals are combined, when estimating motion-in-depth. This challenges the accepted view that observers are essentially blind to eye vergence changes.     

双眼相位整合平衡点检测在单眼弱视患者眼间抑制定量评估中的应用

目的采用双眼相位整合的测量范式定量评估单眼弱视患者的眼间抑制情况,并探讨患者眼间抑制度与其他视功能的相关性。方法前瞻性临床对照研究。收集在安徽医科大学第一附属医院眼科门诊就诊的未治疗过的单眼弱视患者51例,正常对照者25例,采用计算机程序呈现的双眼整合的测量范式进行双眼相位整合平衡点检测,比较单眼弱视患者和正常对照者双眼平衡点的差异,并将弱视患者检测结果与弱视眼视力、立体视锐度及屈光参差程度进行相关性分析。结果弱视组双眼平衡点（BP）值为0.227±0.016,正常对照组BP值为0.984±0.020,两组间差异有统计学意义（t=27.316,P<0.01）;弱视眼视力（r=-0.339,P<0.05）、立体视功能（Titmus：r=-0.421,P<0.01;RDS：r=-0.548,P<0.01;Fishy：r=-0.553,P<0.01）与BP值之间均存在显著的相关关系,屈光参差程度与BP值之间无明显相关性（r=-0.086,P>0.05）。结论双眼相位整合平衡点检测可定量评估弱视患者弱视眼的受抑制程度,有一定的临床应用前景。     

Saliency in a suppressed image affects the spatial origin of perceptual alternations during binocular rivalry

During binocular rivalry, perception alternates between dichoptically presented incompatible images. With larger images, such perceptual alternations will typically start locally and then gradually spread across the image, known as traveling waves of perceptual dominance. Several image-features (such as local contrast) are known to determine where in the image a traveling wave originates. Here we investigate whether orientation contrast in the suppressed image affects these spatial origin(s) of perceptual alternations. The results show that the origins are increasingly biased towards locations of increasing orientation contrast in the suppressed image. This increase in bias is related to the efficiency of visual search for the orientation contrast, tested offline: we find large biases towards orientation contrast when visual search for it is efficient, and small biases when search for it is inefficient. Our results imply that rivalry suppression is not homogenous across the suppressed image, but is dependent on local image-features in the suppressed image. The relation between spatial bias and visual search performance suggests that spatial origins of perceptual alternations are biased to salient locations in the suppressed image. Moreover, the finding that saliency affects the spatial origin of a perceptual alternation is in agreement with the idea that saliency is represented at a monocular, unconscious level of visual processing.     

暗环境下低中度近视优势眼与非优势眼及双眼对比度视力的对照研究

目的比较暗环境下低中度近视优势眼与非优势眼、双眼对比度视力的差异。方法随机选择拟行准分子激光手术的低中度近视患者47例(94只眼),综合验光仪主觉验光,卡洞法确定优势眼,应用多功能视力检查仪分别测量优势眼、非优势眼和双眼在暗环境暗背景条件下,对比度分别为100%、25%、10%和5%的最佳对比度视力。对所有受试者以及区分低中度近视的优势眼、非优势眼及双眼各对比度视力的差异进行统计学分析。结果所有受试者以及区分低中度近视的双眼对比度视力在对比度为25%、10%、5%均优于优势眼和非优势眼(P<0.05),在对比度为100%时,双眼对比度视力与优势眼差异无统计学意义(P>0.05),但优于非优势眼(P<0.05)。随着对比度的下降,单、双眼的对比度视力亦随之下降。结论在暗环境屈光矫正条件下,高对比度时优势眼的对比度视力优于非优势眼,但低对比度时双眼优于优势眼和非优势眼。     

Recent understanding of binocular vision in the natural environment with clinical implications

Technological advances in recent decades have allowed us to measure both the information available to the visual system in the natural environment and the rich array of behaviors that the visual system supports. This review highlights the tasks undertaken by the binocular visual system in particular and how, for much of human activity, these tasks differ from those considered when an observer fixates a static target on the midline. The everyday motor and perceptual challenges involved in generating a stable, useful binocular percept of the environment are discussed, together with how these challenges are but minimally addressed by much of current clinical interpretation of binocular function. The implications for new technology, such as virtual reality, are also highlighted in terms of clinical and basic research application.     

