Vergence System Research Articles

The Impact on Vergence Parameters After Smartphone Gaming.

To evaluate the impact of smartphone gaming on the vergence system of the eye. A 5-month (from March 2023 to August 2023) comparative and experimental research was conducted. Eighty-two participants with a mean age of 21.98 ± 2.26 years were present in the study. Prior to assessing accommodation and vergence system characteristics, participants underwent a comprehensive eye examination. The participants were asked to play a shooting game on a smartphone for 30 minutes at a 40 cm distance. Measurements of the vergence parameters were taken before and after the activity and afterwards were compared. Non-parametric tests were used to compare pre- and post-task measurements. The Wilcoxon signed-rank test was used to compare the variables: Negative fusional vergence (NFV), Positive fusional vergence (PFV), Near point of convergence (NPC), and Vergence Facility (VF), with the alpha error set at 5%. The mean age of the participants was 21.98 ± 2.26 years. Post-task, the vergence parameters: NPC (p < 0.001), NFV for near distance (p < 0.001), PFV for near distance (p < 0.001), and VF (p < 0.001) showed significant decrease in vergence parameters. The study shows smartphone gaming for 30 minutes affects the vergence system, leading to binocular vision anomalies in young individuals.

Nonsurgical Consecutive Exotropia Following Childhood Esotropia: A Multicentered Study

PurposeNon-surgical consecutive exotropia (NCX) occurs when an esotropia (ET) spontaneously converts to exotropia (XT) without surgical intervention. Although considered to occur in early onset accommodative esotropia with high hyperopia, consensus on causation is lacking. We report the clinical characteristics of NCX and assess response to conservative management. DesignRetrospective, multi-centered observational case series. MethodsPatients aged 6 months and older with initial diagnosis of esotropia who converted to exotropia without surgical intervention. Sensory strabismus was excluded. Age, visual acuity, cycloplegic refraction, glasses prescriptions, deviation and binocular vision were collected. ResultsForty-nine children were included with a mean age of 3.5±1.6 and 8.4±3.6 years at time of ET and NCX, respectively. Mean refractive error was +4.40±2.13D and +4.05±2.74D at time of ET and NCX, respectively. Accommodative esotropia occurred in 60% of cases, and only 35.7% were high hyperopes. All but one patient presented with their XT at distance. In response to the XT, a mean decrease in hyperopic prescription of 1.55±0.48D was given (N=17); only 1 case reverted to esotropia. Eventually, 43% had exotropia surgery, with similar rates between those who had refractive management and those who did not. ConclusionsNCX occurs in both accommodative and non-accommodative esotropia; high hyperopia is present in only a third of cases. On average, drift to exotropia occurs within 5 years. Refractive management has a modest result. No predictive risk factors were identified. Our findings challenge hyperopia-linked theories of causation. Non-refractive explanations, such as the role of the vergence system, deserve further study.

Providing Reproducibility and objective control in computer measurement of fusion reserves

As is known, the main indicators of the stable functioning of fusion mechanisms – the physiological basis of binocular perception – are the fusion reserves (FR), an accurate assessment of which is still problematic. To measure the FR, a small mismatch between the accommodation and vergence systems is introduced and gradually increasing to reach certain critical angles at which the fusion mechanisms cease to function, as judged by the subjective sensations of the subjects reporting the break of the binocular image into two monocular ones. The subjectivity of such assessments of FR, as well as poorly studied dependence of FR on the parameters of test objects and measurement procedures, make it difficult to determine standard values and to create databases on RF. To overcome these shortcomings inherent in traditional methods of measuring RF, at the end of the last century, attempts were made to use computer methods (Rozhkova et al., 1996 ab, 1998). This article presents the results of a critical evaluation of the computer method for measuring FR using the author’s interactive computer program FUZIYA (Bolshakov, Rozhkova, 2013), which provides for the generation of variable test images on a special display designed for the polarization method of separating the left and right channels of test object presentation. The purpose of this study was to evaluate the accuracy and reproducibility of the measurement results, as well as to test the effectiveness of the previously proposed method to programmatically provide objective control of the binocular image break. The data obtained confirm the prospects of the approach used and make it possible to clarify the specific forms of its rational application.

