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. 2005 Jun;25(2):222-36.
doi: 10.1002/hbm.20109.

Voxel-based analysis of MRI detects abnormal visual cortex in children and adults with amblyopia

Janine D Mendola  1 , Ian P Conner, Anjali Roy, Suk-Tak Chan, Terry L Schwartz, J Vernon Odom, Kenneth K Kwong
Affiliations

Voxel-based analysis of MRI detects abnormal visual cortex in children and adults with amblyopia

Janine D Mendola et al. Hum Brain Mapp. 2005 Jun.

Abstract

Amblyopia, sometimes called "lazy eye," is a relatively common developmental visual disorder well characterized behaviorally; however, the neural substrates associated with amblyopia in humans remain unclear. We hypothesized that abnormalities in the cerebral cortex of subjects with amblyopia exist, possibly as a result of experience-dependent neuronal plasticity. Anatomic magnetic resonance imaging (MRI) and psychophysical vision testing was carried out on 74 subjects divided into two age ranges, 7-12 years and 18-35 years, and three diagnoses, strabismic amblyopia, anisometropic amblyopia, and normal vision. We report a behavioral impairment in contrast sensitivity for subjects with amblyopia, consistent with previous reports. When the high-resolution MRI brain images were analyzed quantitatively with optimized voxel-based morphometry, results indicated that adults and children with amblyopia have decreased gray matter volume in visual cortical regions, including the calcarine sulcus, known to contain primary visual cortex. This finding was confirmed with a separate region-of-interest analysis. For the children with amblyopia, additional gray matter reductions in parietal-occipital areas and ventral temporal cortex were detected, consistent with recent reports that amblyopia can result in spatial location and object processing deficits. These data are the first to provide possible neuroanatomic bases for the loss of binocularity and visual sensitivity in children and adults with amblyopia.

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Figures

Figure 1
Figure 1
Contrast sensitivity test. A: Depiction of the stimuli. Detection of a centrally located grating was tested with a two alternative forced‐choice paradigm for five spatial frequencies. Subjects discriminate between a grating stimulus (1) and a homogeneous screen (2). The threshold luminance contrast necessary for detection of the grating was determined for each eye separately. B: Performance is plotted as sensitivity (the inverse of threshold) for each diagnostic group as a function of spatial frequency. The amblyopic eyes are impaired relative to the control eyes and fellow eyes, especially for high spatial frequencies. Error bars show standard error of the mean.
Figure 2
Figure 2
Localization of VBM gray matter reductions in visual cortex of children with anisometropia and strabismus compared to normal subjects. A: Statistically significant gray matter volume reductions for the anisometropic children compared to the control children is indicated by a blue color scale. The scale is shown in bottom right corner, and ranges from P = 0.005 to P = 0.0003. The statistical changes are plotted on three inflated views of both hemispheres. From top to bottom row, the lateral, ventral, and medial views of the brain are shown. Left column shows left hemisphere, and right column shows right hemisphere. Cortical gyri and sulci are uniformly light and dark gray, respectively. The cortical surface of one normal child is used for the display. TO, transverse occipital sulcus; CS, collateral sulcus; PO, parietooccipital sulcus; Calc, calcarine sulcus. B: The equivalent comparison is shown for the strabismic group compared to the control group, and all conventions are the same as in A. Ant, anterior pole; Pos, posterior pole.
Figure 3
Figure 3
Localization of VBM gray matter reductions in visual cortex of adults with amblyopia compared to normal subjects. Statistically lower volume of gray matter for both anisometropic and strabismic groups are indicated by blue scale as in Figure 2. The cortical surface of one normal adult is used for the display. Other conventions are the same as for Figure 2.
Figure 4
Figure 4
The 3D calcarine region of interest (ROI) overlaid on one slice for individual subject. A: The unsmoothed gray matter partition of a representative slice is shown, and the right hemisphere 3D calcarine ROI is overlaid in yellow. The ROI was defined from standard atlases. B: The same slice is shown after smoothing. The mean intensity of all voxels in the ROI was determined for every subject for the unsmoothed and smoothed images. The left and right hemispheres were measured separately.
Figure 5
Figure 5
Plot of right hemisphere calcarine gray matter intensity for all subjects. The results of applying the calcarine ROI to the smoothed images of both the adult and child groups are shown. Diagnosis subgroups are shown in an overlaid fashion, identified with a color code. Within each diagnosis subgroup, the subjects have been sorted from highest to lowest intensity values for easier visual comparison. The consistently lower values for amblyopic subjects can be directly observed.
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