The preferred retinal loci when the eyes converge.

The preferred retinal locus (PRL) is the position on the retina to which humans direct stimuli during fixation. In healthy normal eyes, it has been shown to be very stable across time and between different tasks. Previous measurements of the PRL have been made under monocular viewing conditions. The current study examines where the PRLs in the two eyes' retinas are when subjects fixate binocularly and whether they shift when the demand for the eyes to converge is changed. Our apparatus allows us to see exactly where binocular stimuli fell on the two retinas during binocular fixation. Thus, our technique bypasses some of the issues involved in measuring binocular alignment with subjective techniques and previous objective techniques that use conventional eye trackers. These results show that PRLs shift slightly but systematically as the demand for convergence increases. The shifts cause under-convergence (also called exo fixation disparity) for near targets. They are not large enough to cause a break in binocular fusion. The fixation disparity we observed with increasing vergence demand is similar to fixation disparity observed in previous reports.

Association of Accommodation and Convergence with Axial Length Elongation in Children with Basic Intermittent Exotropia: A 12-Month Observational Study.

INTRODUCTION: The aim of the study was to investigate the association of parameters related to accommodation and convergence and axial elongation in basic intermittent exotropia (IXT) patients and the potential clinical predictors of axial length (AL) growth. METHODS: A total of 140 basic IXT patients were recruited in this study. The medians of AL growth in different age brackets were chosen to divide the subjects into group A (slower axial elongation group, n = 69) and group B (faster axial elongation group, n = 71). Parameters of dominant and nondominant eyes were compared and analyzed during the 12-month follow-up period. The parameters, including baseline refraction, angle of deviation, Newcastle control score (NCS), accommodative amplitude (AMP), accommodative facility (AMF), accommodative response, positive or negative relative accommodation (PRA/NRA), and near point of convergence (NPC), were analyzed via univariate and multivariate regression. RESULTS: Subjects in the faster axial elongation group tended to have more myopic spherical equivalents (t = 3.956, p < 0.001), greater AMPs of dominant eyes (t = -2.238, p = 0.027), and fewer near points of convergence (t = 2.347, p = 0.020) than in the slower axial elongation group. For dominant eyes, logistic and linear regression analysis revealed that more negative spherical equivalents (OR = 0.603, p < 0.001; ß = -0.045, p < 0.001), greater AMPs (OR = 1.201, p = 0.027; ß = 0.023, p = 0.010), and less near points of convergence (OR = 0.883, p = 0.021; ß = -0.012, p = 0.019) were correlated with the faster axial elongation. For nondominant eyes, a more myopic spherical equivalent (OR = 0.682; p = 0.001; ß = -0.029, p = 0.005) was the only parameter correlated with faster axial elongation through regression analysis. CONCLUSION: In children with basic IXT, faster axial elongation in the dominant eyes was associated with more myopic spherical equivalents, greater AMPs, and lower NPCs. These accommodative parameters can serve as potential clinical indicators for monitoring myopia progression in addition to AL.

From convergence insufficiency to functional reorganization: A longitudinal randomized controlled trial of treatment-induced connectivity plasticity.