Effect of Vergence Facility Testing on Horizontal Fusional Reserves.

The effect of vergence adaptation on test sequences should be considered in clinical practice. This study aimed to compare the effect of vergence adaptation after different vergence facility (VF) testing methods on following horizontal fusional reserve measurement at near. This cross-sectional study was performed on 50 healthy subjects with a mean ± standard deviation age of 21.18 ± 1.41 years. The baseline horizontal fusional reserves were measured using base-in (BI) and base-out (BO) prisms (∆) at near. Then, VF was measured using 3∆BI/12∆BI flip prism at near, and then the measurement of fusional reserves was repeated. In the next step, fusional reserves were measured after VF testing using 8∆BI/8∆BO flip prism. The values of fusional reserves were compared with their baseline findings. The results of negative fusional reserves after VF measurement using the 3∆BI/12∆BO prisms were significantly lower than the baseline values (blur [P = .03], break [P = .03], and recovery [P = .03]). There were no significant differences between the values of fusional reserves before and after VF testing using the 8∆BI/8∆BO prisms (P > .05). No correlation was observed between fusional reserves and VF responses (P > .05); however, the results revealed a positive correlation between the values of fusional reserves before and after VF testing using both methods (all P < .05). There was no significant difference in VF findings between the methods (P = .23). The measurements of horizontal fusional reserves followed by VF testing were not affected except for the responses of negative fusional reserves, which decreased after VF determination using the 3∆BI/12∆BO method. Although the vergence adaptation does not seem clinically significant, it is recommended to evaluate horizontal fusional reserves before VF measurement or long-enough time after VF testing for the vergence system to return to its nonadapted state.

Measuring the likelihood of VR visual fatigue through ocular biomechanics

Immersion in virtual reality is still linked to symptoms of visual fatigue such as eye strain, dizziness, and overall discomfort. Studies have investigated visual fatigue through pre- and post-immersion tests of the visual function. In this work, we extend on our previous study and derive a visual fatigue likelihood metric using biomechanical analysis. Previously, we have investigated the effect of VR on the vergence system during immersion. The proposed visual fatigue metric exhibited a significant correlation to vergence angle variability which was previously linked to vergence accommodation conflict in VR. We also discuss subjective feedback and its relationship with the proposed visual fatigue metric.

A Complex Structure in the northwestern of Sumatra Fore-arc

The Sumatran offshore region is known as an active seismogenic zone. Consequently, there were many records of great events that caused a big catastrophe, such as the 2004 Sumatra-Andaman earthquake. In order to investigate the geometry and nature of the earthquake ruptures and structures, we utilize the bathymetry and Multi-Channel Seismic (MCS) profiles from the SO-198 research project in 2008 (R/V Sonne) and KH-10-5 research project in 2010 (R/V Hakuho-Maru). We find that the area along the Sunda Trench to the fore-arc high in the northwestern Sumatra are characterized by parallel anticlinal ridges with distinctive vergence regimes. These vergence regimes classified as seaward, mix and landward vergence system. Our data interpretation recognized structures such as Main thrust, Lower thrust, Middle thrust, Upper thrust, piggy-back basin and West Andaman Fault within this region. Our conclusion suggest that the anticlinal seaward and landward vergence are considered as the product of recent deformation rupture. The co-seismic slip from the past earthquake ruptures tends that it was occurred from the deeper part in the entire northwestern of Sumatra fore-arc.

