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At least 1,279 records · Page 71Linked to original sources
PubMed1999

Designing a license plate.

The majority of license plates in Saudi Arabia contain a 7-digit code to represent the registration number of vehicles. This information can be difficult to read, memorize, and reproduce in a short period of time, such as in the case of recall of hit-and-run accidents. The study reported proposes a registration code composed of 3 letters and 3 digits. This alphanumeric code can be converted into a numerical value which would give close to 20 million possible permutations, which would cover the projected number of vehicles to the year 2012. The original and proposed designs would give, in addition to two other alphanumeric codes, were tested on 60 participants using computer animations at three exposure times (1, 2, and 3 s). The results of the ANOVA on the errors committed and Sheffe tests reveal a significant difference (alpha = 0.01) between the 7-digit design and the other designs at all time intervals. Validation of the laboratory experiments were conducted on 15 different participants in the field, with similar findings.

Analysis of Variance↗
PubMedDate not supplied

Measuring short-wavelength-sensitive cone discrimination thresholds using pseudoisochromatic figures displayed on a color monitor.

PURPOSE: To simplify the testing of short-wavelength-sensitive (SWS) cone function in the clinic. METHODS: SWS-cone discrimination thresholds were measured along the tritan axis using pseudoisochromatic figures displayed on a color monitor. A circular 6 degrees field, containing spatially discrete patches of varying sizes and luminances, was presented on a background. A subset of patches formed the target patch in the shape of a C. Eight subjects with normal color vision reported the direction of the gap in the C using a cursor controlled by a joystick. DATA: were expressed in units of SWS-cone trolands. RESULTS: SWS-cone discrimination threshold increased slowly as the SWS-cone trolands of the starting chromaticity increased. The dependence of the threshold on the SWS-cone activation level was similar to literature reports of chromatic discrimination measured with conventional paradigms. CONCLUSIONS: The advantages of this method: (a) It is a simple intuitive task for patients. (b) The paradigm can be implemented with an 8-bit/gun color monitor. (c) The test avoids the need to define equiluminance for the individual patient before the color test is administered. This method can provide a useful technique for measuring SWS-cone function in a clinical population.

Adult↗
PubMed1987

Special diagnostic and therapeutic modalities in pediatric ophthalmology.

Ophthalmology is a specialty rich in instrumentation used for special diagnostic and therapeutic functions. Many of these special modalities are appropriate to pediatric ophthalmology, and this article discusses them in summary fashion for those who may wish to know about the procedures but who may not be involved directly in their use.

Child↗
PubMed1998

MR imaging and CT of orbital infections and complications in acute rhinosinusitis.

The acute onset of orbital and periorbital inflammation presents the clinician with a diagnostic and therapeutic dilemma, the consequence of which may be very serious. The progression from the initial stage of cellulitis to orbital abscess, cavernous sinus thrombosis, brain abscess, meningitis, or visual loss may be quite rapid at times. CT, ultrasonography, and MR imaging play an important role in clinical management of these patients. Indeed, it is the information obtained through orbital imaging that directs the clinician to use the correct therapeutic modality.

Abscess↗
PubMed1998

Entoptic image quality of the retinal vasculature.

Spatial details of entoptically visible retinal vessels were investigated using transcleral and Maxwellian-view stimulators. Nine normal subjects provided detailed drawings of the entoptic images which were digitized and superimposed onto digitized fundus photographs and fluorescein angiograms from the same eyes. Subjects also used a tracing method to locate visible entoptic features. The trans-scleral method provided images similar in detail to standard fundus photography (lacking capillary detail, but capturing larger arteries, veins, arterioles and venules) in the macula and around the disk. The Maxwellian-view method illuminated the fovea (7.7 degree field) and provided foveola capillary detail (capillaries traversing the foveola, the capillary arcade forming the FAZ) as well as the larger foveal vessels supplying the foveola, and often contained more foveal detail that available with fluorescein angiography.

Adult↗
PubMed2001

The electroretinogram and visual evoked potential of freely moving rats.

The vascularised rat retina could be one of the most useful experimental objects in visual neuroscience to understand human visual physiological and pathological processes. We report here on a new method of implantation for studying the visual system of freely moving rats that provides a rat model for simultaneous recording at corneal and cortical level and is stable enough to record for months. We implanted light emitting diodes onto the skull behind the eyeball to stimulate the eye with flashes and to light adapt the retina with constant light levels. A multistrand, stainless steel, flexible fine wire electrode placed on the eyeball was used for electroretinogram recording and screw electrodes (left/right visual and parietal cortical) were used to record the visual evoked potential and the electroencephalogram. In the present report we focus on the new method of implantation for recording the corneal flash electroretinogram of normal, freely moving rats simultaneously with the visual evoked cortical potential showing examples in various visual experiments. We also introduce a program for retinogram and visual evoked potential analysis, which defines various measures (latencies, areas, amplitudes, and durations) and draw attention to the benefits of this method for those involved in visual, functional genomic, pharmacological, and human ophthalmologic research.

