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 waveforms and comparing them to humans with either congenital nystagmus (CN) alone or in conjunction with achiasma. A sling apparatus with head restraints and infrared reflection with either earth- or head-mounted sensors were used. Data were digitized for later evaluation. The horizontal nystagmus (1-6 Hz) was similar to that of human CN. Uniocular and disconjugate nystagmus and saccades were recorded. See-saw nystagmus (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 pedigree is an animal model of CN and the SSN caused by achiasma or uniocular decussation. Given the finding of SSN in all mutant dogs and in a human, achiasma may be sufficient for the development of congenital SSN and, in human infants, SSN should alert the clinician to the possibility of either achiasma or uniocular decussation. Finally, the interplay of conjugacy and disconjugacy suggests independent ocular motor control of each eye with variable yoking in the dog.

Characteristics of foveating and defoveating fast phases in latent nystagmus.

PURPOSE: Under certain conditions, the fast phases of latent/manifest latent nystagmus (LMLN) can defoveate the target of interest instead of foveating it, as was thought to be their only function. LMLN fast phases in the waveforms from four subjects were studied with the goals of better understanding their characteristics and determining what triggers both foveating and defoveating fast phases. METHODS: Eye movement records were made using both the scleral search coil and infrared methods. Relationships of fast-phase sizes with slow-phase positions and velocities before and after fast phases were analyzed, as were relationships of saccade size with peak velocity and duration. RESULTS. The data showed that LMLN with defoveating fast phases occurred in the presence of higher slow-phase velocities. Also, larger saccade sizes corresponded to larger presaccadic and postsaccadic slow-phase velocities. The peak velocities and durations of LMLN fast phases were in the same ranges as normal saccades. CONCLUSIONS: Defoveating fast phases with decreasing-velocity slow phases may be the result of the addition of saccadic pulses to linear slow phases. Mechanisms are suggested to explain the switch from foveating to defoveating fast phases in LMLN.

Pendular nystagmus in patients with peroxisomal assembly disorder.

BACKGROUND: Pendular nystagmus commonly occurs in congenital and acquired disorders of myelin. OBJECTIVE: To characterize the nystagmus in 3 siblings with an infantile form of an autosomal recessive peroxisomal assembly disorder causing leukodystrophy. DESIGN: We examined visual function and measured eye movements using infrared oculography. We noted changes in eye speed and frequency before and after the administration of gabapentin to 1 patient. RESULTS: All 3 siblings showed optic atrophy and pendular nystagmus that was predominantly horizontal, at a frequency of 3 to 6 Hz, with phase shifts of 45 degrees to 80 degrees between the oscillations of each eye. Gabapentin administered to 1 child caused a modest improvement of vision and the reduction of the velocity and frequency of oscillations in the eye with worse nystagmus. CONCLUSION: The pendular nystagmus in these patients was due to their leukodystrophy and may have a similar pathogenesis to the oscillations seen in other disorders affecting central myelin.