Effect of Off-Vertical Tilt and Macular Ablation on Postrotatory Nystagmus in the Squirrel Monkey

Abstract

The slow phase eye velocity (SPEV) and duration of post-rotatory nystagmus (PRN) were studied in squirrel monkeys (Saimiri sciureus) after a ramp speed rotation (0–200°/sec, with 1°/sec² angular acceleration). When the results were compared between straight upright vertical rotation, 9° tilt rotation, and 18° tilt rotation, faster decay both in SPEV and in duration was found in the tilt rotation situations. Difference in nystagmic decay curves by tilting rotation axis could be from the convergence of macula-semicircular canal inputs. Subsequently bilateral macular ablation (two-stage) was performed. The difference in nystagmus decay curves between three different rotations was reduced; therefore, the change of gravity direction perceived through gravity receptors other than macular end organs was minimal and did not produce a difference in three different rotations.