Variability of Fusion Vergence Measurements in Heterophoria

Are Horizontal Fusional Vergences Comparable When Measured Using a Prism Bar and Synoptophore?

Aim

To determine whether horizontal fusional vergences are comparable when measured using a prism bar and synoptophore.

Methods

Thirty two participants (18-23 years) had their blur, break, and recovery points measured for convergence and divergence amplitudes using a prism bar (6 m) and synoptophore. All participants had VA of 0.1 LogMAR or better in either eye, were heterophoric or orthophoric and had binocular single vision. The prism bar target was a 0.2 LogMAR letter. The synoptophore target was the foveal 'rabbit' fusion slides. The prism bar was placed over the dominant eye and the testing speed was two seconds per two prism dioptres (Δ), increasing to five seconds per 5Δ when the increments began to increase in 5Δ. Synoptophore testing speed was two seconds per degree.

Results

The synoptophore measured significantly higher convergence break points than the prism bar (Z = 3.37, p = 0.001). No significant differences were found between both tests for divergence break points (Z = 0.99, p = 0.32). However, both tests displayed wide limits of agreement (LoA) when measuring convergence (-24Δ to + 49.59Δ) and divergence break points (-7.70Δ to + 10.19Δ). Differences when measuring convergence and divergence blur and recovery points were not statistically significant.

Conclusion

There was a statistically and clinically significant difference when measuring convergence break points using the prism bar and synoptophore but no significant difference when measuring divergence break points. However, both tests displayed wide LoA when measuring convergence and divergence break points, indicating they should not be used interchangeably in clinic to measure horizontal fusional vergences.

The Effect of Heterophoria on the Size of Distance and Near Fusion Vergence

AIMS

To demonstrate changes in distance and near fusional vergence measured with prism bars, while compensating for present heterophoria using current ametropia correction. In addition, to determine the differences in values of the AC/A ratio determined by the heterophoric (calculation) and gradient methods.

MATERIAL AND METHODS

The basic sample includes 19 subjects with a mean age of 21.5 ±3.0 years (min. 18, max. 27). We used the Von Graefe technique for examination of distance and near phoria, and prism bars for examination of fusion vergences measured in prism diopters. We divided the basic cohort into six research sets according to the size of distance and near heterophoria. This was a cohort of patients with distance (D OR) and near orthophoria (N OR), a cohort of patients with distance (D EX) and near exophoria (N EX) and a set of patients with distance (D ES) and near esophoria (N ES).

RESULTS

In the case of both groups with exophoria (distance, near) we found a statistically significant result only for negative fusion vergence (NFV). There was a statistically significant increase in NFV in the sample with distance and near exophoria (D EX, p = 0.01 and B EX, p = 0.02, respectively). In our study, we also demonstrated a statistically significant difference (p < 0.001) in the values of the AC/A ratio measured by the gradient and heterophoric methods. The values determined by the gradient method are lower (3.0 ±1.1 pD/D versus 5.8 ±0.9 pD/D) than by the heterophoric method.

CONCLUSION

By comparing fusion vergence values in patients with exophoria and orthophoria, we demonstrated that in the presence of distance or near exophoria there is an increase in ipsilateral fusion vergence. In the case of an increase in ipsilateral fusion vergence, the finding was statistically significant both distance and near (p = 0.01 and p = 0.02, respectively). By contrast, we were unable to prove this fact in the group of patients with esophoria. In our study, we also demonstrated a statistically significant difference (p < 0.001) in the values of the AC/A ratio measured by the gradient and heterophoric methods. The values determined by the gradient method are lower (3.0 ±1.1 pD/D versus 5.8 ±0.9 pD/D) than by the heterophoric method.

Comparison of Measured Fusional Vergence Amplitudes using Prism Bar and Synoptophore in Sudanese Patients with Near Exophoria

Background:

Assessment of the fusional vergence amplitudes constitutes one of the most important diagnostic tools to obtain information about the ability to maintain binocular vision. Several techniques can be used to assess this function. However, those methods are not interchangeable, and the measurement repeatability has been questioned.

Objective:

This study aimed to compare fusional vergence range measurements using prism bars and synoptophore in Sudanese patients with near exophoria

Methods:

The study was a comparative cross-sectional hospital-based, performed in the binocular vision clinic at the Al-Neelain Eye Hospital. Fusional vergence amplitudes (positive and negative) were measured on 122 patients (67 females and 55 males), and the mean age and standard deviation were 16.79 ± 5.22 years old using prism bar and synoptophore methods.

Results:

The findings showed that the higher positive fusional vergence was obtained using the synoptophore method (24.7 ± 7.2 Δ base-out), whereas the prism bar method provided the lower finding (22.6± 7.6 Δ base-out). Conversely, the prism bar method revealed a higher measurement for negative fusional vergence (13.9± 3.9 Δ base-in) than the synoptophore method (12.7± 3.7 Δ base-in). Using the t-test, significant differences were found between all measurements with the two techniques, P<0.05. Measurements of positive and negative fusional vergence amplitudes by the two methods showed no relationship between age and fusional vergence, P>0.05.

