Line bisection as an early method to assess homonymous hemianopia.

Horizontal line bisection task is a common clinical task well known to most neuropsychologists. Typically, patients with visuospatial neglect show a reliable ipsilesional deviation in the bisection of long lines. Less well known in the English literature is the typical line bisection error observed in hemianopic patients who show the opposite deviation. In fact, this contralesional deviation in bisection was well known in the old German scientific literature. In 1894, more than 110 years ago, the German physician Dr. D. Axenfeld published a short case report about line bisection as a "simple method to diagnose hemianopia". His paper is one (if not the first) historical report, describing the "typical hemianopic line bisection error". At the time of its publication, it was a very popular paper in the German scientific community frequently cited by subsequent researchers. Between 1900 and 1920, Axenfeld's observation motivated several further studies using bisection by well-known researchers such as Best, Liepmann, Wilbrand, Poppelreuter and Fuchs. Surprisingly, most of today's clinical and cognitive studies use experimental modifications of line bisection in neglect patients and healthy subjects, often without realizing that this task was originally devised for the assessment of hemianopic patients. Consequently, the hemianopic line bisection error was "neglected" for many decades until its recent "rediscovery". The present paper has three aims. First, Axenfeld's classical report is translated. Second, interpretations arising from early bisection studies (around 1900-1930) in hemianopic patients are summarized and framed within contemporary science. Finally, we attempt to explain why this formerly well-known clinical phenomenon was forgotten later for nearly a century.