Stereoacuity Research Articles

The Role that Binocular Vision and Stereopsis Have in Evaluating Fundus Features

We report two experiments that address the role of stereopsis in viewing the fundus. Thirteen observers viewed stereo slides obtained by lateral displacement of a fundus camera. We quantified the capacity of seven clinicians (normal stereopsis) to resolve depth in a model eye viewed monocularly and binocularly. We also compared the ability of the same seven and six additional clinicians (with reduced stereopsis) to determine the relative position of the cup shown in normal and reverse disparity as well as answering a questionnaire. We determined optimal performance based on a schematic eye. Monocular viewing gives better than expected results with binocularity being of greatest benefit for small disparities. Clinicians perform much worse in stereoscopic judgments than predicted by calculation. Few clinicians report making stereo depth judgments in practice. All amblyopic observers report using hyperacuity cues. This study shows that binocularity and stereopsis are beneficial for judging small disparities under limited circumstances. The level of stereopsis achieved in practice fails to approach the expected limit. We believe that this constriction arises from a known limit to stereo acuity associated with extended fields.

High-grade stereo acuity after early surgery for congenital esotropia.

To evaluate the effectiveness of very early surgery for establishing straight eyes and sensory fusion in patients with congenital esotropia. A review of consecutive patients with congenital esotropia who underwent surgery between 13 and 19 weeks of age. A children's hospital with a teaching affiliation. Seven patients who had surgery between 13 and 19 weeks of age. A bilateral medial rectus recession through a fornix incision with recessions ranging from 5.75 to 6.5 mm in infants younger than 6 months of age. Sensory fusion as measured by stereo acuity and Worth four-dot testing and motor alignment within 8 prism diopters. Five of the seven patients achieved essentially straight eyes with tropias of less than 8 prism diopters after one horizontal surgery. Five patients cooperated with sensory testing, and all showed stereo acuities that ranged from 400 to 40 seconds of arc. Three children had evidence of high-grade stereo acuity by showing stereopsis on random dot stereograms (Randot, Stereo Optical Co, Chicago, Ill) and by fusing the Worth four-dot test at distance and near range. Two of the patients with high-grade stereo acuity achieved a stereo acuity of 40 seconds of arc by Titmus testing; however, one had a late reduction of stereo acuity to 70 seconds of arc. Very early surgery can result in excellent motor alignment and high-grade stereo acuity in some patients with congenital esotropia.

Stereopsis and positional acuity under dark adaptation

Though experience tells us we can perceive depth in dim light, it is not so obvious that one of the chief mechanisms for depth perception, stereopsis, is possible under scotopic conditions. The only studies on human stereopsis in the dark adapted state seem to be those of Nagel [(1902) Zeitschrift für Psychologie, 27, 264–266] and Mueller and Lloyd [(1948) Proceedings of the National Academy of Science, U.S.A., 34, 223–227], both of which used real objects or line stereograms. We tested stereopsis using both random-dot and line stereograms and, in agreement with these studies, found that stereopsis is indeed possible in dark adaptation. We also measured stereo acuity and positional acuity (both of which are examples of hyperacuity) and compared these with grating acuity at several levels of light and dark adaptation. At all illumination levels tested, acuities for stereopsis and relative line position were both higher than for grating acuity. As light levels decreased, positional and grating acuity declined in parallel fashion, whereas stereoacuity declined more steeply.

Effects of intraocular lens malposition on binocular single vision in bilaterally pseudophakic patients

To investigate the relationship between intraocular lens (IOL) malposition and quality of binocular single vision following uncomplicated extracapsular cataract extraction and posterior chamber IOL implantation. Fifty-two bilaterally pseudophakic patients were included. The main outcome measures were visual acuity, stereoscopic acuity, horizontal and vertical amplitudes of fusion and heterophoria, tilting angle and decentration amount of the pseudophacos and summation of these values in somewhat vectorial manner to define the total decentration and tilt of IOLS. The mean total horizontal decentration was 0.19 mm and vertical decentration was 0.90 mm, mean total horizontal tilt being 1.55 degrees and vertical tilt 7.52 degrees. The mean stereoscopic acuity was found to be 1020 seconds of arc. Although the stereoscopic acuity threshold increased as decentration and tilt of IOLS increased, only the horizontal tilt was found to be statistically significantly correlated with stereoscopic acuity (pc0.01). The quality of binocular single vision may be affected by IOL malposition in pseudophakic patients. Therefore, when an IOL implantation is planned, the most appropriate IOL design and surgical technique causing least decentration and tilt should be preferred.

