Schizophrenia and Orthoptic Conditions: A Literature Review

Purpose

A narrative review of the literature reporting ocular abnormalities in patients with schizophrenia was undertaken to determine the types and prevalence of orthoptic conditions in this patient cohort.

Methods

A systematic search of multiple databases yielded 1,974 studies published between January 1992 and January 2022. All were screened for relevance based on their title and abstract.

Results

Seventeen studies were included in the final review. Ocular abnormalities reported in schizophrenia included a high incidence of strabismus, reduced visual acuity and reduced stereopsis compared to controls. Additionally, eye movement abnormalities (including reduced smooth pursuit gain and increased prosaccade latency) were frequently reported. Reduced visual acuity was associated with negative symptoms and reduced quality of life in schizophrenia.

Conclusions

Orthoptists and eye care professionals should be aware that a higher incidence of strabismus, reduced visual acuity, reduced stereoacuity, and eye movement abnormalities are reported in patients with schizophrenia. Further research is required to determine whether, or to what extent, ocular abnormalities and visual disturbances influence or exacerbate the symptoms of schizophrenia, and whether there is an effect of schizophrenia medication on these orthoptic conditions.

Multifaceted Interactions of Stereoacuity, Inter-Ocular Suppression, and Fixation Eye Movement Abnormalities in Amblyopia and Strabismus

Purpose

Amblyopic and strabismus subjects experience inter-ocular suppression, impaired stereoacuity, and increased fixation instability. The purpose of the study was to investigate factors affecting suppression and stereoacuity and examine their relationship to fixation eye movement (FEM) abnormalities.

Methods

We recruited 14 controls and 46 amblyopic subjects (anisometropic = 18, strabismic = 14, and mixed = 14) and 11 subjects with strabismus without amblyopia. We utilized the dichoptic motion coherence test to quantify suppression, and stereoacuity was assessed using the Titmus Fly test. We recorded FEMs using high-resolution video-oculography and classified subjects that did not have nystagmus (n = 27) versus those with nystagmus (n = 32; fusion maldevelopment nystagmus [FMN], n = 10) and nystagmus that did not meet the criteria of FMN (n = 20). We also recorded FEMs under dichoptic viewing (DcV) at varied fellow eye (FE) contrasts and computed the amplitude and velocity of the fast and slow FEMs and vergence instability.

Results

Inter-ocular suppression and stereoacuity deficits were closely correlated with an amblyopic eye (AE), visual acuity, and strabismus angle. Subjects with nystagmus displayed more pronounced stereoacuity deficits than those without nystagmus. Strabismic subjects with and without amblyopia, who demonstrated a fixation switch at 100% FE contrast, had lower inter-ocular suppression than subjects lacking a fixation switch under DcV. Amplitude of fast FEMs and velocity of slow FEMs, and vergence instability were increased as the FE contrast was lowered in both amblyopic and strabismic subjects.

Conclusions

The current study highlights the intricate relationships between AE visual acuity, eye deviation, and FEM abnormalities on suppression and stereoacuity deficits and underscores the need to evaluate FEM abnormalities while assessing dichoptic treatment outcomes.

Acquired comitant esotropias - comparison of surgical outcomes of accommodative vs non-accommodative types

Purpose: To compare the motor and sensory outcomes of strabismus surgery and the factors affecting surgical success in acquired acute non-accomodative esotropia (ANAET) and partially accommodative refractive esotropia (pARET). Methods: A retrospective chart review of patients with ANAET and pARET who underwent unilateral or bilateral horizontal rectus muscle surgery between January 2020 and December 2021 was conducted. Patients with postoperative follow-up of at least six weeks were included. Patients with pattern deviation, lateral incomitance, and near-distance disparity were excluded. Motor success was defined as a postoperative deviation within eight prism diopters of orthophoria. Sensory success was defined as presence of binocular single vision (BSV) for both distance and near (Worth four dot test). The effect of factors like age at onset, age at surgery, amblyopia before surgery, duration of squint before treatment, presence or absence and magnitude of vertical deviation, preoperative angle of deviation, and spherical equivalent on the motor and sensory success in each group were analyzed and compared. Results: 38 patients with ANAET and 33 patients with pARET were included. The mean age of onset of esotropia was 8.55 ± 4.65 years and 4.39 ± 2.27 years (p < .001) and the mean age at surgery was 10.62 ± 4.99 years and 7.89 ± 2.84 years (p = .006) in the ANAET and the pARET group respectively. The mean duration of the final follow-up was 38.51 weeks in the ANAET and 48.68 weeks in the pARET group (p = .089). Patients were successfully aligned for both distance and near in 81.5% of patients in the ANAET and 78.9% of patients in the pARET group at the final follow-up (p. 0.775). A BSV for both distance and near at the final follow-up was seen in 81.2% vs 66.6% of patients in the ANAET and the pARET group respectively (p = .25). A good near stereoacuity (<120 arcsecs) was seen in 60.6% and 41.9% of the ANAET and the pARET groups respectively (p = .175). The percentage of patients in the ANAET group who had orthophoria, any esodeviation, and any exodeviation for distance at the final follow-up was 63.1%, 34.2% and, 2.6%. The percentage of patients in the pARET group in similar categories was 36.3%, 42.4% and, 21.2%. None of the demographic and preoperative factors were found to affect the surgical outcomes in the two groups. Conclusions: The motor and sensory outcomes were similar in the two groups. A higher proportion of ANAET patients remained orthophoric during the follow-up. The patients in the pARET group showed a tendency toward exodrift.

Structure-Function Relationship in Keratoconus: Spatial and Depth Vision

Purpose

The purpose of this study was to determine changes in spatial and depth vision with increasing severity of keratoconus and to model the structure-function relationship to identify distinct phases of loss in visual function with disease severity.

Methods

Best-spectacle corrected, monocular high-contrast visual acuity, contrast sensitivity function (CSF) and stereoacuity of 155 cases (16-31 years) with mild to advanced bilateral keratoconus was determined using standard psychophysical tests. Disease severity was quantified using the multimetric D-index. The structure-function relationship was modeled using linear, positive exponential, negative exponential, and logistic nonlinear regression equations.

Results

The logistic regression model explained the highest proportion of variance for spatial vision, without bias in the residual plots (R2 ≥ 66%, P < 0.001). Visual acuity showed a distinct ceiling phase and a steeper loss rate with increasing D-index (1.8 units/D-index) in this model. The area under the CSF lacked this ceiling phase and had a shallower loss rate (0.28 units/D-index). Stereoacuity loss with D-index was poorly explained by all models tested (P ≤ 0.2). Cases with lower and bilaterally symmetric D-index had better stereoacuity (181.6-376 arc seconds) than those with higher D-index (>400 arc second); both were significantly poorer than controls (approximately 30 arc second).

Conclusions

Vision loss in keratoconus varies with the visual function parameter tested. Contrast sensitivity may be an earlier indicator of spatial vision loss than visual acuity. Depth perception is significantly deteriorated from very early stages of the disease.

Translational Relevance

The study outcomes may be used to forecast longitudinal vision loss in keratoconus and to apply appropriate interventions for timely preservation/enhancement of vulnerable visual functions.

Managing Pediatric Cataract Patients: Amblyopia Treatment and Binocularity Outcomes

Unilateral congenital cataracts present multiple barriers in the development of vision and stereoacuity despite the improved visual optics that early surgery, contact lenses and intraocular lenses (IOL) have provided. With better understanding of the latent period (the timeframe in which the abnormal event has no long-term effect on visual development in the deprived eye) and the critical periods (the age range during which developing brains can be altered in a profound and permanent way by abnormal experience) for stereoacuity and amblyopia we can focus our treatment methods to not only improve vision but also develop binocularity. Fifty years ago, it was believed that it was almost impossible for an eye with a unilateral congenital cataract to achieve good visual acuity. Twenty-five years ago, we believed that it was almost impossible for an eye with a unilateral cataract to achieve stereoacuity. It is time to expand our belief that the best that we can do with the eye in unilateral congenital cataract is to create a spare.

Relationship Between Suppression Scotomas and Stereoacuity in Anisometropic Amblyopia With Successfully Treated Visual Acuity

Purpose

The purpose of this study was to investigate the relationship among suppression scotoma size, stereoacuity, and four-prism base-out test (4ΔBOT) results in anisometropic amblyopia with successfully treated visual acuity.

Methods

We included 103 cases of anisometropic amblyopia successfully treated for visual acuity without strabismus. Stereoacuity was measured using a Randot Stereotest. The size of the suppression scotomas was measured using a new device, the polarized four dot (P4D) test. This is a modification of the Worth 4 dot test (W4D) device. The patients were divided into three groups based on the 4ΔBOT results: normal (group A = 29 cases), subnormal (group B = 48 cases), and abnormal (group C = 26 cases) response groups. The horizontal diameter of the suppression scotomas and stereoacuity in logarithmic values with a base of 20 seconds of arc (″) were compared among the 3 groups.

