Abstract
Objective: Cerebellar diseases frequently affect the ocular motor neural velocity-to-position integrator by increasing its leakiness and thereby causing gaze-evoked nystagmus (GEN) and rebound nystagmus (RN). Minor leakiness is physiological and occasionally causes GEN in healthy humans. We aimed to evaluate the characteristics of GEN/RN in healthy subjects for better differentiation between physiological and pathological GEN/RN.Methods: Using video-oculography, eye position was measured in 14 healthy humans at straight ahead eye position before and after, and during 30 s of ocular fixation at 4 horizontal eccentric targets between 30° and 45°. We determined the eye drift velocity and the prevalence of nystagmus before/during/after eccentric fixation.Results: Eye drift velocities during (range: 0.62 ± 0.53°/s to 1.78 ± 0.69°/s) and after eccentric gaze (range: 0.28 ± 0.52°/s to 1.48 ± 1.02°/s) increased with the amount of gaze eccentricity (30°-45°). During continuous eccentric gaze, eye drift velocities decreased by 0.41 ± 0.18°/s at 30°, and 0.84 ± 0.38°/s at 45° gaze eccentricity. GEN was elicited in 71% of subjects at 30° gaze eccentricity. Twenty-one percent showed RN thereafter. This prevalence increased to 100% (GEN)/72% (RN) at 45° gaze eccentricity. RN found after 30° gaze eccentricity was of low velocity (0.82 ± 0.21°/s) and occurred after minor drift velocity decrease during prior eccentric gaze (0.43 ± 0.15°/s).Conclusion: GEN and RN should be tested using horizontal gaze eccentricities of <30°, since most healthy subjects physiologically show GEN and RN at higher eccentricities. In case of an uncertain result, both the reduction of eye drift velocity during eccentric gaze and the velocity of RN can be analyzed to distinguish physiological from pathological nystagmus.
Highlights
Cerebellar diseases frequently affect the ocular motor neural velocity-to-position integrator
We evaluated the appearance of eye drift and physiological nystagmus before, during, and after prolonged horizontal eccentric gaze between 30◦ and 45◦ in healthy human subjects
Our study provides an in-depth description of eye drift and physiological nystagmus before, during, and after prolonged eccentric gaze at eccentricities between 30◦ and 45◦ in healthy
Summary
Cerebellar diseases frequently affect the ocular motor neural velocity-to-position integrator. This is a neural network within the brainstem and the cerebellum that generates the position command for the ocular motor neurons to enable stable eccentric gaze [1,2,3,4]. Already in its normal state, it exhibits some “leakiness” as indicated by centripetal drifts occurring in darkness in healthy individuals attempting eccentric gaze [5, 6]. GEN is a centrifugal nystagmus occurring at eccentric eye positions, while RN describes a centripetal nystagmus that appears upon the return of gaze to the primary position (straight ahead) after prolonged eccentric gaze. Video-oculography is frequently used for quantification of GEN and RN
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