Deterioration of binocular vision after alcohol intake influences driving performance

In this study, we assessed the influence of moderate alcohol intake on binocular vision, vergence system and simulated driving performance by analyzing the interactions between visual deterioration and driving variables. Thirty young healthy subjects were recruited. For the analysis, we measured: visual function (visual acuity and stereoacuity), phorias and fusional reserves. Also, we checked Sheard’s and Percival’s criteria at near and far. The accommodative convergence/accommodation (AC/A) ratio was calculated and vergence facility was also obtained at near. A driving simulator was used to assess driving performance under natural conditions and after alcohol consumption with a breath alcohol content of 0.40 mg/l. Alcohol intake significantly reduced binocular visual performance and vergence function, except for vertical phorias, horizontal phoria at near and Sheard’s and Percival’s criteria at near. Driving performance parameters also presented a statistically significant deterioration after alcohol consumption. A statistically significant correlation was found between the deterioration in overall visual function and overall driving performance, highlighting the influence of the visual deterioration on the driving performance. Moderate alcohol consumption impairs binocular visual and simulated driving performances, implying a greater safety hazard. In addition, deteriorations in binocular visual function and vergence correlated with simulated driving impairment, which indicates that the deterioration of binocular vision due to alcohol consumption affects driving, thus reducing road safety.

Underlying neurological mechanisms associated with symptomatic convergence insufficiency

Convergence insufficiency (CI) is the most common binocular vision problem, associated with blurred/double vision, headaches, and sore eyes that are exacerbated when doing prolonged near work, such as reading. The Convergence Insufficiency Neuro-mechanism Adult Population Study (NCT03593031) investigates the mechanistic neural differences between 50 binocularly normal controls (BNC) and 50 symptomatic CI participants by examining the fast and slow fusional disparity vergence systems. The fast fusional system is preprogrammed and is assessed with convergence peak velocity. The slow fusional system optimizes vergence effort and is assessed by measuring the phoria adaptation magnitude and rate. For the fast fusional system, significant differences are observed between the BNC and CI groups for convergence peak velocity, final position amplitude, and functional imaging activity within the secondary visual cortex, right cuneus, and oculomotor vermis. For the slow fusional system, the phoria adaptation magnitude and rate, and the medial cuneus functional activity, are significantly different between the groups. Significant correlations are observed between vergence peak velocity and right cuneus functional activity (p = 0.002) and the rate of phoria adaptation and medial cuneus functional activity (p = 0.02). These results map the brain-behavior of vergence. Future therapeutic interventions may consider implementing procedures that increase cuneus activity for this debilitating disorder.

Effects of Virtual Reality Head-mounted Displays on Oculomotor Functions

Purpose: Three-dimensional (3D) video games played using virtual reality head-mounted displays (VR-HMDs) are becoming increasingly popular. However, the use of this technology may lead to visual symptoms and discomfort by disrupting the normal linkage between the accommodation and vergence systems. This study aimed to investigate the effect of playing 3D video games using VR-HMDs on different oculomotor functions (i.e., accommodation and/or vergence system parameters) and to quantify symptoms associated with playing games using VR-HMD technology. Methods: Twenty –six male and female young adults (age range 19–27 years) with normal binocular vision completed this study. Different clinical accommodative and vergence measurements were collected before and after playing 3D video games using a VR-HMD system for 45 minutes. In addition, visual- and non–visual-related symptoms were measured before and after the video game sessions using the standardized Simulator Sickness Questionnaire. Results: The majority of accommodative parameters—including negative relative accommodation, accommodative accuracy, and monocular and binocular accommodative facilities—were significantly affected after playing 3D video games. With respect to vergence system measurements, the horizontal negative fusional vergence range at near and vergence facility test outcomes were affected significantly after the 3D video game sessions. Significant increments in different types of symptoms (i.e., visual and nonvisual) were also observed after playing 3D video games using the VR-HMD system. Conclusions: Playing 3D video games using VR-HMD systems can lead to a deterioration of certain oculomotor functions (i.e., accommodative and vergence systems). Players can be expected to experience eyestrain and discomfort after just 45 minutes of playing.