Results

The mean age at P4D testing was 8.4 ± 2.1 years. The average horizontal diameters of the suppression scotomas were 0.35 ± 0.79Δ, 2.01 ± 0.82Δ, and 5.50 ± 2.72Δ in groups A, B, and C, respectively, showing significant differences (A versus B: P < 0.0001, A versus C: P < 0.0001, and B versus C: P < 0.0001; 1-way ANOVA). The average logarithmic stereoacuity were 1.07 (24.95″), 1.22 (38.84″), and 1.47 (82.79″) in groups A, B, and C, respectively, thereby showing significant differences between the groups (A versus B: P < 0.0001, A versus C: P < 0.0001, and B versus C: P < 0.0001; 1-way ANOVA). Stereoacuity and horizontal diameter of the suppression scotoma were strongly correlated (r = 0.732, P < 0.0001).

Conclusions

The suppression scotoma size measured using P4D correlated significantly with stereoacuity and the 4ΔBOT results.

The Relationship between Fixation Stability and Retinal Structural Parameters in Children with Anisometropic, Strabismic and Mixed Amblyopia

(1) Background: Amblyopia is an ocular condition leading to structural and functional changes. The relationship between these changes is complex and remains poorly understood. (2) Methods: Participants included 31 children aged 5 to 9 years with strabismic (n = 9), anisometropic (n = 16) and mixed (n = 6) unilateral amblyopia, and 14 age-matched non-amblyopic children. The 95% and 63% Bivariate Contour Ellipse Area (BCEA), axial length, Foveal Avascular Zone (FAZ) area, center macular thickness and volume were assessed. The relationship between these parameters was explored. (3) Results: Statistically significant differences were found among the four groups in best corrected distance visual acuity (BCVA) (p < 0.001), BCEA 95% (p = 0.002) and BCEA 63% (p = 0.002), but not in the FAZ area, central macular thickness, central macular volume and axial length. Eyes with amblyopia had poorer BCVA and larger fixation instability than controls. Inter-ocular differences were more significant in patients with strabismic amblyopia, particularly in BCVA (p = 0.003), central macular thickness (p < 0.001) and central macular volume (p = 0.002). In amblyopic eyes, BCEA 95% and 63% were correlated with BCVA, but not with the FAZ area. (4) Conclusion: Amblyopia is associated with a reduction in fixation stability and BCVA, although there is a general lack of correlation with structural changes, suggesting a complex interaction between anatomy and function in amblyopia.

The eRDS v6 Stereotest and the Vivid Vision Stereo Test: Two New Tests of Stereoscopic Vision

Purpose

To describe two new stereoacuity tests: the eRDS v6 stereotest, a global dynamic random dot stereogram (dRDS) test, and the Vivid Vision Stereo Test version 2 (VV), a local or "contour" stereotest for virtual reality (VR) headsets; and to evaluate the tests' reliability, validity compared to a dRDS standard, and learning effects.

Methods

Sixty-four subjects passed a battery of stereotests, including perceiving depth from RDS. Validity was evaluated relative to a tablet-based dRDS reference test, ASTEROID. Reliability and learning effects were assessed over six sessions.

Results

eRDS v6 was effective at measuring small thresholds (<10 arcsec) and had a moderate correlation (0.48) with ASTEROID. Across the six sessions, test-retest reliability was good, varying from 0.84 to 0.91, but learning occurred across the first three sessions. VV did not measure stereoacuities below 15 arcsec. It had a weak correlation with ASTEROID (0.27), and test-retest reliability was poor to moderate, varying from 0.35 to 0.74; however, no learning occurred between sessions.

Conclusions

eRDS v6 is precise and reliable but shows learning effects. If repeated three times at baseline, this test is well suited as an outcome measure for testing interventions. VV is less precise, but it is easy and rapid and shows no learning. It may be useful for testing interventions in patients who have no global stereopsis.

Translational Relevance

eRDS v6 is well suited as an outcome measure to evaluate treatments that improve adult stereodepth perception. VV can be considered for screening patient with compromised stereovision.

Evaluating the relationship between induced aniseikonia and distance stereopsis

Background

The impact of aniseikonia on stereopsis has been studied for decades, however, inconsistency which may be partly attributed to the method of inducing aniseikonia exists among these findings. This study aimed to induce overall and meridional aniseikonia using a three-dimensional (3D) computer and then evaluate the effect of induced aniseikonia on distance stereopsis using contour-based and random-dot-based patterns.

Methods

A 3D laptop was used to produce all of the test symbols. Unlike the usual method of creating aniseikonia with size lenses, which would change not only the size but also the relative position of the test symbols in the two images as seen by the two eyes, a new test system was designed to evaluate the aniseikonia, which only modified the size while maintaining the relative position of the test symbols. This new method reduced the disparities induced by location changing of the paired test targets when inducing aniseikonia. Aniseikonia was induced overall or in one of the meridians. The induced meridional aniseikonia included 180°, 30°, 45°, 60°, and 90°, respectively. The range of induced aniseikonia was 0-30% with an increment of 5%.

Results

Overall magnification affected stereopsis more than magnification in any one of the meridians. The stereoacuity differences between oblique meridians (30°, 45°, and 60°) were not significant until the aniseikonia increased up to 20%. The difference between 180°, 45°, and 90° was significant when the aniseikonia increased up to 10% in the contour-based test and over 20% in the random-dot-based test. The stereoacuity trend was improved gradually, coupled with the angle changing from 180º to 90º in the contour-based pattern, and deteriorated gradually in the random-dot-based pattern.

Conclusions

Overall aniseikonia affected stereopsis more than meridional aniseikonia. The stereoacuity of the contour-based pattern was superior to that of the random-dot-based pattern in the 90° meridian, while the opposite result was obtained in the 180° meridian.

Comparison of stereoacuity in patients of anisometropia, isometropia and emmetropia

Purpose

To compare the stereoacuity in patients with anisometropia, isometropia, and emmetropia.

Methods

A cross-sectional study was conducted on 1403 subjects (range: 5-45 years) divided into anisometropes (n = 403), isometropes (n = 500), and emmetropes (n = 500). There were 258 amblyopic eyes among anisometropes and 156 amblyopic eyes among isometropes. Stereoacuity was measured using the Titmus stereo test consisting of a combination of contour targets.

Results

There were 675 males and 728 females. A significant (P < 0.001) reduction in stereoacuity was found in anisometropes as compared to isometropes and emmetropes. The stereoacuity was even worse in amblyopes as compared to non-amblyopes. Most patients with anisometropia of <3.0 D had fair stereoacuity. However, as the degree of anisometropia increased to >3.0 D, stereoacuity deteriorated gradually. Marked reduction of stereoacuity was observed in severe degree of anisometropia (>6.0 D). Overall, an anisometropia of ≥2.12 D was associated with reduced stereoacuity. Among the anisometropes, it was found to be the poorest in myopia, followed by myopia with astigmatism, hypermetropia with astigmatism, and hypermetropia.

Conclusion

The level of stereoacuity was worse in anisometropes as compared to isometropes and emmetropes. Amblyopes had a greater reduction in stereoacuity than non-amblyopes. Stereoacuity decreased as the degree of anisometropia increased. Among the anisometropes, myopes had worst stereoacuity than hypermetropes.

Differences in stereoacuity between crossed and uncrossed disparities reduce with practice

INTRODUCTION

Stereoacuity, like many forms of hyperacuity, improves with practice. We investigated the effects of repeated measurements over multiple visits on stereoacuity using two commonly utilised clinical stereotests, for both crossed and uncrossed disparity stimuli.

METHODS

Participants were adults with normal binocular vision (n = 17) aged between 18 and 50 years. Stereoacuity was measured using the Randot and TNO stereotests on five separate occasions over a six week period. We utilised both crossed and uncrossed stimuli to separately evaluate stereoacuity in both disparity directions. A subset of the subject group also completed a further five visits over an additional six week period. Threshold stereoacuity was determined by the lowest disparity level at which the subjects could correctly identify both the position and disparity direction (crossed or uncrossed) of the stimulus. Data were analysed by repeated measures analysis of variance.

RESULTS

Stereoacuity for crossed and uncrossed stimuli improved significantly across the first five visits (F_1,21  = 4.24, p = 0.05). The main effect of disparity direction on stereoacuity was not significant (F₁  = 0.02, p = 0.91). However, a significant interaction between disparity direction and stereotest was identified (F₁  = 7.92, p = 0.01).

CONCLUSIONS

Stereoacuity measured with both the TNO and Randot stereotests improved significantly over the course of five repetitions. Although differences between crossed and uncrossed stereoacuity were evident, they depended on the stereotest used and reduced or disappeared after repeated measurements. A single measure of stereoacuity is inadequate for properly evaluating adult stereopsis clinically.

Strabismus, stereoacuity, accommodation and convergence in young adults born premature and screened for retinopathy of prematurity

PURPOSE

The aim of the study was to evaluate strabismus, stereoacuity, accommodation and convergence in prematurely born young adults; screened for retinopathy of prematurity in the neonatal period and compare with term-born individuals of the same age.

MATERIALS AND METHODS

The study participants included 59 prematurely born individuals with a birthweight of ≤1,500 grams and 44 term-born controls, all born during 1988-1990 in Stockholm County, Sweden. Ocular alignment was assessed with a cover test, stereoacuity with the TNO stereo test and the amplitude of accommodation and the near point of convergence with the Royal Air Force Rule.

