Vertical Impulses- Ralp/Larp; Background - Interacoustics EyeSeeCam Instructions For Use Manual

Vertical impulses- RALP/LARP

For testing in the vertical planes you can select RALP and LARP protocols from the recording menu (right
anterior/left posterior and left anterior/right posterior).
Figure 4.4.11-1 Head impulse testing – vertical canals

Background

The function of the horizontal VOR can be easily assessed with vHIT by rapidly rotating the head in the
horizontal plane and measuring the resulting eye counter-rotation in the same plane. For assessing the
function of the vertical semicircular canals, the head is rotated right-downward to left-upward in the plane
of the right anterior and left posterior canals (RALP) or left downward to right-upward in the plane of the
left anterior and right posterior canals (LARP).
The EyeSeeCam protocol utilizes three well-documented properties of the VOR: 1) For fast head
movements the axis of VOR eye rotation is head-fixed, i.e., independent of gaze direction, 2) the rotation
axis can be separated into its horizontal, vertical, and torsional components, i.e., these components can
be treated in isolation, and 3) the physiological frame of reference in which the VOR operates (the so-
called "Listing's" plane) is tilted backwards in pitch, i.e., it leaves the measurement of the vertical eye
movement component unaffected. Even though EyeSeeCam records all three head velocity components,
it eventually calculates the vertical VOR gain as the regression slope between solely the vertical
components of eye and head velocities.
This usage of the vertical eye and head velocity components is best demonstrated in the following polar
plot. The trace of a simulated head thrust with a velocity of 250 °/s in the RP direction (dark red) is plotted
similar to how it would appear in the direction / plane guide. The thrust causes a VOR eye movement in
the opposite direction (black). The isolated components of the head and eye movements along the
vertical plane are shown in red and gray, respectively. It is the lengths of these two vertical components
which are related to each other to calculate vertical VOR gain. Please note that the eye trace and the
vertical components are just shown for clarification and that they do not appear in the direction / plane
guide. Also, the eye trace is not in perfect opposition to the head trace because the VOR gain in the
torsional plane is known to be less than unity (usually around 0.6). Nevertheless, the two vertical
components (gray and red) are of the same length and would thus yield unity vertical VOR gain.
EyeSeeCam vHIT - Instructions for Use - EN Page 30