Biomedical subjects

E Viirre

Publications and source records attributed to E Viirre.

14 recordsLinked to original sources

PubMed1998

The virtual retinal display: a new technology for virtual reality and augmented vision in medicine.

INTRODUCTION: The Virtual Retinal Display (VRD) is a new technology for creating visual images. It was developed at the Human Interface Technology Laboratory (HIT Lab) by Dr. Thomas A. Furness III. The VRD creates images by scanning low power laser light directly onto the retina. This special method results in images that are bright, high contrast and high resolution. In this paper, we describe how the VRD functions, the special consequences of its mechanism of action and potential medical applications of the VRD, including surgical displays and displays for people with low vision. A description of its safety analysis will also be included. In one set of tests we had a number of patients with partial loss of vision view images with the VRD. There were two groups of subjects: patients with macular degeneration, a degenerative disease of the retina and patients with keratoconus. Typical VRD images are on the order of 300 nanowatts. VRD images are also readily viewed superimposed on ambient room light. In our low vision test subjects, 5 out of 8 subjects with macular degeneration felt the VRD images were better and brighter than the CRT or paper images and they were able to reach the same or better level of resolution. All patients with Keratoconus were able to resolve lines of test several lines smaller with the VRD than with their own correction. Further, they all felt that the VRD images were sharper and easier to view. The VRD is a safe new display technology. The power levels recorded from the system are several orders below the power levels prescribed by the American National Standard. The VRD readily creates images that can be easily seen in ambient roomlight and it can create images that can be seen in ambient daylight. The combination of high brightness and contrast and high resolution make the VRD an ideal candidate for use in a surgical display. Further, tests show strong potential for the VRD to be a display technology for patients with low vision.

Equipment Design↗

PubMed1998

Assessing a VR-based learning environment for anatomy education.

The purpose of the research proposed herein is to develop an empirical, methodological tool for the assessment of visual depth perception in virtual environments (VEs). Our goal is to develop and employ a behaviorally-based method for assessing the impact of VE design features on the perception of visual depth as indexed by the performance of fundamental perceptual-motor activities. Specifically, in this experiment we will assess the affect of two dimensions of VE system design--(1) viewing condition or "level of immersion", and (2) layout/design of the VE--on the performance of an engaging, game-like task. The characteristics of the task to be employed are as follows--(1) it places no demands on cognition in the form of problem solving, retrieval of previously learned information, or other analytic activity in order to assure that (2) variations in task performance can be exclusively attributed to the extent to which the experimental factors influence visual depth perception. Subjects' performance will be assessed in terms of the speed and accuracy of task performance, as well as underlying dimensions of performance such as workload, fatigue, and physiological well being (i.e., cybersickness). The results of this experiment will provide important information on the effect of VE immersion and other VE design issues on human perception and performance. Further development, refinement, and validation of this behaviorally-based methodology will be pursued to provide user-centered design criteria for the design and use of VE systems.

Anatomy↗

PubMed1997

Remote medical consultation for vestibular disorders: technological solutions and case report.

Complaints of vertigo and imbalance are common presentations to primary care physicians, yet there are few specialists who diagnose and treat these problems as a significant part of their practices. We demonstrated the feasibility of remote consultation for a patient presenting with vertigo using a two-way digital video and audio network. It was possible to take an appropriate history, examine the patient, and provide a diagnosis and treatment. The patient had a common problem that causes dizziness: benign positional vertigo (BPV). An essential component of the examination was the use of a head-mounted display with embedded cameras. The cameras allowed viewing of the patient's eye movements, which were diagnostic.

Dizziness↗

PubMed1997

Laser safety analysis of a retinal scanning display system.

The Virtual Retinal Display (VRD) is a visual display that scans modulated laser light on to the retina of the viewer's eye to create an image. Maximum permissible exposures (MPE) have been calculated for the VRD in both normal viewing and possible failure modes. The MPE power levels are compared to the measured power that enters the eye while viewing images with the VRD. The power levels indicate that the VRD is safe in both normal operating mode and in failure modes.

Data Display↗

PubMed1997

A magnetic resonance imaging study of double elevator palsy.