RESULTS

Seven of 59 (12%) preterms had manifest strabismus, 4/59 (7%) had esotropia and 3/59 (5%) exotropia. One of 44 (2%) controls had esotropia; no other controls had manifest strabismus. Stereoacuity was within normal limits in 38/59 (64%) preterms and 43/44 (98%) controls, p < 0.01; the difference remained after excluding those with strabismus. A neurological complication at 2.5 years of age was the strongest risk factor for subnormal stereoacuity within the preterm group after excluding those with strabismus. The mean amplitude of accommodation was poorer in the preterms than the controls in better (p < 0.05) and worse eyes (p < 0.05). The preterms were more likely to have an amplitude of accommodation below the minimum, according to Hofstetter's equation. There were no differences between the groups regarding the near point of convergence.

CONCLUSION

Prematurely born young adults had a higher prevalence of strabismus, reduced stereoacuity and worse amplitude of accommodation than term-born controls.

A longitudinal study of local stereoacuity and associated factors in schoolchildren: The Shahroud Schoolchildren Eye Cohort Study

CLINICAL RELEVANCE

Impaired stereoacuity is seen in some children without amblyopia, strabismus, and clinically significant refractive errors. Therefore, there are probably other factors affecting stereoacuity.

BACKGROUND

The aim of this work was to investigate the longitudinal changes of local stereoacuity and associated factors in schoolchildren.

METHODS

The present report is a part of the Shahroud Schoolchildren Eye Cohort Study. The target population was children aged 6 to 12 years in Shahroud, Iran. The second phase of the study was conducted in 2018 by re-inviting all participants in the first phase (2015). After an initial interview, study participants underwent optometric examination and ocular biometry. Stereoacuity was evaluated using Stereo Fly Test. Exclusion criteria were functional amblyopia, strabismus, significant refractive errors, probable ocular pathology/organic amblyopia in either of the two study phases, a history of intraocular surgery or ocular trauma, and incomplete data.

RESULTS

The data of 4666 children were analysed for this report, of which 53.7% were male. The mean age of the studied participants in the second phase was 12.37 ± 1.71 years. The mean stereoacuity was 42.31 (95% CI: 42.05 - 42.57) seconds of arc in the first phase, which reduced to 51.72 (95% CI: 50.79-52.65) seconds of arc in the second phase (P < 0.001). The prevalence of poor stereoacuity was 0.17% (95% CI: 0.06-0.29) in the first phase, which increased to 3.94% (95% CI: 3.34-4.54) in the second phase (P < 0.001). According to the multiple linear regression, older age in the first study phase (β = 0.011, P < 0.001), urban residence (β = -0.019, P = 0.006), increased spherical anisometropia (0.038, P = 0.013), and increased axial length (β = 0.062, P = 0.003) were significantly associated with reduction of stereoacuity (in log scale) after three years.

CONCLUSION

In addition to the known risk factors of amblyopia, strabismus, and significant refractive errors, other factors are also associated with stereoacuity changes in children.

Study on stereoacuity and associated factors in school children aged 7 to 14 years

Purpose:

The study aimed to estimate the prevalence of subnormal stereoacuity in school children and to assess the factors associated with it.

Methods:

In this prospective cross-sectional study, a total of 2,376 school children without amblyopia and manifest squint were screened by the titmus fly test, Snellen chart, tests for heterophoria, anterior segment examination, and fundoscopy. Children with a manifest squint, amblyopia (best-corrected visual acuity [BCVA] <6/18), and history of ocular trauma or surgery, and one-eyed children were excluded. Cycloplegic refraction was done in children with uncorrected or undercorrected refractive errors, and stereoacuity was assessed again with spectacle correction.

Results:

The prevalence of normal stereoacuity by titmus fly test was 93.18% with correction of refractive errors. Girls had slightly better stereopsis compared with boys. The subnormal stereoacuity was significantly associated with refractive error (P < 0.00001, significant at P < 0.05), unilateral refractive error (P < 0.00001, significant at P < 0.05), bilateral refractive error (P < 0.00001, significant at P < 0.05), anisometropia (P < 0.00001, significant at P < 0.05), ametropia (P < 0.00001, significant at P < 0.05), lower BCVA (P < 0.00001, significant at P < 0.05), hyperopia (P < 0.05, significant at P < 0.05), and heterophoria (P = 0.014, significant at P < 0.05). The subnormal stereoacuity was positively correlated with the magnitude of refractive error of the eyes.

Conclusion:

This study underlines the significant impact of identification and correction of refractive errors and squints in school children. The measurement of stereoacuity will be of immense importance and must be included in the screening programs for children.

Evaluation of depth perception and association of severity in Glaucoma patients and suspects

BACKGROUND

To evaluate depth perception in Primary open angle glaucoma (POAG), glaucoma suspects compared to controls and to determine the association between depth perception and severity of glaucoma.

METHODS

This was a hospital based, comparative, cross-sectional study. The ethical clearance was taken from institutional review committee of Institute of Medicine [Reference no.399 (6-11) E² 077-078]. Agematched, equal number of participants in each group (N=20) were evaluated with both Titmus and Frisby stereoacuity tests to measure depth perception as stereopsis threshold in seconds of arc. The participants were selected using the purposive sampling technique.

RESULTS

There was no differences in age, sex, or best corrected visual acuity, intraocular pressure, central corneal thickness (CCT), found among the three groups (POAG, Glaucoma Suspects and Control) respectively. However, there was significant difference in cup disc ratio (CDR) between the groups. Equal number of male and female were there in each group, while in POAG group male to female ratio was 3:2. The mean stereoacuity threshold in control group was 53.5±23.23 seconds of arc with Titmus test and 38.75±18.83 seconds of arc with Frisby stereoacuity test. The difference in threshold was significant between control and glaucoma suspect with Titmus (t=1.991, p=0.05) and with Frisby (t=2.114, p=0.04). The difference was also significant in POAG group by Titmus (t=3.135, p=0.0033) and by Frisby (t=3.014, p=0.004). More so, with increasing severity of glaucoma, the mean threshold of stereopsis increased as seen with both Titmus and Frisby Tests (ANOVA, p < 0.001) CONCLUSION: Primary open angle glaucoma patients and glaucoma suspects, showed significant reduction in depth perception. Decreased stereoacuity was associated with greater glaucomatous visual field loss.

Relationship between visual and neurodevelopmental measures at 2 years with visual acuity and stereopsis at 4.5 years in children born at risk of neonatal hypoglycaemia

PURPOSE

Mild to moderate vision loss affects many children and can negatively impact a child's early literacy and academic achievement. Nevertheless, there is no consensus on which factors present in early childhood indicate the need for long-term ophthalmic follow up, particularly in children with a history of perinatal adversity. This study identified the relationship between visual, cognitive, motor and demographic factors at 2 years of age and visual acuity (VA) and stereoacuity at 4.5 years of age.

METHODS

Five hundred sixteen children identified as being at risk of neonatal hypoglycaemia were recruited soon after birth. At 2 years of age, binocular VA, stereoacuity and non-cycloplegic refraction were measured and a clinical neuro-developmental assessment with the Bayley Scales of Infant Development III (BSID-III) was conducted by a trained examiner. Monocular VA and stereoacuity were measured at 4.5 years of age.

RESULTS

Three hundred twenty-eight children completed both the 2 and 4.5 year vision and neurodevelopmental assessments. Multiple linear regression showed oblique astigmatism and motor function at 2 years were significantly associated with VA at 4.5 years of age, while spherical equivalent refraction, motor scores and stereoacuity at 2 years were significantly associated with stereoacuity at 4.5 years of age. BSID-III motor scores had the best sensitivity (81.8%) and specificity (51.5%) for identifying impaired stereoacuity at 4.5 years. However, all measures at 2 years were poorly associated with VA at 4.5 years old.

CONCLUSION

Vision and neurodevelopmental measures at 2 years were poorly associated with visual function at 4.5 years of age. However, lower scores on tests of motor function at 2 years may be associated with vision abnormalities, particularly reduced stereopsis, at 4.5 years of age and referral for comprehensive vision assessment for these children may be warranted.

Factors associated with the effectiveness of part-time patching for intermittent exotropia in children

PURPOSE

To evaluate the factors associated with the efficacy of low-dose part-time patching in children with intermittent exotropia (IXT).

METHODS

In this prospective observational study, we enrolled 186 patients diagnosed with IXT. Outcome measures included office based control scales, magnitude of exo-deviation, and stereoacuity at near and distance after daily patching for 2 h. We analyzed the clinical data and demographic factors association with improvement of IXT.

RESULTS

The study was completed by 152 subjects of total enrolled patients on a consecutive basis followed up for 1 year. Decrease in the magnitude of exo-deviation, improvement of control, and or gain of stereoacuity were observed in 31.6% patients of the recruited subjects after part-time patching. Multivariate analyses showed that prognostic factors determining improvement to part-time patching included convergence insufficiency (CI) type IXT (p = 0.016), poor distance stereopsis (p = 0.044), and large exotropic deviation at distance (p = 0.025).

CONCLUSIONS

CI-type exotropia, large distance magnitude of exo-deviation, or poor distance stereopsis appear to be associated with a better response to part-time patching. Therefore low dose part-time patching may be a useful non-surgical treatment alternative to delay surgery in these cases.

