Line bisection in hemianopia
- aDepartments of Neurology and Ophthalmology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA, bDivision of Neurology, Sunnybrook Hospital, University of Toronto, Toronto, Ontario, Canada
- Dr J J S Barton, Department of Neurology KS 446, Beth Israel Hospital, 330 Brookline Avenue, Boston, MA 02215, USA. Telephone 001 617 667 1243; fax 001 617 975 5322; email jbarton{at}bidmc.harvard.edu
- Received 8 August 1997
- Revised 14 October 1997
- Accepted 16 October 1997
Abstract
The effect of hemianopia on line bisection is not known. To study this, manual line bisection in 30 patients with unilateral cerebral hemispheric lesions was examined. The mean bisection point in a group of eight patients with left hemineglect was biased rightward (ipsilaterally), as expected. Among the remaining 22 patients, eight had right hemianopic visual defects, eight had left hemianopic visual defects, and six had normal visual fields. Both groups of patients with contralateral visual field defects had mean bisection points biased contralaterally, compared with 68 normal subjects. This bias was less than the ipsilateral (opposite) bias of patients with hemineglect. Contralateral bisection bias was more evident in those whose field defect involved the macular region. No bias was seen in patients with neither field defects nor hemineglect. The contralateral bias in hemianopia may represent either non-veridical spatial representation within a visual hemifield or a consequence of the strategic adaptation of attention into contralateral hemispace after hemianopia.