Frequency of undetected binocular vision anomalies among ophthalmology trainees

PurposeThe use of ophthalmic instruments requires increased effort on the accommodation and vergence system. This study aimed to understand the prevalence of binocular vision anomalies among ophthalmology trainees attending a surgical training program at a tertiary eye care center. MethodsThis prospective cohort study was carried out between April and November 2017 at a tertiary eye care center in South India. All the ophthalmology trainees inducted for the training programs at the institution underwent a comprehensive ophthalmic and binocular vision assessment. Subjects with previous diagnosis of binocular vision dysfunction and vision therapy were excluded. ResultsThe mean (SD) age of the subjects was 29 (3) among which 48 were females. Out of the total 75 subjects, 66 had prior surgical experience [range: 1 to 17 years]. Thirty-eight subjects were asymptomatic and 37 were symptomatic. The most common asthenopic symptom was the presence of headache. Forty-one (55%) out of the 75 had a diagnosis of a non-strabismic binocular vision dysfunction. The range of phoria at distance was orthophoria to 14 Prism Diopter (PD) exophoria (mean +/− SD: −1 +/− 3), and at near 4PD esophoria to 25PD exophoria (mean +/− SD: −4 +/− 5). Based on standard diagnostic criteria, 15 subjects (20%) had convergence insufficiency, 14 (19%) had accommodative infacility, 9 (12%) had intermittent divergent squint (IDS), while 3 subjects (4%) had convergence excess. ConclusionsThis study shows the high frequency of binocular vision dysfunctions among ophthalmology trainees joining a tertiary eye care center.

Effect of Yoga Ocular Exercises on Eye Fatigue.

Background:Comfortable working at near and intermediate tasks depend on the efficiency as well as coordination of accommodation and vergence systems. At present, the need for near and intermediate visual tasks has been dramatically increased, requiring prolonged computer- and gazette-related works. It demands excessive working of the extraocular and ciliary muscles. It may cause eye fatigue and other associated asthenopic symptoms. Globally, eye fatigue is one of the most commonly reported conditions in nonpresbyopic population with asthenopic symptoms. It is necessary to get relief from eye fatigue for better near and intermediate tasks.Materials and Methods:Thirty-two undergraduate optometry students who were symptomatic based on a validated eye fatigue questionnaire were included after a baseline comprehensive eye examination. Based on the eye fatigue symptoms score, they were equally assigned to a control group and an exercise group with sixteen participants in each. The exercise group performed yoga ocular exercises for up to 6 weeks after which the eye fatigue symptoms were reassessed in both groups.Results:In the exercise group, there was a statistically significant reduction in eye fatigue scores (P = 0.003), whereas the eye fatigue scores showed significant increment in the control group after 6 weeks (P = 0.044).Conclusions:Yoga ocular exercises reduce the eye fatigue symptoms score by increasing the efficiency of extraocular muscles. Hence, it could be considered as a therapeutic and nonpharmacologic intervention for reducing the eye fatigue and associated asthenopic symptoms.

Validation of an Objective Method for the Qualitative and Quantitative Assessment of Binocular Accommodative Facility

ABSTRACTPurpose: Assessing binocular accommodative facility (BAF) enables the evaluation of the interaction between the accommodative and vergence systems, which is relevant for the diagnosis of accommodative and binocular disorders. However, the tests used to assess BAF present methodological caveats (e.g., lack of objective control, vergence demands, and image size alterations), limiting its external validity. This study aimed to (i) develop a new objective method to quantitatively and qualitatively evaluate the BAF in free-viewing conditions, and explore its validity by the comparison with the Hart Chart test, and (ii) assess the inter-session reliability of the proposed method.Methods: 33 healthy young adults took part in this study. We used a binocular open-field autorefractor to continuously assess the magnitude of accommodative response during a 60-sec period, while participants repeatedly changed fixation from a far to a near chart when clarity of vision was achieved at each level. Accommodative response data were used to characterize the BAF measurement in quantitative (number of cycles) and qualitative terms (percentage of times that correctly accommodating or dis-accommodating in each level of accommodation as well as the magnitude of the accommodative change).Results: Our data revealed that the new proposed method accurately counted the number of cycles per minute when compared with the Hart Chart test (p = .23, ES = 0.02; mean difference = 0.18 ± 0.85). The inter-session reliability of the proposed method was demonstrated to be excellent (Pearson r and intraclass correlation coefficient: 0.95 to 0.98) for the parameters obtained with the BAF test.Conclusions: The present outcomes evidence that the proposed objective method allows to accurately assess the frequency and precision of BAF by the combination of the classical Hart Chart test and a binocular open-field autorefractometer. Our findings may be of relevance for the diagnosis and treatment of accommodative and binocular disorders.

