Eog Baseline Oscillations in Congenital Nystagmus

Visual acuity in congenital nystagmus is primarily related to the duration of the foveation periods, during which the image of the target is placed on the fovea area and the eye velocity is low. This is true only if the subject is still able to place the target image on the centralmost fovea during the foveation period. In presence of a high variability of the foveation position the target image could not be placed on the centralmost fovea during many foveation periods. An associate vertical nystagmus or a slower horizontal eye movement combined to the horizontal nystagmus could cause such high variability. In several eye-movement recordings of patients affected by congenital nystagmus a very slow oculographic baseline fluctuations have been detected. In these patients the ability to foveate the target seems to depend mainly by the amplitude of the baseline fluctuation. The aim of this paper is to describe and quantitatively characterise these slow movements and try to associate them with the patient visual acuity. Furthermore a method to automatically separate the slow baseline oscillation from the nystagmus is proposed. Our findings suggest that for these patients the maximum effort could be concentrated on the reduction of the eye-position variability during foveation.