Two Cases of Bilateral Reversed Optokinetic Nystagmus

Chung, Woon Kyo; Lee, Seung Soo; Kim, Tae Man; Yoon, Hye Jin

Abstract

Normally, the fast phase of optokinetic nystagmus (OKN) beats on the opposite direction to the movement of an optokinetic stimulus. The fast component of OKN beating in the same direction are called "reversed OKN". Eventhough the mechanism of reversed OKN is still disputed, it is well known that reversed OKN occurs exclusively in patients with congenital nystagmus, or in some cases, with acquired neurologic disease. It is easy to diagnose the congenital nystagmus when the spontaneous nystagmus can be seen at birth. But when the congenital nystagmus can be seen only on eccentric gaze or when the patient has a wide neutral region around the primary position, the abnormal eye movement can not be detected until a medical examination is performed. It is thought that causes of reversed OKN may be the abnormal neural decussation of the visual system or spontaneous nystagmus. Recently, we experienced two cases of bidirectional reversed OKN as a congenital nystagmus. One patient had bilateral reversed optokinetic nystagmus and gaze evoked nystagmus, whereas the other patient had periodic alternative nystagmus and bilateral reversed OKN. Bilateral reversed OKN may be one of the pathognomic signs of congenital nystagmus.