Using biomechanics to investigate the effect of VR on eye vergence system

Vergence-accommodation conflict (VAC) is the main contributor to visual fatigue during immersion in virtual environments. Many studies have investigated the effects of VAC using 3D displays and expensive complex apparatus and setup to create natural and conflicting viewing conditions. However, a limited number of studies targeted virtual environments simulated using modern consumer-grade VR headsets. Our main objective, in this work, is to test how the modern VR headsets (VR simulated depth) could affect our vergence system, in addition to investigating the effect of the simulated depth on the eye-gaze performance. The virtual scenario used included a common virtual object (a cube) in a simple virtual environment with no constraints placed on the head and neck movement of the subjects. We used ocular biomechanics and eye tracking to compare between vergence angles in matching (ideal) and conflicting (real) viewing conditions. Real vergence angle during immersion was significantly higher than ideal vergence angle and exhibited higher variability which leads to incorrect depth cues that affects depth perception and also leads to visual fatigue for prolonged virtual experiences. Additionally, we found that as the simulated depth increases, the ability of users to manipulate virtual objects with their eyes decreases, thus, decreasing the possibilities of interaction through eye gaze. The biomechanics model used here can be further extended to study muscular activity of eye muscles during immersion. It presents an efficient and flexible assessment tool for virtual environments.

Postconcussion: Receded Near Point of Convergence is not Diagnostic of Convergence Insufficiency

To determine the frequency of occurrence of receded near point of convergence (NPC) in patients with chronic concussion-related symptoms and in those with receded NPC to enumerate the frequency of convergence insufficiency and other oculomotor disorders. Retrospective cross-sectional study. Clinic charts were retrospectively reviewed for the prior 3.5 years to identify all patients < 21 years old who were > 28days postconcussion, had chronic concussion-related symptoms, had normal visual acuity, and had received a comprehensive sensorimotor examination. The frequency of receded NPC and oculomotor diagnoses were determined. Of the 83 eligible patients, 74 (89%) had receded NPC. Of these, 70 (95%) had oculomotor disorders; 30 (41%) had disorders of accommodation only; 21 (28%) had convergence insufficiency and accommodation deficits; and 6 (8%) had convergence insufficiency only. Six (8%) had a convergence deficit other than convergence insufficiency (all with concurrent accommodative disorders); 4 (5%) had both a nonspecific vergence dysfunction and accommodation deficits; 2 (3%) had convergence excess only; and 1 (1%) had both convergence excess and accommodative deficits. A receded NPC was present in the majority of young patients with chronic postconcussion symptoms. Associated with numerous underlying oculomotor dysfunctions, the clinical finding of a receded NPC is not synonymous with the diagnosis of convergence insufficiency. Because treatment options for the various oculomotor dysfunctions differ, it is prudent that these patients undergo a thorough examination of their vergence and accommodative systems so that an accurate diagnosis can be made and appropriate treatment prescribed.

(Disparity-Driven) Accommodation Response Contributes to Perceived Depth.

When looking at objects at various distances in the physical space, the accommodation and vergence systems adjust their parameters to provide a single and clear vision of the world. Subtended muscle activity provides oculomotor cues that can contribute to the perception of depth and distance. While several studies have outlined the role of vergence in distance perception, little is known about the contribution of its concommitant accommodation component. It is possible to unravel the role of each of these physiological systems by placing observers in a situation where there is a conflict between accommodation and vergence distances. We thus sought to determine the contribution of each response system to perceived depth by simultaneously measuring vergence and accommodation while participants judged the depth of 3D stimuli. The distance conflict decreased depth constancy for stimulus displayed with negative disparity steps (divergence). Although vergence was unaffected by the stimulus distance, accommodation responses were significantly reduced when the stimulus was displayed with negative disparities. Our results show that biases in perceived depth follow undershoots in the disparity-driven accommodation response. These findings suggest that accommodation responses (i.e., from oculomotor information) can contribute to perceived depth.

