Dynamic Characteristics of the Semicirculo-Ocular System in Humans

Abstract

In order to delincate the physiological function of the vestibulo-ocular system, the transfer function (TF) of the oculomotor system was studied in 11 healthy male subjects, four patients with bilateral loss of labyrinthine excitability and four patients with unilateral loss of labyrinthine excitability.
For this purpose, the following three tests were performed; that is, the eye tracking (ETT) and the pendular rotation tests (PRT) in the dark and light were respectively performed in order to examine the opto-oculomotor, semicircular oculomotor and optosemicircular oculomotor systems.
The results obtained were as follows.
A. Healthy male subjects
1 Horizontal system
a) Regarding the TF of the opto-oculomotor system, the gain and phase were flat in a frequency range from 0.4 to 1.0Hz.
b) Regarding the TF of the semicircular oculomotor system, the gain linearly increased at a rate of 10dB per decade when the frequency increased from 0.2 to 1.5Hz. This system performs derivative control in inducing the eye movement in response to the displacement of the skull.
c) Regarding the TF of the opto-semicircular oculomotor system, the gain and phase were flat in a frequency range from 0.6 to 1.7Hz. The capability of maintainirg of visual fixation in relatien to external objects in spite of head movement increases by the collaboration of the eyes and the semicircular canals.
2 Vertical system
a) Regarding the TF of the opto-oculomotor system, the gain and phase were flat in a frequency range from 0.3 to 1.0Hz.
b) Regarding the TF of the semicircular oculomotor system, the gain linearly increased at a rate of 10dB per decade when the frequency increased from 0.4 to 1.9Hz.
c) Regarding the TF of the opto-semicircular oculomotor system, the gain and phase were flat in a frequency range from 0.6 to 1.9Hz.
B. Patients with bilateral loss of labyrinthine excitability.
1 Horizontal system.
a) Regarding the TF of the opto-oculomotor system, the gain and phase were flat in a frequency range below 1.0Hz.
b) Regarding the TF of the oculomotor system in the PRT in the dark, the gain was scattered.
c) Regarding the TF of the oculomotor system in the PRT in the light, the gain and phase were flat in a frequency range below 1.0Hz.
2 Vertical system.
The TF of the oculomotor system was similar to that of the horizontal system of the patients with bilateral loss of labyrinthine excitability.
C. Patients with unilateral loss of labyrinthine excitability.
1 Horizontal system.
a) Regarding the TF of the opto-oculomotor system, the gain and phase were flat in a frequency range below 1.0Hz.
b) Regarding the TF of the oculomotor system in the PRT in the dark, the gain was irregular but indicated a tendency to increase with increase of frequency.
c) Regarding the TF of the oculomotor system in the PRT in the light, the gain and phase were flat at frequencies slightly exceeding 1.0Hz.
2 Vertical system.
The TF of the oculomotor system was similar to that of the horizontal system of patients with unilateral loss of labyrinthine excitability.
The following conclusion was obtained.
The results thus obtained indicate that the capability of maintaining visual fixation in relation to external subjects is secured through the opto-semicircular coordination. Furthermore, the results show that the semicircular oculomotor system plays an active part in visual fixation during head movement with periodic motion exceeding 1.0Hz.