Conclusion:

Given the significant difference in the results obtained between the two methods for measuring the positive and negative fusional vergence amplitudes, caution should be taken when making decisions regarding fusional vergence assessment in patients with latent and manifest strabismus.

Tweenager Computer Visual Syndrome Due to Tablets and Laptops during the Postlockdown COVID-19 Pandemic and the Influence on the Binocular and Accommodative System

The aim of our study was to compare computer visual syndrome (CVS) in a tweenager student population who use tablets and laptops only to play versus CVS in tweenagers who use these digital devices at school to study, in addition to playing. The tests performed were a validated survey for children for the detection of CVS and accommodative and vergence tests. The CVS item questionnaire was divided into four main groups based on questions concerning the following: (I) the digital device usage time, (II) musculoskeletal and ergonomic nature, (III) visual symptoms, and (IV) ocular surface symptoms. The high-demand digital device group showed worse punctuation in all item groups. From the optometric perspective, when the subjects were classified according to the CVS, high-demand participants presented a clear tendency to exophoria with statistically significant differences in distance vision (−1.94 ± 4.48 Δ) and near vision (−5.78 ± 8.62 Δ) (p < 0.01). Our results establish a relationship between the increased use of electronic devices and computer vision syndrome in the preadolescent population. In addition, this situation is related to the presence of visual, accommodative, and binocular dysfunctions that could affect the efficiency of the visual system.

Examination of Near Point of Convergence Scores in High-School Athletes: Implications for Identifying Binocular Vision Dysfunction After Concussion Injury

OBJECTIVE

To identify normative near point of convergence (NPC) data for healthy high-school-aged athletes (13-19 years old) and determine the percentage of individuals with NPC scores that fall outside the currently accepted clinical cutoff value of 5 cm. Another objective was to determine the relationship between sex, concussion history, and attention deficit disorder/attention deficit hyperactivity disorder (ADD/ADHD) with NPC scores, if any.

DESIGN

Case series.

SETTING

High-school sports medicine clinic.

PATIENTS OR PARTICIPANTS

Near point of convergence was assessed in 718 high-school student athletes (141 females and 577 males) with an average age of 15.96 ± 1.16 years.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

An accommodation convergence ruler was used to measure NPC. Near point of convergence scores were repeated a total of 3 times and the mean used for all statistical analyses.

RESULTS

The NPC scores for all participants averaged 3.58 cm, and the intraclass correlation coefficient for the 3 repeated measurements was 0.956. Approximately 20% of mean NPC scores were above the accepted upper limit of 5 cm. Although a statistically significant effect for sex was identified, the difference between them was considered clinically insignificant. No relationship between NPC and history of concussion or ADD/ADHD was identified.

CONCLUSIONS

Results indicate that in high-school-aged subjects, approximately 20% of individuals may have NPC values that fall outside the current critical cutoff value and may lead to incorrect diagnosis of ocular dysfunction. In addition, NPC does not seem to be affected by the history of concussion or a diagnosis of ADD/ADHD.

Sensitivity and Specificity of Sheard and Percival’s Criteria for the Diagnosis of Young People with Near-heterophoria

BACKGROUND: Sheard and Percival assumed that symptoms from latent strabismus can be avoided if the relevant fusional vergence is adequate to support the heterophoria. AIM: The aim of the study was to determine the sensitivity and specificity of Sheard’s and Percival’s criterion for the diagnosis of heterophoria. METHODS: A cross-sectional hospital-based study was performed at Al-Neelain Eye Hospital Khartoum, Sudan from February to October 2019. Heterophoria was measured using Maddox Wing and fusional vergence using a prism bar. Thereafter, Sheard’s and Percival’s criteria were used for the diagnosis of heterophoria. RESULTS: A total of 230 participants (age = 15–30 years; mean age = 19.34 ± 3.325 years) were recruited for this study. The Sheard’s criteria showed a high sensitivity of 87.2% and a low specificity of 8.0% for the diagnosing of exophoria, with positive and negative predictive values of 65.5% and 26%, respectively. The criteria showed a relatively low sensitivity of 77.8% and a specificity of 9.0% in the diagnosis of esophoria, with a positive and negative predictive values of 56% and 20%, respectively. Percival criteria showed high sensitivity 84.2% and low specificity 9.1% in diagnosing esophoria, with a positive and negative predictive value of 61.5% and 25%, respectively. On the other hand, the criteria showed low sensitivity 67.4% and specificity 13.8% in diagnosing exophoria, with positive and negative predictive value 61.9% and 17%, respectively. CONCLUSION: Sheard’s and Percival’s criteria are useful in diagnosing binocular vision problems. Sheard’s criteria are accurate in diagnosing near exophoria and Percival’s criteria are more accurate in diagnosing near esophoria. Therefore, these criteria provide good clues and predictions for the diagnosis of binocular vision problems.

