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Biomedical subjects

D S Zee

Publications and source records attributed to D S Zee.

171 records · Page 10Linked to original sources
PubMedDate not supplied

Head-shaking nystagmus in patients with unilateral peripheral vestibular lesions.

In certain patients with peripheral or central vestibular lesions, a transient nystagmus appears after shaking the head rapidly for 10 to 20 cycles. We recorded such a "head-shaking nystagmus" using the scleral eye coil in six subjects with unilateral peripheral vestibular lesions. Horizontal head shaking elicited horizontal nystagmus with slow phases that were initially directed toward the side of the lesion and upward. All subjects showed a prolonged, lower-amplitude reversal phase after the initial response following horizontal head shaking. The main features of these results can be explained by an analytic model that incorporates a central velocity-storage mechanism that perseverates vestibular inputs, Ewald's second law, and adaptation of primary vestibular afferent activity.

Adaptation, Physiological↗
PubMedDate not supplied

The effect of the rotational magnification of corrective spectacles on the quantitative evaluation of the VOR.

The gain of the vestibulo-ocular reflex (slow-phase eye velocity/chair velocity, measured in the dark) was compared in 11 normal healthy subjects who habitually wore corrective spectacles of varying strength. The rotational magnification (or prismatic effect) induced by habitually wearing corrective spectacles caused the VOR gain measured in darkness to vary systematically with diopter of correction. Even when allowances were made for the inherent variability of measurement of the VOR gain, myopes tended to have lower gains and hyperopes higher gains. This study demonstrates that the clinician should account for spectacle adaptation to properly interpret the results of vestibular function tests.

Adaptation, Ocular↗
PubMedDate not supplied

Tilt suppression of vestibulo-ocular reflex in patients with cerebellar lesions.

The effect of tilt on the time constant of post-rotatory nystagmus was determined in a group of normal subjects and patients with cerebellar lesions. The normal subjects showed a vestibular response that decayed with a time constant of 19.6 s when upright and 7.2 s after tilt prone. Patients with midline cerebellar lesions near the uvula and nodulus had time constants that were normal in the upright position but were unaffected by head tilt. Patients with cerebellar lesions due to the Arnold-Chiari malformation showed behavior that was intermediate between that of normal subjects and the patients with midline lesions. These results provide evidence that in humans, the midline cerebellum regulates a neural network in the brainstem that perseverates peripheral vestibular input.

Adolescent↗
PubMedDate not supplied

Head-shaking nystagmus during vestibular compensation in humans and rhesus monkeys.

Nystagmus evoked after rapid horizontal head-shaking is believed to be a sensitive indication of the existence and location of a unilateral vestibular lesion. Its origin is the directional asymmetry in vestibular responses of the healthy labyrinth (Ewald's second law). For nystagmus to appear after the head has stopped moving, however, the directionally asymmetric responses must have been stored during the head-shaking to be discharged afterwards. Our results confirm the notion that head-shaking nystagmus is most likely generated by a directional preponderance in vestibular responses but only in combination with a functioning central velocity-storage mechanism. If velocity-storage is lost completely, as may occur during the acute phase of a unilateral peripheral vestibular lesion, even a large vestibular preponderance does not lead to head-shaking nystagmus. Thus, to interpret the results of the head-shaking test the condition of the velocity-storage mechanism must be taken into account.

Adolescent↗
PubMedDate not supplied

Considerations on the mechanisms of alternating skew deviation in patients with cerebellar lesions.

Alternating skew deviation, in which the side of the higher eye changes depending upon whether gaze is directed to the left or the right, is a frequent sign in patients with posterior fossa lesions, including those restricted to the cerebellum. Here we propose a mechanism for alternating skews related to the otolith-ocular responses to fore and aft pitch of the head in lateral-eyed animals. In lateral-eyed animals the expected response to a static head pitch is cyclorotation of the eyes. But if the eyes are rotated horizontally in the orbit, away from the primary position, a compensatory skew deviation should also appear. The direction of the skew would depend upon whether the eyes were directed to the right (left eye forward, right eye backward) or to the left (left eye backward, right eye forward). In contrast, for frontal-eyed animals, skew deviations are counterproductive because they create diplopia and interfere with binocular vision. We attribute the emergence of skew deviations in frontal-eyed animals in pathological conditions to 1) an imbalance in otolithocular pathways and 2) a loss of the component of ocular motor innervation that normally corrects for the differences in pulling directions and strengths of the various ocular muscles as the eyes change position in the orbit. Such a compensatory mechanism is necessary to ensure optimal binocular visual function during and after head motion. This compensatory mechanism may depend upon the cerebellum.

Animals↗
PubMedDate not supplied

A versatile stereoscopic visual display system for vestibular and oculomotor research.

Testing of the vestibular system requires a vestibular stimulus (motion) and/or a visual stimulus. We have developed a versatile, low cost, stereoscopic visual display system, using "virtual reality" (VR) technology. The display system can produce images for each eye that correspond to targets at any virtual distance relative to the subject, and so require the appropriate ocular vergence. We elicited smooth pursuit, "stare" optokinetic nystagmus (OKN) and after-nystagmus (OKAN), vergence for targets at various distances, and short-term adaptation of the vestibulo-ocular reflex (VOR), using both conventional methods and the stereoscopic display. Pursuit, OKN, and OKAN were comparable with both methods. When used with a vestibular stimulus, VR induced appropriate adaptive changes of the phase and gain of the angular VOR. In addition, using the VR display system and a human linear acceleration sled, we adapted the phase of the linear VOR. The VR-based stimulus system not only offers an alternative to more cumbersome means of stimulating the visual system in vestibular experiments, it also can produce visual stimuli that would otherwise be impractical or impossible. Our techniques provide images without the latencies encountered in most VR systems. Its inherent versatility allows it to be useful in several different types of experiments, and because it is software driven it can be quickly adapted to provide a new stimulus. These two factors allow VR to provide considerable savings in time and money, as well as flexibility in developing experimental paradigms.

Convergence, Ocular↗