Ocular microtremor in oculomotor palsy

Objectives: Ocular microtremor (OMT) is a high frequency tremor of the eyes present in all individuals. Recent reports suggest that OMT may be a usefu l indicator of brainstem function. However, the actual origin of ocular mic rotremor remains controversial. This study aims to provide evidence that OM T has a neurogenic origin. Materials and Methods: The OMT activity of five subjects with unilateral oc ulomotor nerve palsy and one subject with complete unilateral internal and external ophthalmoplegia were recorded from both eyes of each subject using the piezoelectric strain gauge technique, with the normal eye acting as a control. Five parameters of OMT activity were studied in each subject: the peak count. the power of the high frequency peak, the percentage power betw een 60 and 100 Hz, the percentage power between 70 and 80 Hz, and the 10 dB cut-off point. Results: in the Five subjects with oculomotor nerve palsy, the mean peak co unt in the normal eye was 88.4 Hz (SD+/-16.9) and in the affected eye was 5 9 Hz (SD+/-8.6), P < 0.0096. There was also a fall in the peak power, the p ower between 60 and 100 Hz, and the power between 70 and 80 Hz. In subject six, who had complete opthalmoplegia, there was no evidence of OMT activity in the denervated eye. Conclusions: These results suggest that innervation of the extraocular musc les is necessary for normal OMT activity, and OMT therefore has a neurogeni c origin.