Ocular microtremor in oculomotor palsy.
OBJECTIVE
Ocular microtremor (OMT) is a high frequency tremor of the eyes present in all individuals. Recent reports suggest that OMT may be a useful indicator of brainstem function. However, the actual origin of ocular microtremor remains controversial. This study aims to provide evidence that OMT has a neurogenic origin.


METHODS
The OMT activity of five subjects with unilateral oculomotor 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 between 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 count in the normal eye was 88.4 Hz (SD+/-16.9) and in the affected eye was 59 Hz (SD+/-8.6), P < 0.0096. There was also a fall in the peak power, the power 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 muscles is necessary for normal OMT activity, and OMT therefore has a neurogenic origin.
Bolger
C
C
Mercer's Institute for Research on Ageing, St. James's Hospital, Dublin, Ireland.
Bojanic
S
S
Sheahan
N F
NF
Coakley
D
D
Malone
J F
JF
D000328:Adult; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015835:Ocular Motility Disorders / Q000175:diagnosis / Q000209:etiology*; D009801:Oculomotor Muscles / Q000294:innervation; D009802:Oculomotor Nerve / Q000473:pathology; D015840:Oculomotor Nerve Diseases / Q000150:complications* / Q000175:diagnosis; D009886:Ophthalmoplegia / Q000150:complications / Q000175:diagnosis; D014202:Tremor / Q000175:diagnosis / Q000209:etiology*