Strabismic amblyopes show a bilateral rightward bias in a line bisection task: Evidence for a visual attention deficit

Neurologically normal observers show a consistent leftward bias when asked to bisect a horizontal line ("pseudoneglect"). In this study, we found that subjects with strabismic and strabismic-anisometropic amblyopia show a consistent rightward bias ("minineglect") in a line bisection task. The bias was seen in both eyes, but affected more strongly the amblyopic eye. Purely anisometropic amblyopes show a similar bias, affecting only the amblyopic eye. The group of strabismics with alternating fixation did not differ significantly from normal observers. These errors are reminiscent of the attentional neglect of the left extrapersonal space, shown by subjects with lesions in the right posterior parietal cortex. We suggest that an early strabismus might lead to a functional deficit of the dorsal cortical pathway, in addition to the well-known impairments on the ventral visual pathway. We conclude that strabismic amblyopes might show subtle attentional deficits, in addition to their unilateral vision loss.