The spatial and neural deficit of human amblyopia

Abstract

Abstract Purpose Human functional imaging studies confirm deficits of V1 identified from animal models and suggest additional extrastriatal areas of dysfunction. This study aims to investigate spatial visual and neural deficits in human amblyopia. Methods Participants were 6 adults (mean age=20±2 years) with amblyopia; anisometropia (n=2); mixed (n=4) and 3 normal adults (mean age=31±4 years). Cortical activation for each eye was measured using functional magnetic resonance imaging (fMRI) and psychophysical methods. Stimuli included four attributes of spatial vision known to be deficient in individuals with amblyopia: visual resolution, contrast sensitivity, vernier acuity and global motion. In each subject, retinotopic mapping experiments were also performed to establish locations of different visual areas and to act as regions of interest. All paradigms used a block design: 18 seconds stimulus ‘on’ alternated with 18s ‘control’, stimulus subtending 15x15 degrees and flickering at a temporal frequency of 8 Hz. The scans were performed on a Siemens Trio 3.0 Tesla System at Royal Holloway University. Results All participants with amblyopia had residual amblyopia following treatment. Mean logMAR visual acuity was 0.24 (sd 0.06) and ‐0.08 (sd 0.06) for amblyopic and fellow eyes respectively. Mean visual acuity for the normals was ‐0.06 (sd 0.06). Global motion was reduced significantly in the amblyopic (p=0.04) and fellow eyes (p=0.05) of observers compared to the normals; amblyopic eye: 54%(25%); fellow eye: 41%(16%); normals: 25%(7%). Conclusion Amblyopic observers show significant deficits of global motion for amblyopic and fellow eye stimulation. This is suggestive of extrastriatal deficits of amblyopia in addition to those in V1.