See-saw nystagmus in dogs and humans: an international, across-discipline, serendipitous collaboration.

Abstract

Before the 1991 report of achiasma in dogs, [1] there was general acceptance that all vertebrates had decussation at the optic chiasm. [2] Exactly how, within the space of a few years, the achiasmatic condition came to be recognized in two mammalian species is an interesting confluence of interpersonal scientific communication and some serendipity. Serendipity, a word coined by Walpole in a letter written in 1754, [3] based on a fairy tale he had written several years earlier, [4] has a long history in science. [5-9] In 1991, Robert Williams, PhD (a Memphis neuroanatomist/biologist), who had been studying the anatomy of mutant Belgian sheepdogs that had no optic chiasm, sent me videos of their eye movements, asking if they were like human congenital nystagmus (CN). I replied that although they appeared to be similar, we would have to document the waveforms of the dominant horizontal oscillation. Also visible in the video were vertical components, which are less common in human CN, and what appeared to be transient see-saw nystagmus (SSN), a disconjugate vertical nystagmus with a conjugate torsional component such that each eye intorts as it goes upward and extorts as it goes downward. [10] SSN is not part of the human CN condition, and congenital SSN is extremely rare. [11-13] I traveled to Memphis in 1992 and (with Williams) confirmed, by both direct observation and additional videos, the presence of SSN in one dog and vertical components of the nystagmus in the others. I discussed the canine condition with Josephine Shallo-Hoffmann, PhD (working in the vestibuloocular laboratory of Michael Gresty, PhD, in London) in 1991 …