Stereopsis Test Research Articles

Judgments by monkeys of apparent depth in dynamic random-dot stereograms

Young macaques discriminated apparent depths of targets embedded in dynamic random dot stereograms; a test of stereopsis. In a ‘same/different’ paradigm, the discrimination took longer if the pair of stimuli appeared to be in same depth plane, than when they appeared to be located in a different depth plane. The decision time was an inverse function of the disparity difference. Apparent depth discrimination performance decreased as a function of disparity, with no differences in judgments regarding crossed or uncrossed disparities.

The relative afferent pupillary defect and a novel method of fusion recovery with the Worth 4-dot test.

To examine the relation of the relative afferent pupillary defect and commonly used clinical tests of visual cortex binocular cell activity, namely, fusion and stereopsis. Sixty-seven subjects with neuro-ophthalmologic disorders underwent measurement of relative afferent pupillary defect and assessment of binocular sensory status by fusion on the Worth 4-dot test and stereopsis on the Titmus stereo test. Recovery of fusion on the Worth 4-dot test and improvement of stereopsis were tested by placing increasing neutral density filters in front of the eye that did not have the afferent pupillary defect. Recovery of fusion on the Worth 4-dot test occurred with use of neutral density filters (Worth 4-dot neutralization test). No improvement of stereopsis was observed. A significant positive association was identified between the measured afferent pupillary defect and the measured log filter required for fusion (r = .83, P < .001 by the Spearman rank correlation coefficient). In no case was a relative afferent pupillary defect observed when fusion without use of neutral density filters was present at baseline. For subjects with relative afferent pupillary defects, the measurements of the Worth 4-dot neutralization test were equal before and after pupillary dilation. The relative afferent pupillary defect is a dynamic process that results from an imbalance of brightness sensitivity between the two eyes. Altering the latency ("timing") and amplitude of the light stimuli by use of neutral density filters can restore fusion on the Worth 4-dot neutralization test but does not alter stereopsis. The Worth 4-dot neutralization test may be a useful adjunct in the assessment of visual dysfunction.

“Starkfest” Vision and Clinic Science Special Issue

The effects of horizontal heterophoria on Howard-Dolman stereopsis scores were investigated in a population of 1765 stereophotogrammetrists with no obvious impediment to binocular vision as determined in a vision screening. Exophoria over the 1 to 7 delta range showed no systematic and statistically valid effect on stereopsis but esophoria did show an effect. In a related population of 1339 stereophotogrammetrists, subjects with as little as 1 delta (+/- 0.5 delta) of vertical heterophoria exhibited a small but statistically significant decrease in stereopsis test scores compared to those with vertical orthophoria. Therefore, a heterophoria had different effects on stereoacuity depending on whether it was in the exo, eso, or vertical direction. An explanation for the difference is proposed using the known dependence of heterophoria and stereoacuity on fixation disparity.

The Effect of the M43 and M17 Protective Masks on Stereoacuity

The purpose of this study was to evaluate the effects of the M17 and M43 protective masks on stereoacuity. Twelve subjects were tested on the Keystone diagnostic series stereopsis test at nearpoint and the Howard-Dolman apparatus at 40 cm and 6 m. Stereopsis was evaluated without a mask and with the M43 and M17 masks. Stereoacuity was decreased at near point with both masks and was not significantly affected at the 6-m distance.

Artifacts in fusion and stereopsis testing based on red/green dichoptic image separation.

A red/green anaglyph stereotest (TNO) was administered to a group of patients who had anisometropic amblyopia, and the Worth 4-Dot test for fusion to two groups of strabismus patients. Both tests were administered twice, with the red/green lens position of the glasses reversed between eyes for the second administration. Twelve of 15 patients with anisometropic amblyopia exhibited a stereo acuity difference of 2:1 or more, and 18 of 89 strabismic patients changed Worth 4-Dot fusion or suppression status, between the two positions of the glasses. A group of seven strabismic patients who showed the reversal effect on the Worth 4-Dot test had the results of one glass' position discrepant with those of a geometrically identical achromatic test. It appears that the red/green format can introduce artifacts in binocular vision testing. Testing twice, with the red/green glasses reversed between trials, will prevent misinterpretation of binocular status and may provide diagnostically useful information.

