The horizontal dark oculomotor rest position.

BACKGROUND: This study sought to investigate whether eye dominance and age are related to the stimulus-free oculomotor resting state described via the dark disconjugate position (near or far), the dark conjugate position (left to right), and the near dissociated phoria. METHODS: Nineteen non-presbyopes and 25 presbyopes with normal binocular vision participated in two identical sessions. The left-eye and the right-eye positions were recorded using a video-based infrared eye tracker while the subjects were in total darkness. Dark disconjugate responses and dark conjugate responses were calculated by computing the difference and the average of the left-eye and the right-eye response, respectively. The right-eye decaying to the phoria level was recorded for 15 s. RESULTS: A one-way ANOVA assessed statistical differences in dark conjugate and dark disconjugate positions, comparing 1) the right-eye and the left-eye sensory and/or motor dominant groups and 2) the non-presbyope and presbyope groups. The test-retests of the dark disconjugate position, the dark conjugate position and the near dissociated heterophoria were high between sessions (r > 0.85; p < 0.00001). For non-presbyopes the right-eye (left-eye) motor and sensory dominant subjects showed a rightward (leftward) dark conjugate position (p < 0.01). The dark disconjugate position was receded in presbyopes compared to non-presbyopes (p < 0.0001). CONCLUSION: The data support that the left-eye, or the right-eye, motor and sensory dominance predicts the direction of the dark conjugate position. Future studies could investigate the underlying neural substrates that may, in part, contribute to the resting state of the oculomotor system in a stimulus-free environment. Knowledge of the brain-behavior governing visual-field preference has implications for understanding the natural aging process of the visual system.

Concurrent vision dysfunctions in convergence insufficiency with traumatic brain injury.

PURPOSE: This study assessed the prevalence of convergence insufficiency (CI) with and without simultaneous vision dysfunctions within the traumatic brain injury (TBI) sample population because although CI is commonly reported with TBI, the prevalence of concurrent visual dysfunctions with CI in TBI is unknown. METHODS: A retrospective analysis of 557 medical records from TBI civilian patients was conducted. Patients were all evaluated by a single optometrist. Visual acuity, oculomotor function, binocular vision function, accommodation, visual fields, ocular health, and vestibular function were assessed. Statistical comparisons between the CI and non-CI, as well as inpatient and outpatient subgroups, were conducted using χ and Z tests. RESULTS: Approximately 9% of the TBI sample had CI without the following simultaneous diagnoses: saccade or pursuit dysfunction; third, fourth, or sixth cranial nerve palsy; visual field deficit; visual spatial inattention/neglect; vestibular dysfunction; or nystagmus. Photophobia with CI was observed in 16.3% (21 of 130), and vestibular dysfunction with CI was observed in 18.5% (24 of 130) of the CI subgroup. Convergence insufficiency and cranial nerve palsies were common and yielded prevalence rates of 23.3% (130 of 557) and 26.9% (150 of 557), respectively, within the TBI sample. Accommodative dysfunction was common within the nonpresbyopic TBI sample, with a prevalence of 24.4% (76 of 314). Visual field deficits or unilateral visual spatial inattention/neglect was observed within 29.6% (80 of 270) of the TBI inpatient subgroup and was significantly more prevalent compared with that of the outpatient subgroup (p < 0.001). Most TBI patients had visual acuities of 20/60 or better in the TBI sample (85%; 473 of 557). CONCLUSIONS: Convergence insufficiency without simultaneous visual or vestibular dysfunctions was observed in about 9% of the visually symptomatic TBI civilian population studied. A thorough visual and vestibular examination is recommended for all TBI patients.

Short-term adaptations of the dynamic disparity vergence and phoria systems.

