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RS Jampel; Ocular Motor Kinematics: The Law of the Fixation Planes . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2648.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To present the results of experiments in oculomotor kinematics and evidence for the Law of the Fixation Planes (FP; draw a plane through the fovea, the centrode of rotation, and any locus on the retinal raphe). Methods: (1) Video-oculography and cinematography of normal and abnormal human eye movements during head movements and with the head held stable in space. Computer analysis of video clips frame-by-frame with AdobeTM algorithms. (2) Stimulation of the oculomotor and trochlear nerves, brainstem and cerebral cortex of the monkey (Macaca mulatta) combined with ablations of extraocular muscles.(3) Haploscopic analysis of the fusion reflex in different head positions Results: During head tilt: If the head tilts slowly the eyes move in sync with the head. If the head accelerates to a velocity above about 60 degs/sec, the eyes counter roll around an anterior-posterior axis. The maximum magnitude of the counterroll is about 15 degs at high velocities of head tilt. The eyes then forward rotate in the direction of the head tilt causing the eyes to catch up to, and occasionally to overshoot, the head. When the head comes to rest in any tilted position there is no static counterrotation of the eyes. With the head held steady: The FPs rotate around the collinear X-axes of the two eyes. The visual line rotates within the FP.The oblique muscles share a common axis that is fixed in the FP at an angle of about 39 degs with the sagittal head planes.The vertical recti share a common axis that is fixed in the fixation plane at an angle of about 67 degs with the sagittal head planes. These axes rotate with the FP around the X-axis. The magnitude of the fusion reflex is the same in all head positions. Conclusion: With the head held stable in any position, the obliques muscles in cooperation with the vertical recti prevent static ocular counterrolling. The retinas are oriented to the brain and not the horizon. The horizontal recti rotate the visual line within the FP. The vertical extraocular muscles rotate the eyes around the collinear X-axis. Torsional eye movements occur only during head tilting and when the tilting exceeds a velocity of about 60 degs/sec. The Law of the Fixation Planes: The function of extraocular muscles is to maintain the FPs of the two eyes coplanar in all stable head positions and in all gaze directions. Retinal correspondence is maintained in all directions of fixation by the fusion reflex. Each locus of emergence of the visual line from the fixation plane has constant and unique coordinates ( angles of latitude and longitude ).
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