Definition of thresholds for stereoscopic depth.

In the laboratory, thresholds for stereoscopic depth perception are usually determined by asking observers to discriminate between a stimulus with a given depth offset and its mirror image. Threshold is most often defined as the disparity difference that yields 75% or 83% correct responses. Disparities used for clinical tests of stereopsis are much higher. Here it is argued that, among other factors, this is because of the fact that clinical tests usually require the detection of a depth difference (offset versus no offset), rather than the discrimination between two directions of depth difference (in front versus behind). From a formal comparison of the two tasks, the data show that discrimination, or classification is easier by at least a factor of 2 than detection. The contribution of variations of the threshold criterion and learning to the differences between stereoacuity as measured in laboratory and clinic is also discussed. These differences are relevant to the design of tests for clinical use.

TNO stereopsis test as an aid to the prevention of amblyopia*

In this investigation, carried out under a Youth Health Care postgraduate course in Nijmegen, the stereopsis of a school population of 730 children, aged 4-18 years, was recorded and clinically evaluated. Stereopsis was measured using the TNO test, a random-dot stereo test especially designed for the early detection of amblyopia. The main aims of this study were to establish the validity of the TNO test as a screening test for amblyopia, obtain information about the variability and age dependence of stereopsis, and to evaluate the efficacy of amblyopia prevention. The most important findings can be summarized as follows: 1. All amblyopes are detected by the TNO test's recommended referral criterion of 240 sec arc (binocular threshold parallax in sec arc). 2. The red-green anaglyphs used in the test do not pose problems for individuals with a colour vision deficiency. 3. The ability to discriminate depth improves by a factor of two over the age interval 4-12 years. 4. A stereoacuity of < or = 120 sec arc is a good predictor of normal or correctable normal vision, and may therefore help in evaluating the often incomplete results of eye tests of young children. 5. Where there is an increased perinatal risk, there is a greater chance of disturbed binocular vision. 6. It is estimated that 75% of amblyopes remain amblyopic, possibly because of delayed detection; 60% of the amblyopes in the population examined were not identified before the age of 5 years.

Binocularity in accommodative esotropia.

One hundred twenty-seven medical records of patients with accommodative esotropia met our inclusion criteria and were analyzed. All included patients were within 10 prism diopters of orthophoria and had stereopsis and other binocular sensory test results recorded at their latest visit. Bifixation, defined as stereopsis of 50 arc seconds or better, was present in 31 patients (24%) with an average follow up of 89 months. Monofixation (peripheral fusion) was present in the remaining 96 patients (76%) with an average follow up of 84 months. Patients with bifixation were less likely to have presented with constant esotropia (19% vs 39% [P = .04]) and were more likely to be aligned within 8 delta of orthophoria in their first glasses (84% vs 21% [P < .0001]). No patient with bifixation had constant esotropia longer than 4 months. In addition, patients with bifixation were less likely to have worn bifocals (39% vs 59% [P = .09]), or undergone esotropia surgery (23% vs 62% [P < .0001]). These data suggest that maintenance of bifixation is possible in accommodative esotropia if the eyes are straightened before or shortly after the esodeviation becomes constant. With this early therapy, amblyopia and deterioration of ocular alignment are also less likely.

Examinations on the New Lang Test

The New Lang-II stereopsis test employs, as compared to the Lang-I test, smaller disparities and a less dense arrangement of random dots. In 162 subjects the authors comparatively evaluated the results of the Lang-I and Lang-II tests. Ninety percent of subjects with normal binocular vision passed both tests without making any mistake (n = 127). However, about 70% of patients with microstrabismus failed both tests (n = 35). Little difference was found between the results of both tests.

Results of early surgery for infantile esotropia in normal and neurologically impaired infants.

