Functional anatomy of the extraocular muscles during vergence.

Magnetic resonance imaging (MRI) now enables precise visualisation of the mechanical state of the living human orbit, enabling inferences about the effects of mechanical factors on ocular kinematics. We used 3-dimensional (3D) magnetic search coil recordings and MRI to investigate the mechanical state of the orbit during vergence in humans. Horizontal convergence of 23 degrees from a remote to a near target aligned on one eye was geometrically ideal, and was associated with lens thickening and extorsion of the rectus pulley array of the aligned eye with superior oblique muscle relaxation and inferior oblique muscle contraction.

Three dimensional kinematics of rapid compensatory eye movements in humans with unilateral vestibular deafferentation.

Saccades executed with the head stationary have kinematics conforming to Listing's law (LL), confining the ocular rotational axis to Listing's plane (LP). In unilateral vestibular deafferentation (UVD), the vestibulo-ocular reflex (VOR), which does not obey LL, has at high head acceleration a slow phase that has severely reduced velocity during ipsilesional rotation, and mildly reduced velocity during contralesional rotation. Studying four subjects with chronic UVD using 3D magnetic search coils, we investigated kinematics of stereotypic rapid eye movements that supplement the impaired VOR.

Shifts in listing's plane produced by vertical axis rotation: sustained ocular torsion due to semicircular canal stimulation.

Purpose: With the head upright and stationary, ocular torsion is confined by Listing's Law (LL), so that three-dimensional eye rotational axes form Listing's plane (LP). During head rotation, the vestibulo-ocular reflex violates LL by driving ocular torsion opposite to head torsion, sometimes out of LP. Saccades originating from non-Listing's initial torsional positions remain in a plane offset from, but parallel to, the original LP.

Temporal dynamics of semicircular canal and otolith function following acute unilateral vestibular deafferentation in humans.

Dynamic changes of deficits in canal and otolith vestibulo-ocular reflexes (VORs) to high acceleration, eccentric yaw rotations were investigated in five subjects aged 25-65 years before and at frequent intervals 3-451 days following unilateral vestibular deafferentation (UVD) due to labyrinthectomy or vestibular neurectomy. Eye and head movements were recorded using magnetic search coils during transients of directionally random, whole-body rotation in darkness at peak acceleration 2,800 degrees/s2. Canal VORs were characterized during rotation about a mid-otolith axis, viewing a target 500 cm distant until rotation onset in darkness.

Effect of unilateral vestibular deafferentation on the initial human vestibulo-ocular reflex to surge translation.

Transient whole-body surge (fore-aft) translation at 0.5 G peak acceleration was administered to six subjects with unilateral vestibular deafferentation (UVD), and eight age-matched controls. Subjects viewed eccentric targets to determine if linear vestibulo-ocular reflex (LVOR) asymmetry might lateralize otolith deficits.

Vestibulo-ocular reflex to transient surge translation: complex geometric response ablated by normal aging.

The linear vestibulo-ocular reflex (LVOR) to surge (fore-aft) translation has complex kinematics varying with target eccentricity and distance. To determine normal responses and aging changes, 9 younger [age, 28 +/- 2 (SE) yr] and 11 older subjects (age, 69 +/- 2 yr) underwent 0.5 g whole body surge transients while wearing binocular scleral search coils.

Human surge linear vestibulo-ocular reflex during tertiary gaze viewing.

The otolith-mediated linear vestibulo-ocular reflex (IVOR) was studied in 9 normal humans undergoing transient whole-body surges at 0.5 g peak acceleration while viewing targets eccentrically placed in tertiary positions that combined horizontal and vertical eccentricities at distance of 15, 25, or 50 cm both in darkness and light. Mean velocity gain (+/-SEM) for the horizontal component was 0.

Human angular vestibulo-ocular reflex initiation: relationship to Listing's law.

An ideal vestibulo-ocular reflex (VOR) generates ocular rotations compensatory for head motion. During visually guided movements, Listing's law (LL) constrains eye rotation to axes in Listing's plane (LP). Recently, it has been reported that the VOR axis is not collinear with the rotation axis of the head, but is influenced by eye position in the orbit.

Human angular vestibulo-ocular reflex axis disconjugacy: relationship to magnetic resonance imaging evidence of globe translation.

Magnetic resonance imaging (MRI) demonstrates that the lateral rectus pulley shifts 0.5 mm inferiorly relative to the medial rectus in 20 degrees upgaze, but 0.5 mm superiorly in 20 degrees downgaze, whereas the globe translates 0.

Initiation and cancellation of the human heave linear vestibulo-ocular reflex after unilateral vestibular deafferentation.

The effect of unilateral vestibular deafferentation (UVD) on the linear vestibulo-ocular reflex (LVOR) was studied in 11 humans an average of 52 months following surgical UVD. Controls consisted of seven healthy age-matched subjects. The LVOR was evoked by directionally random, transient whole body interaural (heave) translation with a peak acceleration of 0.

Vestibular catch-up saccades augmenting the human transient heave linear vestibulo-ocular reflex.

Vestibular catch-up saccades (VCUS) cued by the semicircular canals can supplement the deficient angular vestibulo-ocular reflex during transient rotations to stabilize gaze in people with unilateral vestibular deafferentation (Tian et al. 2000). However, a possible analogous role for VCUS to augment a deficient linear vestibulo-ocular reflex (LVOR) has not been carefully studied.

Effect of aging on the human initial interaural linear vestibulo-ocular reflex.

To determine age-related changes, the initial linear vestibulo-ocular reflex (LVOR) of eight older subjects of mean age 65+/-7 years (mean +/- SD, range 56-75 years) was compared with that of nine younger subjects of mean age 24+/-5 years (range 18-31 years) in response to random transients of whole-body heave (interaural) translation at peak acceleration of 0.5 g delivered by a pneumatic actuator. Binocular eye rotations were measured with magnetic search coils, while linear head position and acceleration were measured with a potentiometer and piezoelectric accelerometer.

Dynamic visual acuity during passive and self-generated transient head rotation in normal and unilaterally vestibulopathic humans.

To determine whether dynamic visual acuity (DVA) during head rotations on the stationary body can lateralize unilateral vestibular deafferentation and detect non-labyrinthine compensation mechanisms, 15 normal and 11 subjects with unilateral vestibular deafferentation underwent manually imposed and self-generated transient yaw head rotations during measurement of binocular DVA. DVA was measured by a four-alternative, forced choice, staircase procedure with optotype presentation only when head velocity exceeded thresholds of 50 degree or 75 degree/s. Eye and head movements were recorded using search coils to characterize ocular motor strategies.