Stereoacuity Among Patients with Refractive Error at University of Gondar, Northwest Ethiopia

PURPOSE

This study aimed to assess the level of stereopsis, proportion of poor stereopsis, and factors influencing stereopsis in adults with refractive error.

METHODS

This was a cross-sectional, descriptive study conducted on 153 adults with refractive error at Gondar University Hospital Tertiary Eye Care Center from April 08 to June 07, 2019. Structured questionnaires and ophthalmic instruments (Retinoscope, Worth Four Dot test and TNO Stereo plates) were used to collect the data. Data were entered and analyzed with Statistical Package for Social Sciences (SPSS) version 20. The result was summarized using summary statistics such as mean. Chi-squared test of association was applied between stereopsis and independent variables.

RESULTS

The level of stereopsis after correction of refractive error ranged from 1.89 to 2.65 log arc second. Before correction of refractive error, poor stereopsis was observed in 46.4% of the participants, while after correction, it dropped to 39.8% (CI: 95%: 31.1%-47.8%). Stereopsis after correction had a significant association with age, best visual acuity, type of refractive error, and fusional status at distance with a p value < 0.05.

CONCLUSION

Given refractive error corrected, the mean stereopsis in patients with refractive error was 2.42 log arc second. Proportion of poor stereopsis was noted in 39.8% of the participants corrected for refractive error. Age, best corrected visual acuity, type of refractive error, and fusional status had a significant association with stereopsis. Further studies on stereoacuity on a large scale are recommended.

An Evaluation of the Agreement Between a Computerized Stereoscopic Game Test and the TNO Stereoacuity Test

PURPOSE

Stereo-anomaly is commonly associated with amblyopia. An investigation was conducted to determine whether the measurements of stereoacuity obtained with the stereoacuity reference test (TNO Test) show an agreement with a computer stereoscope video game.

METHODS

Thirty-two subjects (mean age 9.37±2.00 years) with an amblyopia history were selected for a blind and randomized study of stereoacuity improvement through a new random dot game. A masked examiner measured the stereoacuity three times per subject using the TNO test (at the beginning, at the end and after 6 months of the treatment). A second masked examiner measured stereoacuity using the new computerized game after the TNO masked evaluation.

RESULTS

The Pearson's correlation coefficient one test against the other was r² = 0.767 and the Bland-Altman plot was r²= 0.069 (mean difference -0.03 log sec). Using three categories: poor (840-300 seconds of arc), coarse (480-210 seconds of arc) and moderate-fine stereoacuity (210-30 seconds of arc). Positive predictive values were 89.5% for moderate-fine; 72.7% for coarse; and 90.0% for poor stereoacuity. In addition, the agreement was evaluated using the Kappa coefficient (K= 0.743) with a 0.95 confidence interval and lower and upper Kappa limits were (0.628 and 0.858), respectively. Kappa coefficient and limits were still good when analyzing data before (K =0.663, 0.420 and 0.906) and after the treatment (K= 0.765, 0.632 and 0.899).

CONCLUSION

The Computerized Stereoscopic Game test allows the measure of stereoacuity. It can be used for both the purpose of detecting stereo vision deficits or tracking stereo vision development.

The effect of induced monocular blur by bangerter filters on measures of visual acuity and stereoacuity

To evaluate the effect of monocular blur induced by Bangerter filters (BF) on visual acuity (VA) and stereoacuity. Monocular blur was induced by a range of Trusetal BF strengths (0.1, 0.2, 0.4, 0.6) to 23 visually normal adult volunteers (aged 18-25, mean age 20.33 ± 1.79 years). The right monocular and binocular logMAR VA and distance stereoacuity using the FD2 were measured at 6 m with no filter (baseline) and with each filter strength. The order of testing the filters was randomized. Results were analyzed using one factor repeated measures ANOVAs, t-tests using Bonferroni correction and Pearson's product moment correlation. All filters degraded right monocular distance VA from baseline, but less significantly between the 0.4 and 0.6 filters than the other filters (p < .05 and p < .001, respectively). Degradation was in concordance with the labeled filter density, excluding filter strength 0.4. For all filter strengths, binocular VA was significantly but not clinically reduced from baseline (p < .05). Filters statistically and clinically significantly degraded distance stereoacuity from baseline (p < .001). A significant negative correlation existed between the mean degraded right monocular VA and stereoacuity (r = -0.998, p < .02). Trusetal BF significantly reduced monocular VA and stereoacuity but binocular VA remained within normal levels. The impact on VA and stereoacuity in a normal population can be of clinical relevance when applied to the use of BF for management of amblyopia and intractable diplopia. It is advised that clinicians ensure the desired level of degradation has been achieved in clinic before prescribing a particular filter strength.

Monocular and binocular end-points after epiretinal membrane surgery and their correlation to patient-reported outcomes

PURPOSE

This study evaluates current available endpoints for epiretinal membrane (ERM) surgery and examine their correlation to patient reported outcomes (PRO).

METHODS

Retrospective study including 38 eyes of 38 patients who underwent cataract extraction and subsequent vitrectomy for idiopathic ERM. The fellow eye was phakic with good visual acuity. The registered outcomes were monocular and binocular visual acuity, stereoacuity, M-chart metamorphopsia score, aniseikonia and aniseikonia tolerance range (ATR). Two questionnaires were completed: the convergence insufficiency symptom survey and Visual Function Questionnaire (VFQ-39).

RESULTS

Median total aniseikonia was 11% (range 0-35). There was a statistically significant correlation between the mean total M-chart score of the study eye and VFQ-Near (Spearman rho: VFQ-Near: -0.54, p < 0.01). There was no correlation between the best corrected visual acuity (BCVA) of the project eye, binocular BCVA, stereoacuity, ATR or mean total aniseikonia and PRO (Spearman p-values > 0.05). There was no correlation between mean total aniseikonia and mean total M-chart score (Spearman rho: 0.21 p = 0.26). There was a large variation between the mean total M-chart scores and questionnaire results.

CONCLUSION

The mean total M-chart score is currently the best end-points to predict PRO of ERM surgery; however, it is possible to have high M-chart values and have no visual complaints.

Effect of birth order on stereoacuity in Chinese preschool children: a cross-sectional study

OBJECTIVE

This study aimed to investigate the relationship between birth order and stereoacuity among Chinese children aged 60-72 months.

DESIGN

Cross-sectional.

PARTICIPANTS

1342 children with complete data on the questionnaire, stereoacuity and refraction were included.

RESULTS

The mean stereoacuity was 53.2±1.7, 56.9±1.9 and 60.9±1.5 s of arc in the first-born group, second-born group and third-born group, respectively. Lower birth order was significantly correlated with better stereoacuity (p=0.036). Third-borns (OR=3.02, p=0.027) were at higher risk of having subnormal stereoacuity compared with first-borns in the multivariate analysis.

CONCLUSION

Later-borns had poorer stereoacuity than first-borns.

ASTEROID stereotest v1.0: lower stereo thresholds using smaller, denser and faster dots

PURPOSE

In 2019, we described ASTEROID, a new stereotest run on a 3D tablet computer which involves a four-alternative disparity detection task on a dynamic random-dot stereogram. Stereo thresholds measured with ASTEROID were well correlated with, but systematically higher than (by a factor of around 1.5), thresholds measured with previous laboratory stereotests or the Randot Preschool clinical stereotest. We speculated that this might be due to the relatively large, sparse dots used in ASTEROID v0.9. Here, we introduce and test the stereo thresholds and test-repeatability of the new ASTEROID v1.0, which uses precomputed images to allow stereograms made up of much smaller, denser dots.

METHODS

Stereo thresholds and test/retest repeatability were tested and compared between the old and new versions of ASTEROID (n = 75) and the Randot Circles (n = 31) stereotest, in healthy young adults.

RESULTS

Thresholds on ASTEROID v1.0 are lower (better) than on ASTEROID v0.9 by a factor of 1.4, and do not differ significantly from thresholds on the Randot Circles. Thresholds were roughly log-normally distributed with a mean of 1.54 log₁₀ arcsec (35 arcsec) on ASTEROID v1.0 compared to 1.70 log₁₀ arcsec (50 arcsec) on ASTEROID v0.9. The standard deviation between observers was the same for both versions, 0.32 log₁₀ arcsec, corresponding to a factor of 2 above and below the mean. There was no difference between the versions in their test/retest repeatability, with 95% coefficient of repeatability = 0.46 log₁₀ arcsec (a factor of 2.9 or 1.5 octaves) and a Pearson correlation of 0.8 (comparable to other clinical stereotests).

CONCLUSION

The poorer stereo thresholds previously reported with ASTEROID v0.9 appear to have been due to the relatively large, coarse dots and low density used, rather than to some other aspect of the technology. Employing the small dots and high density used in ASTEROID v1.0, thresholds and test/retest repeatability are similar to other clinical stereotests.

Stereotest Comparison: Efficacy, Reliability, and Variability of a New Glasses-Free Stereotest

Purpose

To test the validity of the ASTEROID stereotest as a clinical test of depth perception by comparing it to clinical and research standard tests.

Methods

Thirty-nine subjects completed four stereotests twice: the ASTEROID test on an autostereo 3D tablet, a research standard on a VPixx PROPixx 3D projector, Randot Circles, and Randot Preschool. Within 14 days, subjects completed each test for a third time.

