Midline tilting between seeing and nonseeing areas in hemianopia.

The line separating the seeing from the nonseeing parts of the visual field was found to be tilted away from the expected vertical position in 24 of 200 patients diagnosed as having various types of hemianopia, including homonymous hemianopia, homonymous quadrant hemianopia, homonymous scotomata, and bitemporal hemianopia. The causes of these defects include vascular accidents, trauma, tumor, and neurosurgery for convulsive disorders. Once discovered by standard monocular field testing methods, the existence of the tilting phenomenon was distinguished from testing artifact by employing binocular fixation and red-green glasses along with red and green test objects. A difference in the overlapping fields of the two eyes was found to exist only in areas where corresponding lines between seeing and nonseeing fields were separated by a tilting away from the vertical in one or both eyes. This can occur superiorly or inferiorly with homonymous scotomata, and in bitemporal hemianopia as well as in homonymous hemianopia or quadrant hemianopia. This incongruity of fields is possibly explained by a variation in anatomic determination of crossing from noncrossing fibers at the level of the retina.