Abstract
An eye tracking test (ETT), saccade, optokinetic nystagmus (OKN) test and optokinetic-after nystagmus (OKAN) test are the visual stimulation tests most commonly performed. In this article, I will examine the methods, interpretation of the results and pitfalls of those tests. The function of smooth pursuit is evaluated in an ETT. Smooth pursuit is very susceptible to central nervous system damage. Because smooth pursuit is easily affected by the age and arousal, these conditions should be considered in evaluating the results of an ETT. In saccade, the latent time, maximal eye speed and accuracy are evaluated. Saccade may be occasionally the only test that can detect the failure of the central nervous system. OKN is divided into two types by the instructions to the examinees. When examinees are instructed to look at the stripes so as to count them, one by one, OKN is Schau-Nystagmus. When examinees are instructed to stare vacantly in front of them, OKN is Stier-Nystagmus. Schau-Nystagmus differs significantly from Steir-Nystagmus in terms of the speed and form of nystagmus. It is important to clarify the instructions given to the patient. In a qualitative analysis of OKN, nystagmus are superimposed over the stripes with a computer and pursuit movements and catching movements of the target are separately examined. OKN is able to be evaluated in detail in a qualitative analysis, whereas the optokinetic pattern test (OKP) is a clinically convenient method for visually detecting slow and fast phase asymmetry of OKN. OKAN has been thought to be concerned with the velocity storage mechanism. Therefore OKAN test is significant in the study of the function of the peripheral and central vestibular system.