INTRODUCTION: Convergence Insufficiency (CI) is the most prevalent oculomotor dysfunction of binocular vision that negatively impacts quality of life when performing visual near tasks. Decreased resting-state functional connectivity (RSFC) is reported in the CI participants compared to binocularly normal control participants. Studies report that therapeutic interventions such as office-based vergence and accommodative therapy (OBVAT) can improve CI participants' clinical signs, visual symptoms, and task-related functional activity. However, longitudinal studies investigating the RSFC changes after such treatments in participants with CI have not been conducted. This study aimed to investigate the neural basis of OBVAT using RSFC in CI participants compared to the placebo treatment to understand how OBVAT improves visual function and symptoms. METHODS: A total of 51 CI participants between 18 and 35 years of age were included in the study and randomly allocated to receive either 12 one-hour sessions of OBVAT or placebo treatment for 6 to 8 weeks (1 to 2 sessions per week). Resting-state functional magnetic resonance imaging and clinical assessments were evaluated at baseline and outcome for each treatment group. Region of interest (ROI) analysis was conducted in nine ROIs of the oculomotor vergence network, including the following: cerebellar vermis (CV), frontal eye fields (FEF), supplementary eye fields (SEF), parietal eye fields (PEF), and primary visual cortices (V1). Paired t-tests assessed RSFC changes in each group. A linear regression analysis was conducted for significant ROI pairs in the group-level analysis for correlations with clinical measures. RESULTS: Paired t-test results showed increased RSFC in 10 ROI pairs after the OBVAT but not placebo treatment (p < 0.05, false discovery rate corrected). These ROI pairs included the following: Left (L)-SEF-Right (R)-V1, L-SEF-CV, R-SEF-R-PEF, R-SEF-L-V1, R-SEF-R-V1, R-SEF-CV, R-PEF-CV, L-V1-CV, R-V1-CV, and L-V1-R-V1. Significant correlations were observed between the RSFC strength of the R-SEF-R-PEF ROI pair and the following clinical visual function parameters: positive fusional vergence and near point of convergence (p < 0.05). CONCLUSION: OBVAT, but not placebo treatment, increased the RSFC in the ROIs of the oculomotor vergence network, which was correlated with the improvements in the clinical measures of the CI participants.

Visually induced vertical vergence as a motion processing biomarker associated with postural instability.

The present study explored visually induced vertical vergence (VIVV) as non-specific motion processing response. Healthy participants (7 male, mean age 28.57 ± 2.30; 9 female, mean age 27.67 ± 3.65) were exposed to optokinetic stimuli in an HTC VIVE virtual reality headset while VIVV, pupil-size, and postural sway was recorded. The methodology was shown to produce VIVV in the roll plane at 30 deg/s. Subsequent trials consisted of 40 s optokinetic motion in yaw, pitch, and roll directions at 60 deg/s, and radial optic flow; optokinetic directions were inverted after 20 s of motion. Median VIVV amplitude changes were normalized to the clockwise roll rotation, analysed, and correlated with changes in pupil-size and body sway. VIVV, pupil-size, and body sway were all affected by changes in optokinetic direction. Post-hoc analyses showed significant VIVV responses during optokinetic yaw and pitch rotations, as well as during radial optic flow stimulations. VIVV magnitudes were universally correlated with pupil-size and body sway. In conclusion, VIVV was expressed in all tested dimensions and may consequently serve as a visual motion processing biomarker. Failing to support binocularity while responding to optokinetic directionality, VIVV may reflect an eye-movement response associated with increased postural instability and stress, similar to a dorsal light reflex.

Vergence and accommodation deficits in paediatric and adolescent patients during sub-acute and chronic phases of concussion recovery.

INTRODUCTION: Visual function deficits have been reported in adolescents following concussion. We compared vergence and accommodation deficits in paediatric and adolescent patients at a tertiary medical centre in the sub-acute (15 days to 12 weeks) and chronic (12 weeks to 1 year) phases of concussion recovery. METHODS: The study included patients aged 7 to <18 years seen between 2014 and 2021, who had a binocular vision (BV) examination conducted within 15 days and 1 year of their concussion injury. Included patients had to have 0.10 logMAR monocular best-corrected vision or better in both eyes and be wearing a habitual refractive correction. BV examinations at near included measurements of near point of convergence, convergence and divergence amplitudes, vergence facility, monocular accommodative amplitude and monocular accommodative facility. Vergence and accommodation deficits were diagnosed using established clinical criteria. Group differences were assessed using nonparametric statistics and ANCOVA modelling. RESULTS: A total of 259 patients were included with 111 in the sub-acute phase and 148 in the chronic phase of concussion recovery. There was no significant difference in the rates of vergence deficits between the two phases of concussion recovery (sub-acute = 48.6%; chronic = 49.3%). There was also no significant difference in the rates of accommodation deficits between the two phases of concussion recovery (sub-acute = 82.0%; chronic = 77.0%). CONCLUSION: Patients in both the sub-acute and chronic phases of concussion recovery exhibited a high frequency of vergence and accommodation deficits, with no significant differences between groups. Results indicate that patients exhibiting vision deficits in the sub-acute phase may not resolve without intervention, though a prospective, longitudinal study is required to test the hypothesis.

