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Abstract
The contralesional line bisection error in unilateral homonymous hemianopia is a frequent
but neglected clinical phenomenon. Our knowledge about this bisection error is based
on small samples of hemianopic patients. Moreover, horizontal line bisection has never
been investigated in other unilateral visual field defects. The present study is the
first to examine line bisection in a large, representative sample of patients with
unilateral homonymous visual field defects. We investigated horizontal line bisection
in 129 patients with left- or right-sided homonymous hemianopia (60.5%), upper and
lower quadranopia (24.8%), and paracentral scotoma (14.7%), and determined the magnitude
and direction of line bisection error. The contralesional horizontal line bisection
error was present not only in patients with hemianopia but also in those with upper
or lower quadranopia or paracentral scotoma. Neither the type nor the severity of
the visual field defect was found to determine the bisection error. Only the side
of the field defect seemed to determine the horizontal direction of the bisection
error (left-/rightward). The contralesional bisection error is not a specifically
"hemianopic" phenomenon. It is frequently associated with any unilateral homonymous
visual field defect, i.e., hemianopia, upper/lower quadranopia, paracentral scotoma.
Moreover, our results further support the recent finding that the contralesional bisection
error is not a direct consequence of the visual field defect. Yet, they also suggest
that, although the visual field defect does not seem to be the primary cause of the
contralesional bisection error, it may nevertheless contribute to it.