Transient analysis of non-linear VOR nystagmus - clinical implications

We present an alternate method for the analysis of eye movements in the vestibular ocular reflex (VOR), called vestibular nystagmus. Classically, a central ´integrator´ (gaze holding) is assumed to have a large time constant, so that VOR dynamics are presumed to be seen in the behaviour of ´envelopes´ of slow-phase eye velocity. This method often cannot distinguish between healthy normals and compensated patients, and theoretically it is inappropriate in a switched system like the VOR. Our transient analysis method instead allows for simultaneous estimation of central and vestibular time constants, by incorporating the effects of transients in each slow-phase segment. We analyzed data from both unilateral vestibular patients and normal subjects to illustrate the effects of various analysis methods on estimated VOR parameters. The new method allows for robust detection of vestibular abnormalities even after compensation, and can be used for the analysis of any eye reflexes.