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Frequency and amplitude in scotopically stimulated optokinetic nystagmus
1Research Laboratory, St. Erik's Eye Hospital, Karolinska Institute, Stockholm, Sweden.
Background:
It was previously shown that optokinetic nystagmus (OKN) gain (eye velocity/target velocity) increases with increasing target luminance at a constant target velocity during scotopic vision. Eye velocity was defined as the amplitude of the eye jerk divided by the period time. The dependence of frequency and amplitude of eye jerks in scotopic OKN on target luminance and velocity was investigated in the present study.
Method:
A total of nine subjects were examined for OKN with various target luminance and velocities under scotopic conditions. Monocular OKN was elicited by a vertical grating projected in a hemisphere. The eye movement was recorded by DC EOG.
Results:
It was found that when a constant target velocity is used, both the frequency and amplitude of eye jerks increase with an exponential decline as target luminance increases. The maximum frequency and amplitude obtained at high target luminance are independent of target velocity. The exponential decline constants for both frequency and amplitude decrease with increased target velocity.
Conclusion:
Both frequency and amplitude of eye jerks are responsible for changes in OKN gain when target luminance and velocity change.