Development of Postrotatory Nystagmus Time Constants

Abstract

Models of the slow phase portion of postrotatory nystagmus in the adult include time constants which describe primary and secondary nystagmus. The cupular time constant (T₁) is believed to reflect the activity of the cupula of the semicircular canal, while the adaptation time constant (T_a) defines the rate of change of the baseline firing rate. Values for T₁ and T_a have been published for the adult. In this study 37 normal infants under one year of age and 12 children, 3 to 13 years of age were examined for postrotatory nystagmus, and values for the two time constants were determined. The cupular time constant does not change with age and is concluded to be at an adult level at birth. This is correlated with the relative maturity of ear morphology at birth. The adaptation time constant increases from 79.5 sec at one month of age to 260.7 sec at 12-13 years of age, implying that maturation of adaption is a relatively slow process.