Assessment of Cortical Dysfunction in Patients with Intermittent Exotropia: An fMRI Study

<div><p>Neural imaging studies have found the connection between strabismus and brain cortex. However, the pathological mechanisms of intermittent exotropia are still not fully understood. In the present study, changes of binocular fusion related cortices in intermittent exotropia were investigated with blood oxygen level dependent functional magnetic resonance imaging. Activated cortices induced by fusion stimulus were found to be distributed in several regions such as bilateral middle occipital gyrus, bilateral middle temporal gyrus, left superior parietal lobule and so on. Compared with normal subjects, the increased activation intensity was observed in bilateral superior parietal lobule and inferior parietal lobule in subjects with intermittent exotropia. These findings indicate that binocular fusion involves a complicated brain network including several regions. And cortical activities of bilateral superior parietal lobule and inferior parietal lobule compensate for the binocular fusion dysfunction in intermittent exotropia.</p></div

Brain activitation in normal subjects with the binocular fusion stimulus.

<p>Brain activitation in normal subjects with the binocular fusion stimulus.</p

Increased brain activitation in intermittent exotropia subjects compared with controls under the condition of binocular fusion stimulus.

<p>Increased brain activitation in intermittent exotropia subjects compared with controls under the condition of binocular fusion stimulus.</p

Brain activities images of normal subjects with the binocular fusion stimulus.

<p>(A) Glass brain shows activated areas. (B) Activation areas are showed in sagittal, coronal and horizon planes. The yellow, pink, blue, red, green and white arrows point to the posterior cingulated gyrus, precuneus, postcentral gyrus, superior frontal gyrus, middle temporal gyrus and middle occipital gyrus, respectively.</p

Statistical maps of group comparison of mean diffusion (MD) value on a voxelwise basis.

<p>The group’s mean FA skeleton (green) was overlaid on the Montreal Neurological Institute template. Sea level immigrants show significantly lower MD value than high altitude residents (p<0.001, corrected).</p

White matter volume changes in sea level immigrants versus high altitude residents.

<p>Sections (sagittal, coronal, and axial view) depicting regions showing decreased white matter in the right superior frontal gyrus (p<0.001, uncorrected).</p

Brain activities images of intermittent exotropia subjects with the binocular fusion stimulus.

<p>(A) Glass brain shows activated areas. (B) Activation areas are showed in sagittal, coronal and horizon planes. The red and green arrows point to the middle occipital gyrus and fusiform gyrus, respectively.</p

Brain images of increased activation in intermittent exotropia subjects compared with controls.

<p>(A) Glass brain shows activated areas. (B) Activation areas are showed in sagittal, coronal and horizon planes. The red and green arrows point to the superior parietal lobule and inferior parietal lobule, respectively.</p

Correlations of gray matter volume with diastolic pressure and vital capacity.

<p>(A) In both sea level immigrants and high altitude residents, gray matter volume in the cerebellum lobule 8 correlated with diastolic pressure. (B) In sea level male immigrants, gray matter volume in the insula correlated with vital capacity. (C) In sea level immigrants, gray matter volume in the insula correlated with the change of tide volume (ΔT)/the change of SaO2 (ΔSaO2) ratio.</p

Regional information of changed gray and white matter volume.

<p>Regional information of changed gray and white matter volume.</p