Normative Data for Nonstrabismic Binocular Vision Parameters in African Schoolchildren

SIGNIFICANCE

With reported population differences in parameters of nonstrabismic binocular vision, the present study investigated and reports normative data among a sample of African children.

PURPOSE

This study aimed to determine expected binocular visual function data among schoolchildren in the Central Region of Ghana.

METHODS

The study used a prospective cross-sectional design and used a multistage cluster sampling approach. Eligible normal participants selected through the administration of Convergence Insufficiency Symptom Survey questionnaire (score <16) and preliminary vision screening underwent comprehensive binocular vision testing. Only data for participants who expressed no difficulty with the specific procedures were analyzed.

RESULTS

A total of 1261 normal participants (11 to 17 years [mean, 14.75 ± 1.530 years]) were selected for comprehensive binocular vision testing in the normative data study. The means with ±1 standard deviation for normative data for the nonstrabismic binocular vision parameters include the following: accommodative target near point of convergence (NPC) break (6.10 ± 1.67 cm), NPC recovery (8.17 ± 1.67 cm), fixation light with red-green anaglyph (RG NPC) break (8.51 ± 2.43 cm), RG NPC recovery (10.95 ± 2.60 cm), cover test distance phoria (0.12 ± 0.79 exophoria), cover test near phoria (2.1 ± 2.3 exophoria), modified Thorington test near phoria (1.9 ± 2.5 exophoria), negative relative accommodation (+2.54 ± 0.75 D), positive relative accommodation (-2.58 ± 0.81 D), and the accommodative convergence over accommodation ratio (2.80 ± 1.07:1). Age (in years)-predicted normal linear regression equations for NPC break (5.13 + 0.07 × age), RG NPC break (10.00 - 0.10 × age), RG NPC recovery (12.83 - 0.13 × age), positive relative accommodation (2.05 + 0.04 × age), and the gradient accommodative convergence over accommodation ratio (3.97 - 0.08 × age) serve as a guide.

CONCLUSIONS

The study provides expected data that optometrists may use with similar aged Black African populations.

Prevalence of Heterophoria in Tibetan Grade-One Students: The Lhasa Childhood Eye Study

INTRODUCTION

The study aims to explore the prevalence of heterophoria and associate factors in Tibetan grade-one students.

METHODS

The Lhasa Childhood Eye Study (LCES) is a school-based cohort study. 1942 grade-one students from 7 elementary schools were randomly sampled by stratified cluster sampling. Ocular examinations were performed in participants, including ocular motility, distance and near visual acuity, cycloplegic autorefraction, and stereoacuity. The near (33 cm) and distance (6 m) fixation cover test was used to differentiate orthophoria, heterophoria, and heterotropia, and the magnitude of the phoria was measured by the Maddox rod and prisma.

RESULTS

Of 1856 grade-one students completing all the ocular examinations, 1852 participants finished the ocular alignment test. The mean age was 6.82 ± 0.46 years (range 6∼10 years); 981 (52.97%) were males, and 871 (47.03%) were females. The prevalence of phoria was 22.89% (n = 424). At distance fixation, the prevalence of heterophoria, exophoria, and esophoria was 4.64%, 4.21%, and 0.43% separately, while at near fixation, the prevalence was 22.73%, 22.35%, and 0.38%. No vertical phoria was detected. The mean magnitude of heterophoria at near and distance fixation was -7.63 ± 5.15 PD (exo: -7.83 ± 4.91 PD, eso: +5.67 ± 3.61 PD) and -4.84 ± 5.94 PD (exo: -6.26 ± 4.20 PD, eso: +8.13 ± 3.04 PD). The prevalence of esophoria was associated with hyperopia (OR = 6.38, 95% CI: 1.15-35.28, P = 0.03; OR = 5.42, 95% CI: 1.04-28.24, P = 0.04) and amblyopia (OR = 16.02, 95% CI: 1.81∼141.96, P = 0.01; OR = 11.37, 95% CI: 1.34∼96.52, P = 0.03) at near and distance fixation. The prevalence of exophoria was associated with myopia at near fixation (OR = 2.43, 95% CI: 1.47-4.00, P<0.01). In the near heterophoria group, the proportion of children with abnormal stereoacuity was 23.26% (n = 97), significantly higher (χ 2 = 5.70, P = 0.017) than that in orthophoria (17.99%, n = 244).

CONCLUSIONS

In Lhasa, grade-one pupils have a lower prevalence of heterophoria. Near exophoria was associated with myopia, while esophoria was related to hyperopia and amblyopia both near and distance. Heterophoria may be one of the affected factors for reducing stereoacuity.

