Hermann Wilbrand was a German author of a multi-volume textbook on the neurology of vision at the turn of the 20 ^th century. The textbook was the most comprehensive ever done up to that time and became a benchmark against which others were judged. In his description of the anatomy of the optic chiasm, Wilbrand described what came to be known as “Wilbrand’s Knee”, a looping forward into the opposite optic nerve of ventral decussating fibers before they continue on to the optic tract. The “knee” added interest to visual field interpretation, made for lovely diagrams, and incidentally kept surgeons away from the chiasm when excising optic nerve tumors.

Horton has made it clear that “Wilbrand’s Knee” was an artifact of one eye having been previously enucleated, with subsequent shifting of intact fibers at the chiasm once retrograde degeneration in one optic nerve had occurred. So the whole thing was a will-o‘-the-wisp. Secondary authors picked it up uncritically and passed it onto unsuspecting students. There are probably few texts without such errors, if we could only track them down. This is the dilemma of the textbook writer, who cannot be expected to verify everything alone, but must take many things on faith, and is sometimes undone by it.