Comparing clinical measures of near point of convergence and accommodation from the lateral canthus and browline in a paediatric and adolescent population.

PURPOSE: Clinicians measure the near point of convergence (NPC) and the amplitude of accommodation (AA) from the spectacle plane, the bridge of the nose or the lateral canthus when assessing visual function. These values are compared to standard clinical criteria to diagnose vergence and accommodation deficits, despite varying reference points. This prospective study explored measuring relative to the spectacle plane and from the lateral canthus for NPC and monocular AA, and the resulting clinical implications of diagnosing visual deficits. METHODS: Participants were seen by a single clinician for an eye examination. NPC was measured from the forehead and the lateral canthus of the right eye. Monocular AA was measured from the brow and the lateral canthus. Differences between measurements were analysed using non-parametric statistical tests including Wilcoxon Signed Rank, as well as linear regression and a linear mixed effects model to adjust for inter-eye correlation and repeated measures. Chi-square tests were used to assess differences in rates of abnormal findings. RESULTS: Data were collected from 70 participants (53% female, median age 13 [11-15] years). On average, measuring NPC from the lateral canthus yielded a value 1.8 cm higher than measuring from the forehead. Measuring AA from the lateral canthus resulted in an average difference of 1.5 cm compared to measuring from the brow. A total of 39% and 76% of subjects failed NPC compared to clinical norms when measured from the forehead or the lateral canthus, respectively, while 7% and 40% failed AA when measured from the brow or the lateral canthus, respectively. CONCLUSION: With the variable anatomy of the eye, it is imperative to account for the measurement point when assessing visual function. Measuring from the lateral canthus greatly increased the failure rates for NPC and AA compared with measuring from the forehead and brow, respectively.

Relationships between fusional convergence, suppression depth, and exotropia control in intermittent exotropia.

Purpose: To assess the correlation between the contribution rates of fusional convergence from the dominant and non-dominant eye and suppression depth and exotropia control. Study design: Cross-sectional prospective study. Methods: The fusional convergence of 25 participants with intermittent exotropia (mean age 10.8 ± 3.4; range 6-18 years) was measured with an eye-tracking system. The contribution rate was defined based on the amplitude of fusional convergence during refusion relative to the exo-deviation angle. The suppression depth was assessed, and exotropia control was evaluated using the intermittent exotropia Office Control Score. We analyzed the correlations between the contribution rate from the dominant and non-dominant eyes and the suppression depth or control score. Results: There was a negative correlation between the dominant eye's contribution rate and the suppression depth in both eyes (r = -0.85, 95% confidence interval [CI]: -0.97 to - 0.20 in the fixated dominant eye and r = -0.91, 95%CI: -0.95 to - 0.40 in the fixated non-dominant eye). There was a negative correlation between the dominant eye's contribution rate and the control score at a 4-meter distance (r = -0.53, 95%CI: -0.76 to - 0.17). Conclusion: Suppression in intermittent exotropia patients could affect the fusional convergence in the dominant eye.

Diagnostic Protocol for Accommodative and Vergence Anomalies - A Review.

