INFRARED METHODS FOR STUDYING NYSTAGMUS AND EYE DEVIATIONS IN COMPLETE DARKNESS WITH SPECIAL REFERENCE TO VERTICAL NYSTAGMUS

Abstract

Two infrared methods for direct evaluation of oculostatic signs in darkness are presented. Both methods are suitable for clinical work. In this first study they were used to observe vertical darkness nystagmus under reliable control of the ocular position. Fifty healthy subjects had no nystagmus in any gaze position in ordinary light. In darkness a slight, but distinct, somewhat irregular up-beat nystagmus on forward gaze was observed in five of these (in addition, a slight horizontal nystagmus appeared in nine subjects). Down-beat nystagmus, which was not observed in any of the cases, is consequently of unique importance as a pathological sign. Twenty-two patients with multiple sclerosis showed no vertical nystagmus at straight forward gaze in ordinary light. On examination in darkness, a vertical nystagmus appeared in the straight forward (primary) position of the eyes in twelve of the patients. The rapid phase was directed downward in eight, upward in four patients. In five patients the vertical nystagmus was associated with a tonic eye deviation in the direction of the slow phase. In one patient, nystagmus persisted at voluntary gaze in the direction of the slow phase. Thus, in these six patients it may be designated as third degree vertical nystagmus in darkness. (At gaze deviation towards the rapid phase it became visible (group I) in ordinary light as a “gaze-deviational” nystagmus.) The relation between the so-called gaze deviation nystagmus, spontaneous vertical darkness nystagmus in multiple sclerosis and vestibular nystagmus is briefly discussed.