Visual Binocular Disorders and Their Relationship with Baropodometric Parameters: A Cross-Association Study

The aim of this study was to establish a relationship between nonstrabismic binocular dysfunction and baropodometric parameters. A total of 106 participants underwent binocular vision assessment by evaluating horizontal heterophoria, horizontal and vertical fusional vergence ranges, and vergence facility. Posturography was measured using the FreeMED baropodometric platform. Among the variables that the software calculates are foot surface, foot load, and foot pressure. Our results showed that in the participants with positive fusional vergence (PFV) (near) blur and recovery values outside the norm, there are statistically significant differences between the total foot area (p < 0.05), forefoot area (p < 0.05), forefoot load (p < 0.05), and rearfoot load (p < 0.05), in all of the cases of left foot vs. right foot. In the group of subjects who did not meet Sheard's criterion (distance), that is, those with unstable binocular vision, there was a statistically significant difference (p < 0.01) between maximum left and right foot pressure. In conclusion, our results establish a relationship between nonstrabismic binocular dysfunctions and some baropodometric parameters.

Synchronization of a Removable Optical Element with an Eye Tracker: Test Case for Heterophoria Measurement

Purpose

Heterophoria describes the deviation of the optical axes in the absence of binocular fusion. Eye trackers (ET) can provide an objective assessment but are not broadly used clinically. We examined the feasibility of combining an infrared (IR) pass-filter, IR detector, and an off-the-shelf ET. The proposed setup was validated against the broadly used cover test (CT). Furthermore, the setup was used to examine whether testing conditions can affect the measurements.

Methods

An IR detector was attached to a handheld IR-pass filter that blocks visible light to provide occlusion while passing IR light for eye tracking. The detector senses the IR illumination of the eye tracker, creating a recordable signal of the occluder position synchronized with eye positions acquired by the SMI Red250 tracker. The mean of three measurements of each condition, three versus ten seconds occlusion, the occluded eye, and ET versus CT results were compared using the Wilcoxon test, correlation and Bland and Altman plots. Differences between measurements that were within 2^Δ were considered clinically insignificant.

Results

Thirty normally-sighted subjects (mean age 24.50 ± 2.20, range 20-28) with heterophoria ranging between 14^Δ exophoria and 4^Δ esophoria were recruited. There was no significant difference between the occluded eyes. However, there was a difference between 3 and 10 seconds' cover duration. The CT data were more similar to the 10 seconds cover duration, although differences were less than the clinical resolution of 2^Δ.

Conclusions

An inexpensive off-the-shelf ET can be used to measure heterophoria with controlled testing parameters.

Translational Relevance

Our study demonstrated a robust technique for synchronization of an optical element such as an IR cover, with an off-the-shelf commercial eye tracker. The synchronization of optical elements with eye tracking, which has been described here for heterophoria, can be adapted for other clinical measurements.

A review of normative data for parameters of functional non-strabismic binocular vision

Background: There was a need to document population-expected normative data for parameters of non-strabismic binocular vision (NSBV) as the analysis and diagnosis of binocular vision disorders required comparison of patient’s clinical signs with expected data in their specific population.Aim: This article sought to review and map population-expected continental normative data for visual function parameters for evaluating the functional non-strabismic accommodative and vergence system, as these systems are very relevant to evaluate the comfort of visual system.Method: Search engines – namely, Google Scholar, Microsoft Academic, Web of Science database and Ovid MEDLINE database – were used to search studies published in English across different continents using keywords such as ‘normative or expected data’ and ‘specific NSBV parameter’. Results were summarised in tables for easy comparison; data were presented based on the geographical location, year of publication, demographics of the population studied and the techniques used for measuring the parameters. A summary of observed challenges with reviewed works and recommendations for the future studies are indicated. The article is delimited to studies published between 1910 and September 2019 only.Results: Most of the studies investigated specific parameters of either accommodation only or vergence only; few recent studies have comprehensively investigated both parameters. Most studies were conducted in North America followed by Asia and Europe, with a few in Africa. No studies were found with Oceania populations. There were discrepancies and differences in methodologies and techniques used by the studies reviewed and normative data varied among different continents and different populations within each continent.Conclusion: As the observed differences in reviewed studies could be attributed to differences in test techniques, the future studies should consider using identical, reliable, repeatable, objective and subjective techniques with good methodological designs to clarify these results. More studies should be conducted in African and Oceania populations.

Prevalence of heterophoria in a population of school children in central China: the Anyang Childhood Eye Study

AIM

To investigate the prevalence of heterophoria and the relationship between heterophoria and refractive error in a school-based study conducted in central China.