PURPOSE: To review the diagnostic protocols of non-strabismic binocular vision anomalies. METHODS: We carried out a literature search on published articles of non-strabismic accommodative and vergence anomalies in different international optometry and ophthalmology journals found in the Pubmed, ResearchGate, Google Scholar, and MEDLINE databases. RESULTS: The diagnostic criteria and normative data from the nine articles selected show discrepancies and variability in methodologies and techniques in the overall assessment of Non-Strabismic Binocular Vision Anomalies (NSBVA). Near point of convergence measurement is the most common assessment, whereas the vergence facility is the least commonly used assessment in terms of evaluating convergence insufficiency. Near point of convergence > 10 cm alone is the most sensitive sign to detect convergence insufficiency in a community set-up but high positive relative accommodation (>3.50D) is the most sensitive sign to diagnose accommodative excess. On the other hand, monocular accommodative facility < 7 CPM has the highest sensitivity to confirm the diagnosis of accommodative infacility. This review also indicates that the more clinical signs that are included in a set of diagnostic criteria, the lower the prevalence rate for that diagnosis. CONCLUSIONS: There is no standardized and diagnostically validated protocol for the assessment of NSBVAs. Variable cutoff values obtained using different methods and the selection of diagnostic criteria by various researchers have led to discrepancies that highlight the need for diagnostic validity of available protocols (combination of tests) for each anomaly. Clinical signs such as positive relative accommodation (PRA) for accommodative excess, near point of convergence (NPC) for convergence insufficiency and monocular accommodative facility (MAF) for accommodative infacility were found to be useful diagnostic signs of these anomalies. Studies should be carried out for accommodative and vergence dysfunctions using proper designs and methods to validate diagnostic criteria for all age groups. Standardization of assessment protocol and cutoff criteria will also aid in calculating prevalence for non-strabismic binocular vision anomalies.

Long-term Ocular Alignment and Sensory Outcomes After Medial Rectus Recession for High AC/A Ratio Esotropia.

PURPOSE: To report long-term ocular alignment and sensory outcomes after medial rectus recession for high accommodative convergence/accommodation (AC/A) ratio esotropia. METHODS: The medical records of consecutive patients who had undergone unilateral or bilateral medial rectus recession for high AC/A ratio esotropia and were observed postoperatively for a minimum of 5 years were reviewed retrospectively. RESULTS: A total of 34 patients were included. Twenty-three patients (68%) used bifocals preoperatively. The mean age at surgery was 11.5 ± 4.4 years (range: 2.5 to 19.0 years). The mean postoperative follow-up was 7.5 ± 2.3 years (range: 5.0 to 15.25 years). Overall, 21 patients (62%) had surgical success at their last follow-up visit. Age at surgery, preoperative angle of distance and near deviation, distance-near disparity, and preoperative bifocal wear did not predict motor outcome after surgery. Preoperative presence of peripheral binocular single vision was a significant favorable factor for surgical success. At the last follow-up visit, 21% of patients had a recurrence of high AC/A ratio esotropia and 9% each had consecutive exotropia (intermittent [3%] and constant [6%]) and basic esotropia. Peripheral binocular single vision was achieved in 64% of patients and stereopsis in 28%. Bifocal segment was eliminated postoperatively in 70% of patients. CONCLUSIONS: Nearly two-thirds of patients with high AC/A ratio esotropia achieved a successful long-term motor outcome and peripheral binocular single vision, and nearly one-fourth achieved stereopsis. Recurrence of high AC/A ratio esotropia occurred in some patients, and consecutive exotropia and basic esotropia in a few. Bifocal segment was eliminated postoperatively in 70% of patients. [J Pediatr Ophthalmol Strabismus. 2024;61(5):344-350.].

Temporal dynamics of ocular torsion and vertical vergence during visual, vestibular, and visuovestibular rotations.

