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Tara L. Alvarez - One of the best experts on this subject based on the ideXlab platform.
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functional activity within the frontal eye fields posterior parietal cortex and cerebellar vermis significantly correlates to symmetrical vergence Peak Velocity an roi based fmri study of vergence training
Frontiers in Integrative Neuroscience, 2014Co-Authors: Tara L. Alvarez, Raj S Jaswal, Suril Gohel, Bharat B BiswalAbstract:Convergence insufficiency (CI) is a prevalent binocular vision disorder with symptoms that include double/blurred vision, eyestrain, and headaches when engaged in reading or other near work. Randomized clinical trials support that Office-Based Vergence and Accommodative Therapy with home reinforcement leads to a sustained reduction in patient symptoms. However, the underlying neurophysiological basis for treatment is unknown. Functional activity and vergence eye movements were quantified from seven binocularly normal controls (BNC) and four CI patients before and after 18 hours of vergence training. An fMRI conventional block design of sustained fixation versus vergence eye movements stimulated activity in the frontal eye fields (FEF), the posterior parietal cortex (PPC) and the cerebellar vermis (CV). Comparing the CI patients’ baseline measurements to the post vergence training data sets with a paired t-test revealed the following: 1) the percent change in the BOLD signal in the FEF, PPC and CV significantly increased (p<0.02), 2) the Peak Velocity from 4° symmetrical convergence step responses increased (p<0.01) and 3) patient symptoms assessed using the CI Symptom Survey (CISS) improved (p<0.05). CI patient measurements after vergence training were more similar to levels observed within BNC. A regression analysis revealed the Peak Velocity from BNC and CI subjects before and after vergence training was significantly correlated to the percent BOLD signal change within the FEF, PPC and CV (r=0.6;p<0.05). Results have clinical implications for understanding the behavioral and neurophysiological changes after vergence training in patients with CI, which may lead to the sustained reduction in visual symptoms.
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Analysis of Saccades and Peak Velocity to Symmetrical Convergence Stimuli: Binocularly Normal Controls Compared to Convergence Insufficiency Patients
Investigative ophthalmology & visual science, 2013Co-Authors: Tara L. Alvarez, Eun H. KimAbstract: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.
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Sustained Fixation Induced Changes in Phoria and Convergence Peak Velocity
PloS one, 2011Co-Authors: Eun H. Kim, Vincent R. Vicci, Sang J. Han, Tara L. AlvarezAbstract: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
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EMBC - The frequency of saccades correlates to Peak Velocity in symmetrical disparity vergence
Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Inte, 2011Co-Authors: Eun H. Kim, Tara L. AlvarezAbstract:A pure vergence stimulus requires the two eyes to turn equally inward or outward theoretically resulting in a pure symmetrical vergence response. However, saccades, a rapid conjugate eye movement, are frequently observed in vergence responses. This investigation sought to systematically quantify whether the occurrence of saccades within symmetrical vergence responses is correlated to vergence Peak Velocity. Eye movements are quantified using a limbus tracking system from three subjects. Symmetrical convergence and divergence 4° step responses with an initial position located at far or near which are known to evoke different Peak velocities are analyzed. Data are quantified via Peak Velocity. A saccade detecting algorithm is utilized to quantify the frequency of saccades in the transient portion (first second) of vergence responses. Near convergence responses are slower than far convergence and far divergence responses are slower compared to near divergence movements. The occurrence of saccades is negatively correlated to vergence Peak Velocity. When the Velocity is slower, the number of saccades increases. This study suggests that the brain may initiate a saccade to facilitate a slow vergence movement, potentially to allow object recognition before binocular fusion.
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The relationship between phoria and the ratio of convergence Peak Velocity to divergence Peak Velocity.
Investigative ophthalmology & visual science, 2010Co-Authors: Eun H. Kim, Bérangère Granger-donetti, Vincent R. Vicci, Tara L. AlvarezAbstract: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.
Eun H. Kim - One of the best experts on this subject based on the ideXlab platform.
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Analysis of Saccades and Peak Velocity to Symmetrical Convergence Stimuli: Binocularly Normal Controls Compared to Convergence Insufficiency Patients
Investigative ophthalmology & visual science, 2013Co-Authors: Tara L. Alvarez, Eun H. KimAbstract: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.
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Sustained Fixation Induced Changes in Phoria and Convergence Peak Velocity
PloS one, 2011Co-Authors: Eun H. Kim, Vincent R. Vicci, Sang J. Han, Tara L. AlvarezAbstract: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
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EMBC - The frequency of saccades correlates to Peak Velocity in symmetrical disparity vergence
Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Inte, 2011Co-Authors: Eun H. Kim, Tara L. AlvarezAbstract:A pure vergence stimulus requires the two eyes to turn equally inward or outward theoretically resulting in a pure symmetrical vergence response. However, saccades, a rapid conjugate eye movement, are frequently observed in vergence responses. This investigation sought to systematically quantify whether the occurrence of saccades within symmetrical vergence responses is correlated to vergence Peak Velocity. Eye movements are quantified using a limbus tracking system from three subjects. Symmetrical convergence and divergence 4° step responses with an initial position located at far or near which are known to evoke different Peak velocities are analyzed. Data are quantified via Peak Velocity. A saccade detecting algorithm is utilized to quantify the frequency of saccades in the transient portion (first second) of vergence responses. Near convergence responses are slower than far convergence and far divergence responses are slower compared to near divergence movements. The occurrence of saccades is negatively correlated to vergence Peak Velocity. When the Velocity is slower, the number of saccades increases. This study suggests that the brain may initiate a saccade to facilitate a slow vergence movement, potentially to allow object recognition before binocular fusion.