METHODS

A total of 2363 7^th-grade children were recruited into the cross-sectional school-based Anyang Childhood Eye Study (ACES) by cluster sampling method. Heterophoria was examined using alternate cover and cover-uncover testing. The Maddox rod and prism test were conducted at 33 cm and 6 m distance fixation. Uncorrected viual acuity (UCVA) and best-corrected viual acuity (BCVA) were recorded as logarithm of the minimum angle of resolution (logMAR) with cycloplegic autorefraction by administrating of Mydrin-P and 1.0% cyclopentolate. Hyperopia was defined as the spherical equivalent (SE) refraction of +0.50 D or greater, and higher hyperopia was defined as +2.00 D or greater. Emmetropia was defined as the SE refraction in the range of -0.49 to +0.49 D, and myopia was in the SE refraction range from -0.50 D to less.

RESULTS

Totally 2260 students in grade 7 were examined. Response rate among eligible children was 95.64%. Totally 486 children, 22.66% of the population, were diagnosed with heterophoria in which 479 were diagnosed with exophoria at near distance, and 6 with esophoria. Totally 89 (4.15%) children were diagnosed with heterophoria in which 82 had exophoria, and 7 had esophoria at far distance. Exophoria was common at near fixation (22.33%). Myopia was examined to be related to exophoria at near distance (OR 3.03, 95%CI 2.33-3.95) and far distance fixation (OR 1.90, 95%CI 1.09-3.32).

CONCLUSION

Exophoria is a predominant heterophoria for 7^th-grade junior school in central China. Significant associations are discovered between heterophoria and refractive error. Hyperopia is associated with esophoria, and myopia is associated with exophoria.

Phoria Adaptation: The Ghost in the Machine

Importance: Phoria adaptation is a central tonus mechanism that provides plasticity to binocular alignment. However, its slow dissipation inevitably adulterates our clinical strabismus measurements.Purpose: To examine the role of phoria adaptation in normal binocular control, understand its neural substrate, and explore how it can alter our clinical measurements in common forms of strabismus.Methods: Investigation into the role of phoria adaptation in maintaining binocular alignment and its role in altering clinical strabismus measurement.Results: Phoria adaptation permeates all aspects of binocular alignment. It accounts for the stability of orthophoria, "latent" phorias, tenacious proximal fusion in intermittent exotropia, large fusional vertical amplitudes in congenital superior oblique muscle palsy, the "eating up" of prisms in accommodative esotropia, the smaller measured distance deviation in patients with high AC/A ratio or convergence excess, absence of physiologic skew deviation during head tilt, fusional divergence amplitudes, and spread of comitance. This binocular control system probably arises from a cerebellar learning mechanism that involves input via climbing fibers to the inferior olive, which provide a powerful timing and error signal to the cerebellar Purkinje cells to produce activity-dependent modification analogous to long-term potentiation.Conclusions: Phoria adaptation is generated by a central neural integrator that provides inertia, plasticity, and positional stability to human binocular vision.

Normative values for clinical measures used to classify accommodative and vergence anomalies in a sample of high school children in South Africa

AIM

To determine normative values for stereoacuity, accommodative and vergence measures for high school populations.

METHODS

Using a multi-stage random cluster sampling, 1211 children (481 males and 730 females) between 13 and 18 years of age, with a median age of 16 years, were selected. Visual acuity, stereoacuity and suppression, refractive errors, near point of convergence, heterophoria and fusional vergences, as well as, amplitude of accommodation, accommodative response, facility and relative accommodation were evaluated.

RESULTS

Most data did not have a normal distribution. The range of normality for the vergence measures were: near point of convergence break, 5-10cm, recovery, 6-13cm, near lateral phoria, 2.5-6 prism dioptre (pd) (nasal), near vertical, orthophoria to 0.50pd, negative fusional vergence break, 12-23pd, recovery, 8-17pd, positive fusional vergence break, 16-35 and recovery 11-24pd. For accommodative measures, the range of normality for accommodative measures was: amplitude of accommodation, 12-18pd, accommodative response, plano to +0.75D, binocular accommodative facility, 5-12 cycles per minute (cpm), negative relative accommodation, 1.75-2.50DS, positive relative accommodation, -2.0 to -3.0DS and 17-69s arc for stereoacuity.

CONCLUSION

This study provides norms for clinical measures which could be used to classify accommodative and vergence parameters for children aged 13-18 years in this population or beyond. Findings should be applied in the context of the measurement techniques and the associated limitations outlined in this report.

Binocular Function in Subjects with Orthotropic Duane Retraction Syndrome

Introduction and Purpose: The aim of this study is to evaluate binocular vision parameters such as near point of accommodation (NPA), near point of convergence (NPC), fusional vergence ranges in subjects with orthotropic Duane retraction syndrome (DRS) and to compare with normal age-matched controls Patients and Methods: A total of 24 subjects (14 Type 1, 2 Type 2, 8 Type 3 DRS) who were diagnosed to have DRS and 15 normals were included in the study. The following binocular vision parameters were assessed in all subjects: amount of the deviation (for near and distance in all gazes), NPC, NPA, positive and negative fusional vergence (PFV and NFV) reserve and stereopsis. Results: Accommodative amplitude was normal in subject with DRS (median (95% confidence interval (CI):15D (11.9-18.1)) compared to age-matched controls. However, NPC was significantly receded (median [95% CI]:17 cm [14.4-19.6]). PFV reserve and NFV reserve were reduced in subjects with DRS. Subjects with Type 3 DRS have poor PFV reserve and NFV reserve for distance when compared to Type 1 DRS (p = 0.009 and 0.006 respectively). Stereopsis was poor in the subjects with DRS (p < 0.001). Conclusion: Subjects with DRS have good accommodation, but have poor convergence and fusional vergence. Stereopsis was noted to be poor as well.