Results

ASTEROID stereo thresholds correlated well with research standard thresholds (r = 0.87, P < 0.001), although ASTEROID underestimated standard threshold (mean difference = 11 arcsec). ASTEROID results correlated less strongly with Randot Circles (r = 0.54, P < 0.001) and Randot Preschool (r = 0.64, P < 0.001), due to the greater measurement range of ASTEROID (1–1000 arcsec) compared to Randot Circles or Randot Preschool. Stereo threshold variability was low for all three clinical stereotests (Bland–Altman 95% limits of agreement between test and retest: ASTEROID, ±0.37; Randot Circles, ±0.24; Randot Preschool, ±0.23). ASTEROID captured the largest range of stereo in a normal population with test–retest reliability comparable to research standards (immediate r = 0.86 for ASTEROID vs. 0.90 for PROPixx; follow-up r = 0.68 for ASTEROID vs. 0.88 for PROPixx).

Conclusions

Compared to clinical and research standards for assessing depth perception, ASTEROID is highly accurate, has good test–retest reliability, and measures a wider range of stereo threshold.

Translational Relevance

The ASTEROID stereotest is a better clinical tool for determining baseline stereopsis and tracking changes during treatment for amblyopia and strabismus compared to current clinical tests.

Comparison of blur and magnification effects on stereopsis: overall and meridional, monocularly- and binocularly-induced

PURPOSE

To determine whether monocularly- and binocularly-induced spherical and meridional blur and aniseikonia had similar effects on stereopsis thresholds.

METHODS

Twelve participants with normal binocular vision viewed McGill modified random dot stereograms to determine stereoacuities in a four-alternative forced-choice procedure. Astigmatism was induced by placing trial lenses in front of the eyes. Twenty-three conditions were used, consisting of zero (no lens), +1 D and +2 D spheres and cylinders at axes 180, 45 and 90 in front of the right eye, and the following binocular combinations of both lens powers: R × 180/L × 180, R × 45/L × 45, R × 90/L × 90, R sphere/L sphere, R × 180/L × 90, R × 45/L × 135, R × 90/L × 180. Aniseikonia was induced by placing magnifying lenses in front of the eyes. Twenty-three conditions were used, consisting of zero, 6% and 12% overall magnification and both magnifications at axes 180, 45 and 90 in front of the right eye only, and the following binocular combinations using 3% and 6% lenses: R × 90/L × 90, R × 45/L × 45, R × 180/L × 180, R overall/L overall, R × 90/L × 180, R × 45/L × 135, and R × 180/L × 90.

RESULTS

Stereopsis losses for binocular blur effects with parallel axes (non-anisometropic) were the same as for monocular blur effects of the same axes, and these were strongly dependent on axis (spherical blur and ×90 had the greatest effects). Binocular blur effects with orthogonal axes had greater effects than with parallel axes, with the axis combination of the former having no effect (e.g. R × 90/L × 180 was similar to R × 45/L × 135). For induced aniseikonia, splitting the magnifications between the eyes improved stereopsis slightly, and the effects were not dependent on axis.

CONCLUSION

Binocular blur affects stereopsis similarly to monocular meridional blur if axes in the two eyes are parallel, whereas the effect is greater if the axes are orthogonal. In meridional aniseikonia, splitting magnification between the right and left lenses produces a small improvement in stereopsis that is independent of axis direction and right/left combination.

A comparative study of stereoacuity in patients with various grades of cataract and bilateral pseudophakia

Purpose

To compare the stereopsis in patients with various grades of cataract and bilateral pseudophakia.

Methods

A cross-sectional observational study was conducted at a tertiary care center in South India from December 2016 to September 2018, wherein the stereoacuity of patients having bilateral senile cataract or bilateral pseudophakia, was measured using the Titmus Fly chart. Those with any form of squint, glaucoma or retinal pathology were excluded. The patients were divided into three groups based on the severity of cataract, determined by the Lens Opacification Classification System (LOCS)-III. Group 4 included those with bilateral pseudophakia. Statistical analysis was performed using one-way ANOVA test with post hoc analysis using the Bonferroni test, to study the difference of stereoacuity between the groups.

Results

A total of 200 patients were evaluated. The mean stereoacuity was 65.2 ± 18.2, 114.8 ± 83.42, 402.4 ± 223.7 and 107.2 ± 71.68 arc seconds in groups 1, 2, 3 and 4, respectively (P < 0.001). The mean best corrected visual acuity (BCVA) in LogMAR units was 0.19 ± 0.15, 0.37 ± 0.24, 0.82 ± 0.26 and 0.14 ± 0.13 in groups 1, 2, 3 and 4, respectively (P = 0.01). On comparison between four groups, there was a generalised decrease in BCVA and stereoacuity with increasing grades of cataract except for group 4 which included the bilateral pseudophakics. On post hoc analysis to analyse intergroup variation a statistically significant difference in stereo acuity was noticed when group 3 was compared to other groups.

Conclusion

Stereoacuity decreases with increasing grades of cataract. Better stereoacuity is seen in patients with bilateral pseudophakia when compared with high grades of cataract.

Factors limiting sensitivity to binocular disparity in human vision: Evidence from a noise-masking approach

Our visual system uses the disparity between the images received by the two eyes to judge three-dimensional distance to surfaces. We can measure this ability by having subjects discriminate the disparity of rendered surfaces. We wanted to know the basis of the individual differences in this ability. We tested 53 adults with normal vision using a relative disparity detection task. Targets were wedge-shaped surfaces formed from random dots. These were presented in either crossed or uncrossed disparity relative to a random dot background. The threshold disparity ranged from 24 arc seconds in the most-able subject to 275 arc seconds in the least-able subject. There was a small advantage for detecting crossed-disparity targets. We used the noise-masking paradigm to partition subject performance into two factors. These were the subject's equivalent internal noise and their processing efficiency. The parameters were estimated by fitting the linear amplifier model. We found both factors contributed to the individual differences in stereoacuity. Within subjects, those showing an advantage for one disparity direction had enhanced efficiency for that direction. Some subjects had a higher equivalent internal noise for one direction that was balanced out by an increased efficiency. Our approach provides a more thorough account of the stereo-ability of our subjects compared with measuring thresholds alone. We present a normative set of results that can be compared with clinical populations.

Stereoacuity, Fusional Vergence Amplitudes, and Refractive Errors Prior to Treatment in Patients with Attention-Deficit Hyperactivity Disorder

Objectives:

To evaluate stereoacuity, fusional vergence amplitudes, and refractive errors in patients with attention-deficit hyperactivity disorder (ADHD).

Materials and Methods:

Twenty-three patients who were newly diagnosed as having ADHD and had not started medication, and 48 children without ADHD were included. Retrospective data analysis of comprehensive eye examination, stereoacuity, and fusional vergence amplitudes of the patients were performed.

Results:

The mean age at ADHD diagnosis was 10.68±2.34 (7-16) years in the ADHD group (14 male, 9 female) and 12.23±2.16 (7-15) years in the control group (25 male, 23 female) patients (p=0.605). The mean stereoacuity was 142.14±152.65 (15-480) sec/arc in patients with ADHD and 46.3±44.11 (15-240) sec/arc in the control group (p<0.001). For ADHD patients, the mean convergence and divergence amplitudes at distance were 19.87±8.40 (6 to 38) prism diopter (PD) and -9.09±-4.34 (-4 to -25) PD, and 37.30±12.81 (14 to 70) PD and -13.13±-3.45 (-4 to -20) PD at near, respectively. The mean cycloplegic spherical equivalent was 1.06±1.13 (-1 to 4.63) diopter in ADHD patients, with 6 patients having significant refractive errors (hyperopia in 4 patients, astigmatism in 2 patients). There were no significant differences between groups in terms of spherical equivalents (p=0.358) or convergence and divergence amplitudes at distance (p=0.289 and p=0.492, respectively) or near (p=0.452 and p=0.127, respectively).

Conclusion:

Fusional vergence amplitudes did not present significant difference, while the mean value of stereoacuity was significantly lower in newly diagnosed ADHD patients prior to treatment.

Effects of simulated anisometropia and aniseikonia on stereopsis

PURPOSE

Stereopsis depends on horizontally disparate retinal images but otherwise concordance between eyes. Here we investigate the effect of spherical and meridional simulated anisometropia and aniseikonia on stereopsis thresholds. The aims were to determine effects of meridian, magnitude and the relative effects of the two conditions.

METHODS

Ten participants with normal binocular vision viewed McGill modified random dot stereograms through synchronised shutter glasses. Stereoacuities were determined using a four-alternative forced-choice procedure. To induce anisometropia, trial lenses of varying power and axes were placed in front of right eyes. Seventeen combinations were used: zero (no lens) and both positive and negative, 1 and 2 D powers, at 45, 90 and 180 axes; spherical lenses were also tested. To induce aniseikonia 17 magnification power and axis combinations were used. This included zero (no lens), and 3%, 6%, 9% and 12% at axes 45, 90 and 180; overall magnifications were also tested.