Eye movements when reading disappearing text: the importance of the word to the right of fixation

In a series of experiments, the currently fixated word (word n) and/or the word to the right of fixation (word n+1) either disappeared or was masked during readers' eye fixations. Consistent with prior research, when only word n disappeared or was masked, there was little disruption to reading. However, when word n+1 either disappeared or was masked (either at the onset of fixation on word n or after 60 ms), there was considerable disruption to reading. Independent of whether word n and/or word n+1 disappeared or was masked, there were robust frequency effects on the fixation on word n. These results not only confirm the robust influence of cognitive/linguistic processing on fixation times in reading, but also again confirm the importance of preprocessing the word to the right of fixation for fluent reading.     

Prevalence and associations of dry eye syndrome in an older population: the Blue Mountains Eye Study

This report describes the prevalence of self-reported dry eye syndrome and associations with systemic and ocular factors in an older Australian population. Participants of the Extension Blue Mountains Eye Study, aged 50 or older (mean age 60.8 years, n = 1174) completed a comprehensive eye examination and dry eye questionnaire. At least one dry eye symptom was reported by 57.5% of participants, with 16.6% reporting moderate to severe symptoms, more frequent in women (age-adjusted odds ratio [OR] 1.5, 95% confidence interval [CI] 1.1-2.2). Three or more symptoms were reported by 15.3% of participants, also more frequent in women (age-adjusted OR 1.7, CI 1.2-2.4). No age-related trends or significant ocular associations were observed. After adjusting for age and sex, systemic factors significantly associated with dry eye syndrome included history of arthritis, asthma, gout, use of corticosteroids, antidepressants and hormone replacement therapy. In this older population, dry eye syndrome was common and has associations with female gender and systemic diseases.     

Prevalence and risk factors of ocular trauma in an urban south-east Asian population: the Singapore Malay Eye Study

Purpose:  To describe the prevalence and risk factors of ocular trauma in an urban Asian population.
Methods:  A population-based survey of 3280 (78.7% response rate) Malay people aged 40–80 years residing in Singapore was conducted in 2004–2006. Interviewer-administered questionnaire was used to ascertain a history of ocular trauma, defined as any eye injury requiring medical attention from a doctor.
Results:  Of the 3264 participants, 149 (5.0%, 95% confidence intervals [CI] 4.1–6.0%) reported a history of ocular trauma. Of those, 30.2% had trauma from a blunt object, 33.6% from a sharp object, and 22.1% from chemical burns. After adjusting for age and sex, men had a higher prevalence of ocular trauma than women (8.3% vs. 2.1%, age-adjusted odds ratio [OR] 4.7, CI 3.1–7.1), and younger persons had a higher risk of ocular trauma (per year increase in age, OR 0.98, CI 0.96–0.99). Consumption of alcohol was associated with higher likelihood of having ocular injury (OR 4.3, CI 2.2–8.4).
Conclusions:  One in 20 persons in this urban south-east Asian population had a history of ocular trauma. Younger persons, men and consumption of alcohol were risk factors for ocular trauma.     

The age- and gender-specific prevalences of refractive errors in Tehran: the Tehran Eye Study

purpose?To determine the age- and gender-specific prevalences of refractive errors in Tehran through a population-based study. methods?A total of 6497 citizens representing a cross-section of the population of Tehran were sampled from 160 clusters using a stratified, random, cluster sampling strategy. Eligible people were enumerated through a door-to-door household survey in the selected clusters and were invited to participate. All participants were transferred to a clinic for an extensive eye examination and interview. Refractive error was determined using manifest and cycloplegic refraction. Myopia was defined as the spherical equivalent of ?0.5 diopters (D) or more and hyperopia was defined as the spherical equivalent of more than +0.5?D. results?Of those sampled, 4565 (70.3%) people participated in the study. Refraction data for 4354 participants aged five years and over are presented. The age- and gender-standardized prevalence of myopia based on manifest refraction was 21.8% (95% confidence interval [CI], 20.1 to 23.5) and that for hyperopia was 26.0% (95% CI, 24.5 to 27.6). The prevalences based on cycloplegic refraction were 17.2% (95% CI, 15.6 to 18.8) and 56.6% (95% CI, 54.7 to 58.6), respectively. Prevalences of myopia and hyperopia differed significantly among the age and gender groups (P < 0.001). Astigmatism of 0.75 cylinder diopter or greater was present in 29.6% (95% CI, 28.0 to 31.3) of right eyes with manifest refraction and in 30.3% (95% CI, 28.5 to 32.1) with cycloplegic refraction. Among the study population, 6.1% (95% CI, 5.3 to 6.8%) had anisometropia of 1?D or more. conclusions?This report has provided details of the refractive status in the population. We have documented prevalences of myopia, hyperopia, astigmatism and anisometropia by age and gender, identifying more affected age- and gender-groups for prevention programs in the community.