OBJECTIVE: The pathophysiology of double elevator palsy is poorly understood. We assessed two patients with this condition using magnetic resonance imaging (MRI) to evaluate the appearance of the extraocular muscles. DESIGN: Cross-sectional study. SETTING: Radiology department of a university-affiliated hospital in London, Ont. PATIENTS: Two patients from a private ophthalmology practice who had undergone complete transpositions of the horizontal rectus muscles to treat hypotropia associated with double elevator palsy. INTERVENTION: MRI. A volume scanning technique was used to obtain maximum information about the muscles. OUTCOME MEASURE: Appearance of the extraocular muscles. RESULTS: In both patients MRI showed decreased volume of the superior rectus muscle on the affected side. The other rectus muscles were normal. This suggested either congenital hypoplasia or paresis of the involved superior rectus muscle. In addition, the full tendon transpositions of the medial and lateral recti did not appreciably change the middle and deep orbital pathways of the transposed horizontal rectus muscles. CONCLUSIONS: MRI may be a useful adjunct to saccadic velocity assessments in differentiating between primary inferior rectus restriction, primary superior rectus paresis and congenital supranuclear elevator deficiency.

Adolescent↗

PubMed1996

Vestibular telemedicine and rehabilitation. Applications for virtual reality.

This paper will discuss the use of Virtual Reality (VR) technologies in the rehabilitation of patients with vestibular disorders and in the provision of remote medical consultations for those patients. Patients with a vestibular problem are very common (vertigo is the second most common neurological complaint after headache) and yet there are very few vestibular neurotologists: specialists in their diagnosis and treatment. New treatments for various disorders causing vertigo now exist. This means that appropriate diagnosis can significantly improve patients' well-being. Remote medical diagnosis and treatment facilities could make the few vestibular disorder specialists much more available to patients. An analysis of the technological and economic factors influencing the provision of this service is necessary. The main long term effect of many vestibular disorders is damage to the sensing apparatus of the inner ear. The damage can lead to inappropriate interaction between visually driven orientation sensing and sensing of orientation by the inner ear. The consequence for the patient is vertigo (a sensation of turning), motion sickness and imbalance. Current rehabilitation efforts are intended to drive the nervous system to adapt to the disordered vestibular input. Adaptation appears to occur slowly in many subjects, even those within rehabilitation programs. An appropriately designed VR experience could greatly increase the rate of adaptation in these patients.

Humans↗

PubMed1996

Distributed medical intelligence. A systems approach for developing and integrative health care information distribution infrastructure.

Recent trends in healthcare informatics and telemedicine indicate that systems are being developed with a primary focus on technology and business, not on the process of medicine itself. Distributed Medical Intelligence promotes the development of an integrative medical communication system which addresses the process of providing expert medical knowledge to the point of need.

Artificial Intelligence↗

PubMed1988

Monocular adaptation of the saccadic system and vestibulo-ocular reflex.

This study asks whether or not adaptation of saccades and the VOR is constrained to be conjugate by Hering's Law. Changes in saccades and the VOR produced by surgically weakening one of the horizontal recti by recession or tenotomy were examined in monkeys with the affected eye patched. After the restoration of vision a rapid monocular recalibration of both saccades and the VOR was observed in preparations with a small or moderate muscle weakening. Preparations with a severe weakening exhibited little monocular adaptation but when the normal eye was patched exhibited a strong conjugate adaptation. Thus the results indicate that saccades and the VOR have the capacity for monocular recalibration but that this capacity is more limited than that for conjugate changes.

Adaptation, Physiological↗

PubMed1987

The pattern of changes produced in the saccadic system and vestibuloocular reflex by visually patching one eye.

The purpose of the present study was to determine whether, in the absence of visual input to one eye, saccades remained equal in the two eyes. The same question was addressed for the VOR gain of the two eyes. After 1 wk during which one eye was continuously patched, the saccadic properties of only the unseeing eye showed changes consisting of a change, usually a decrease, in saccadic step magnitude, postsaccadic drift with an exponentially decaying component in the temporal direction, and the appearance of a vertical component as well as vertical postsaccadic drift during horizontally directed saccades. Effects were also observed in the VOR consisting of a change in gain and a vertical component during horizontal head rotation. As with saccades, the vertical component in the patched eye was upward when the eye was deviated nasally. When the patch was removed, normal function was restored within 1 day to the previously patched eye without impairing the function of the unpatched eye. These results suggest that the conjugate nature of saccades and the VOR is in part the consequence of a selective, visually driven, calibration mechanism, which can alter commands to motoneurons of one muscle of a conjugate muscle pair without affecting commands to the other. The similarity of changes observed in the VOR and saccades after patching suggests that elements common to both are altered in the absence of vision.