The ability to adapt is critical to survival and varies between individuals. Adaptation of one motor system may be related to the ability to adapt another. This study sought to determine whether phoria adaptation was correlated with the ability to modify the dynamics of disparity vergence. Eye movements from ten subjects were recorded during dynamic disparity vergence modification and phoria adaptation experiments. Two different convergent stimuli were presented during the dynamic vergence modification experiment: a test stimulus (4° step) and a conditioning stimulus (4° double step). Dynamic disparity vergence responses were quantified by measuring the peak velocity (°/s). Phoria adaptation experiments measured the changes in phoria over a 5-min period of sustained fixation. The maximum velocity of phoria adaptation was determined from an exponential fit of the phoria data points. Phoria and dynamic disparity vergence peak velocity were both significantly modified (P < 0.001). The maximum velocity of phoria adaptation was significantly correlated with the changes in convergence peak velocity (r > 0.89; P < 0.001). There was a strong correlation between the ability to adaptively adjust two different oculomotor parameters: a tonic and dynamic component. Future studies should investigate additional interactions between these parameters, and the ability to adaptively change other oculomotor systems such as the saccadic or smooth pursuit system. Understanding the ability to modify phoria, dynamic disparity vergence, and other oculomotor parameters can yield insights into the plasticity of short-term adaptation mechanisms.

Vision therapy in adults with convergence insufficiency: clinical and functional magnetic resonance imaging measures.

PURPOSE: This research quantified clinical measurements and functional neural changes associated with vision therapy in subjects with convergence insufficiency (CI). METHODS: Convergence and divergence 4° step responses were compared between 13 control adult subjects with normal binocular vision and four CI adult subjects. All CI subjects participated in 18 h of vision therapy. Clinical parameters quantified throughout the therapy included: nearpoint of convergence, recovery point of convergence, positive fusional vergence at near, near dissociated phoria, and eye movements that were quantified using peak velocity. Neural correlates of the CI subjects were quantified with functional magnetic resonance imaging scans comparing random vs. predictable vergence movements using a block design before and after vision therapy. Images were quantified by measuring the spatial extent of activation and the average correlation within five regions of interests (ROI). The ROIs were the dorsolateral prefrontal cortex, a portion of the frontal lobe, part of the parietal lobe, the cerebellum, and the brain stem. All measurements were repeated 4 months to 1 year post-therapy in three of the CI subjects. RESULTS: Convergence average peak velocities to step stimuli were significantly slower (p = 0.016) in CI subjects compared with controls; however, significant differences in average peak velocities were not observed for divergence step responses (p = 0.30). The investigation of CI subjects participating in vision therapy showed that the nearpoint of convergence, recovery point of convergence, and near dissociated phoria significantly decreased. Furthermore, the positive fusional vergence, average peak velocity from 4° convergence steps, and the amount of functional activity within the frontal areas, cerebellum, and brain stem significantly increased. Several clinical and cortical parameters were significantly correlated. CONCLUSIONS: Convergence peak velocity was significantly slower in CI subjects compared with controls, which may result in asthenopic complaints reported by the CI subjects. Vision therapy was associated with and may have evoked clinical and cortical activity changes.

Adaptation to Progressive Additive Lenses: Potential Factors to Consider.

People develop presbyopia as part of the normal aging process. Most presbyopes adapt to progressive additive lens (PALs), while others do not. This investigation sought to determine whether the ability to modify disparity vergence or phoria was correlated to PALs adaptation. In experiment 1, a double-step paradigm quantified the ability to modify convergence responses in sixteen presbyopes. In experiment 2, thirty-one incipient presbyopes participated in a 5-minute sustained fixation task to evoke phoria adaptation where the magnitude and rate of phoria adaptation were measured. Then, the experiment was repeated after wearing PALs for one month. Linear regression analyses were conducted between the following parameters: near point of convergence, positive fusional vergence at near, vergence facility, net change in the magnitude of phoria adaptation, and the rate of phoria adaptation. The ability to change convergence average peak velocity was significantly greater (p < 0.03) in presbyopic PALs adapters compared to presbyopic PALs non-adapters. The rate of phoria adaptation and vergence facility were significantly greater (p < 0.03) in incipient presbyopic PALs adapters compared to incipient presbyopic PALs non-adapters. Vergence facility and the rate of phoria adaptation may have potential clinical utility in differentiating which patients may adapt to PALs and which ones will have more difficulty.

The influence of age on adaptation of disparity vergence and phoria.