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The relationship between phoria and the ratio of convergence Peak Velocity to divergence Peak Velocity.
Investigative ophthalmology & visual science, 2010Co-Authors: Eun H. Kim, Bérangère Granger-donetti, Vincent R. Vicci, Tara L. AlvarezAbstract: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.
G R Sutherland - One of the best experts on this subject based on the ideXlab platform.
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Age-related transmural Peak mean velocities and Peak Velocity gradients by Doppler myocardial imaging in normal subjects
European heart journal, 1996Co-Authors: Przemysław Palka, Aleksandra Lange, Alan D Fleming, L N Fenn, K P Bouki, T R D Shaw, Keith A A Fox, W N Mcdicken, G R SutherlandAbstract:Doppler myocardial imaging is a new cardiac ultrasound technique based on the principles of colour Doppler imaging which can determine myocardial velocities by detecting the changes of phase-shift of the ultrasound signal returning directly from the myocardium. To determine the normal range of transmural velocities in healthy hearts a prospective study was carried out involving 42 normal subjects (age from 21 to 78, mean 47±16 years). Using M-mode Doppler myocardial imaging the Peak values of the mean Velocity and Velocity gradient across the left ventricular posterior wall were measured during standardized phases of the cardiac cycle. Peak mean velocities had the following values during the cardiac cycle: isovolumic contraction −1·3±1·2cm. s−1, early ventricular ejection 4·2±1·2cm. s−1, late ventricular ejection 1·8±1·1cm. s−1, isovolumic relaxation −2·0±0·8cm .s−1, rapid ventricular filling −6·6±2·2cm. s−1, atrial contraction −2·8±1·8cm. s−1, atrial relaxation 1·2±1·1cm. s−1. Peak Velocity gradients were: isovolumic contraction 1·3±1·9 s−1, early ventricular contraction 4·7±1·9s−1, late ventricular contraction 1·1 ±1·0 s−1, isovolumic relaxation −0·6±0·5 s−1, rapid ventricular filling 6·1±3·4 s−1, atrial contraction 2·6±1·7 s−1, atrial relaxation 0·0±0·3 s−1. Linear regression analysis showed that with the increase of age, Peak Velocity gradient decreases during rapid ventricular filling (r=0·83; P
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age related transmural Peak mean velocities and Peak Velocity gradients by doppler myocardial imaging in normal subjects
European Heart Journal, 1996Co-Authors: Przemyslaw Palka, Aleksandra Lange, Alan D Fleming, L N Fenn, K P Bouki, T R D Shaw, Keith A A Fox, W N Mcdicken, G R SutherlandAbstract:Doppler myocardial imaging is a new cardiac ultrasound technique based on the principles of colour Doppler imaging which can determine myocardial velocities by detecting the changes of phase-shift of the ultrasound signal returning directly from the myocardium. To determine the normal range of transmural velocities in healthy hearts a prospective study was carried out involving 42 normal subjects (age from 21 to 78, mean 47±16 years). Using M-mode Doppler myocardial imaging the Peak values of the mean Velocity and Velocity gradient across the left ventricular posterior wall were measured during standardized phases of the cardiac cycle. Peak mean velocities had the following values during the cardiac cycle: isovolumic contraction −1·3±1·2cm. s−1, early ventricular ejection 4·2±1·2cm. s−1, late ventricular ejection 1·8±1·1cm. s−1, isovolumic relaxation −2·0±0·8cm .s−1, rapid ventricular filling −6·6±2·2cm. s−1, atrial contraction −2·8±1·8cm. s−1, atrial relaxation 1·2±1·1cm. s−1. Peak Velocity gradients were: isovolumic contraction 1·3±1·9 s−1, early ventricular contraction 4·7±1·9s−1, late ventricular contraction 1·1 ±1·0 s−1, isovolumic relaxation −0·6±0·5 s−1, rapid ventricular filling 6·1±3·4 s−1, atrial contraction 2·6±1·7 s−1, atrial relaxation 0·0±0·3 s−1. Linear regression analysis showed that with the increase of age, Peak Velocity gradient decreases during rapid ventricular filling (r=0·83; P <0·0001) and increases during atrial contraction (r=0·86; P <0·0001) while Peak mean Velocity increases only during atrial contraction (r=0·80, P <0·0001). Thus, there was no correlation between increasing age and systolic Peak mean Velocity and Peak Velocity gradient but both diastolic filling phases rapid ventricular filling and atrial contraction demonstrated age-related changes. In summary, this study has determined the age-related range of normal transmural myocardial velocities within the left ventricular posterior wall in healthy hearts during the cardiac cycle. We conclude that these measurements of Peak mean velocities and Peak Velocity gradients, should form the baseline for subsequent Doppler myocardial imaging clinical studies on myocardial diseases processes.