A prospective study was performed over a 4-year period of 56 infants presenting with infantile esotropia to assess development of binocularity after surgical alignment before 2 years of age. In 50% of cases infantile esotropia was associated with neurological problems or prematurity. Forty-three cases have undergone surgery (mean age 15.7 months +/- 3.46); 86% were aligned (+/- 10 dioptres) at 2 years. Eighty-seven per cent of normal children and 74% of children with neurological problems or prematurity were aligned at last follow-up (mean 27.2 months since surgery). Tests of fusion and stereopsis have to date been possible upon 21 'successfully' aligned infants and although most have evidence of peripheral sensory fusion none showed stereopsis to more than one test. Although early surgery achieves a good cosmetic result in normal children and those with neurological problems, our findings question its ability to promote the development of even gross stereopsis in most children.

Stereopsis, Accommodative and Vergence Facility: Do They Relate to Dyslexia?

The relation between visual functions and reading performance has been the subject of conflicting opinion over the years. The purpose of this study is 2-fold: first, to examine factors other than visual acuity, i.e., stereopsis, accommodative facility and vergence facility, which might show a greater impact on reading achievement; and second, to utilize well defined dyslexic and normal controls to ensure that the reading deficits were not caused by overt neurological, psychological, educational, or environmental factors. Thirteen normal readers and 13 dyslexics were carefully matched by rigorous quantitative criteria. The performance of both groups on tests of visual acuity and stereopsis was similar. The dyslexic readers tended to show better accommodative facility. Dyslexics performed significantly worse than the matched normal readers on a test of vergence facility. These results, in agreement with those reported by other studies, indicate that less efficient dynamic vergence facility may contribute to reading impairment, unlike other static functions such as visual acuity and stereopsis. It may be that the vergence problems of the dyslexics are related to sequential oculo-motor abnormalities. The dyslexics' vergence problems may also be partly responsible for their large number of small eye movements.

Testing Stereopsis in the Preschool Child: Is It Clinically Useful?

The evaluation of stereoacuity should provide an unambiguous assessment of binocular function in infants and young children. Unfortunately, clinical measures of stereopsis in these young patients often result in stereotheresholds poorer than the criteria suggested to differentiate normal from anomalous binocular vision. Thus, two experiments were conducted to determine whether the large stereothresholds frequently demonstrated on tests designed for young children are diagnostic of normal binocular function in preschool children. The first experiment investigated the salience of the monocular cues in the Lang and Frisby stereotests in normal preschool children (2 to 5 years old). None of the children who passed either the Frisby or the Lang stereotest under binocular conditions were able to pass either test monocularly, even after passing the test binocularly. In the second experiment, preschool children with abnormal binocular vision were tested with the Lang and Frisby stereotests to determine if large disparities (730 to 800 seconds of arc [arcsec]) could be passed without normal binocular vision. None of the children with strabismus passed either stereotest. However, two children with anisometropia passed the Frisby test and one of these children also passed the Lang test. These results suggest that in the absence of other clinical findings to the contrary, the demonstration of gross stereopsis with either the Frisby (730 arcsec) or Lang (733 or 800 arcsec) test in the preschool child implies normal binocular function. Thus, clinical tests of stereopsis for infants and preschool children, like those used routinely for adults, can provide evidence of binocular function without approaching stereothreshold.

Stereopsis Testing to Reduce Overreferral in Preschool Vision Screening

Three- and 4-year-old children who obtain the minimum failing visual acuity result of one-line difference between eyes in preschool vision screening with isolated optotypes have a high rate of overreferral. We evaluated the Random Dot E Stereotest (RDES) to determine if a passing result at a high threshold on this test, as administered by lay screeners, could safely nullify referral for a minimum failing visual acuity test result. Fifty-eight children with a "one-line difference" result also had the RDES administered to them during screening at distances of 40 cm and 1.5 m. Upon subsequent ophthalmologic examination, 45 of these children were found to be normal, and 13 had abnormal findings. Thirty-nine of the children with normal examinations had correctly passed the RDES at 1.5 m. Seven of the 13 children with abnormal findings had correctly failed the RDES. Thus, the specificity of stereotesting was 87% and the sensitivity was 54%. Among the six children who falsely passed the stereopsis test during screening, best-corrected visual acuity was no worse than 20/40 and no child had greater than a one-line difference in acuity. Therefore, no amblyopia was missed. If a passing result on the stereotest at 1.5 m had been allowed to nullify a one-line difference referral, overreferral would have decreased 87% but underreferral would have increased 46%. We cannot yet recommend modifying current visual acuity referral criteria based on stereopsis testing results until the sensitivity of stereopsis screening by lay screeners at a sufficient threshold is improved.

