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PubMed1999

The influence of heterophoria measurements on subsequent associated phoria measurement in a refractive routine.

The influence of measuring heterophoria on a subsequent associated phoria measurement was investigated in 50 subjects. After refraction, heterophoria was measured by either von Graefe's technique or Maddox rod and wing. The effect of these procedures was assessed by associated phoria measurements taken before and after the dissociated measures. It is shown that subjects with a history of unstable binocular vision are likely to have an associate phoria induced or changed by the previous dissociated phoria measurement, particularly if von Graefe's technique is employed. It is recommended that, especially for near, associated phoria should be assessed before the dissociated phoria in subjects who are regarded as having a history of unstable binocular vision.

Adult↗
PubMed2001

General binocular disorders: prevalence in a clinic population.

The purpose of this paper was to study the prevalence of nonstrabismic accommodative and binocular dysfunctions in a clinical population. We examined 265 symptomatic patients who were chosen from an optometric clinic. We performed several tests to diagnose any form of refractive, accommodative or binocular dysfunction. Of the 265 subjects examined, 59 patients (22.3%) had some form of accommodative or binocular dysfunction and required not just the correction of the refractive error but a specific treatment for each of the problems diagnosed. The remaining subjects were classed as having refractive anomalies. The frequency of binocular dysfunctions was 12.9%, and 9.4% for accommodative anomalies. Convergence excess (4.5%) was more prevalent than convergence insufficiency (0.8%) and accommodative excess (6.4%) more prevalent than accommodative insufficiency (3%).

Accommodation, Ocular↗
PubMed2004

Binocular interaction and performance of visual tasks.

Binocular vision implies the fusion of the right and left retinal images to perceive a single image. For this, interocular interaction is required. We measured the reaction times to carry out a visual fixation task in order to determine whether binocular interaction influences performance. Several combinations of test and distraction stimuli were monocularly and binocularly presented to one monkey and three human subjects. The overall median reaction times were 340 ms for the animal and 308, 342 and 381 for human subjects 1, 2 and 3 respectively. Reaction time was shorter when the test stimulus was presented binocularly. Moreover, we observed that the presence of a distraction stimulus increased the reaction time and that a correlated distraction stimulus had a greater influence on this increase than an uncorrelated distraction stimulus. These findings indicate that with binocular vision a more rapid performance of a visual task occurs.

Adult↗
PubMed2002

Further evidence for a reversed crossing of foveal projections in schizophrenic vulnerability.

Further evidence in support of the thesis developed in a previous article published in Medical Hypotheses (Sept. 2000) proposing that schizophrenic vulnerability might consist of the temporal instead of the nasal foveal projections crossing over in the chiasma opticum has been provided by an experiment in which pinholes are used to isolate foveally stimulated from peripherally stimulated vergence. By shifting the pinholes inwards or outwards a dilemma is created regarding the fusion of the edges of the two pinholes or of a single diode light seen at the inner or outer edges of the pinholes. It was revealed that schizophrenic patients never solved the dilemma in favour of what was represented on the temporal foveal halves while this was always the case in the control group. At best, the patients fusioned neither the diode light nor the pinhole edges but saw both double. An explanation is given as to how this disturbance might be based on the interchange of nasal and temporal foveal projections and might lead to the dissociation of the visual goals of the two eyes, as shown in a previous test. The cause of markers of schizophrenic vulnerability mentioned in literature, in particular saccaded SPEM, P50 response and hyperdopaminergia, is related to such an interchange and suggestions are made for further experiments. Finally, the difficulty of schizophrenic patients to distinguish between reality and illusion is attributed to a disconnection of spatial and object perception.

Accommodation, Ocular↗
PubMed2005

Assessment of visual function in children with methylmalonic aciduria and homocystinuria.

The aim of this study was to assess various aspects of visual function in 6 patients (age range: 9 months to 7 years and 8 months) with methylmalonic aciduria and homocystinuria. All patients had an ophthalmological examination and were tested with a battery of age-appropriate tests assessing various aspects of visual function such as acuity, visual fields and visual attention. None of the patients had significant retinal abnormalities but all 6 had nystagmus which was associated with strabismus in 3 of the 6. They all had some abnormalities on the behavioral tests assessing visual function which appeared to be related to the age of the patients. Visual impairment was more severe in the 3 patients below 3 years of age and milder in the older patients. The presence and the severity of abnormalities, in contrast, did not depend on the age at onset or the age when treatment was started and were only partly related to brain MRI findings. Severe hydrocephalus and basal ganglia involvement were associated with severe visual impairment, but abnormal visual findings were also present in the children with normal MRI and isolated mild periventricular changes. Our results suggest that age, brain lesions and other factors may be responsible for visual abnormalities in methylmalonic aciduria and homocystinuria. Further studies using early and sequential assessment of visual function are needed to establish whether the differences observed between younger and older children may be related to the duration of therapy.

Attention↗
PubMed1991

[A new simple test for quantitative determination of near aniseikonia].

