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Tara Alvarez, Rajbir Jaswal, Suril Gohel, Bharat B Biswal; Functional Activity Significantly Correlates to Symmetrical Vergence Peak Velocity: An fMRI study of Vision Therapy. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2661.
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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. 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 vision therapy. 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). Peak velocity was computed for 4 degree convergence step responses.
Comparing the CI patient’s baseline to the after vision therapy data sets with a paired t-test revealed the following: 1) the percent BOLD signal change significantly increased within the CV (p<0.05), FEF (p<0.01) and PPC (p<0.01), 2) the peak velocity from 4° symmetrical vergence 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 vision therapy were more similar to those observed within BNC. A regression analysis revealed the peak velocity from BNC and CI patients before and after vision therapy was significantly correlated to the percent BOLD signal change within the FEF (r=0.5;p<0.05), PPC (r=0.7;p<0.01); and CV (r=0.6;p<0.01).
Results have clinical implications for understanding the behavioral and neurophysiological changes after vision therapy in patients with CI, which may lead to the sustained reduction in symptoms.
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