Wilbrand knee.

Wilbrand and Saenger(1) studied optic chiasms after unilateral enucleation, noting inferonasal crossing fibers curved anteriorly into the contralateral optic nerve (Wilbrand knee; figure, A). This explains contralateral superotemporal visual field defects (junctional scotomas) with optic nerve lesions at the chiasmal junction. However, Wilbrand knee may be an enucleation artifact.(2) The anisotropic light-reflecting properties of myelinated axons permitted imaging of normal human chiasms. Thin sections (25 µm) were illuminated and digitally imaged from 3 incident angles. Each of the images was pseudocolored (red, green, or blue) and merged, revealing an anomalously oriented fiber tract (appearing white) that reversed direction at the optic nerve-chiasm junction, found in inferior (figure, C) but not in superior sections (figure, B), consistent with Wilbrand and Saenger's original description.