Measurement of fusional vergence: a systematic review

Background: Fusional amplitudes are important for clinical practice in diagnosing and managing binocular vision anomalies. Several measurement methods can be used to assess fusional amplitudes. However, those methods are not interchangeable, and measurement repeatability has been questioned. Objectives: To compare the normative values of tests for the measurement of fusional vergence and to investigate sources of heterogeneity of diagnostic accuracy including: age, variation in method of assessment, study design and size, type (convergent, divergent, vertical, cyclo) and severity of strabismus (constant/intermittent/latent). Data sources: Bibliographic databases were searched up to March 2018, including Cochrane registers, PubMed, Web of Science^TM, Google Scholar and Science Citation Index. Trial registers and conference proceedings were hand searched. Review methods: The review observed and reported according to the PRISMA guidelines and was registered with PROSPERO. The I² was used to show the percentage of observed total variation across studies that is due to real heterogeneity rather than chance. The results of the different studies and the overall effect (meta-analysis under the random effects model) are shown. Results: Eighty-one studies were included in the review. Heterogenous information about break vergence amplitudes is reported for the step vergence method (I² > 50%; p < 0.05) in children. Four parameters were reported consistently to affect measurements; age, method of assessment, order of testing and target size. For the smooth vergence technique break vergence values heterogeneity was not present in children and adults (I² = 0%; p > 0.05). Limitations: The results are based on cross-sectional studies that were performed independently of each other, with different examiners, methods of examination and different populations. Conclusions: The source of heterogeneity between studies for vergence break points measured with the step vergence method seems to be linked with age. Normal vergences reported in children had considerable heterogeneity compared with adults. In clinical practice, the population-based vergence ranges measured with the step vergence method in children should not be used as one single criterion. For the smooth vergence technique, normative population data can be used.

Nonstrabismic binocular dysfunctions and cervical complaints: The possibility of a cross-dysfunction

The aim of this study is to establish a relationship between non-strabismic binocular dysfunction and neck pain. One hundred twelve participants underwent binocular vision assessment by evaluating horizontal heterophoria, horizontal and vertical fusional vergence ranges and vergence facility. The subjects were classified into two groups: binocular anomalies and normal binocular function. Neck complaints were measured with the Neck Disability Index, visual analogue scale, cervical range of motion, deep-flexor muscle activation score (AS) and performance index (PI). Our results showed that participants with low AS had significantly altered values of lateral phoria (near) (mean = -6.99 SD ± 6.96 PD) and PFV (near) blur (mean = 9.49 SD ± 5.45 PD) against those who presented normal AS (lateral phoria (near) mean = -3.64 SD ± 6.37 PD; PFV (near) blur mean = 12.84 SD ± 6.20 PD). In addition, participants with NFV (near) recovery outside the norm had a significantly lower right side-bending (mean = 35.63 SD ± 8.35 PD) than those within the standard (mean = 39.64 SD ± 9 PD). The subjects with binocular vision impairment showed a diminished response to the deep cervical musculature, with low AS and PI, as well as a tendency to suffer from cervicalgia of more than three months’ evolution and a lower range of motion.

Functional anatomy of human extraocular muscles during fusional divergence

We employed magnetic resonance imaging to quantify human extraocular muscle contractility during centered target fusion and fusional divergence repeated with each eye viewing monocularly at 20 cm through 8Δ and at 400 cm through 4Δ base in prism. Contractility, indicated by posterior partial volume (PPV) change, was analyzed in transverse rectus and in medial and lateral superior oblique (SO) muscle compartments and by cross-sectional area change in the inferior oblique (IO). At 20 cm, 3.1 ± 0.5° (SE) diverging eye abduction in 10 subjects was associated with 4.2 ± 1.5% whole lateral rectus (LR) PPV increase ( P < 0.05) and 1.7 ± 1.1% overall medial rectus (MR) PPV decrease attributable to 3.1 ± 1.8% reduction in the superior compartment ( P < 0.025), without change in its inferior compartment or in muscles of the aligned eye. At 400 cm, 2.2 ± 0.5° diverging eye abduction in nine subjects was associated with 6.1 ± 1.3% whole LR PPV increase ( P < 10^-5) but no change in MR, with compartmentally similar relaxation in the LR and MR of the aligned eye. Unlike convergence, there were no IO or SO contractile changes for divergence to either target nor any change in rectus pulley positions. Results confirm and extend to proximal divergence the unique role of the superior MR compartment, yet no MR role for far divergence. Corelaxation of aligned eye LR and MR combined with failure of MR relaxation during divergence is consistent with the limited behavioral range of divergence. NEW & NOTEWORTHY Magnetic resonance imaging shows that the lateral rectus muscle must overcome continued contraction by its opponent the medial rectus when humans diverge their visual axes to achieve single, binocular vision. While the upper but not lower compartment of the medial rectus assists by relaxing for near targets, it does not do so when targets are far away. This behavior violates Sherrington's law of reciprocal action of antagonists and conventional assumptions about the ocular motor system.

