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.