RESULTS

For induced anisometropia, stereopsis loss increased as cylindrical axis rotated from 180° to 90°, at which the loss was similar to that for spherical blur. For example, for 2 D meridional anisometropia threshold increased from 1.53 log sec arc (i.e. 34 sec arc) for x 180 to 1.89 log sec arc (78 sec arc) for x 90. Anisometropia induced with either positive or negative lenses had similar detrimental effects on stereopsis. Unlike anisometropia, the stereopsis loss with induced meridional aniseikonia was not affected by axis and was about 64% of that for overall aniseikonia of the same amount. Approximately, each 1 D of induced anisometropia had the same effect on threshold as did each 6% of induced aniseikonia.

CONCLUSION

The axes of meridional anisometropia but not aniseikonia affected stereopsis. This suggests differences in the way that monocular blur (anisometropia) and interocular shape differences (aniseikonia) are processed during the production of stereopsis.

Awareness among medical students regarding the binocularity level in the course of future specialty choice

BACKGROUND

Vision standards exist in many occupations with particular reference to medical science. The presence of a sufficient level of binocular vision is especially important in surgical specialty to perform visually demanding procedures. The purpose of this study was to reveal the level of awareness of one's binocular status among medical students, and the significance of having binocular vision in terms of specialty choice.

MATERIAL AND METHODS

self-constructed questionnaire was given to all subjects enrolled in the study. The first group comprised 53 students from the second and third year of the Medical University of Lodz, who then underwent an ophthalmological examination with binocularity assessment. The second group included 57 students of the last years of the Medical Faculty, who did the same survey and outlined how the ophthalmology course improved their knowledge of stereoacuity and vision requirements for the chosen specialty. Statistical analysis was performed using Person's χ² test.

RESULTS

Overall, 32% (N = 17) of the students from the first group and 84% (N = 48) from the second group stated to be familiar with the term "binocularity" and its importance in performing surgical procedures. The awareness of the existing occupational contraindications related to low visual acuity and binocularity was declared by 16% (N = 9) and 54% (N = 31) of the subjects included in each group, respectively. University lectures were indicated as the main source of knowledge by 28% (N = 15) of the individuals from the first group and by 59% (N = 39) from the second group. The ophthalmology course was considered to be sufficiently covering the basics needed for the future doctor by 34 resident physicians (60%).

CONCLUSIONS

The medical students' awareness of their own binocular status appears low. There is a strong need for implementing at least some quality standards for visual assessment to decide if a given student has an adequate eye function to participate in surgical procedures. Med Pr. 2020;71(1):9-16.

Concurrent maturation of visuomotor skills and motion perception in typically-developing children and adolescents

Perceptual and visuomotor skills undergo considerable development from early childhood into adolescence; however, the concurrent maturation of these skills has not yet been examined. This study assessed visuomotor function and motion perception in a cross-section of 226 typically-developing children between 4 and 16 years of age. Participants were tested on three tasks hypothesized to engage the dorsal visual stream: threading a bead on a needle, marking dots using a pen, and discriminating form defined by motion contrast. Mature performance was reached between 8 and 12 years, with youngest maturation for kinematic measures for a reach-to-grasp task, and oldest maturation for a precision tapping task. Performance on the motion perception task shared no association with motor skills after controlling for age.

Comparative analysis of the Lang Stereopad in a non-clinic population

Aim: New methods of measurement require testing to evaluate test validity. This study compares stereoacuity results of the Lang Stereopad to other common clinical stereoacuity assessments in a normal vision population. Methods: A prospective cross-sectional study was conducted comparing the Lang Stereopad stereoacuity results to results from the Lang II, Frisby, and TNO stereo tests. Mean stereoacuity values and their correlation with inter-ocular visual acuity difference were compared for each stereo test. Results: 98 subjects (mean age of 33.5 years, SD 14.1; 39 males and 59 females) with normal parameters of visual function underwent multiple stereotest assessments. Median stereoacuity values were the lowest (i.e. more detailed stereoacuity) when using the Frisby stereotest (median 40"; 20-170" [minimum-maximum]) and TNO stereotest (median 60"; 15-480"). In comparison, medians were about double at 100" (50-800") for the Lang Stereopad and greater at 200" (200-200") for the Lang II stereotest. There was no correlation for each stereotest with interocular visual acuity differences. Conclusions: The Lang Stereopad test is easy to administer and it has certain advantages such as no requirement for additional test glasses. It is a useful assessment to add to the clinical armamentarium for binocular assessment of stereopsis. The Lang Stereopad does not agree well with other stereo tests such as the TNO and Frisby but provides a greater stereoacuity test range than the Lang II. The Lang Stereopad now requires testing in a clinical population in which stereoacuity is a pre-requisite part of the assessment.

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.

From suppression to stereoacuity: a composite binocular function score for clinical research

PURPOSE

This study aimed to validate a binocular function score that is based on common clinical measures of visual function, providing a more complete analysis of binocular outcomes, against laboratory-based dichoptic tests of threshold stereoacuity and depth of suppression.

METHODS

Scores on a composite binocular function (BF) score derived from clinical stereoacuity measures (Randot Preschool Stereoacuity Test and Randot Butterfly) and the Worth 4 Dot test were determined in adults (n = 20; age 24.8 ± 7.2 years) and children (N = 77; age 8.3 ± 1.7 years) with abnormal binocular vision from strabismus or amblyopia. Adults had threshold stereoacuity measured with a novel, computerised dichoptic psychophysical test of stereopsis. Depth of suppression (dichoptic eye chart inter-ocular contrast balance test) was determined in both adults and children.

RESULTS

Clinical Randot stereoacuity was measurable in 50% of adult and 61% of child participants. Threshold stereoacuity was measurable in 65% of the adult participants. The presence of suppression or simultaneous perception (flat fusion or diplopia) was measurable in all participants, enabling assignment of a BF score to all participants in both groups. In adults, the BF score was highly correlated with the psychophysical threshold stereoacuity measure (ρ = 0.71; p < 0.001). In both adults and children, there was also a high correlation between the BF score and inter-ocular contrast balance (adult ρ = 0.90; child ρ = 0.86; p < 0.001).

CONCLUSIONS

The composite BF score is a convenient and valid scale of binocularity that can be used to extend the stereoacuity measure in cohorts where nil stereoacuity is common and thus could be considered as an outcome measure in clinical trials.

ASTEROID: A New Clinical Stereotest on an Autostereo 3D Tablet

Purpose

To describe a new stereotest in the form of a game on an autostereoscopic tablet computer designed to be suitable for use in the eye clinic and present data on its reliability and the distribution of stereo thresholds in adults.

Methods

Test stimuli were four dynamic random-dot stereograms, one of which contained a disparate target. Feedback was given after each trial presentation. A Bayesian adaptive staircase adjusted target disparity. Threshold was estimated from the mean of the posterior distribution after 20 responses. Viewing distance was monitored via a forehead sticker viewed by the tablet's front camera, and screen parallax was adjusted dynamically so as to achieve the desired retinal disparity.

Results

The tablet must be viewed at a distance of greater than ∼35 cm to produce a good depth percept. Log thresholds were roughly normally distributed with a mean of 1.75 log₁₀ arcsec = 56 arcsec and SD of 0.34 log₁₀ arcsec = a factor of 2.2. The standard deviation agrees with previous studies, but ASTEROID thresholds are approximately 1.5 times higher than a similar stereotest on stereoscopic 3D TV or on Randot Preschool stereotests. Pearson correlation between successive tests in same observer was 0.80. Bland-Altman 95% limits of reliability were ±0.64 log₁₀ arcsec = a factor of 4.3, corresponding to an SD of 0.32 log₁₀ arcsec on individual threshold estimates. This is similar to other stereotests and close to the statistical limit for 20 responses.

Conclusions

ASTEROID is reliable, easy, and portable and thus well-suited for clinical stereoacuity measurements.

Translational Relevance

New 3D digital technology means that research-quality psychophysical measurement of stereoacuity is now feasible in the clinic.

Microstructural properties of the vertical occipital fasciculus explain the variability in human stereoacuity

Seeing in the three-dimensional world—stereopsis—is an innate human ability, but it varies substantially among individuals. The neurobiological basis of this variability is not understood. We combined diffusion and quantitative MRI imaging with a psychophysical measurements, and found that variability in stereoacuity is associated with microstructural differences in the right vertical occipital fasciculus, a white matter tract connecting dorsal and ventral visual cortex. This result suggests that the microstructure of the pathways that support information transmission across dorsal and ventral visual areas plays an important role human stereopsis.

Stereopsis is a fundamental visual function that has been studied extensively. However, it is not clear why depth discrimination (stereoacuity) varies more significantly among people than other modalities. Previous studies have reported the involvement of both dorsal and ventral visual areas in stereopsis, implying that not only neural computations in cortical areas but also the anatomical properties of white matter tracts connecting those areas can impact stereopsis. Here, we studied how human stereoacuity relates to white matter properties by combining psychophysics, diffusion MRI (dMRI), and quantitative MRI (qMRI). We performed a psychophysical experiment to measure stereoacuity and, in the same participants, we analyzed the microstructural properties of visual white matter tracts on the basis of two independent measurements, dMRI (fractional anisotropy, FA) and qMRI (macromolecular tissue volume; MTV). Microstructural properties along the right vertical occipital fasciculus (VOF), a major tract connecting dorsal and ventral visual areas, were highly correlated with measures of stereoacuity. This result was consistent for both FA and MTV, suggesting that the behavioral–structural relationship reflects differences in neural tissue density, rather than differences in the morphological configuration of fibers. fMRI confirmed that binocular disparity stimuli activated the dorsal and ventral visual regions near VOF endpoints. No other occipital tracts explained the variance in stereoacuity. In addition, the VOF properties were not associated with differences in performance on a different psychophysical task (contrast detection). These series of experiments suggest that stereoscopic depth discrimination performance is, at least in part, constrained by dorso-ventral communication through the VOF.