A paucity of research exists to investigate whether the normal aging process influences the ability to adapt disparity vergence and phoria. Vergence eye movements and dissociated phoria were recorded from 49 healthy subjects (ages 20-70years) using an objective eye movement tracking system. Four-degree vergence responses were modified using a double-step protocol. Dynamics of vergence were quantified via peak velocity. The phoria adaptation experiment measured the magnitude (net change in phoria level) and rate (magnitude divided by the time constant) of phoria adaption during 5min of sustained fixation on a binocular target (40cm/8.44° from midline). The magnitude of phoria adaptation decreased as a function of age (r=-0.33; p=0.04). The ability to adapt vergence peak velocity and the rate of phoria adaptation showed no significant age-related influence (p>0.05). The data suggest that the ability to modify the disparity vergence system and the rate of phoria adaptation are not dependent on age; whereas, the magnitude of phoria adaptation decreases as part of the normal adult aging process. These results have clinical and basic science implications because one should consider age when assessing the changes in the magnitude of phoria adaptation which can be abnormal in those with oculomotor dysfunctions.

Larval development of the molecular forms of Anopheles gambiae (Diptera: Culicidae) in different habitats: a transplantation experiment.

We compared the development of the molecular forms of Anopheles gambiae s.s. in different larval habitats. First stage larvae (L1s) of wild-caught females were placed into cages in natural habitats of the M form (rice fields) or the S form (puddles/ quarries). Each cage was covered with cloth, allowing exchange of water, solutes, and small particles, including microorganisms, and was seeded with 100 L1s of a single form (M or S) or by a mixture of 50:50 of M and S forms. Emergence success of both forms in puddles and quarries was three-fold higher than in the rice fields. The emergence rate of the S form was higher than that of the M form in both habitats, but the form x habitat interaction was not significant. In temporary larval sites such as puddles, emergence success of the M form was lower in mixed cages than in single form cages, whereas the reverse was true for the S form, suggesting competition between the forms. The median developmental time was not significantly different between forms. Although these findings demonstrate differences between forms, they do not suggest that their spatial segregation is determined by differences in their exploitation of the physical and chemical conditions in these environments. These results should be regarded with caution because small numbers of first stage larvae could pass through the cloth of the cages.

Use of conventional and real-time polymerase chain reaction for confirmation of Mycobacterium avium subsp. paratuberculosis in a broth-based culture system ESP II.

The ESP II Culture System (ESP II), a broth-based culture system, has been modified and optimized for culturing Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) in animal feces since 2000. Conventional and real-time polymerase chain reaction (PCR) assays based on the IS900 sequence were performed as confirmatory tests for M. paratuberculosis in ESP II liquid culture medium. There were no differences between test results of conventional and real-time PCR assays. During the 5-week incubation period, if acid-fast bacilli (AFB) were detected in ESP culture-positive samples, IS900 PCR assays were performed to confirm whether those AFB were M. paratuberculosis. At the end of the 5-week incubation, AF staining was performed on all ESP II-negative cultures to screen any false-negative cultures; IS900 PCR assays were performed on AFB-positive cultures. During a period of 1 year, of a total of 18,499 ESP II cultures, 2,814 (15.2%) PCR confirmation assays were performed. Of those, 2,259 (80%) were both ESP and PCR positive; 104 (4%) were ESP positive and PCR negative; 423 (15%) were ESP negative and PCR positive; 28 (1%) were both ESP and PCR negative. The AF-staining step after the 5-week incubation produced 423 (15%) more PCR-positive cultures. Of a total of 2,814 AFB-positive cultures, 132 (5%) were not confirmed as M. paratuberculosis. Further studies are needed for speciation of non-M. paratuberculosis isolates.

Lateralized resting-state functional connectivity in the task-positive and task-negative networks.

