THE CONGENITAL AND SEE-SAW NYSTAGMUS IN THE PROTOTYPICAL ACHIASMA OF CANINES - COMPARISON TO THE HUMAN ACHIASMATIC PROTOTYPE

We applied new methods for canine eye-movement recording to the study of achiasmatic mutant Belgian Sheepdogs, documenting their nystagmus w aveforms and comparing them to humans with either congenital nystagmus (CN) alone or in conjunction with achiasma. A sling apparatus with he ad restraints and infrared reflection with either earth- or head-mount ed sensors were used. Data were digitized for later evaluation. The ho rizontal nystagmus (1-6 Hz) was similar to that of human CN. Uniocular and disconjugate nystagmus and saccades were recorded. See-saw nystag mus (SSN), not normally seen with human CN, was present in all mutants (0.5-6 Hz) and in the one human achiasmat studied thus far. This pedi gree is an animal model of CN and the SSN caused by achiasma or uniocu lar decussation. Given the finding of SSN in all mutant dogs and in a human, achiasma may be sufficient for the development of congenital SS N and, in human infants, SSN should alert the clinician to the possibi lity of either achiasma or uniocular decussation. Finally, the interpl ay of conjugacy and disconjugacy suggests independent ocular motor con trol of each eye with variable yoking in the dog. Published by Elsevie r Science Ltd. All rights reserved.