Extraocular muscle intracellular and motor nerve responses to semicircular canal stimulation

Observations on the Tullio phenomenon

Vestibular responses (vertigo, nystagmus-like eye movements) to acoustic stimuli are known as the "Tullio phenomenon". Detailed electro-oculographic analysis of this reaction, as observed in a 30-year-old patient, revealed the following: a maximum amplitude of eye movement (mainly vertical) was achieved by sine wave bursts of high intensity, a frequency of 500 to 1000 Hz and a duration of 100 ms. The ocular deviation was composed of a fast initial component, followed by a slower resetting movement that was often divided into two parts of different velocities. At longer stimulus durations (more than 100 ms) the electro-oculogram showed a fractionation of the eye deviation, terminating in an "off-response". Various positions of the patient's head influenced the direction of the eye motion. The possibility that the Tullio phenomenon may be due to an abnormal excitation of the statolith organs is discussed.

The vertical vestibulo-ocular reflex and ocular resonance

A technique is described for the measurement of retinal image motion under conditions of forced angular vibration of the head in pitch at frequencies between 10 and 100 Hz. The experimental technique has been used in nine normal subjects, and in two subjects with vestibular dysfunction; one with unilateral, the other with bilateral deficit. Eye movements compensatory in phase were recorded at frequencies between 10 and 25 Hz in all normal subjects. The ratio of angular retinal image motion to angular head motion (ocular gain) over these frequencies was in the range 0.82-0.94. When the head was vibrated at frequencies above 30 Hz angular motion of the retinal image exceeded that of the head and showed progressive phase delay. Ocular gain reached a peak of 3.0 at 70 Hz and a less clearly defined peak of 1.3 at about 35 Hz. These findings are suggestive of mechanical resonances within the orbit, possibly involving intra-ocular structures.