Studies on functional brain lateralization using functional magnetic resonance imaging (fMRI) have generally focused on lateralization of local brain regions. To explore the lateralization on the whole-brain level, lateralization of functional connectivity using resting-state fMRI (N=87, right handed) was analyzed and left- and right-lateralized networks were mapped. Four hundred two equally spaced regions of interest (ROI) covering the entire gray matter were divided into 358 task-positive and 44 task-negative ROIs. Lateralization of functional connectivity was analyzed separately for the task-positive and task-negative regions to prevent spuriously high lateralization indices caused by negative correlations between task-positive and task-negative regions. Lateralized functional connections were obtained using k-means clustering analysis. Within the task-positive network, the right-lateralized functional connections were between the occipital and inferior/middle frontal regions among other connections, whereas the left-lateralized functional connections were among fusiform gyrus and inferior frontal and inferior/superior parietal regions. Within the task-negative network, the left-lateralized connections were mainly between the precuneus and medial prefrontal regions. Specific brain regions exhibited different left- or right-lateralized connections with other regions, which suggest the importance of reporting lateralized connections over lateralized seed regions. The mean lateralization indices of the left- and right-lateralized connections were correlated, suggesting that the lateralization of connectivity may result from complementary processes between the lateralized networks. The potential functions of the lateralized networks were discussed.

Analysis of saccades and peak velocity to symmetrical convergence stimuli: binocularly normal controls compared to convergence insufficiency patients.

PURPOSE: To assess the potential peak velocity asymmetry between the left-eye and right-eye movement responses stimulated by symmetrical vergence steps in those with normal binocular vision and those with convergence insufficiency (CI) before and after vergence training. This study also evaluated whether vergence training influenced convergence peak velocity and the prevalence of saccades within the first second of the response. METHODS: The peak velocities of the left-eye, right-eye, and combined vergence response evoked from symmetrical 2°, 4°, and 6° convergence step stimuli were assessed in 10 controls and 7 CI subjects. Four of the CI subjects participated in vergence training. An asymmetry ratio was calculated as the peak velocity of the slower eye movement response divided by the peak velocity of the faster eye movement response. RESULTS: Controls were significantly more symmetrical (left-eye peak velocity was approximately equal to right-eye peak velocity) compared to CI subjects (P < 0.001). After vergence training, the CI subjects' left-eye and right-eye movements became significantly more symmetrical, convergence peak velocity increased, and the prevalence of saccades within the first 1 second decreased (P < 0.01). Peak convergence velocity was significantly correlated to the prevalence of saccades observed within the first second of the response (r = 0.8; P < 0.05). CONCLUSIONS: Data suggest that vergence training improves the symmetry between the left-eye and right-eye movements, increases convergence peak velocity, and decreases the prevalence of saccades within the first second of the response, which facilitates binocular coordination in CI patients. Saccades may be a compensatory mechanism used by CI subjects when convergence peak velocity is reduced.

Task vs. rest-different network configurations between the coactivation and the resting-state brain networks.

There is a growing interest in studies of human brain networks using resting-state functional magnetic resonance imaging (fMRI). However, it is unclear whether and how brain networks measured during the resting-state exhibit comparable properties to brain networks during task performance. In the present study, we investigated meta-analytic coactivation patterns among brain regions based upon published neuroimaging studies, and compared the coactivation network configurations with those in the resting-state network. The strength of resting-state functional connectivity between two regions were strongly correlated with the coactivation strength. However, the coactivation network showed greater global efficiency, smaller mean clustering coefficient, and lower modularity compared with the resting-state network, which suggest a more efficient global information transmission and between system integrations during task performing. Hub shifts were also observed within the thalamus and the left inferior temporal cortex. The thalamus and the left inferior temporal cortex exhibited higher and lower degrees, respectively in the coactivation network compared with the resting-state network. These results shed light regarding the reconfiguration of the brain networks between task and resting-state conditions, and highlight the role of the thalamus in change of network configurations in task vs. rest.

Regional homogeneity of resting-state fMRI contributes to both neurovascular and task activation variations.