Success rates in testing monocular acuity and stereopsis in infants and young children

This study demonstrated how success in stereopsis and monocular acuity testing in the under-fives changes with age. Monocular testing was least successful with 1-2-year olds, while success with stereopsis testing increased linearly to 100% by 3 years. The differing patterns mean that a reasonable degree of success with one test or the other is likely whatever a child's age. Since the demonstration of either stereopsis or normal monocular acuities rules out the presence of any gross visual anomaly, the age-appropriate use of the two types of testing will facilitate the early detection of any abnormality.

Stereoscopic contours and optokinetic nystagmus in normal and stereoblind subjects

Moving stereoscopic contours in a dynamic random-dot stereogram have been previously shown to induce optokinetic nystagmus in subjects with normal stereopsis. For this to be validated as an objective test of stereopsis, stereoblind subjects must also be shown not to develop OKN, especially since it has been shown that the optomotor system of stereoblind individuals retains sensitivity to some cyclopean stimuli. In this report we verify that stereoblind subjects do not have an optomotor response to stereoscopic contours—regardless of the alignment angle at which the stereo image pair is presented.

Stereopsis testing in a preschool vision screening program.

We conducted a preschool vision screening study using stereopsis testing with the Random Dot E and Lang stereotests as a complement to visual acuity measurement. Over 6000 children were screened. Stereopsis testing at a threshold of 600 seconds of arc was cognitively easier for the children than visual acuity measurement. At this threshold there was no effect on reducing the rate of visual acuity overreferrals, but ten children with abnormal binocular vision were detected who were not referred by visual acuity criteria. Though a large number of children passed only one of the two stereotests, there was no significant difference in their degree of difficulty. Stereopsis testing with these two stereotests may be a useful adjunct to preschool vision screening programs though further studies are required.

The Pulfrich Effect in Anisometropic Amblyopia and Strabismus

Using a device based on the Pulfrich effect, we examined 70 patients with various strabismus problems and 20 normal subjects for gross stereopsis. We found an excellent correlation between this dynamic stereopsis test and random dot stereograms. Additionally, in several instances the Pulfrich device was easier to use and interpret correctly than random dot stereograms. The Pulfrich effect can be elicited reliably in patients as young as 3 1/2 years of age. Three patients with anisometropic amblyopia and stereopsis were found to possess a spontaneous Pulfrich effect.

Stereoscopic vision and psychomotor learning in dental students

A testing mechanism is needed for reliably predicting students' problems in acquiring dental psychomotor skills. Students and dental educators could then be made aware of potential problems well in advance of required manual course work. Because testing for stereoscopic vision has long been a part of perceptual-motor ability screening for the U.S. Air Force, a similar stereopsis test was used to examine the role of stereopsis in dental psychomotor learning and its potential as a predictor of student performance. The Lameris TNO Test for stereoscopic vision was given as an adjunct to the Perceptual Ability (PAT/3D) portion of the Dental Admission Test. Both test results were then compared to freshman students' performance in preclinical operative dentistry. Multiple regression analyses indicated that a high degree of stereopsis was not a prerequisite for success in acquiring dental psychomotor skills.

Identification and Follow-Up of Visual Impairments in Hearing-Impaired Populations