Recovery of fusional convergence after systematic practice

Fusional convergence was trained systematically with orthoptic devices in three patients with a severe deficit in convergent fusion resulting from vascular (one case) or traumatic (two cases) brain damage. Within a single-subject baseline design two of the three patients showed a significant, and the third patient a moderate, recovery of fusional range. All patients showed a significant improvement in visual acuity for objects close by, improved reading performance and an increase in stereo acuity (two cases). The results suggest a considerable potential for recovery of oculomotor functions in brain-damaged patients when appropriate treatment methods are applied.

Oculomotor functions in a Swedish population of dyslexic and normally reading children

Eighty-six nine-year-old dyslexic children were matched to control children with regard to age, sex, class in school, and intelligence. Orthoptic and eye movement analysis were performed on all children. It was concluded that the dyslexic pupils did not differ significantly from control children in terms of strabismus, accommodation, stereo acuity, vergence function or ocular dominance. Eye movement recordings did not show any qualitative differences between the groups in vergence dynamics during synoptophore investigations.

Development of binocular vision in the kitten's striate cortex

Studies of the development and plasticity of the visual pathway are well documented, but a basic question remains open: what is the physiological status of the system prior to extensive visual experience? Somewhat conflicting answers have been put forward, and in a major area, binocular vision, reports have ranged from severe immaturity to well-developed maturity. This is an important question to resolve since binocular cells in the visual cortex are thought to be the neural substrate for stereoscopic depth perception. We have addressed this question by recording from single cells in the striate cortex of kittens at postnatal ages 2, 3, and 4 weeks and from adults for comparison. Gratings with sinusoidal luminance distribution are presented to left, right, or both eyes. For each cell, we determine optimal values for orientation and spatial frequency. Relative phase (retinal disparity) is then varied in a dichoptic sequence so that binocular interaction may be studied. Results are as follows. In the normal adult, we have shown in previous work that most binocular interaction in the visual cortex can be accounted for on the basis of linear summation. Results from 3 and 4 week postnatal kittens are closely similar to those from adults. All types of binocular interaction found in adults are present in kittens. This includes phase-specific and non-phase-specific suppression or facilitation. Furthermore, monocular and binocular tuning characteristics are comparable in kittens and adults. The clear changes that occur with age are optimal spatial frequencies and peak responses. In addition, at 2 weeks, there is a substantially higher proportion of monocular cells compared to other ages and correspondingly, lower relative numbers of cells that exhibit phase-specific or suppressive binocular interactions. From increases in optimal spatial frequency and interpupillary distance with age, we calculated predicted changes in binocular disparity thresholds (stereo acuity) with age. Although there are methodological limits with respect to the behavioral testing of young kittens, the predicted results are comparable to some of the values obtained. Considered together, our results show that the physiological apparatus for binocular vision is functional at an early stage in postnatal development. It is possible that the connections that underlie this function are developed rapidly during early postnatal experience. An alternative possibility is that there is an elaborate genetic organization of binocular vision, but our study does not address this issue directly. A combination of these factors may be applicable.(ABSTRACT TRUNCATED AT 400 WORDS)

Binocular fusion and stereopsis associated with early surgery for monocular congenital cataracts.

Despite improved visual acuity results in infants undergoing early surgery for monocular congenital cataracts, virtually all reports indicate a lack of binocular vision and the presence of strabismus in these patients. We report herein the presence of motor fusion and stereopsis in patients who have undergone early surgery for monocular congenital cataracts. Of 13 patients with congenital cataracts who were operated on by age 9 weeks, five (38%) had essentially straight eyes and evidence of motor fusion with a minimum of 1 year of follow-up. Three (60%) of five patients demonstrated sensory fusion, two with Titmus testing and one with Randot Stereo Acuity (Stereo Optical Co Inc, Chicago, Ill) of 250 seconds of arc. We conclude that binocular fusion and stereo visual acuity are obtainable in patients with monocular congenital cataracts.

Levodopa and childhood amblyopia.