Stereopsis: are we assessing it in enough depth?

The assessment of stereoacuity is an integral part of the ophthalmic assessment, with the responses used to inform clinical management decisions. Stereoacuity impacts on many aspects of life, but there are discrepancies reported where people without measurable stereoacuity report appreciating 3-D vision. This could be due, in part, to the presentation of the stimuli. A literature review was undertaken to evaluate current assessment techniques, how they relate to patient outcomes, identify the limitations of current tests and discuss how they could be improved. Recent evidence has been collated on currently available tests, used commonly within vision clinics, with normative data provided allowing responses to the tests to be interpreted. The relevance of the results is evaluated in relation to a range of outcomes, where a reduced level of stereopsis has a negative impact on the ability of an individual to perform many tasks, and can lead to an increase in difficulty interacting in the world. Current tests are limited in the aspects of stereoacuity they assess and their ability to precisely measure stereopsis. The world is not static, yet clinical tests are limited to measuring static stereoacuity, even though higher grades of depth perception can be identified in the presence of changing depth. Presentation methods of stereoacuity tests have remained similar over time, with a limited number of disparity levels assessed. New assessment methods are becoming available that include automated staircase testing to present multiple levels of disparity using digital technology. Current clinical tests are limited in their presentation, and are poor at detecting/measuring stereoacuity in those with limited stereopsis. Given the relevance of the stereoacuity measurement to management choices and functional outcomes, new testing methods would be beneficial to fully assess stereoacuity, both static and dynamic.

Ewald Hering's (1899) On the Limits of Visual Acuity: A Translation and Commentary: With a Supplement on Alfred Volkmann's (1863) Physiological Investigations in the Field of Optics

Towards the end of the 19th Century, Hering and Helmholtz were arguing about the fineness of visual acuity. In a talk given in 1899, Hering finally established beyond reasonable doubt that humans can see spatial displacements smaller than the diameter of a foveal cone receptor, an ability we nowadays call 'hyperacuity' and still the topic of active research. Hering suggested that this ability is made manifest by averaging across the range of locations stimulated during miniature eye movements. However, this idea was made most clear only in a footnote to this (not well known) publication of his talk and so was missed by many subsequent workers. Accordingly, particularly towards the end of the 20th Century, Hering has commonly been mis-cited as having proposed in this paper that averaging occurs purely along the lengths of the edges in the image. Here, we present in translation what Hering actually said and why. In Supplementary Material, we additionally translate accounts of some background experiments by Volkmann (1863) that were cited by Hering.

Influence of Test Distance on Stereoacuity in Intermittent Exotropia

AIMS

To investigate influence of test distance on stereoacuity in intermittent exotropia (X[T]) using the same test conditions for both near and far distances.

METHODS

Subjects were 38 consecutive patients with X(T). All the patients were between ages 6 and 15 years and had decimal visual acuity of 1.0 or better. Another inclusion criterion was presence of phoric condition at near and far distances. Stereoacuity was measured at a near distance of 40 cm and at a far distance of 5 m. The following test conditions were used for both test distances: separation of the two eyes using polarized glasses, and a target with a random dot pattern. All the stereograms had the same subtended angle of 2.5º, and binocular disparity of 480, 240, 120, and 60 arcsec. We used two stereogram types with crossed and uncrossed disparities.

RESULTS

Far stereoacuity of 38 subjects measured with the crossed disparity was significantly worse than near stereoacuity (P<0.05, Wilcoxon signed-ranks test), although 30 (78.9%) of the 38 subjects showed no differences in stereopsis between the near and far distances. Far stereoacuity of 38 cases measured with the uncrossed disparity was significantly worse than at near (P<0.05, Wilcoxon signed-ranks test), although 20 (52.6%) of the 38 subjects showed no differences between stereoacuity at near and far. In comparison of stereoacuity with crossed disparity and uncrossed disparity, stereoacuity with crossed disparity was significantly better than that with uncrossed disparity both at near and far (P<0.05, Wilcoxon signed-ranks test).

CONCLUSIONS

Stereoacuity in X(T) was different according to test distance when measured controlling subtended angle of stereogram at both distances. Far stereoacuity was significantly worse than near stereoacuity when measured using test targets with both crossed and uncrossed disparities. Additionally, stereoacuity measured with crossed disparity was better than that with uncrossed disparity at both distances.

Stereoacuity after small aperture corneal inlay implantation

Purpose

The aim of this study was to compare stereoacuity before and after KAMRA corneal inlay implantation for the correction of presbyopia.

Patients and methods

This is a prospective study of 60 patients who underwent KAMRA inlay implantation. Patients were examined before and 6 months after surgery for stereoacuity, uncorrected distance visual acuity (UDVA), and uncorrected near visual acuity (UNVA).

Results

The mean stereoacuity before surgery was 29.5±28.1 arcsec (range: 20–200) and at 6 months was 29.8±26.4 arcsec (range: 20–200). The decline in stereoacuity was not statistically significant. At 6 months follow-up, UDVA was 20/25 or better in all 60 patients and UNVA was J2 (20/25) or better in 51 (85%) patients.

Conclusion

There is no significant change in stereoacuity following KAMRA inlay implantation. The KAMRA inlay is a good treatment option for improving near vision in presbyopic patients while preserving stereoacuity and distance vision.

Modified Test Protocol Improves Sensitivity of the Stereo Fly Test

BACKGROUND AND PURPOSE

Stereoacuity measurement is a common element of pediatric ophthalmic examinations. Although the Stereo Fly Test is routinely used to establish the presence of coarse stereopsis (3000 arcsecs), it often yields a false negative "pass" due to learned responses and non-stereoscopic cues. We developed and evaluated a modified Stereo Fly Test protocol aimed at increasing sensitivity, thus reducing false negatives.

PATIENTS AND METHODS

The Stereo Fly Test was administered according to manufacturer instructions to 321 children aged 3-12 years. Children with a "pass" outcome (n = 147) were re-tested wearing glasses fitted with polarizers of matching orientation for both eyes to verify that they were responding to stereoscopic cues (modified protocol). The response to the standard Stereo Fly Test was considered a false negative (pass) if the child still pinched above the plate after disparity cues were eliminated. Randot^® Preschool Stereoacuity and Butterfly Tests were used as gold standards.

RESULTS AND CONCLUSIONS

Sensitivity was 81% (95% CI: 0.75 - 0.86) for standard administration of the Stereo Fly Test (19% false negative "pass"). The modified protocol increased sensitivity to 90% (95% CI: 0.85 - 0.94). The modified two-step protocol is a simple and convenient way to administer the Stereo Fly Test with increased sensitivity in a clinical setting.

Monocular blur alters the tuning characteristics of stereopsis for spatial frequency and size

Our sense of depth perception is mediated by spatial filters at different scales in the visual brain; low spatial frequency channels provide the basis for coarse stereopsis, whereas high spatial frequency channels provide for fine stereopsis. It is well established that monocular blurring of vision results in decreased stereoacuity. However, previous studies have used tests that are broadband in their spatial frequency content. It is not yet entirely clear how the processing of stereopsis in different spatial frequency channels is altered in response to binocular input imbalance. Here, we applied a new stereoacuity test based on narrow-band Gabor stimuli. By manipulating the carrier spatial frequency, we were able to reveal the spatial frequency tuning of stereopsis, spanning from coarse to fine, under blurred conditions. Our findings show that increasing monocular blur elevates stereoacuity thresholds 'selectively' at high spatial frequencies, gradually shifting the optimum frequency to lower spatial frequencies. Surprisingly, stereopsis for low frequency targets was only mildly affected even with an acuity difference of eight lines on a standard letter chart. Furthermore, we examined the effect of monocular blur on the size tuning function of stereopsis. The clinical implications of these findings are discussed.

Intraexaminer repeatability and agreement in stereoacuity measurements made in young adults

AIM

To determine the repeatability and agreement of stereoacuity measurements made using some of the most widely used clinical tests: Frisby, TNO, Randot and Titmus.

METHODS

Stereoacuity was measured in two different sessions separated by a time interval of at least 24h but no longer than 1wk in 74 subjects of mean age 20.6y using the four methods. The study participants were divided into two groups: subjects with normal binocular vision and subjects with abnormal binocular vision.

RESULTS

Best repeatability was shown by the Frisby and Titmus [coefficient of repeatability (COR): ±13 and ±12s arc respectively] in the subjects with normal binocular vision though a clear ceiling effect was noted. In the subjects with abnormal binocular vision, best repeatability was shown by the Frisby (COR: ±69s arc) and Randot (COR: ±72s arc). In both groups, the TNO test showed poorest agreement with the other tests.

CONCLUSION

The repeatability of stereoacuity measures was low in subjects with poor binocular vision yet fairly good in subjects with normal binocular vision with the exception of the TNO test. The reduced agreement detected between the tests indicates they cannot be used interchangeably.

