While functional magnetic resonance imaging (fMRI) has identified which regions of interests (ROIs) are functionally active during a vergence movement (inward or outward eye rotation), task-modulated coactivation between ROIs is less understood. This study tested the following hypotheses: (1) significant task-modulated coactivation would be observed between the frontal eye fields (FEFs), the posterior parietal cortex (PPC), and the cerebellar vermis (CV); (2) significantly more functional activity and task-modulated coactivation would be observed in binocularly normal controls (BNCs) compared with convergence insufficiency (CI) subjects; and (3) after vergence training, the functional activity and task-modulated coactivation would increase in CIs compared with their baseline measurements. A block design of sustained fixation versus vergence eye movements stimulated activity in the FEFs, PPC, and CV. fMRI data from four CI subjects before and after vergence training were compared with seven BNCs. Functional activity was assessed using the blood oxygenation level dependent (BOLD) percent signal change. Task-modulated coactivation was assessed using an ROI-based taskmodulated coactivation analysis that revealed significant correlation between the FEF, PPC, and CV ROIs. Prior to vergence training, the CIs had a reduced BOLD percent signal change compared with BNCs for the CV ( p < 0.05), FEFs, and PPC ( p < 0.01). The BOLD percent signal change increased within the CV, FEF, and PPC ROIs ( p < 0.001) as did the task-modulated coactivation between the FEFs and CV as well as the PPC and CV ( p < 0.05) when comparing the CI pre-and post-training datasets. Results from the Convergence Insufficiency Symptom Survey were correlated to the percent BOLD signal change from the FEFs and CV ( p < 0.05).

This study sought to investigate whether stimulation to the fovea or the parafovea with different color combinations influenced the temporal and dynamic features of 4° disparity vergence step responses. Twelve unique types of stimuli were displayed within a haploscope presented along the participant’s midsagittal plane. Vergence eye movement responses from fifteen naive participants were recorded using video-based infrared eye tracking instrumentation. Latency and peak velocity from left and right eye movement responses were quantified. Results show that the type of stimulus projection (foveal versus parafoveal) significantly (p<0.001) influences the vergence response latency but did not impact peak velocity. Vergence responses to eccentric circles with 6° eccentricity targeting the parafovea resulted in a significantly faster response latency compared to vergence responses to a cross with 2° eccentricity stimuli targeting the fovea. Results have implications for the stimulus design of a variety of applications from virtual reality to vision therapy interventions.

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Convergence insufficiency (CI) is a prominent vergence dysfunction. The purpose of this study is to investigate the underlying components of vergence responses in CI patients. Two, four and six degree convergent steps at two different initial positions and four degree divergent step stimuli were presented to three CI subjects. The goal was to use an independent component analysis (ICA) algorithm to dissect the vergence responses into two components (the transient and sustained) for comparison. Preliminary data show that the transient component of the vergence system is modified after six weeks of optometric vision training. Data suggest that neuroplasticity is evoked via optometric vision training implying training modifies a portion of the brain responsible for generating the transient component signals.

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