Comparison of symmetrical prism adaptation to asymmetrical prism adaptation in those with normal binocular vision

This study sought to determine whether symmetrical compared to asymmetrical horizontal prisms (base-out or base-in) evoked different rates of phoria adaptation. Sixteen young adults with normal binocular vision participated in a symmetrical phoria adaptation experiment using a 3Δ base-out or 3Δ base-in binocular prism flipper and an asymmetrical phoria adaptation experiment using a 6Δ base-out or 6Δ base-in monocular wedge prism. The experiments were randomized and counterbalanced to reduce the influence of the prism stimulation order. Asymmetrical base-out prism adaptation was significantly faster than symmetrical prism adaptation for subjects with normal binocular vision. Asymmetrical phoria adaptation with base-in prism was not significantly different from symmetrical phoria adaptation implying that there are directional asymmetries (convergent versus divergent eye movements) in the slow fusional component of vergence. Data suggest that a potential interaction between the version system and the slow fusional vergence system may exist. Results have clinical relevance because patients with convergence or divergence insufficiency/excess may potentially show more pronounced differences between symmetrical and asymmetrical phoria adaptation compared to binocularly normal controls. These differences might also be relevant to clinical measurements such as vergence fusional range, which can be measured symmetrically (with Risley prisms in a phoroptor) or asymmetrically (with prism bar).

Vergence and Strabismus in Neurodegenerative Disorders.

Maintaining proper eye alignment is necessary to generate a cohesive visual image. This involves the coordination of complex neural networks, which can become impaired by various neurodegenerative diseases. When the vergence system is affected, this can result in strabismus and disorienting diplopia. While previous studies have detailed the effect of these disorders on other eye movements, such as saccades, relatively little is known about strabismus. Here, we focus on the prevalence, clinical characteristics, and treatment of strabismus and disorders of vergence in Parkinson’s disease, spinocerebellar ataxia, Huntington disease, and multiple system atrophy. We find that vergence abnormalities may be more common in these disorders than previously thought. In Parkinson’s disease, the evidence suggests that strabismus is related to convergence insufficiency; however, it is responsive to dopamine replacement therapy and can, therefore, fluctuate with medication “on” and “off” periods throughout the day. Diplopia is also established as a side effect of deep brain stimulation and is thought to be related to stimulation of the subthalamic nucleus and extraocular motor nucleus among other structures. In regards to the spinocerebellar ataxias, oculomotor symptoms are common in many subtypes, but diplopia is most common in SCA3 also known as Machado–Joseph disease. Ophthalmoplegia and vergence insufficiency have both been implicated in strabismus in these patients, but cannot fully explain the properties of the strabismus, suggesting the involvement of other structures as well. Strabismus has not been reported as a common finding in Huntington disease or atypical parkinsonian syndromes and more studies are needed to determine how these disorders affect binocular alignment.

Near Point of Convergence and Gait Deficits in Adolescents After Sport-Related Concussion.