A pilot study was undertaken to address the tolerance and efficacy of levodopa/carbidopa treatment for amblyopia in older amblyopic children who failed to respond to conventional occlusion therapy. Five amblyopic children, between the ages of 7 and 12 years, and two normal adults were given between 100 mg/25 mg and 400 mg/100 mg of levodopa/carbidopa, respectively, depending on body weight. A symptoms questionnaire was completed, with temperature, respiration, heart rate, and blood pressure taken periodically to assess tolerance. Blood samples were taken, via a heparin well, to assess the pharmacokinetics of levodopa, dopamine, noradrenaline, and DOPAC. Snellen visual acuity, contrast sensitivity, stereo acuity, and pattern VERs were measured periodically to assess efficacy. The results revealed a high prevalence of side effects including emesis and nausea (four of seven subjects). Pharmacokinetics revealed that maximum serum levels of levodopa occurred 30 minutes to 1 hour after drug ingestion and decreased by 50% after 2 to 4 hours. One hour after drug ingestion, Snellen visual acuity temporarily improved from an average of 20/159 to 20/83 in the amblyopic eyes. Contrast sensitivity and pattern VERs (10-minute checks) temporarily improved in both dominant and amblyopic eyes, whereas visual function remained stable in normal eyes. The improvements in visual function started to decrease 5 hours after drug ingestion. The results are discussed in the context of developing a therapeutic trial of levodopa/carbidopa for childhood amblyopia.

Spatial uncertainty in stereoacuity tests: Implications for clinical vision test design

In an attempt to design a new stereo vision test we found that the spatial uncertainty effect had substantial impact on the measured stereo acuity thresholds. This effect is present whenever there is uncertainty of where the critical information occurs in a visual target. We studied the spatial uncertainty effect for stereo acuity and for line length estimation. In addition, we determined the temporal uncertainty effect in a stereoacuity test. In foveal vision, uncertainty effects increased visual thresholds, sometimes dramatically. For example, for an uncertainty factor of 25 (i.e., the critical information occurred randomly in any of 25 positions) stereo thresholds increased more than four-fold compared to those obtained without uncertainty. Although the uncertainty effect has been well described theoretically, we think that it is not always appreciated in the design of clinical or experimental visual tests. In tests aimed at determining visual thresholds, spatial and temporal uncertainty factors should be minimized.

A New Method for Evaluating Distance Stereo Acuity

A new standardized method for evaluating distance stereo acuity has been developed, using the graphic capacity of a high-frequency microprocessor and liquid crystal binocular glasses. Images are alternately presented at a frequency of 60 cycles per second to each eye, using synchronized liquid crystal shutter glasses. The amount of disparity in the stereo patterns can be altered to allow a measurement as refined as 15 seconds of arc ("). This instrument is now commercially available as part of the Mentor B-Vat system. We evaluated distance Random Dot and Contour circle stereo acuity of 50 normal subjects using this new method and compared these results to conventional Titmus and Randot circles at near. The distance stereo acuity mean results were 139" for the Random Dot test and 41.1" for the Contour circles. The near stereo acuity results were 41.8" for the Titmus circles and 27" for the Randot circles. Statistically, the Titmus results at near can be compared to the Contour circles at distance. The distance Random Dot test results demonstrate much less stereoability than the other test. The application of these new distance stereotests will be discussed.

Stereoscopic acuity in ocular pursuit of moving objects

Relatively little parallelism was found to exist between still and moving objects with regard to three-dimensional vision. Hence, additional dynamic vision testing may be necessary. This is true for both dynamic stereoscopy and dynamic parallactoscopy. The binocular rotational prismometer or parallactoscopometer proved to be highly suitable for testing within that context. There are specific situations in transport, occupational, and sports medicines in which stereoacuity should be tested in conjunction with oculomotoricity, taking into due consideration the inseparable physiological links between the two.

Stereoscopic Eye Exercises and Visual Acuity

The present study was done to investigate the effects of stereoscopic eye exercises on visual acuity, testing 20 college students (9 men and 11 women, ages 18 to 35 yr.). Visual acuity was assessed before and after the exercises through six tests: far vision--both eyes, right eye; left eye; and near vision--both eyes, right eye, left eye. Statistically significant improvements were found on five of the six pretest-posttest comparisons: far vision--both eyes, right eye, and left eye; and near vision--both eyes, right eye, and left eye. Changes in far vision, right eye only approached significance. Limitations of the present study were discussed, and recommendations for research were presented.

The Validity of Titmus Vision Testing Results

A comparison was made between results obtained through the Titmus Vision Tester and those obtained through more common open field optometric procedures. Specific tests performed with the Titmus Vision Tester included near and distance visual acuities, distance lateral and vertical phorias, color discrimination, and stereo acuity. Results were also obtained using Snellen near and distance charts for visual acuities, Maddox rod for vertical and lateral phorias at distance (neutralized with prism), Ishihara plates for color discrimination, and Stereofly Wirt Dot for stereo acuity. The purpose was to determine whether results obtained by the Titmus Vision Tester are significantly different from those obtained by performing the above specific tests on the patient population.

