Torsional optokinetic nystagmus: normal response characteristics.
OBJECTIVE
Few studies have investigated normal response characteristics of torsional optokinetic nystagmus (tOKN). The authors have investigated the effect of stimulus velocity and central/peripheral stimulation on tOKN.


METHODS
Torsional OKN was elicited using a sinusoidal grating rotating at velocities of 3 degrees /s to 1000 degrees /s in clockwise and anticlockwise directions. To investigate the effect of central stimulation, stimulus size was varied from 2.86 degrees to 50.8 degrees. An artificial scotoma placed over a 50.8 degrees stimulus was varied from 2.86 degrees to 43.2 degrees to investigate peripheral stimulation. Eight subjects participated in each experiment and torsional eye movements were recorded using video-oculography. The mean slow phase velocity (MSPV) and gain were calculated.


RESULTS
The maximum gain occurred in response to 8 degrees /s stimulation. The MSPV increased up to a stimulus velocity of 200 degrees /s achieving a maximum of 3 degrees /s in both directions. MSPV was linearly correlated with the log of stimulus velocity. The smallest field size, rotating at 40 degrees /s, evoked 10% of the gain elicited by the largest display. When the most peripheral stimulus was used, the gain was maintained at 50% of the gain evoked when the full display was used.


CONCLUSIONS
A wide range of stimulus velocities can elicit tOKN and peripheral field stimulation contributes significantly to its response.
Farooq
S J
SJ
Department of Ophthalmology, University of Leicester, Robert Kilpatrick Clinical Sciences Building, Leicester Royal Infirmary, PO Box 65, Leicester LE2 7LX, UK. sjf18@le.ac.uk
Proudlock
F A
FA
Gottlob
I
I
D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D014102:Torsion Abnormality; D014741:Video Recording; D014787:Vision Tests