The course of the fibers of the optic nerves through the chiasm—the crossing of the medial fibers and the noncrossing of the lateral fibers—accounts for the bitemporal visual loss due to chiasmal lesions and the homonymous visual loss due to postchiasmal lesions. Much of perimetry is based on this arrangement.
Medical historians agree that the earliest published account of a partial crossing of the fibers of the optic nerves at the chiasm appears as a modest "Query" in Isaac Newton's "Opticks,"1 which was first published in 1704. The concept was entirely original with Newton. For several years I have been curious about the background of his thinking. How did he happen to be interested in the crossing of the optic nerves? What information relevant to the subject was available to him? What was the opinion of his contemporaries about it?
Newton (1642-1727) (Fig. 1) was a mathematician and physicist
RUCKER CW. The Concept of a Semidecussation of the Optic Nerves. AMA Arch Ophthalmol. 1958;59(2):159-171. doi:10.1001/archopht.1958.00940030025001