Motility Changes and Diplopia After Baerveldt Glaucoma Drainage Device Implantation or After Trabeculectomy

Purpose

The purpose of this study was to quantify any diplopia and motility changes after the implantation of a Baerveldt glaucoma implant (BGI) or after trabeculectomy (TE).

Methods

We analyzed 51 patients with a BGI and 52 patients with a TE from a prospective cohort study. To quantify any diplopia, we asked patients about the presence of diplopia at 1 year after surgery. To quantify any ocular motility changes, we measured ductions in eight gaze directions, the patients' ocular alignment and their fusion range before and 1 year after surgery.

Results

In the BGI group, 14 patients (28%) experienced diplopia compared with one patient (2%) in the TE group (P < 0.001). Duction changes were more commonly observed in the BGI group (35%) than in the TE group (19%). In the BGI group, ductions were mostly restricted in elevation (13%; P < 0.001), in abduction (13%), in elevation in 25° adduction (13%; P = 0.044), and in elevation in 25° abduction (25%; P < 0.001). In 32% of the patients, their near horizontal ocular alignment shifted, notably in exodirection (P = 0.04). The fusion range decreased significantly in the horizontal direction (−12.6° ± 10.3°, mean ± standard deviation; P = 0.01).

Conclusions

BGI surgery was significantly associated with postoperative diplopia and impaired eye motility (reduced ductions), mostly present in abduction, elevation, elevation in 25° adduction, and elevation in 25° abduction. Even without impaired ductions, diplopia could come about.

Translational Relevance

By studying diplopia across glaucoma patients prospectively with diplopia questionnaires and extensive orthoptic measurements, we gain better insight into its occurrence.

Prevalence of heterophoria and its association with near fusional vergence ranges and refractive errors

Background: Heterophoria is an error of binocular alignment that manifests only during monocular viewing or in conditions that disrupt binocular vision. Heterophoria is compensated for by fusional vergence through a mechanism that involves both sensory and motor fusion. The distribution of heterophoria has not been studied extensively in schoolchildren in South Africa and studies quantifying the magnitude of association between heterophoria and fusional vergences are scarce.Purpose: The aim of this study was to determine the prevalence of heterophoria and investigate its associations with fusional vergences and refractive errors.Methods: This was a cross-sectional study design and comprised data from 1056 high school students aged 13–18 years, who were randomly selected from 13 out of a sample frame of 60 high schools in uMhlathuze municipality in the province of KwaZulu-Natal, South Africa. The sample comprised 403 (38%) males and 653 (62%) females. The participants’ mean age was 15.89 ± 1.58 years. Visual acuity, refractive errors, heterophoria and fusional vergences were evaluated using conventional optometric techniques.Results: The overall prevalence of orthophoria at distance was 80.1% (95% confidence interval [CI]: 77.7% – 82.6%), that of exophoria was 13.9% (CI: 11.9% – 16.0%), while that of esophoria was 6.0% (CI: 4.5% – 7.4%). At near, the prevalence estimates were as follows: exophoria, 542 (51.3%, CI: 48.3% − 54.2%); orthophoria, 36.6% (CI: 33.9% − 39.5%); esophoria, 12.1% (CI: 10.2% − 14.0%). On the severities of near phoria, the frequencies were as follows: mild (1–7 prism dioptres [pd]), 41% (CI: 38.3% – 44.1%); moderate (8–13 pd), 9.7% (CI: 7.8% – 11.5%); and severe (> 13 pd), 1.1% (CI: 0.6% – 1.8%). For the severities of fusional vergences, the distributions were as follows: positive fusional vergences, mild (15–22 pd), 88.3% (CI: 86.4% – 90.4%); moderate (> 7 to < 15 pd), 10.1% (CI: 8.2% – 11.9%); and severe (≤ 7 pd), 1.6% (CI: 0.9% – 2.4%). For negative fusional vergences, the percentage of anomalous cases (≥ 22 pd) was 14.2% (CI: 12.3% – 16.3%), while that for normal (< 22) was 85.8% (CI: 83.7% – 87.7%). For vertical phoria, the prevalence was 2.7% and 3.6% at near. There was a weak but significant inverse correlation between near exophoria and positive fusional vergence break (r = −0.10, p = 0.01), whereas exophoria and negative fusional vergence break were positively correlated (r = 0.14, p = 0.01). Esophoria was inversely correlated with negative fusional vergence break values (r = 0.13, p= 0.01) and was positively correlated with positive fusional vergence break (r = 0.13, p = 0.03). Chi-square tests showed that exophoria was associated with astigmatism (p = 0.01), while esophoria was significantly associated with myopia (p = 0.01), astigmatism (p = 0.01) and anisometropia (p = 0.01).Conclusion: The data for far and near distance, horizontal and vertical heterophoria were not normally distributed. Orthophoria was most prevalent at far, exophoria at near and there was a significant association between phoria and fusional vergence. The significant associations between phoria and fusional vergence were at lower levels of fusional vergences.