Ocular torsion and vertical divergence reflect the brain's sensorimotor integration of motion through the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) to roll rotations. Torsion and vergence however express different response patterns depending on several motion variables, but research on their temporal dynamics remains limited. This study investigated the onset times of ocular torsion (OT) and vertical vergence (VV) during visual, vestibular, and visuovestibular motion, as well as their relative decay rates following prolonged optokinetic stimulations. Temporal characteristics were retrieved from three separate investigations where the level of visual clutter and acceleration were controlled. Video eye-tracking was used to retrieve the eye-movement parameters from a total of 41 healthy participants across all trials. Ocular torsion consistently initiated earlier than vertical vergence, particularly evident under intensified visual information density, and higher clutter levels were associated with more balanced decay rates. Additionally, stimulation modality and accelerations affected the onsets of both eye movements, with visuovestibular motion triggering earlier responses compared to vestibular motion, and increased accelerations leading to earlier onsets for both movements. The present study showed that joint visuovestibular responses produced more rapid onsets, indicating a synergetic sensorimotor process. It also showed that visual content acted as a fusional force during the decay period, and imposed greater influence over the torsional onset compared to vergence. Acceleration, by contrast, did not affect the temporal relationship between the two eye movements. Altogether, these findings provide insights into the sensorimotor integration of the vestibulo-ocular and optokinetic reflex arcs.

Effects of vision therapy on near exodeviation in children with convergence insufficiency treated during the convergence insufficiency treatment trials.

PURPOSE: To report the change in the magnitude of near exodeviation in children with symptomatic convergence insufficiency successfully treated with office-based vergence/accommodative therapy in the Convergence Insufficiency Treatment Trial-Attention and Reading Trial. METHODS: A total of 131 children 9-14 years of age with symptomatic convergence insufficiency classified as successfully treated with office-based vergence/accommodative therapy at the 16-week outcome visit were included. Masked examiners measured the near ocular deviation by the prism and alternate cover test at baseline, primary outcome and 1-year post-treatment. The mean change in near deviation was calculated from baseline to primary outcome, from primary outcome to 1-year post-treatment and from baseline to 1-year post-treatment. RESULTS: Of the 131 participants successfully treated with vergence/accommodative therapy, 120 completed the 1-year post-treatment visit. A significant change in near exodeviation was observed at baseline to primary outcome (2.6Δ less exo, p < 0.001, moderate effect size d = 0.61) and at baseline to 1-year post-treatment (2.0Δ less exo; p < 0.001, small effect size d = 0.45). The change from primary outcome to 1-year post-treatment (0.6Δ more exo; p = 0.06, small effect size d = 0.11) was not significant. Forty per cent (48/120) of participants had a decrease in near exodeviation >3.5∆ (expected test/retest variability) between baseline and the primary outcome examination. Of the 120 participants, one (1.0%) was esophoric at the primary outcome and was subsequently exophoric at 1-year post-treatment. Four participants (3.3%) who were orthophoric or exophoric at the primary outcome were esophoric (all ≤3∆) at the 1-year post-treatment visit. CONCLUSION: On average, the near exodeviation was smaller in size immediately after the discontinuation of vergence/accommodative therapy (2.6∆, moderate effect size) and 1 year post vergence/accommodative therapy (2.0∆, small effect size) in children with convergence insufficiency who were successfully treated; 40% had a clinically meaningful decrease in exophoria. The development of near esophoria was rare.

Vergence-Accommodation Conflict: Increased Presbyopia in Virtual Reality.

BACKGROUND: Performance and symptoms in completing a visual search task on a PC monitor and using a head-mounted display (HMD) were compared for different viewing conditions and between users of different ages. PATIENTS AND METHODS: Twenty-three young (M = 30 y, SD = 7 y) and 23 older (M = 52 y, SD = 5 y) participants performed a visual search task presented on a PC monitor. The task was repeated using an HMD for a near and a far virtual viewing distance. Reaction times (RT), detection sensitivity (d'), and symptoms were recorded for the three different viewing conditions. RESULTS: RT and d' were not affected by the viewing condition (p > 0.05). In contrast, symptoms significantly depended on the viewing condition but were, in part, not significantly affected by age. It is interesting to note that although not significant, young participants reported more ocular symptoms than older participants in the near vision task carried out using the HMD. DISCUSSION: HMD increases visual symptoms. However, HMD could be, in part, a remedy to problems when using visual aids for near work, in particular for presbyopes.

