PMC4766290_01
PMC4766290_02
(A) Visual field assessment of CVI patient obtained by Humphrey automated visual perimetry (see text for test details). A bilateral field defect involving the inferior visual fields (with a more dense defect involving the left side) in each eye evident on the gray scale plot (top panel) and confirmed on the pattern deviation plot (bottom panel). (B) Axial T1-weighted MRI images (MP-RAGE pulse sequence) in a normally sighted control (top panel) and CVI patient (lower panel). Enlarged lateral ventricles with irregular posterior borders are apparent in the CVI patient (black arrow). (C) Corresponding white matter tractography of the optic radiations (sagittal view) revealed with HARDI in the same individuals. Note in the control subject, the complete arborization of the superior and inferior banks of the optic radiations extending from the thalamus to the occipital cortex in both hemispheres (open arrows). In contrast, the CVI patient shows markedly fewer projections and in particular, along the superior bank of the optic radiations (white arrows). The paucity of connections along the superior bank along with a greater deficit of connections in the right (R) compared to the left (L) hemisphere correspond to the location of the visual field deficit of the CVI patient characterized by automated perimetry.
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F1
Automated perimetry using the Humphrey Field Analyzer revealed a stable, bilateral visual field defect involving the inferior visual fields (Figure 1A). Standard T1-weighted MRI imaging of the CVI patient revealed markedly enlarged ventricles characteristic of PVL as compared to the age/gender matched control (Figure 1B). Figure 1C).
Activation of early retinotopic areas using fMRI. (A) Cortical flattening of an occipital cortical patch from the right hemisphere of a normally sighted control. For reference, colored dashed lines are in the same position in both the inflated and flattened views (orange, calcarine sulcus; red, lateral occipital; green, medial, dorsal occipital; and blue, medial ventral occipital). The boundaries of early visual areas (V1-V3) are shown and separated in dorsal (d) and ventral (v) parts. (B) Occipital patch projections showing cortical activation in the control (upper panel) and CVI patient (lower panel) in response to visual stimulation using meridians as well as upper and lower wedges (blue and yellow colors correspond to location of activation in response to visual stimulation). Overall, the organization of early visual areas appears largely intact in the CVI patient. However, selectivity for stimulation within the lower visual field was reduced compared to the sighted control (note the left hemisphere is flipped for easier visual comparison). (C) Comparison of relative activation in V1 between the CVI patient and the control subject for the cortical representation of each visual field quadrant (expressed as a percentage) confirms that the largest impairment in activation was in dorsal V1 (V1d) and in the right hemisphere (RH) corresponding the left inferior visual field deficit obtained on perimetry.
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F2
In order to permit visualization of multiple visual cortical areas, each cortical hemisphere was computationally inflated to reveal buried sulcal regions and an occipital lobe "flat patch" was created for each subject hemisphere by making cuts in the vertex mesh (along the calcarine sulcus and the anterior extent of the occipital lobe) and unfurling this mesh into a 2D representation (see Figure 2A for further details). Functional MRI assessments resulting from the stimulation of horizontal and vertical visual field meridians were used to reveal the boundaries between visual cortical areas and the boundaries of early visual areas (i.e., V1-V3, see Figure 2A). These areas were robustly identified in each hemisphere in both the CVI and control participants suggesting that the overall organization of early visual areas is largely intact in the CVI patient despite the maldevelopment of geniculo-striate projections (compare upper and lower panels of Figure 2B). Specifically, activation within primary visual cortical representations of the lower visual field (V1d) in the right and left hemisphere of the CVI patient exhibited respectively only 21.5 and 22.2% of the activation observed in the same lower visual field representations in the control participant (Figure 2C).