Human Angular Vestibulo-Ocular Reflex Axis Disconjugacy: Relationship to Magnetic Resonance Imaging Evidence of Globe Translation

• Published in: Annals of the New York Academy of Sciences 2005-04, Vol.1039 (1), p.15-25
• Main Authors: DEMER, JOSEPH L., CRANE, BENJAMIN T., TIAN, JUN-RU
• Format: Article
• Language: English
• Subjects: Binoculars; extraocular muscles; eye movement; Fixation, Ocular - physiology; Globes; Horizontal; Human; Humans; Magnetic Resonance Imaging; Movement - physiology; Oculomotor Muscles - anatomy & histology; pulley; Pulleys; Reflex, Vestibulo-Ocular - physiology; Rotational; vestibulo-ocular reflex; Vision, Binocular; Yaw
• ISSN: 0077-8923; 1749-6632
• DOI: 10.1196/annals.1325.003

: Magnetic resonance imaging (MRI) demonstrates that the lateral rectus pulley shifts 0.5 mm inferiorly relative to the medial rectus in 20° upgaze, but 0.5 mm superiorly in 20° downgaze, whereas the globe translates 0.7 mm nasally in adduction and 0.2 mm nasally in abduction. If pulleys influence ocular kinematics, these effects would predict disconjugate alterations of the yaw vestibulo‐ocular reflex (VOR) rotational axes. Binocular eye and head movements were recorded using three‐dimensional search coils in 8 humans (age 24 ± 2 years, mean ± SE) undergoing directionally randomized, transient, whole‐body yaw (2800°/s2 peak) in darkness while fixating straight ahead, as well as ± 18° vertically. Eye and head rotational velocity axes were expressed as quaternions in Listing coordinates. In the initial 70 ms, the ocular axis varied with vertical gaze by one‐quarter the angle of target elevation, but this effect summed significantly with a disconjugate effect of horizontal duction. In central gaze, the mean adducting eye (AD) rotational axis tilted 3.4 ± 0.8° forward relative to the head axis, while that of the abducting eye (AB) tilted 0.6 ± 0.8° backward. In downgaze, the AD rotational axis tilted 8.6 ± 1.0° forward, and AB 5.7 ± 1.2° forward. In upgaze, the AD rotational axis tilted backward by 0.1 ± 0.7°, and AB backward 3.4 ± 0.9°. We suggest that nasal globe translation relative to the fixed trochlea produces binocular extorsion accounting for yaw VOR axis disconjugacy, and thus a horizontal duction dependence in VOR rotational axis summating with classic dependence of VOR axis on vertical gaze. Confirmation of predicted duction‐dependent VOR disconjugacy supports the idea that rectus pulleys influence kinematics for all eye movements.