A quantitative test for the measurement of near distance aniseikonia is presented which is easy to handle. It combines the advantages of the Awaya near distance test with those of the Aulhorn phase difference haploscope: On the one hand the test can easily measure aniseikonia without a large apparatus, on the other hand it allows an exact comparison of the test objects due to the free mobility of the test objects. This is important because of the frequently accompanying motility disorders.

Aniseikonia↗
PubMed1991

[Results of full binocular correction versus conventional methods].

UNLABELLED: 163 patients suffering from different serious troubles were treated with binocular full correction (BFC) i.e. examination by Polatest and prismatic correction. Before, they all had seen other ophthalmologists. The former diagnose and therapy are listed and compared with those of the author. RESULTS: After a 2 2/3 years average follow-up period 68% of the patients were complaintless, 23% felt better. All patients reached at least binocular single vision, although initially 13% had no binocular vision and 1% complained about diplopia. 70% got ideal binocular vision (initially 0%). In the beginning 50 patients suffered from reduced visual acuity. It improved in all cases with differences of v.a. from 2-4/10 to 10/10. From the shown results the author concludes that conventional binocular diagnostic and therapeutic methods do no longer meet the state of the art. It is postulated that BFC should be accepted by school-medicine and that ophthalmologists and orthoptists should be trained in BFC. Only in this way ophthalmologists may fulfil their task to free patients from the many complaints caused by binocular troubles. The used terminology about BFC is explained in the appendix.

Adolescent↗
PubMed1990

[Post-concussion decrease in aniseikonia tolerance].

Besides loss of convergence and accommodation, head injuries can cause fusion deficiency. Part function of sensory fusion is tolerance to sphaerical and meridional aniseikonia. We will present a patient, whose aniseikonia tolerance decreased after a brain concussion.

Aniseikonia↗
PubMed2000

Interobserver test-retest reliability of the Randot preschool stereoacuity test.

PURPOSE: Random dot stereoacuity can be quantified to between 40 and 800 seconds of arc in preschool children by using the Randot Preschool Stereoacuity test (Stereo Optical Co, Inc, Chicago, Ill). To incorporate this test into clinic and research settings, the reliability of its stereoacuity scores obtained by separate examiners needs to be evaluated. The purpose of this study was to evaluate its interobserver test-retest reliability. METHODS: Participants included 102 consecutive children with binocular sensory function ranging from fine to no measurable stereopsis. Clinical research participants included children with anomalous binocular vision caused by strabismus, cataracts, anisometropia, and ptosis. In a prospective study, random dot stereoacuity was measured twice under masked testing conditions by 2 examiners within a 1-hour period. RESULTS: Interobserver test-retest reliability of the Randot Preschool Stereoacuity test is high among a population of children with diverse binocular sensory function. The correlation coefficient between individual test scores was highly significant (r = 0.97, P<.001). Mean differences between the 2 scores (0.021 log seconds of arc) were not significantly different from zero (t(99) = 1.33, P>.1). The upper and lower limits of agreement were narrow, reflecting both the large sample size and the small variation between the 2 test scores. Interobserver test-retest reliability of the Randot Preschool Stereoacuity test was nearly constant across levels of functional stereoacuity, patient categorization, and age at the time of the test. CONCLUSIONS: The high agreement between the Randot Preschool Stereoacuity test scores by 2 independent observers supports its use in clinical management and research settings for the quantitative assessment of binocular sensory vision, as well as in multicentered research studies.

Child↗
PubMed1992

Learning to see random-dot stereograms.

In the present study some specific properties of the learning effects reported for random-dot stereograms are examined. In experiment 1 the retinal position-specific learning effect was reproduced and in a follow-up experiment it was shown that the position specificity of learning can be accounted for by selective visual attention. In experiments 2 and 3 evidence was obtained that suggests that observers can learn, to a certain degree, monocular random-dot patterns and that this learning facilitates the depth percept. This result indicates that the traditional belief that random-dot stereograms are devoid of monocularly recognizable or useful forms should be reconsidered. In the second set of experiments the learning of two binocular surface properties of random-dot stereograms, depth edges and internal depth regions, was investigated. It was shown in experiment 4 that the depth edges of random-dot stereograms are not learned, whereas the results of experiment 5 indicate that the internal depth regions are learned. Finally, in experiment 6 it was shown that depth edges are learned when the internal depth regions of the stereogram are ambiguous. The results are discussed in terms of the importance of the particular type of stimulus used in the learning process and in terms of perceptual learning and attention.

Attention↗
PubMed1992

Mobility of normal observers under conditions of reduced visual input.

