Suppression of post-caloric nystagmus in experimental perilymph fistula

Albino guinea pigs (n = 28) were used to establish an animal model of the perilymph fistula (PLF) by suctioning 2-4 microliters of perilymph via the left round window membrane. At times varying from 1-3 weeks post-operatively, 9 animals had no caloric response, 5 had a weak caloric response and none had post-caloric nystagmus (PCN). The remaining 14 animals had caloric irregularity in lesioned ears; 12 of these (87%) also did not have PCN. Morphological study of the latter revealed an intact contour of the membranous labyrinth in the lateral semicircular duct and partial collapse of the utricular wall, a condition called the "floating labyrinth". We therefore believe that effective suppression of PCN in the experimental PLF is due to failure in short-term adaptation, caused by lesions in the peripheral vestibular organs, such as the floating labyrinth.