Modification of the titmus fly test to improve accuracy

INTRODUCTION

In spite of its well-known flaws, the Titmus test is still the most commonly available and frequently utilized stereotest worldwide. Detecting stereopsis in the patient with small-angle strabismus is an important part of the sensorimotor exam. Because these patients often have only gross stereopsis, stereoacuity may have to be evaluated with the House Fly plate alone. This study evaluates an alternative method of presentation designed to decrease the false positive rate of the Titmus Fly test.

METHODS

A group of orthotropic volunteers with normal binocular vision, a group of patients with small angle strabismus, and a group of patients whose angle of strabismus was large enough to preclude stereopsis were tested with the Titmus Fly using two different presentations and compared.

RESULTS

The sensitivity of the Titmus Fly test was 79%, but specificity was only 26% due to the large number of false positive responses detected with the modified presentation. Patients with childhood-onset strabismus who have been repeatedly exposed to this test over many visits were particularly vulnerable to overestimation of stereoacuity.

CONCLUSION

If the Titmus fly test is the only stereoacuity measure that can be used due to the presence of manifest strabismus, modifying the presentation of the test plate with this method will improve accuracy and precision of results.

Characterizing the role of disparity information in alleviating visual crowding

The ability to identify a target is reduced by the presence of nearby objects, a phenomenon known as visual crowding. The extent to which crowding impairs our perception is generally governed by the degree of similarity between a target stimulus and its surrounding flankers. Here we investigated the influence of disparity differences between target and flankers on crowding. Orientation discrimination thresholds for a parafoveal target were first measured when the target and flankers were presented at the same depth to establish a flanker separation that induced a significant elevation in threshold for each individual. Flankers were subsequently fixed at this spatial separation while the disparity of the flankers relative to the target was altered. For all participants, thresholds showed a systematic decrease as flanker-target disparity increased. The resulting tuning function was asymmetric: Crowding was lower when the target was perceived to be in front of the flankers rather than behind. A series of control experiments confirmed that these effects were driven by disparity, as opposed to other factors such as flanker-target separation in three-dimensional (3-D) space or monocular positional offsets used to create disparity. When flankers were distributed over a range of crossed and uncrossed disparities, such that the mean was in the plane of the target, there was an equivalent or greater release of crowding compared to when all flankers were presented at the maximum disparity of that range. Overall, our results suggest that depth cues can reduce the effects of visual crowding, and that this reduction is unlikely to be caused by grouping of flankers or positional shifts in the monocular image.

Correlation between depth perception by three-rods test and stereoacuity by distance Randot Stereotest

Background

The examination of depth perception with three-rods test, in addition to visual acuity testing, is required to obtain motor vehicle license to drive taxies and trucks, according to the Road Traffic Act in Japan. The aim of this study was to examine whether the results of the three-rods test would correlate with the results of static stereopsis tests, used in ophthalmic practice.

Methods

This study involved 54 normal subjects, 9 women and 45 men, with ages ranging from 18 to 25 (mean, 20.8) years. All had visual acuity of 0.8 or better with or without glasses or contact lenses correction and had no strabismus at the distant (5 m) or near (0.3 m) fixation. TNO Stereotest and Titmus Stereotest were examined at 40 cm while Distance Randot Stereotest was at 3 m. At three-rods test, a central rod was moved at the speed of 50 mm/sec forward and backward automatically against two laterally located fixed rods, placed inside the illuminated box. An examinee at the distance of 2.5 m observed the rods inside the box from a small viewing window and pushed a button to stop the central rod in alignment with the fixed rods. Erred distance (mm) of the central rod from the fixed rods as a mean of 4 measurements was correlated with stereoacuity in second of arc, measured by three kinds of the stereopsis tests.

Results

The erred distance of three-rods test was positively correlated with static stereoacuity at distance measured with Distance Randot Stereotest (ρ = 0.418, p = 0.0023, Spearman rank correlation test) and also with the other stereopsis tests at near fixation. The stereoacuity at near fixation, measured by TNO Stereotest and Titmus Stereotest, was positively correlated with each other (ρ = 0.431, p = 0.0017).

Conclusion

Three-rods test, examining depth perception, together with the response by eye-hand coordination, gave consistent results with distant static stereoacuity when measured with Distance Randot Stereotest.

Perceptual learning improves stereoacuity in amblyopia

PURPOSE

Amblyopia is a developmental disorder that results in both monocular and binocular deficits. Although traditional treatment in clinical practice (i.e., refractive correction, or occlusion by patching and penalization of the fellow eye) is effective in restoring monocular visual acuity, there is little information on how binocular function, especially stereopsis, responds to traditional amblyopia treatment. We aim to evaluate the effects of perceptual learning on stereopsis in observers with amblyopia in the current study.

METHODS

Eleven observers (21.1 ± 5.1 years, six females) with anisometropic or ametropic amblyopia were trained to judge depth in 10 to 13 sessions. Red-green glasses were used to present three different texture anaglyphs with different disparities but a fixed exposure duration. Stereoacuity was assessed with the Fly Stereo Acuity Test and visual acuity was assessed with the Chinese Tumbling E Chart before and after training.

RESULTS

Averaged across observers, training significantly reduced disparity threshold from 776.7″ to 490.4″ (P < 0.01) and improved stereoacuity from 200.3″ to 81.6″ (P < 0.01). Interestingly, visual acuity also significantly improved from 0.44 to 0.35 logMAR (approximately 0.9 lines, P < 0.05) in the amblyopic eye after training. Moreover, the learning effects in two of the three retested observers were largely retained over a 5-month period.

CONCLUSIONS

Perceptual learning is effective in improving stereo vision in observers with amblyopia. These results, together with previous evidence, suggest that structured monocular and binocular training might be necessary to fully recover degraded visual functions in amblyopia. Chinese Abstract.

Stereoacuity of preschool children with and without vision disorders

PURPOSE

To evaluate associations between stereoacuity and presence, type, and severity of vision disorders in Head Start preschool children and determine testability and levels of stereoacuity by age in children without vision disorders.

METHODS

Stereoacuity of children aged 3 to 5 years (n = 2898) participating in the Vision in Preschoolers (VIP) Study was evaluated using the Stereo Smile II test during a comprehensive vision examination. This test uses a two-alternative forced-choice paradigm with four stereoacuity levels (480 to 60 seconds of arc). Children were classified by the presence (n = 871) or absence (n = 2027) of VIP Study-targeted vision disorders (amblyopia, strabismus, significant refractive error, or unexplained reduced visual acuity), including type and severity. Median stereoacuity between groups and among severity levels of vision disorders was compared using Wilcoxon rank sum and Kruskal-Wallis tests. Testability and stereoacuity levels were determined for children without VIP Study-targeted disorders overall and by age.

RESULTS

Children with VIP Study-targeted vision disorders had significantly worse median stereoacuity than that of children without vision disorders (120 vs. 60 seconds of arc, p < 0.001). Children with the most severe vision disorders had worse stereoacuity than that of children with milder disorders (median 480 vs. 120 seconds of arc, p < 0.001). Among children without vision disorders, testability was 99.6% overall, increasing with age to 100% for 5-year-olds (p = 0.002). Most of the children without vision disorders (88%) had stereoacuity at the two best disparities (60 or 120 seconds of arc); the percentage increasing with age (82% for 3-, 89% for 4-, and 92% for 5-year-olds; p < 0.001).

CONCLUSIONS

The presence of any VIP Study-targeted vision disorder was associated with significantly worse stereoacuity in preschool children. Severe vision disorders were more likely associated with poorer stereopsis than milder or no vision disorders. Testability was excellent at all ages. These results support the validity of the Stereo Smile II for assessing random-dot stereoacuity in preschool children.

Manufacturer changes lead to clinically important differences between two editions of the TNO stereotest

PURPOSE

Stereoacuity tests used in clinical practice should be repeatable and reproducible. However, it has been observed in a clinical setting that new editions of the TNO stereotest appear to give different values from those obtained using previous versions. The purpose of the present research was to investigate this observation.

METHODS

One hundred and twenty-one Dutch subjects, 88 (73%) females and 33 (27%) males, with an average age of 34.0 years (range 18-55) had their stereoacuity measured using two different versions of the TNO stereoacuity test (TNO 13 and TNO 15). The TNO was tested in a counterbalanced order so that consecutive subjects started with alternate editions to avoid bias.

RESULTS

There was a significant difference (p < 0.001) between the median value for stereoacuity measured with TNO 13 (30 s of arc) and TNO 15 (60 s of arc). The bias between the two test versions was -0.23 Log arcseconds (95% limits of the differences: 0.15 to -0.60 Log arcseconds).

CONCLUSION

This study reveals that results obtained with two different editions of a commonplace stereoacuity test are not comparable. New versions come on the market at regular intervals and the assumption that they will give the same results as previous versions may not be valid. Besides the statistically significant difference between the TNO 13 and TNO 15, the Bland-Altman plot also showed a considerable bias and the 95% limits of the differences between the TNO 13 and TNO 15 are more than two steps on the Log arcsecond scale. This difference between two editions of the TNO stereotests is not clinically acceptable and therefore it is inappropriate to use the two versions of the test interchangeably. It is important in both research and clinical records to specify the edition of the TNO test used.