Home vision therapy and prism prescription in presbyopic persons with convergence insufficiency: study protocol for a randomized controlled trial.

BACKGROUND: Convergence insufficiency is a common issue in the field of binocular vision. Various treatment options have been suggested for managing this condition, but their efficacy in individuals with presbyopia remains unclear. The objective of this study is to compare the effectiveness of home-based vision therapy and prism prescription, in presbyopic patients with convergence insufficiency. METHODS/DESIGN: It is a randomized, prospective, double-blind clinical trial, with total of 150 participants randomly assigned to the three groups. The Control Group will receive a new near glasses as a conventional prescription, along with aimless and random eye movement exercises that do not have any convergence or accommodation effects. The Home Vision Therapy Group will receive new near glasses with accommodative and convergence eye exercises. The Prism Group will receive a near prismatic glasses prescribed using the Sheard's criterion. All treatments will be administered for a period of 2 months, and measurements of the modified convergence insufficiency symptoms survey (CISS), near point convergence, near phoria, and positive fusional vergence will be taken at baseline, one month later, and at the end of the treatment. DISCUSSION: We aim to identify which component - either the prism prescription or the home vision therapy - is more effective in improving binocular abilities and reducing patients' symptom scores. TRIAL REGISTRATION: ClinicalTrials.gov NCT05311917 with last update on 04/22/2023.

Accommodative response and visual fatigue following a non-congruent visual task in non-asthenopic and asthenopic individuals.

PURPOSE: Asthenopia is related to near vision activities or visual tasks that dissociate accommodation from vergence. Since the results of previous studies using objective measures to diagnose asthenopia are inconsistent, this study compared optometric tests and objective metrics of accommodation in non-asthenopic and asthenopic young adults before and after a visual fatigue task. METHODS: The accommodative response was recorded objectively for 6 min at a 3.33 D accommodative demand using an autorefractor, before and after a 5-min non-congruent visual task. Accommodation was disassociated from vergence with a ±2.00 D accommodative flipper while reading at the same distance. Optometric tests and subjective evaluations of asthenopia were performed before and after the task. Twenty-six non-presbyopic adults (23.15 ± 2.56 years) were included and identified as asthenopic (n = 14) or non-asthenopic (n = 12) based on their score on the Computer Vision Syndrome Questionnaire. RESULTS: A mixed ANOVA found no significant difference between the groups for objective (accommodative response) or subjective metrics (feeling of fatigue, optometric tests), although all participants reported greater visual fatigue after the task. A significant effect of time (before and after the non-congruent task) was identified for the overall sample for mean accommodative lag (+0.10 D, p = 0.01), subjective visual fatigue (+1.18, p < 0.01), negative relative accommodation (-0.20 D, p = 0.02) and near negative fusional reserve (blur: +2.46Δ, p < 0.01; break: +1.89Δ, p < 0.01; recovery: +3.34Δ, p = 0.02). CONCLUSIONS: The task-induced asthenopia, measured both objectively and subjectively, was accompanied by a change in accommodative lag, greater visual fatigue and a decrease in negative relative accommodation. Conversely, near negative fusional reserves seem to adapt to the task. No significant differences were found between the two groups with respect to accommodative metrics (objective) or subjective and optometric tests.

Pupillary dynamics, accommodation and vergence in concussion.

Concussion, which is usually associated with head injuries, has received considerable attention in recent years because of its possible long-term cognitive and visual consequences. The review summarised the mild traumatic brain injury literature. Pupillary dynamics, which are primarily mediated by the autonomic nervous system, play an important function in regulating the amount of light entering the eye, but they can be dramatically impacted after a concussion. This can result in aberrant pupillary responses, which may have ramifications for light sensitivity, a common post-concussion symptom. In concussed individuals, accommodation and vergence - the visual processes responsible for focusing on near and distant objects - might be interrupted, potentially leading to fuzzy vision, eyestrain, and difficulty with tasks that require precise visual coordination. Understanding the delicate interplay between these three components of vision in the setting of concussions is critical for creating more targeted diagnostic and rehabilitative techniques, ultimately enhancing the quality of life for those who have had head injuries.