Contrast and duration of exposure differentially affect vernier and stereoscopic acuity

Although stereoacuity and vernier acuity both yield comparable thresholds well below the eye's resolution limit, the neural circuits for these two classes of visual responses do not process the signals in an identical manner. It had previously been demonstrated that hyperacuity is more resistant to image blur than stereoacuity and that the zones within which two targets must be placed to achieve the lowest thresholds differ quite radically. Two further differences are reported here: reduced contrast affects stereoacuity more severely than hyperacuity, as also does shortening of exposure into a range of tens of milliseconds, even when the Bunsen-Roscoe-Bloch law has been factored out.

Effect of luminance and contrast on stereoscopic acuity

The threshold of binocular depth perception was measured in 11 healthy volunteers. A three-rod arrangement was employed in which both the luminance of the rods and that of the adapting field could be adjusted independently. This allowed fixing the contrast when the effect of luminance was studied or fixing the luminance when the effect of contrast was investigated. The observation distance was 400 mm. Thresholds were expressed as angular disparities and were based on 75% correct responses. Points of subjective equality were also determined. Lowest thresholds (2.85 +/- 0.67 s of arc) were found for a moderate contrast of 0.5 whereas low (0.05) and high (0.95) contrast both produced significantly higher thresholds (luminance 250 cd/m2). Altering the field luminance (50, 250, 1600 cd/m2) under constant contrast conditions (0.95) did not measurably influence stereoscopic acuity.

3D reconstruction and interpretation in human binocular vision by processing of disparity information

After a review of fundamental definitions in binocular vision-binocular convergence, retinal disparity and their perceptual correlates (fusion, diplopia, suppression and stereoscopic depth)-psychophysical data on Panum's area and their spatial and temporal characteristics are presented. Specific features of stereopsis as the visual perception of three-dimensional space based on binocular disparities are described: horizontal disparity processing for depth perception, global stereopsis according to Julesz, and the disparity gradient limit for binocular matching. A discussion of stereoscopic acuity and of the neurophysiological basis of stereopsis is also included.

Hyperacuity, superresolution and gap resolution in human stereopsis

Different types of stereoscopic acuity were studied with tasks adapted from studies of visual direction acuity. Dynamic, random-element stereograms portraying multiple surfaces in depth and a temporal 2AFC procedure were used for all measurements. The three tasks required detection of a depth offset (Hyperacuity task), a depth-axis thickening (Superresolution task), and a depth-axis gap between surfaces (Gap Resolution task). Thresholds for the three tasks were on the order of 3 sec arc, 30 sec arc and 200 sec arc of retinal disparity, respectively. These results are comparable to those for the analogous visual direction tasks on which they were patterned, suggesting that the underlying judgments involved are similar. Results are used to estimate the intrinsic noise of horizontal disparity processing.

How contrast affects stereoacuity.

Stereoacuity and its dependence on contrast were measured at four spatial frequencies separated by 1 octave steps. Using a method of adjustment, observers adjusted the retinal disparity of an aperiodic narrow-band stimulus until it appeared in the depth plane defined by two flanking reference lines. Variations in contrast affected stereoacuity (the standard deviation of ten depth settings), with better performance observed at higher contrasts. Data were fit with straight lines (on a log-log plot), indicating a power-law dependence on contrast; the slope was steeper at lower spatial frequencies. These findings are consistent with the idea that disparity is computed from the responses of size-tuned mechanisms characterized by nonlinear contrast transfer functions. In a second experiment, the effects of interocular differences in contrast on stereoacuity were studied for two conditions. In the first condition, one eye always viewed a high-contrast target while the other eye viewed targets of successively lower contrast; in the second condition, one eye always saw a target of near-threshold contrast while the other eye saw targets of successively higher contrast. When the fixed contrast was high, stereoacuity deteriorated steadily as the interocular difference in contrast increased; the loss of stereoacuity was greatest at the lowest spatial frequency. When the fixed contrast was low, however, small increases in the contrast to one eye had no deleterious effect on stereoacuity. Once interocular contrast settings exceeded a certain difference, stereoscopic acuity began to deteriorate at lower spatial frequencies. These results address the issue of the stage of visual processing at which contrast exerts its influence on stereopsis.

7-1 立体視知覚特性を考慮した2眼式立体画像の伝送に関する一検討

7-1 立体視知覚特性を考慮した2眼式立体画像の伝送に関する一検討