Neural Mechanism of Vision Therapy for Patients With Convergence Insufficiency

Study Overview
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Brief Summary
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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. CI is present in 4% of the population where approximately 27% of CI patients do not improve even with validated therapy. The project will quantitatively study changes in convergence eye movements and neural substrates before and after validated therapy in CI patients. This knowledge can lead to improvements in currently validated therapy, reduction in therapy sessions, and reduced healthcare costs.

Detailed Description
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Convergence insufficiency (CI), a prevalent binocular vision disorder in adults and children, is characterized by greater exophoria at near than at distance, reduced fusional convergence amplitude, receded near point of convergence, and a reduced accommodative convergence over accommodation ratio (AC/A). CI is associated with symptoms that include double/blurred vision, eyestrain, and headaches when engaged in reading or other near work, thus interfering with activities of daily living. The recent NEI/NIH multi-center randomized clinical trial, the Convergence Insufficiency Treatment Trial (CITT), demonstrated the effectiveness of Office-Based Vergence and Accommodative Therapy with home reinforcement (OBVAT) for CI, reporting 73% of patients have sustained improvements of vision function and symptoms. The team published the first fMRI neural substrate data evoked using convergence eye movements in CI patients before and then post-OBVAT. The team's results suggest that with the reduction of visual symptoms, the following were observed: 1) an increase in the percent signal change of functional activity in the frontal eye fields, posterior parietal cortex and the cerebellar vermis, 2) an increase in convergence peak velocity, 3) a decrease in the near point of convergence, 4) an increase in positive fusional amplitude and 5) a reduction in the amount of exophoria at near. The aims of the current proposal are to test the following two hypotheses as potential underlying mechanisms of CI that may be improved post OBVAT: 1) a reduced ability to adapt vergence in near and far space via the 'slow' component of vergence and 2) a reduced ability to quickly diminish disparity error via the 'fast' component of vergence. Not only will our quantitative methods integrated with established CITT standards address important questions about potential mechanisms causing CI, this proposal seeks to identify how a validated vergence therapy may remediate symptoms. This proposal will determine whether either of these two potential mechanisms are causing CI by quantifying the following: 1) rate and magnitude of phoria adaptation, 2) forced vergence fixation disparity curves, 3) peak velocity of convergence eye movements (studying visual cues such as disparity, accommodation and proximal stimuli in isolation and combination), and 4) the functional activity of the fast and slow vergence neural substrates prior to, and then after, OBVAT. The assembled study team is particularly knowledgeable in terms of OBVAT, convergence insufficiency, optometry, vision science, oculomotor research, functional imaging, modeling and statistics with the necessary resources to successfully complete both aims of this study. Results from the project's aims can lead to targeted treatments with improved success rates, potentially reducing the time to remediate symptoms, and ultimately reducing health care costs.

Official Title
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Functional Neural Mechanism of Vision Therapy for Patients With Convergence Insufficiency

Conditions
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Convergence Insufficiency

Intervention / Treatment
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* Behavioral: Office Based Vergence and Accommodative Therapy


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: diagnosis of symptomatic convergence insufficiency binocularly normal control Exclusion Criteria: history of head trauma any systematic disease that can interfere with vergence or accommodation such as multiple sclerosis

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 35 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: CI OBVAT<br>Patients with Convergence Insufficiency in Active Vision Therapy | Behavioral: Office Based Vergence and Accommodative Therapy<br>* Exercises that will stimulate disparity vergence or accommodation independently and then combined will be used.<br>|
| Sham Comparator: CI Sham therapy<br>CI Sham therapy | Behavioral: Office Based Vergence and Accommodative Therapy<br>* Exercises that will stimulate disparity vergence or accommodation independently and then combined will be used.<br>|
| Active Comparator: Controls OBVAT<br>Control receive active therapy | Behavioral: Office Based Vergence and Accommodative Therapy<br>* Exercises that will stimulate disparity vergence or accommodation independently and then combined will be used.<br>|
| Sham Comparator: Controls Sham<br>Subjects with Normal Binocular Vision will receive a therapy that appears to be therapeutic but does not have any binocular coordination benefits. | Behavioral: Office Based Vergence and Accommodative Therapy<br>* Exercises that will stimulate disparity vergence or accommodation independently and then combined will be used.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Disparity Vergence Response Amplitude | how accurate a patient can fixate on a new target | through study completion, an average of 1 year |