The importance in mobility performance of the rate of presentation of visual information, binocular versus monocular vision, the use of multiple rather than single reference points, and local motion parallax was investigated in two experiments. In each experiment ten subjects walked a triangular mobility course in a totally darkened room; the only visible targets were light emitting diodes (LEDs), mounted on poles, at the apices of the triangle. The LEDs were mounted so that one or two could be used in a trial; if two were used the distance between them was varied horizontally (in experiment 1) and vertically (in experiment 2). The subjects walked around the course under a range of conditions, including two 'optimal trials' in full light. The LEDs were flashed for 1 ms at frequencies of 0.5, 1 and 5 Hz in experiment 1 and at 1 and 5 Hz in experiment 2. Mobility was measured with the use of an ultrasonic locator system which measured the subject's position on the course 10 times per second. The mean velocity of the subject in traversing the course was significantly reduced when the flash rate was slower, when the subject had one eye occluded, or when there was only one LED on the pole; when the spacing between the LEDs was varied, either vertically or horizontally performance was unaffected. These results imply that the frequency of updating of visual information is important in determining mobility performance, as are binocular cues, but that local motion parallax is not important. The number of LEDs on each pole had a significant effect on mobility performance an 'object' (two lights) gave more information than a point reference.

Adult↗
PubMed1993

Visual alchemy: stereoscopic adaptation produces kinetic depth from random noise.

Observers perceive incoherent motion and no hint of depth when viewing stochastic motion, in which stimulus elements move in all possible directions. As earlier work has shown, depth can be specified by introducing a brief interocular delay between the presentation of corresponding animation frames of this 'noise' to the left and right eyes. A study is reported in which observers were adapted to a stereoscopic display consisting of coherent planes of motion at different depths. This stereoscopic adaptation caused incoherent depthless motion to take on the qualities of structure and depth, and it could nullify the depth induced by interocular delay. The findings are interpreted within the context of a neural model consisting of units selectively responsive to different directions of motion at different planes of depth.

Depth Perception↗
PubMed1993

New depth to the Müller-Lyer illusion.

It is demonstrated that when the two halves of the Müller-Lyer illusion are shown separately to the two eyes this can result in a perception of the binocularly viewed shaft as slanted in depth. For short fin lengths, the magnitude of this slant can be predicted by the extent of the ordinary two-dimensional illusion. This result is discussed in relation to Julesz's claim that stereoscopic matching of the images in the two eyes must precede whatever process is responsible for the Müller-Lyer illusion (whereas the reported illusion seems to imply the reverse). The cyclopean Müller-Lyer demonstration on which Julesz's argument is based is reexamined. It is suggested that the matching of coarse-scale features in the images in the two eyes may help to explain both the cyclopean and the reported three-dimensional Müller-Lyer illusion.

Depth Perception↗
PubMed1993

The familiar-size cue to distance and stereoscopic depth perception.

The role of the familiar-size cue to distance in stereoscopic depth perception was examined in two experiments. In experiment 1 subjects judged the depth of a binocularly viewed interval, the far point of which was defined by either a familiar or an unfamiliar object, and in experiment 2 subjects adjusted the depth of the interval so that its extent appeared equal to the length of a vertical reference extent positioned on the surface of the object. Although familiar size influenced depth estimates (experiment 1) it did not influence matching judgments (experiment 2). The findings are discussed with reference to the issue of the nature of the familiar-size effects on judgments of stereoscopic depth.

Depth Perception↗
PubMed1995

A restatement and modification of Wells-Hering's laws of visual direction.

The laws of visual direction proposed by Wells some 200 years ago and Hering over 100 years ago are restated as three laws with the terminology of these two pioneers. This restatement serves both to honour their work and to strengthen some of the weaknesses in their original treatises. Second, two simple experiments, or tests of the laws, which the readers can readily perform by using their fingers as stimuli, are illustrated. Third, one of the three laws is modified to incorporate recent findings. Fourth, two recent experiments relevant to these new laws are described briefly, and their theoretical and methodological implications are discussed.

History, 18th Century↗
PubMed1995

Transparent surfaces and illuminated holes.

A single stimulus determined the alternative perceptions of an illusory transparent grey disk or of an internally illuminated circular hole. A square on a far background was visible through this disk or hole. Subjects rated the grey colour of the transparent disk or the phenomenal illumination inside the hole. The luminance difference relative to the transparent disk and the square and that relative to this disk and its background determined the probability of perceiving the transparent disk or the hole. Rated colour and illumination substantially depended only on this second difference. These results have implications for models of phenomenal transparency and illumination based on the idea that proximal contours activate neural representations of phenomenal attributes.

Humans↗
PubMed1995

Texture discrimination at the cyclopean retina.

One of the open questions within the study of texture discrimination is whether the underlying neural mechanisms are located within the two monocular pathways, or whether they are located at more central areas that process binocular information. This question is considered here in psychophysical experiments of texture discrimination involving stereograms. The results show that texture discrimination for differences in form and size occur after binocular fusion. Moreover, the suitability of random-dot stereograms versus line-figure stereograms for this research has been studied. It was found that discrimination for differences in form was better with line-figure stereograms whereas discrimination for differences in size was better with random-dot stereograms.

Depth Perception↗