Effect of Induced Vertical Disparity on Horizontal Fusional Reserves

PURPOSE

The aim of this study was to investigate the effects of induced vertical disparity on horizontal fusional reserves at near.

MATERIALS AND METHODS

In 170 healthy subjects wearing best corrective refraction, the negative and positive horizontal fusional reserves were measured with base-in (BI) and base-out (BO) prisms, respectively, in the presence of 0.5 prism diopters (^∆) and 1^∆ vertical prisms placed in trial frames in front of the right eye. The prism power was slowly increased step by step until the subject reported sustained blur, break, and recovery. These were compared to horizontal fusional reserves in the same subjects without a vertical prism. Data were analyzed in SPSS.17 software using a repeated measures ANOVA.

RESULTS

Induced vertical disparity decreased negative fusional reserves (NFR) horizontally and was more significant with 1^∆ vertical disparity (P<0.001). There were significant differences between the blur (P<0.001), break (P<0.001), and recovery (P<0.001) for NFR before and after induced vertical disparity and no significant difference between blur (P=0.173) and recovery points (P=0.261) with a marginal difference for break points (P=0.045) for the positive fusional reserves (PFR).

CONCLUSION

Inducing vertical disparity even with small magnitudes affects all 3 aspects (blur, break, and recovery) of horizontal negative fusional reserves while only break is affected in positive fusional reserves. These changes are statistically significant but do not seem to be clinically significant except for cases accompanied by symptoms.

Fusional Amplitudes: Developing Testing Standards

PURPOSE

The stability of binocular vision depends upon good fusional amplitudes, but the clinical assessment of fusional amplitudes varies around the world. The purpose of this study was to determine whether or not there is variation in the assessment of fusional amplitudes in normal subjects. The author looked at the testing distance, the order of testing, the role of examiner encouragement, and the subject's level of alertness.

METHODS

In a prospective study using a modified crossover design, the author assessed fusional amplitudes in 99 subjects with normal eye exams. The measurements were done in two separate sessions on different days with each subject being randomized as to the order of fusional vergence testing. All subjects were assessed without and with encouragement in the first session. In the second session, all were assessed at different testing distances.

RESULTS

The author previously presented data on 50 subjects. In this expanded cohort, statistical significance was reached confirming the previous findings that convergence is significantly affected by encouragement, divergence is significantly reduced if assessed after convergence, and near amplitudes are significantly higher than distance amplitudes. Finally, there is a negative correlation between age and convergence break point.

CONCLUSIONS

The results of this study demonstrate that divergence is significantly reduced if assessed after convergence in the subject with normal binocular function. Next, convergence is significantly affected by the use of encouragement. Measurements at near produced significantly higher results for all of the convergence and divergence tests. Finally, there is a significant negative correlation between age and convergence break point. We need to develop a standard of testing fusional amplitudes so there is consistency in the clinical assessment.

Effect of Illumination on Ocular Status Modifications Induced by Short-Term 3D TV Viewing

Objectives. This study aimed to compare changes in ocular status after 3D TV viewing under three modes of illumination and thereby identify optimal illumination for 3D TV viewing. Methods. The following measures of ocular status were assessed: the accommodative response, accommodative microfluctuation, accommodative facility, relative accommodation, gradient accommodative convergence/accommodation (AC/A) ratio, phoria, and fusional vergence. The observers watched 3D television for 90 minutes through 3D shutter glasses under three illumination modes: A, complete darkness; B, back illumination (50 lx); and C, front illumination (130 lx). The ocular status of the observers was assessed both before and after the viewing. Results. After 3D TV viewing, the accommodative response and accommodative microfluctuation were significantly changed under illumination Modes A and B. The near positive fusional vergence decreased significantly after the 90-minute 3D viewing session under each illumination mode, and this effect was not significantly different among the three modes. Conclusions. Short-term 3D viewing modified the ocular status of adults. The least amount of such change occurred with front illumination, suggesting that this type of illumination is an appropriate mode for 3D shutter TV viewing.