How Could Canal-pluggings Result in Intensive Direction Changing Type of Positional Nystagmus?

Abstract

The objectives of this study in Rhesus monkeys is to observe the sequences which appear in the oculo-spinal-motor system after selected semicircular canals had been plugged. The left anterior and the right posterior canals in a monkey “LARP”, the left anterior and posterior canals in “LALP”, and the left lateral canal in “LL” were plugged under intubation general anesthesia. Three-dimensional eye recordings were performed, using two scleral coils. Behavior, posture, and vestibulo-ocular reflex were studied. Compensation was established in the light within 2 days. In darkness, no spontaneous nystagmus was recorded in the sitting position. The monkey “LALP” developed marked positional nystagmus. When the head position was changed up to 360d` in 15d` steps, horizontal, vertical and torsional eye movements showed remarkable changes. Spontaneous direction changing nystagmus in darkness was also recorded in “LALP”. To conclude, direction changing positional nystagmus, which was seen for several months after the canal plugging, was difficult to explain by the damage to the adjacent ampullary and/or otolithic endor-gans. but may be explained by the limited otolithic compensation in the earth parallel plane for the defective dynamic canal inputs. These observations and conclusions were from experiments using three monkeys only and should still be confirmed in more extended experiments.

Key Words:

• canal-plugging
• positional nystagmus
• Rhesus monkey
• 3-dimen-sional eye movement recording
• magnetic search coils