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A new device to quantify ocular counterroll using retinal afterimages
Q Arshad1, D Kaski, D Buckwell
1Academic Department of Neuro-Otology, Charing Cross Hospital Campus, Imperial College London, London, UK.
Background:
The integrity of vertical semicircular canal and otolith function remains difficult to assess in the clinical setting, partly due to difficulties in recording ocular counterroll. Here, we quantify static ocular counterroll from head tilt using a new head-mounted device.
Methods:
The device consists of an LED positioned 42 cm in front of one eye and a striated lens which produces a streak of light on the retina. The LED is illuminated at full intensity (80 cd) to generate a retinal afterimage. Subsequently, in darkness, the subject's head is tilted in the roll plane. Finally, the LED is illuminated dimly (0.2 cd) and the subject rotates the striated lens to superimpose the dim light streak onto the afterimage. An angular scale indicates the angle through which the lens is rotated, giving a measure of the ocular counterroll. To validate the device, we recorded binocular counterroll simultaneously with 3D computerised video-oculography of the other eye in 16 normal subjects; 2 patients with acquired bilateral loss of vestibular function were also tested.
Results:
In the normal subjects, there was no significant difference between the two techniques (p=0.24) when recording ocular counterroll and the correlation between the two techniques was R2=0.78. The 2 avestibular patients essentially showed no ocular counterroll with both techniques.
Conclusions:
We have devised a non-invasive, quick and reliable test of ocular counterroll. The lack of response in the 2 avestibular patients indicates that this device is clinically applicable to assess otolith function.
