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Transient torsion during and after saccades
D Straumann1, D S Zee, D Solomon
1Department of Neurology, Johns Hopkins Hospital, Baltimore, MD 21287, USA.
Vision Research
|December 1, 1995
Summary
Listing's law is violated during saccades, with eyes exhibiting transient torsion (blips) outside the normal plane. These saccade-evoked torsional movements, particularly during vertical gaze shifts, suggest complex ocular motor control mechanisms.
Area of Science:
- Ophthalmology
- Neuroscience
- Biomechanics
Background:
- Listing's law describes the normal rotational behavior of the eye in its socket.
- Saccades are rapid eye movements that shift gaze.
- Deviations from Listing's law during saccades are not fully understood.
Purpose of the Study:
- To analyze torsional eye movements (blips) during and after horizontal and vertical saccades.
- To investigate whether Listing's law is violated during saccadic eye movements.
- To explore potential underlying mechanisms of saccade-evoked torsion.
Main Methods:
- Analysis of torsional eye movements in five normal subjects.
- Recording of eye rotations during horizontal and vertical saccades in different gaze directions.
- Quantification of torsional amplitudes and durations relative to saccade onset and offset.
Main Results:
- Horizontal saccades in downward gaze caused abducting eye extorsion and adducting eye intorsion; directions reversed in upward gaze.
- Peak torsional amplitudes (1-2 degrees) occurred during saccades, with subsequent drifts back to Listing's plane.
- Vertical saccades evoked stereotyped torsion and cyclovergence, with inter-subject variability.
Conclusions:
- Listing's law is demonstrably violated during saccadic eye movements.
- Saccade-evoked torsion may indicate properties of the 3D velocity-to-position integrator or the ocular plant.
- Transient torsional deviations highlight the dynamic nature of eye movement control.