Fig. 18 The horizontal IN and vertical component of see-saw nystagmus in (A) an achiasmatic Belgian sheepdog, during binocular (OU) viewing and (B) an achiasmatic human, during right-eye fixation. Note that the left eye in (B) was approximately 15° esotropic. Where indicated, traces were shifted for clarity. REH—right eye horizontal, LEH—left eye horizontal, REV—right eye vertical, and LEV—left eye vertical. In (B), REV and LEV were shifted -15° for clarity.