James C. Carr - One of the best experts on this subject based on the ideXlab platform.
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Interval changes in aortic Peak Velocity and wall shear stress in patients with bicuspid aortic valve disease.
The international journal of cardiovascular imaging, 2019Co-Authors: Ozair Rahman, Michael Scott, Emilie Bollache, Kenichiro Suwa, Jeremy D. Collins, James C. Carr, Paul W.m. Fedak, Patrick M. Mccarthy, S. Chris Malaisrie, Alex J. BarkerAbstract:Bicuspid aortic valve (BAV) is associated with abnormal valve-mediated hemodynamics including high Velocity jets and elevated wall shear stress (WSS). This study investigated interval changes in flow and WSS in a multi-year follow-up study. This cross-sectional study included n = 44 patients with BAV (age = 44.9 ± 12 years), n = 17 patients with tricuspid aortic valve and thoracic aortic dilatation (TAV with dilation, age = 54.6 ± 16.5 years), and n = 9 healthy controls (age = 49.3 ± 14.7 years) underwent baseline and serial aortic 4D flow MRI (follow-up duration: BAV: 2.6 ± 0.7 years, TAV with dilation: 2.7 ± 0.5 years, controls: 1.1 ± 0.5 years). Data analysis included quantification of aortic dimensions, Peak systolic velocities, as well as regional 3D WSS in the ascending aorta. At baseline, BAV patients demonstrated uniformly elevated Peak Velocity and WSS compared to TAV with dilation and control groups (Peak Velocity 2.2 m/s vs. 1.6 m/s vs. 1.5 m/s, p < 0.004; WSS: 0.74 Pa vs. 0.45 Pa vs. 0.55 Pa, p < 0.001). For BAV, Peak Velocity increased from baseline to follow up (2.2 ± 0.8 to 2.3 ± 0.9 m/s, p < 0.001) while WSS decreased (0.74 ± 0.22 to 0.65 ± 0.21 Pa, p < 0.001). Aortic growth was minimal for both BAV (0.05 cm/year) and TAV with dilation (0.03–0.04 cm/year) patients. For BAV patients, increase of ascending aorta Peak velocities indicated worsening of valve function at follow-up. Compared to TAV with dilation patients, BAV patients demonstrated a reduction in WSS which may indicate a compensatory mechanism to reduce elevated WSS forces by aortic remodeling.
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Inline Directionally Independent Peak Velocity Evaluation Reduces Error in Peak Antegrade Velocity Estimation in Patients Referred for Cardiac Valvular Assessment
AJR. American journal of roentgenology, 2012Co-Authors: Philip A. Hodnett, Jeremy D. Collins, Christopher Glielmi, Amir H. Davarpanah, Timothy G. Scanlon, Emily Ward, Peter Weale, James C. CarrAbstract:OBJECTIVE. The purpose of this article is to evaluate the utility of a tool in quantifying the Peak antegrade Velocity when assessing patients with cardiac valvular pathology. MATERIALS AND METHODS. Directionally independent Peak Velocity evaluation (MaxVelocity, Siemens Healthcare) phase-contrast cardiac MRI was performed for 44 patients referred to our institution with a diagnosis or concern for aortic valvular disease or undergoing imaging for thoracic aortic aneurysm. In addition, standard through-plane phase-contrast MR angiography at the level of the aortic valve was performed. The MaxVelocity technique provides a simple tool to extract the magnitude of the Peak Velocity, independently of its direction, from phase-contrast imaging with Velocity encoding. Recent echocardiography (within 1 month) and assessment of Peak forward Velocity at the level of the aortic valve were required for inclusion in the study. RESULTS. The MaxVelocity technique shows significantly lower error in estimating Peak antegra...
Angel R. Leon - One of the best experts on this subject based on the ideXlab platform.
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Usefulness of the Peak Velocity difference by tissue Doppler imaging technique as an effective predictor of response to cardiac resynchronization therapy
The American journal of cardiology, 2004Co-Authors: Dean Notabartolo, John D. Merlino, Andrew L. Smith, David B. Delurgio, Fernando V. Vera, Kirk A. Easley, Randolph P. Martin, Angel R. LeonAbstract:Cardiac resynchronization therapy (CRT) improves symptoms and functional status in heart failure patients; however, current selection criteria need improvement. A novel tissue Doppler imaging parameter, the Peak Velocity difference (PVD), defined as the greatest difference in time to Peak Velocity between any of 6 left ventricular regions, may better select responders to CRT. Subjects were divided into 2 groups based on the PVD. Clinical and echocardiographic parameters significantly improved in subjects with dyssynchrony by the baseline PVD and had a better overall response to CRT.