The task induced blood oxygenation level dependent signal changes observed using functional magnetic resonance imaging (fMRI) are critically dependent on the relationship between neuronal activity and hemodynamic response. Therefore, understanding the nature of neurovascular coupling is important when interpreting fMRI signal changes evoked via task. In this study, we used regional homogeneity (ReHo), a measure of local synchronization of the BOLD time series, to investigate whether the similarities of one voxel with the surrounding voxels are a property of neurovascular coupling. FMRI scans were obtained from fourteen subjects during bilateral finger tapping (FTAP), digit-symbol substitution (DSST) and periodic breath holding (BH) paradigm. A resting-state scan was also obtained for each of the subjects for 4min using identical imaging parameters. Inter-voxel correlation analyses were conducted between the resting-state ReHo, resting-state amplitude of low frequency fluctuations (ALFF), BH responses and task activations within the masks related to task activations. There was a reliable mean voxel-wise spatial correlation between ReHo and other neurovascular variables (BH responses and ALFF). We observed a moderate correlation between ReHo and task activations (FTAP: r=0.32; DSST: r=0.22) within the task positive network and a small yet reliable correlation within the default mode network (DSST: r=-0.08). Subsequently, a linear regression was used to estimate the contribution of ReHo, ALFF and BH responses to the task activated voxels. The unique contribution of ReHo was minimal. The results suggest that regional synchrony of the BOLD activity is a property that can explain the variance of neurovascular coupling and task activations; but its contribution to task activations can be accounted for by other neurovascular factors such as the ALFF.

The influence of the amplitude of low-frequency fluctuations on resting-state functional connectivity.

Studies of brain functional connectivity have provided a better understanding of organization and integration of large-scale brain networks. Functional connectivity using resting-state functional magnetic resonance imaging (fMRI) is typically based upon the correlations of the low-frequency fluctuation of fMRI signals. Reproducible spatial maps in the brain have also been observed using the amplitude of low-frequency fluctuations (ALFF) in resting-state. However, little is known about the influence of the ALFF on the functional connectivity measures. In the present study, we analyzed resting-state fMRI data on 79 healthy old individuals. Spatial independent component analysis and regions of interest (ROIs) based connectivity analysis were performed to obtain measures of functional connectivity. ALFF maps were also calculated. First, voxel-matched inter-subject correlations were computed between back-reconstructed IC and ALFF maps. For all the resting-state networks, there was a consistent correlation between ALFF variability and network strengths (within regions that had high IC strengths). Next, inter-subject variance of correlations across 160 functionally defined ROIs were correlated with the corresponding ALFF variance. The connectivity of several ROIs to other regions were more likely to correlate with its own regional ALFF. These regions were mainly located in the anterior cingulate cortex, medial prefrontal cortex, precuneus, insula, basal ganglia, and thalamus. These associations may suggest a functional significance of functional connectivity modulations. Alternatively, the fluctuation amplitudes may arise from physiological noises, and therefore, need to be controlled when studying resting-state functional connectivity.

Longitudinal validation of a tool for asthma self-monitoring.

OBJECTIVES: To establish longitudinal validation of a new tool, the Asthma Symptom Tracker (AST). AST combines weekly use of the Asthma Control Test with a color-coded graph for visual trending. METHODS: Prospective cohort study of children age 2 to 18 years admitted for asthma. Parents or children (n = 210) completed baseline AST assessments during hospitalization, then over 6 months after discharge. Concurrent with the first 5 AST assessments, the Asthma Control Questionnaire (ACQ) was administered for comparison. RESULTS: Test-retest reliability (intraclass correlation) was moderate, with a small longitudinal variation of AST measurements within subjects during follow-ups. Internal consistency was strong at baseline (Cronbach's α 0.70) and during follow-ups (Cronbach's α 0.82-0.90). Criterion validity demonstrated a significant correlation between AST and ACQ scores at baseline (r = -0.80, P < .01) and during follow-ups (r = -0.64, -0.72, -0.63, and -0.69). The AST was responsive to change over time; an increased ACQ score by 1 point was associated with a decreased AST score by 2.65 points (P < .01) at baseline and 3.11 points (P < .01) during follow-ups. Discriminant validity demonstrated a strong association between decreased AST scores and increased oral corticosteroid use (odds ratio 1.13, 95% confidence interval, 1.10-1.16, P < .01) and increased unscheduled acute asthma visits (odds ratio 1.23, 95% confidence interval, 1.18-1.28, P < .01). CONCLUSIONS: The AST is reliable, valid, and responsive to change over time, and can facilitate ongoing monitoring of asthma control and proactive medical decision-making in children.

The changes in phoria and convergence to divergence peak velocity ratio are correlated.