Animals↗

PubMed1986

A reexamination of the gain of the vestibuloocular reflex.

The properties of the vestibuloocular reflex (VOR) when the axis of rotation is behind the eyes and fixation of a near target is required were studied in the monkey. The magnitude of VOR gain in each eye was found to be above 1.0 and near the ideal value for stabilizing a retinal image. Evidence that this large VOR gain was not visually mediated was provided by the observations that no reduction in gain and no phase lag were observed at high frequencies of head rotation (2 Hz), large gain was observed in the dark, and large gain was observed within 10-20 ms of the start of head rotation. The magnitude of VOR gain was found to increase with increasing radius of head rotation and also to increase with decreasing target distance. When the distances from the two eyes to the target were different the instantaneous velocities and VOR gains of the eyes were also different. The dependence on radius of rotation indicates that the VOR is mediated by a combination of otolith and canal inputs. A general model for otolith-canal interaction is proposed in which VOR gain is based on a computation of target location relative to the head. This model simplifies to the classical VOR reflex when a cyclopean eye is subjected only to angular displacement.

Adaptation, Ocular↗

PubMedDate not supplied

Cine magnetic resonance imaging of ocular motility.

We describe a technique of generation of a cine motion picture of ocular movements in a patient with Duane Type II exotropia. With the magnetic resonance scanning unit, multiple scans can be sequenced to give a graphic animation to the eyes as targets are fixated across the visual field. With this technique, we were able to clearly view the contractility of the extraocular muscles and note the changes in pulling directions of the muscles in this patient. The restriction of movement due to the cocontraction of the horizontal rectus muscles was readily apparent.

Adult↗

PubMedDate not supplied

Ocular pursuit movement assessment by magnetic resonance imaging.

We describe a new technique for generating cinematic magnetic resonance images. This method produces more physiological imaging of extraocular muscles than our previous method. In addition, this technique provides more comfort for the study subject and results in less head movement artifact.

Humans↗

PubMedDate not supplied

Prenatal ethanol exposure alters rat brain morphology but does not affect amygdaloid kindling.

Exposure of the mammalian fetus to ethanol causes a variety of nervous system abnormalities, but the evidence relating to seizure susceptibility is contradictory. Therefore, offspring of rat dams that had consumed a mean of 6.9 g/kg/day of ethanol were compared with pair-fed and free-fed controls on rate of electrical kindling of the amygdala and on open field measures of activity. The Ethanol-exposed males displayed increased ambulation and the Ethanol females displayed increased rearing and defecation in an open field. However, there was no significant difference between the groups in rate of kindling. Although the gross size of the brains measured on a coronal section through the anterior tip of the hippocampus did not differ significantly among the groups, there was a highly significant reduction in percent brain tissue area and a corresponding increase in percent ventricle area in the Ethanol group.

Amygdala↗

PubMedDate not supplied

Adaptation of the VOR in patients with low VOR gains.

Six subjects with histories of vertigo and with vestibulo-ocular reflex (VOR) gains less than 0.5 were tested in an adaptation protocol. After initial VOR testing in the dark, the subjects had a computer-driven visual display system placed on their heads. The system had the capability for variation of visual image magnification. The magnification was set to be 5% greater than the subject's average VOR gain. Subjects then performed active head movements as they carried out a visual searching task looking for objects in a panoramic scene. After 6 minutes with each image, the magnification was increased by 3 to 5%. The process was repeated for a total of 5 images, for a total increase in magnification of approximately 20% over 30 minutes. The VOR gain was measured again. In 17 of 18 conditions tested, the VOR gain increased. The average increase was 16%. Significant increases in VOR gain occurred at 0.32 and 0.64 Hz. The VOR gain increase in these patients occurred in a visual environment that lowered VOR gain in normal subjects. These results suggest that the VOR has an adaptation mechanism tuned to correct for small changes in required gain. Further research is necessary to determine if this method can result in persistent VOR gain improvements and reduction in symptoms and disability in patients with vestibular disorders.

Adaptation, Physiological↗