This publication provides an overview of a project on identification of visual problems and follow-up conducted by the National Technical Institute for the Deaf (NTID) at Rochester Institute of Technology (RIT).1 This project had three main objectives: (a) to determine the most appropriate means for identifying NTID students with visual impairments and make recommendations for medical and personal/social follow-up (Objective 1); (b) to determine the types and incidence of visual impairments among these students (Objective 2); and (c) to conduct research that would assist in the provision of appropriate counseling relative to academic and career opportunities/experiences for persons with both auditory and visual impairments (Objective 3). Several approaches were investigated as possible means for assessing the visual functioning of NTID students (Objective 1). Subsequently, some of these approaches were used to determine the types and incidence of visual impairments within this population (Objective 2). The approaches investigated were: (a) a vision questionnaire (personal/family ocular history) for students; (b) an off-campus general health physical examination; (c) an off-campus opthalmological examination; (d) an on-campus ophthalmological examination (standard to which all other assessment results were compared); and (e) an on-campus visual screening program. This screening program included the use of Bausch and Lomb Orthorater Vision Testers (a vision screening instrument used in assessing visual acuity, color vision, and binocular vision), the Ishihara Color Vision Test (a test designed to evaluate the ability to discriminate colors), and Titmus Stereopsis Tests (a series of tests designed to assess the ability to perceive objects in three dimensions using both eyes). Visual parameters assessed included near and far (distance) acuity (the ability of the eyes to resolve or differentiate detail), color vision (the ability to discriminate colors), and binocular vision (muscle balance and depth perception). In addition, three psychophysical screening tests for the presence of retinitis pigmentosa (RP) (a progressive loss of vision due to retinal degeneration) were investigated; one approach involved a test for assessment of dark-adapted visual sensitivity (the ability to see in darkness or dim illumination), and the other approach involved two tests for temporal processing of visual stimuli. The methodology designed to investigate appropriate counseling relative to academic and career opportunities/experiences for persons with auditory and visual impairments (Objective 3) was as follows: (a) literature review; (b) interviews with content/technical experts at NTID to identify both visual skills believed to be important for students to succeed in various technical areas, and academic and career recommendations relative to students having both hearing and visual impairments; and (c) in-class and on-the-job follow-up for NTID students and graduates having visual impairments (e.g., observations and interviews). Based on the data collected using the above methodologies, recommendations have been made for identification and follow-up of NTID students with visual impairments. These recommendations address: (a) the rationale and methodology for a recommended visual screening program; (b) the pass-fail criteria for referral for an in-depth examination by an ophthalmologist; and (c) recommended follow-up procedures, including medical treatment and correction, personal/social follow-up, and counseling relative to academic/career experiences. The implications and application of this project to all persons with hearing impairments, including younger age groups, are also discussed. Given the importance of vision to persons with hearing losses, it is recommended that: (a) an in-depth ophthalmological examination be done routinely upon discovery of a hearing loss; (b) reassessment of visual functioning, as well as auditory functioning, be done periodically for all persons with severe to profound hearing losses; (c) interpreters be used as appropriate to help ensure adequate communication during both visual assessment/examination procedures and any necessary follow-up; and (d) information be provided for hearing-impaired persons, parents, and professionals concerning the importance of visual assessment and visual hygiene for persons with hearing loss. The need for further research relative both to the status of the visual system and how to best facilitate the use of the visual modality for learning among hearing-impaired persons is emphasized. Also, the need for further investigation of academic and career experiences appropriate for persons having both auditory and visual impairments, and the need for training of instructional staff to work with these persons, are stressed.

Method of Delivery and Developmental Outcome At Five Years of Age

A controlled follow-up study examined the impact of delivery method on developmental outcome of the child. The modes of delivery investigated were low forceps delivery (188 infants), midcavity forceps delivery (51 infants), forceps rotation with forceps delivery (57 infants), manual rotation with forceps delivery (67 infants), elective caesarean section (101 infants) and spontaneous delivery (control, 207 infants). Breech presentation (100 infants) was separately compared with the vertex presentation groups. Sample selection controlled for complications during pregnancy and low birthweight and was restricted to married English-speaking mothers. The children were assessed at the age of five years on verbal and non-verbal subtests of a standardized intelligence scale, tests of gross motor coordination, and auditory and visual tests. A full paediatric examination was also performed. Breech presentation children performed less well on tests of balance and fine motor coordination and on visual acuity and stereopsis testing than children who presented in the vertex position. No deleterious effect of delivery method was found. In the absence of other complicating events (like a poor antenatal history, prematurity, and a disorganized home environment) delivery complication constitutes an early risk factor which the growing child is able to overcome.