PURPOSE: Phoria is used in the diagnosis of binocular dysfunctions, such as convergence insufficiency. A common treatment for convergence insufficiency is vision therapy, yet it is controversial whether the phoria changes as a result of rehabilitation. Phoria can vary due to the duration and/or the type of prior visual tasks. The variability potentially observed within phoria measurements leads to difficulties in confidently assessing changes within longitudinal studies. Hence, we propose to measure phoria and vergence peak velocities on separate days to evaluate whether a more robust measurement can be attained. METHODS: Eleven subjects with normal binocular vision participated in two identical experimental sessions. Four-degree convergence and divergence steps stimulated from targets at far, middle, and near initial vergence positions were recorded using a limbus tracking system. Near dissociated phoria was measured after a set of step stimuli. The vergence ratio was defined as the convergence peak velocity divided by the divergence peak velocity. Linear regression analyses calculated the correlation between the phoria and the vergence ratio, and the difference between phoria measurements and vergence ratio measurements, recorded on different days. RESULTS: Near dissociated phoria measurements and vergence ratios were highly correlated for all three initial vergence positions (r > 0.85, p < 0.005). The change in phoria was significantly correlated to the change in vergence ratio (r > 0.94, p = 0.0001). The slope of the linear regression analysis between the phoria and the vergence ratio using individual subject data was repeatable between the sessions (r = 0.99, p < 0.00001) despite large changes in phoria observed in a few individuals. CONCLUSIONS: The change in phoria is significantly correlated to the change in vergence ratio. For longitudinal studies including the efficacy of vision therapies for patients with binocular dysfunctions, we suggest assessing both phoria and vergence velocities to reduce the variability potentially observed from different days.

The frequency of horizontal saccades in near and far symmetrical disparity vergence.

In a natural environment, saccade and vergence eye movements shift gaze in different directions and distances. In a laboratory setting, targets can be positioned precisely to elicit symmetrical vergence movements; however, saccades occur during the vergence movement even though the stimulus should not stimulate a saccadic response. These saccades may facilitate the response when the kinematics of the vergence component are modest as indicated by reduced velocities. Hence, the purpose of this study is to assess whether the frequency of saccades within vergence responses are correlated with vergence peak velocity. Ten subjects with normal binocular vision participated in this study. Eye movements were quantified using a limbus tracking system. Stimuli included 4° symmetrical convergence and divergence steps with an initial vergence angle at far (2° and 6°, respectively) and near (12° and 16°, respectively) which are known to evoke different vergence peak velocities. A saccade detecting algorithm was utilized to compute the percentage of saccades present within all vergence responses. A repeated measures ANOVA confirmed with a post hoc Bonferroni test demonstrated that convergence steps at near were slower than convergence steps at far, whereas divergence steps at far were slower than divergence steps at near in all subjects (p<0.02). When the vergence peak velocity was slow, a greater number of saccades was observed. The average vergence peak velocities were inversely correlated to the number of saccades observed within the transient portion defined as after the latency to 400 ms of the movement (r=-0.41; p=0.008), between 400 ms and 1s of the response (r=-0.35; p=0.03) and within the steady-state period occurring between 1s and 3s of the response (r=-0.44; p=0.005). Peak velocity of vergence is dependent on the stimulus initial vergence angle. An increased prevalence of saccades was observed in vergence responses with reduced peak velocity, compared to responses with greater peak velocity. Prior research supports that saccades increase the peak velocity of vergence during combined vergence and saccadic tasks. This may in part explain the increased presence of saccades within vergence responses with reduced peak velocities. The recruitment of saccades may be utilized because of the longer period of diplopia resulting from slower vergence movements.

Development of a novel tool for engaging children and parents in asthma self-management.

This paper describes the development and evaluation of an innovative application designed to engage children and their parents in weekly asthma self-monitoring and self-management to prompt an early response to deteriorations in chronic asthma control, and to provide their physicians with longitudinal data to assess the effectiveness of asthma therapy and prompt adjustments. The evaluation included 2 iterative usability testing cycles with 6 children with asthma and 2 parents of children with asthma to assess user performance and satisfaction with the application. Several usability problems were identified and changes were made to ensure acceptability of the application and relevance of the content. This novel application is unique compared to existing asthma tools and may shift asthma care from the current reactive, acute care model to a preventive, proactive patient-centered approach where treatment decisions are tailored to patients' individual patterns of chronic asthma control to prevent acute exacerbations.

