Damped pendular rotation nystagmus after unilateral labyrinthectomy or unilateral lateral semicircular canal block in squirrel monkeys.

Using a damped pendular rotation table, which provided an oscillation of 15.5 sec, per-rotatory nystagmus, was evaluated in six squirrel monkeys that underwent unilateral labyrinthectomy and five that underwent unilateral lateral semicircular canal block, both pre- and postoperatively. The bidirectional summation of the nystagmic slow-phase eye speed after unilateral labyrinthectomy and after unilateral lateral semicircular canal block showed similar reduction to about 60 per cent of the values obtained in the pre-operative status. Under the present test situation, both slow-phase eye speed and number of nystagmic beats in the monkeys after unilateral lateral semicircular canal block were larger by the ampullopetal stimulation than those evoked by ampullofugal stimulation. The relation between slow-phase eye speed and number of beats showed similar tendency when we compared pre-operative controls and the group after unilateral lateral semicircular canal block, but the monkeys after unilateral labyrinthectomy depicted different tendencies.