Neurootological Examination in Patients with Unilateral Cerebral Lesion

The directional preponderance (DP) of caloric nystagmus was examined in 33 patients with unilateral cerebral vascular lesions. Only lesions which included unilateral internal capsule were chosen by CT-scan. The maximum slow-phase velocity (SPV) was measured by the ENG recordings of caloric nystagmus with 44°C and 30°C stimulations with eyes open inthe dark. The patients then fixed their eyes on a light 50 cm away for 10 seconds at 60 seconds after the beginning of the irrigation with 30°C fluid. The maximum SPV before or after fixation was used as the value in the dark and the mean SPV during the 10 seconds of fixation as the value in the light.The SPV could be measured in 33 patients. DP to the ipsilateral side of the lesion (ipsi-LS) was observed in 17 patients (55%) and DP to the contralateral side (contra-LS) in 14 (45%) with eyes open in the dark-not a significant difference. However, significant tonic eye deviation over 20 degrees to the slow-phase side was observed in 15 patients during nystagmus only to the ipsi-LS and in 2 patients during nystagmus to both sides in the dark.The SPV of nystagmus to the ipsi-LS was significantly (p<0.01) higher than that to the contra-LS in the light.Our results suggest that the tonic imbalance may be reversed because of the cortico-fugal tonic fibers to the vestibulo-ocular system, contralaterally in fixation and ipsilaterally in non-fixation, obstructed in unilateral internal capsule.