VisualEyes: a modular software system for oculomotor experimentation.

Eye movement studies have provided a strong foundation forming an understanding of how the brain acquires visual information in both the normal and dysfunctional brain.(1) However, development of a platform to stimulate and store eye movements can require substantial programming, time and costs. Many systems do not offer the flexibility to program numerous stimuli for a variety of experimental needs. However, the VisualEyes System has a flexible architecture, allowing the operator to choose any background and foreground stimulus, program one or two screens for tandem or opposing eye movements and stimulate the left and right eye independently. This system can significantly reduce the programming development time needed to conduct an oculomotor study. The VisualEyes System will be discussed in three parts: 1) the oculomotor recording device to acquire eye movement responses, 2) the VisualEyes software written in LabView, to generate an array of stimuli and store responses as text files and 3) offline data analysis. Eye movements can be recorded by several types of instrumentation such as: a limbus tracking system, a sclera search coil, or a video image system. Typical eye movement stimuli such as saccadic steps, vergent ramps and vergent steps with the corresponding responses will be shown. In this video report, we demonstrate the flexibility of a system to create numerous visual stimuli and record eye movements that can be utilized by basic scientists and clinicians to study healthy as well as clinical populations.

Sustained fixation induced changes in phoria and convergence peak velocity.

PURPOSE: This study sought to investigate the influence of phoria adaptation on convergence peak velocity from responses located at different initial vergence positions. METHODS: Symmetrical 4° convergence step responses and near dissociated phoria (measured at 40 cm from the subject's midline) were recorded from six subjects with normal binocular vision using an infrared limbus tracking system with a haploscope. Two different sustained fixations (1° and 16° convergent rotation along the subject's midline) were used to study whether phoria had an influence on the peak velocity of convergence responses located at two initial vergence positions (1° or 'far' steps and 12° or 'near' steps). RESULTS: Phoria was significantly adapted after a sustained fixation task at near (16°) and far (1°) (p<0.002). A repeated measures ANOVA showed that convergence far steps were significantly faster than the near steps (p<0.03). When comparing convergence steps with the same initial vergence position, steps measured after near phoria adaptation were faster than responses after far adaptation (p<0.02). A regression analysis demonstrated that the change in phoria and the change in convergence peak velocity were significantly correlated for the far convergence steps (r = 0.97, p = 0.001). A weaker correlation was observed for the near convergence steps (r = 0.59, p = 0.20). CONCLUSION: As a result of sustained fixation, phoria was adapted and the peak velocity of the near and far convergence steps was modified. This study has clinical considerations since prisms, which evoke phoria adaptation, can be prescribed to help alleviate visual discomfort. Future investigations should include a systematic study of how prisms may influence convergence and divergence eye movements for those prescribed with prisms within their spectacles.

The relationship between phoria and the ratio of convergence peak velocity to divergence peak velocity.

PURPOSE: The purpose of this study was to investigate the relationship between phoria and the dynamics of vergence eye movements as described by the ratio of convergence average peak velocity to divergence average peak velocity, termed the vergence peak velocity ratio. METHODS: Phoria and vergence step responses were recorded. Three measures of phoria were assessed: baseline phoria, which is the initial phoria measurement; adapted phoria, which is the phoria measured after a visual task; and change in phoria, which is defined as adapted phoria minus baseline phoria. Phoria was modified in two experiments: vergence steps located at different initial positions and different sustained convergent fixations. Four linear regression analyses were conducted to study the interactions among baseline phoria and vergence peak velocity ratio, adapted phoria and vergence peak velocity ratio, baseline and adapted phoria, and baseline phoria and change in phoria. RESULTS: Baseline and adapted phoria were significantly correlated to vergence peak velocity ratio. Adapted phoria and baseline phoria were also significantly correlated. The change in phoria induced by the vergence steps or a sustained fixation task was independent of the baseline phoria. CONCLUSIONS: These data support that phoria is a factor in the asymmetry between peak velocity of convergence and divergence and that baseline phoria level is not a factor in the amount of change observed in phoria level (adapted phoria minus baseline phoria). Future oculomotor models of vergence should incorporate phoria within the design.