Diagnostic Importance of OCT Pachymetry in Keratoconus.

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.

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.

Distance horizontal fusional facility (DFF): A new diagnostic vergence test for the acquired brain injury (ABI) population.

PURPOSE: To report the retrospectively-based, clinical diagnostic findings for the horizontal, distance, fusional facility (DFF) test in the non-TBI (traumatic brain inury), ABI (acquired brain injury) population. METHODS: The DFF test (4 pd base-out/2 pd base-in) was assessed and compared retrospectively in the first author's optometric practice in three clinical populations: (1) post-mTBI, visually-symptomatic (n = 52), (2) post-ABI, non-mTBI, visually-symptomatic (n = 34), and (3) visually-normal, visually asymptomatic (n = 44). RESULTS: The DFF values in each group were significantly different from each other (p < 0.05). The mean non-TBI, ABI group value was significantly lower than found in the mTBI group, and both were significantly lower than the mean found in the normal cohort (p < 0.05). There was a significant reduction in DFF with increased age (p < 0.001). ROC values for the AUC ranged from excellent to acceptable (0.94-0.74). CONCLUSION: The DFF test is a new and useful way to assess horizontal, distance, dynamic, fusional facility in those with presumed non-mTBI, ABI neurological conditions to assist in its diagnosis.

Success rates, near-response patterns, and learning trends with free-fusion stereograms.

Free-fusion stereograms are routinely used for demonstrating various stereoscopic effects. Yet, untrained observers find it challenging to perform this task. This study showed that only less than 1/3rd of sixty-one pre-presbyopic adults with normal binocular vision could successfully free-fuse random-dot image pairs and identify the stereoscopic shapes embedded in these patterns. Another one-third of participants performed the task with poor success rates, while the remaining could not perform the task. There was a clear dissociation of vergence and accommodative responses in participants who were successful with free-fusion, as recorded using a dynamic infrared eye tracker and photorefractor. Those in the unsuccessful cluster either showed strong vergence and accommodation or weak vergence and strong accommodation during the task. These response patterns, however, were specific to the free-fusion task because all these participants generated good convergence/accommodation to real-world targets and to conflicting vergence and accommodative demands stimulated with prisms or lenses. Task performance of the unsuccessful cluster also improved significantly following pharmacological paralysis of accommodation and reached the performance levels of the successful cluster. A minority of participants also appeared to progressively learn to dissociate one of the two directions of their vergence and accommodation crosslinks with repeated free-fusion trials. These results suggest that successful free-fusion might depend upon how well participants generate a combination of volitional and reflex vergence responses to large differences in disparity with conflicting static accommodative demands. Such responses would require that only one direction of the vergence-accommodation crosslinks be active at any given time. The sequence of near-responses could also be learnt through repeated trials to optimize task performance.

Convergence Excess Esotropia: Review.

Convergence excess esotropia is a condition characterized by an esotropia which is greater for near fixation than for distance fixation after full hypermetropic correction with a single focus lens. Convergence excess esotropia may be classified according to the AC/A ratio into two subtypes: accommodative type and non-accommodative type. Bifocal glasses are a suitable option for the management of patients with a high AC/A ratio and for the hypoaccommodative type. However, the overall success rate with bifocals is still low even in selected patients. Surgery is often eventually needed for most patients with convergence excess esotropia. Surgical options that do not directly address the variability of the angle of deviation entail medial rectus recession with the target angle based on the distance deviation, the near deviation, an augmented formula based on an intermediate angle, or on a prism adaptation test. Surgical options that directly address the variability of the angle include partial myotomy, medial rectus muscle posterior scleral fixation with or without recession, pulley fixation, slanting recession, Y-splitting, or combined recession-resection of the medial rectus muscle. The review article summarizes the surgical outcome of these strategies and suggests an algorithm for the management of patients with convergence excess esotropia.