BIVARIATE NORMAL VALUES OF OPTOKINETIC NYSTAGMUS TEST

Abstract

Comparisons of right and left optic stimulations with the two optokinetic pattern tests (OKP) are available for diagnosing equilibrium disorders. Also availabile are numerical data of OKP, which are calculated by an OKP-analyzing computer to assist the thinking of clinicians. But there is no criterion for deciding normal or abnormal two-dimensional numerical results of OKP by right and left directional optic stimulation. We established bivariate normal values and normal ranges based on the numerical data of OKP. Variables of OKP for establishing bivariate normal values and ranges were the total number of nystagmus, the cumulative slow phase amplitudes and velocities of nystagmus, and the average fast phase velocities. The reference samples were selected from 1482 numeric data of OKP regarded as normal. Normal ranges are shown as ellipses, which were drawn intuitively through the 5% critical ratio points of bivariate normal distributions, to distinguish normal from abnormal. Normal values were expressed by Mahalanobis generalized distance (MGD), which is the distance from mean values to sample values of bivariates. The normal values of each variable had a 95% confidence coefficient for calculating the MGD from the center to the margin of the ellipses. It seems that simple discrimination between normal and abnormal bivariable OKPs was obtained using our normal values and ranges calculated by Mahalanobis generalized distance.