Biomedical subjects

M E Faldon

Publications and source records attributed to M E Faldon.

4 recordsLinked to original sources

PubMed2001

Horizontal ocular vergence and the three-dimensional response to whole-body roll motion.

We evaluated the human binocular response to roll motion in the dark and during visual fixation with horizontal convergence. Six normal human subjects were exposed to manually driven, whole-body rotation about an earth-vertical, naso-occipital axis, under two conditions: (I) oscillation at 0.4 Hz (peak velocity 69+/-3.8 degree/s) in the dark, and whilst fixating an axial light-emitting diode at 48 cm ('near') and at 206 cm ('far'); (II) constant velocity rotation (56.5+/-3.1 degree/s) for 40 s, clockwise and counter-clockwise, in the dark, and sudden stops. Eye and head movements were monitored using scleral search coils. In head-fixed, angular velocity coordinates roll motion always evoked conjugate ocular torsion, with small conjugate horizontal and disconjugate vertical components. The resultant binocular eye responses were rotations about convergent axes. During oscillation with target fixation the convergence of the rotation axes was larger than that predicted by target geometry, producing disconjugate oscillations of vertical gaze about the target ('skewing'). Fast-phase eye movements were primarily resetting rotations about the same convergent rotation axes as the slow phases, but the small vertical velocity components had oscillatory, asymmetrical profiles. In response to velocity steps the slow-phase eye velocity decayed exponentially with time constants of 4.5+/-1.5 s for the torsional component and 5.8+/-1.9 s for the 'vertical vergence' component (right eye-left eye recordings). We conclude that in normal human subjects dynamic vertical canal stimulation with horizontal gaze convergence evokes rotation of the eyes about convergent axes and a small skewing of the eyes.

Adult↗

PubMed1997

Evaluating 3D semicircular canal function by perception of rotation.

OBJECTIVE: We aimed to develop a clinical test of 3D canal dysfunction by perceptual matching of motion stimuli as an alternative to vestibular ocular reflex assessment. STUDY DESIGN: The study was a comparison with age-matched controls. SETTING: The study was performed in a clinical neurophysiology laboratory. PATIENTS: Ten patients with acute unilateral vestibular nerve section and 9 patients in the chronic stage of recovery, 2 acute-stage and 2 chronic-stage patients with posterior canal plugging, and 35 healthy individuals were studied. INTERVENTIONS: Seated on a motorized rotating chair in darkness, subjects were exposed to discrete, raised cosine velocity (60 degrees/s peak) rotations, for random displacements < or = 180 degrees rightward and leftward. They responded by rotating themselves back to the starting position with a joystick control. Horizontal canals were tested with head upright, ipsilateral versus contralateral vertical canal pairs were tested with the head down, face horizontal and co-planar anterior-posterior canal pairs were tested with the head down and turned approximately 45 degrees to the left or right. MAIN OUTCOME MEASURES: These were accuracy and symmetry of responses. RESULTS: Normal responses were approximately accurate returns to start. Nine patients with acute nerve section were hypometric (undershooting start) when displaced toward the lesion but normometric to the intact side. Eight chronic-stage nerve section patients with chronic dysfunction were hypometric to the lesion for vertical canal stimuli, but one third showed normal responses for horizontal canal testing. Patients with posterior canal plugging were hypometric specifically toward the plugged canal. CONCLUSIONS: The method reliably identifies acute and chronic dysfunction of vertical canals and acute dysfunction of horizontal canals. Dysfunction of a single canal can be specified.

Adolescent↗

PubMed1996

Optically induced plasticity of the cervico-ocular reflex in patients with bilateral absence of vestibular function.

The horizontal cervico-ocular reflex (COR) was examined in five labyrinthine-defictive subjects (LDS), during both passive oscillations of the head on the trunk (HTexam) and of the trunk under the earth-fixed head (THexam) at 0.1-0.5 Hz, peak angular displacement +/- 30 degrees. Subjects were tested in the dark, before and immediately after adaptation to binocular magnifying (x1.9) and reducing (x0.6) lenses. During long-term adaptation, the LDS were exposed to the normal environment for 5 h while wearing lenses. Short-term adaptation experiments (15-20 min) consisted of sustained ocular following of a small LED in an otherwise dark room and in full-room illumination. This LED was either stationary in space whilst the subjects moved their head actively, or fixed on the chair and rotating with the trunk during head-fixed stimulation. In all five patients, magnifying lenses increased COR gain (peak slow-phase eye velocity/peak stimulus velocity), whereas reducing lenses reduced the gain. Under HTexam the gain changes were greater, more consistent and the phases approximately compensatory to head displacement, whereas during THexam the gain decreased and phase increased at higher frequencies. COR adaptation was observed during foveal stimulation alone, but the effects were stronger with added background illumination. Results during an imaginary target task showed that the gain can be influenced strongly by mental set. Our findings indicate a highly modifiable COR in subjects with loss of vestibular function. Both peripheral and foveal retinal information contribute to the plastic changes in COR gain. Somatosensory cues from the trunk as well as cognitive/perceptual factors may be involved in the modification of the COR, by providing information about the relevance of eye movements, and contribute to the stabilisation of gaze in space.

Adult↗

PubMed1995

Perceptual studies in patients with vestibular neurectomy.

Twelve patients undergoing unilateral vestibular neurectomy for the treatment of refractory vertigo were investigated. Vestibular motion perception was assessed using a self-rotational task and "vestibular remembered saccades". Cervical perception was also measured with remembered saccades. The tests were performed pre- and post-operatively to examine changes in vestibular and cervical perception following an acute vestibular lesion, and to monitor the progress of vestibular compensation. These perception tests were carried out in conjunction with a conventional evaluation of the vestibular ocular reflex (VOR), using electro-oculography. The patients' subjective symptoms at each stage of testing were also quantified with questionnaires. Generally, in the vestibular tests, for stimulation to the operated side, responses became strongly hypometric directly after the neurectomy, with a partial recovery during convalescence. In the cervical test, responses were bilaterally reduced immediately after operation. Results from both of the vestibular perception tests were significantly correlated with the VOR assessment of vestibular function. Scores for the patients' subjective symptoms of "vertigo" were only significantly correlated with the vestibular perception tests, and not with the conventional measures of vestibular function. Perceptual measurements afford useful complementary information in the assessment of vestibular patients.

Adult↗