To prospectively examine gait characteristics of participants acutely after concussion with and without receded near point of convergence (NPC), compared with healthy controls. Cross-sectional study. Sports-medicine clinic. Patients examined after concussion (n = 33; mean ± SD = 7.2 ± 3.1 days) and a group of uninjured athletes (n = 31) completed a Postconcussion Symptom Scale, underwent NPC testing, and single/dual-task gait assessments. Near point of convergence was defined as the patient-reported diplopia distance when a fixation target moved toward the nose. Receded NPC was defined as a distance >5 cm from the tip of the nose. Spatiotemporal gait characteristics in single-task and dual-task conditions were evaluated with analysis of variance; correlations were calculated between NPC and gait measures. Eighteen of 33 (55%) patients with concussion presented with receded NPC. Those with receded NPC exhibited slower gait speed (single-task = 1.06 ± 0.14 m/s vs 1.19 ± 0.15 m/s; dual-task = 0.80 ± 0.13 m/s vs 0.94 ± 0.13 m/s; P = 0.003) and shorter stride lengths (single-task = 1.11 ± 0.10 m vs 1.24 ± 0.11 m; dual-task = 0.97 ± 0.11 m vs 1.09 ± 0.11 m; P = 0.001) than healthy controls. Near point of convergence was moderately correlated with dual-task average walking speed for the normal NPC group (ρ = -0.56; P = 0.05). Postconcussion Symptom Scale scores did not significantly differ between groups (27 ± 18 vs 28 ± 16). After concussion, adolescents with receded NPC exhibited significant gait-related deficits compared with healthy controls, whereas those with normal NPC did not. Vergence and gross motor system dysfunction may be associated after concussion. Gait and vergence measures may contribute useful information to postconcussion evaluations.

Imaging of Convergence Insufficiency Treatment Effects (ICITE) Pilot Study: Design and Methods

Background: The blood-oxygen-level-dependent (BOLD) signal from functional magnetic resonance imaging (fMRI) identifies brain activation during specific tasks.1,2 This paper describes the design and methodology of the Imaging of Convergence Insufficiency Treatment Effects (ICITE) Study, a two-phase study comparing BOLD activations during vergence eye movements in symptomatic convergence insufficiency (CI) subjects (1) to those with normal binocular vision (NBV) and (2) after office-based vergence/accommodative therapy (OBVAT) versus office-based placebo therapy (OBPT). Methods: Young adults, 18 to 30 years, with NBV or symptomatic CI (near exophoria at least 4Δ [prism diopters] greater than at distance, receded near point of convergence [NPC], and insufficient positive fusional vergence [PFV]) were enrolled. During fMRI scanning, subjects were instructed to fuse a random-dot stereogram stimulus with vergence demands ranging from -3Δ to +25Δ. CI subjects were then randomized to 12 weeks of OBVAT or OBPT. Vision and fMRI examination at outcome were performed by a masked examiner. BOLD signal at baseline was compared between NBV and CI patients. Later, the BOLD response at baseline was compared to that following vision therapy for those with CI. Conclusion: The imaging results are expected to advance understanding of neurological mechanisms of CI and the effects of therapy on the vergence system, which in turn may guide development of future research that could lead to new treatment strategies.

Response of supraoculomotor area neurons during combined saccade-vergence movements.

Combined saccade-vergence movements allow humans and other primates to align their eyes with objects of interest in three-dimensions. In the absence of saccades, vergence movements are typically slow, symmetrical movements of the two eyes in opposite directions. However, combined saccade-vergence movements produce vergence velocities that exceed values observed during vergence alone. This phenomenon is often called "vergence enhancement", or "saccade-facilitated vergence," though it is important to consider that rapid vergence changes, known as "vergence transients," are also observed during conjugate saccades. We developed a visual target array that allows monkeys to make saccades in all directions between targets spaced at distances that correspond to ~1° intervals of vergence angle relative to the monkey. We recorded the activity of vergence-sensitive neurons in the supra-oculomotor area (SOA), located dorsal and lateral to the oculomotor nucleus while monkeys made saccades with vergence amplitudes ranging from 0 to 10°. The primary focus of this study was to test the hypothesis that neurons in the SOA fire a high frequency burst of spikes during saccades that could generate the enhanced vergence. We found that individual neurons encode vergence velocity during both saccadic and non-saccadic vergence, yet firing rates were insufficient to produce the observed enhancement of vergence velocity. Our results are consistent with the hypothesis that slow vergence changes are encoded by the SOA while fast vergence movements require an additional contribution from the saccadic system. NEW & NOTEWORTHY Research into combined saccade-vergence movements has so far focused on exploring the saccadic neural circuitry, leading to diverging hypotheses regarding the role of the vergence system in this behavior. In this study, we report the first quantitative analysis of the discharge of individual neurons that encode vergence velocity in the monkey brain stem during combined saccade-vergence movements.