The line bisection task in the acute stage of hemianopia and neglect

The line bisection task is a common clinical bedside tool for the assessment of spatial neglect and homonymous hemianopia (HH). While neglect patients show an ipsilesional deviation, hemianopic patients are usually known to displace their midline contralesionally towards the scotoma. Evidence for the “hemianopic line bisection error (LBE)“ came from hemianopic patients in a chronic stage of brain damage (mostly occipital stroke). As it seems to represent a compensatory shift of attention the LBE may be absent in the acute stage. If so, is the line bisection task a reliable bedside tool to distinguish hemianopia from hemineglect in the acute stage of stroke?

We compared the line bisection task in hemianopic patients as well as hemineglect patients in their acute stage of stroke with healthy control subjects. At the bedside participants (n=21) were instructed to bisect 6 lines (20cm) equally distributed on a horizontal sheet of paper with a vertical dash. The LBE was expressed in % of total line length deviated from the centre with negative signs for leftward deviation. Controls bisected the lines very accurately (LBE=0.1%±0.3, mean±SEM). Patients with left spatial hemineglect showed a significant ipsilesional rightward deviation compared to controls (15.3%±2.9). Left and right hemianopic patients (LH, RH) showed a small but significant ipsilesional deviation towards their intact hemifield when compared to controls (LH: 1.4%±0.5, RH: –2.0%±1.2). The ipsilesional deviation in LH patients was significantly smaller than in left hemineglect patients.

In summary, the LBE found in acute hemineglect patients replicates the findings of a distinct ipsilesional deviation in chronic neglect patients. Surprisingly, acute hemianopic patients showed a similar ipsilesional (though smaller) LBE but no typical deviation towards the scotoma like hemianopic patients in a chronic stage. Taking into account the presence of an ipsilesional deviation in both hemianopic and hemineglect patients in their acute stage of stroke, at that early time the line bisection task may be a less reliable tool to distinguish both conditions. We conclude that (i) the common “hemianopic line bisection error“ may be absent in acute hemianopic patients and (ii) a small ipsilesional deviation in the line bisection task does not necessarily refer to spatial neglect but may be an early finding in acute homonymous hemianopia.