Measuring visual field distortions in amblyopia

Abnormal visual experience early in life alters the functional architecture of visual cortex and results in marked deficits in monocular visual acuity and binocular function – collectively referred to as amblyopia. Recently, we have shown there are also distortions in the visual field representation of amblyopic individuals (Hussain et al., 2015). Here, we attempt to map the associated changes in early visual cortex of subjects with amblyopia, using high-resolution magnetic resonance imaging (MRI) at 7 T. To measure visual field representations functionally, we used anatomical and functional MRI (GE-EPI, 1.5 mm isotropic voxels, TR = 2 s, TE = 25 ms) and standard retinotopic mapping stimuli in healthy and amblyopic participants. Stimuli were presented to each eye, monocularly. Outside the scanner, we also assessed fixation stability in each participant. We used the population receptive field (pRF) method to estimate polar angle, eccentricity maps, and pRF sizes (Dumoulin et al., 2008). Our results reveal systematic differences in the maps of normal and amblyopic subjects. We relate these changes to behavioural maps measured using a dichoptic positional matching technique, and individual anatomy.