Animals↗
PubMed1987

Benign schwannoma of the pterygopalatine fossa with intracranial extension: a case report.

The authors present a rare case of benign schwannoma arising in the pterygopalatine fossa. The patient, an 18-year-old female, initially noticed blurring of her left eye but later, sudden loss of her left vision occurred. Radiological and computed tomographic studies outlined a mass occupying the left pterygopalatine fossa, which extended into the middle cranial fossa, the maxillary, ethmoid and sphenoid sinuses and the orbit. The histology of a transantral biopsy was reported as a benign schwannoma. The tumor was successfully removed by a transmaxillary approach. The eye symptoms disappeared four weeks following surgery. The nerve of origin of the tumor was not identified. The authors posturate that erosion of the skull base with mild to moderate extension into the middle cranial fossa, does not appear to be a contraindication for excising a schwannoma by the transmaxillary approach in this area.

Adolescent↗
PubMed2002

Virtual-reality techniques resolve the visual cues used by fruit flies to evaluate object distances.

Insects can estimate distance or time-to-contact of surrounding objects from locomotion-induced changes in their retinal position and/or size. Freely walking fruit flies (Drosophila melanogaster) use the received mixture of different distance cues to select the nearest objects for subsequent visits. Conventional methods of behavioral analysis fail to elucidate the underlying data extraction. Here we demonstrate first comprehensive solutions of this problem by substituting virtual for real objects; a tracker-controlled 360 degrees panorama converts a fruit fly's changing coordinates into object illusions that require the perception of specific cues to appear at preselected distances up to infinity. An application reveals the following: (1) en-route sampling of retinal-image changes accounts for distance discrimination within a surprising range of at least 8-80 body lengths (20-200 mm). Stereopsis and peering are not involved. (2) Distance from image translation in the expected direction (motion parallax) outweighs distance from image expansion, which accounts for impact-avoiding flight reactions to looming objects. (3) The ability to discriminate distances is robust to artificially delayed updating of image translation. Fruit flies appear to interrelate self-motion and its visual feedback within a surprisingly long time window of about 2 s. The comparative distance inspection practiced in the small fruit fly deserves utilization in self-moving robots.

Animals↗
PubMedDate not supplied

ON and OFF activity gradients in the lateral geniculate nucleus of the cat: a combined 14C 2-deoxyglucose and D,L-2-amino-4-phosphonobutyric acid study.

Experiments on the lateral geniculate nucleus (LGN) of the cat based on 14C 2-deoxyglucose (2-DG) autoradiography and intraocular injections of 2-amino-4-phosphonobutyric acid (APB) provided evidence for gradients of metabolic activity in the ON and OFF pathways in layer A, but only very weakly, if at all, in layer A1. Alert and freely moving cats were exposed to square-wave gratings over a 45-min period after injection of the 2-DG. When one eye had been treated previously with APB, contralateral layer A showed a clear gradient of 2-DG label indicating that the remaining OFF pathway was most active ventrally in the layer and, by implication, that the ON pathway is normally most active dorsally. No gradient was apparent in layer A1 ipsilateral to the APB eye. Control experiments based on binocular injections of tetrodotoxin (TTX) demonstrated that no gradients were present in the baseline activity within the layers. Finally, monocular injections of TTX provided evidence for gradients of nondominant eye activity in layers A and A1 that were maximal near the interlaminar zone between layers A and A1 and declined in mirror-symmetric fashion toward the dorsal border of A and the ventral border of A1. Combined with earlier anatomical studies showing depth-dependent patterns of geniculo-cortical projection, these results indicate that in the cat, as in several other species, the visual input to striate cortex is partly organized around ON and OFF pathways. In addition, the results suggest that a systematic variation of binocular interaction, perhaps related to ocular dominance, exists through the depths of the geniculate layers.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminobutyrates↗
PubMed2006

One-dimensional and multi-dimensional studies of the exocentric distance estimates in frontoparallel plane, virtual space, and outdoor open field.

The aim of this study is twofold: on the one hand, to determine how visual space, as assessed by exocentric distance estimates, is related to physical space. On the other hand, to determine the structure of visual space as assessed by exocentric distance estimates. Visual space was measured in three environments: (a) points located in a 2-D frontoparallel plane, covering a range of distances of 20 cm; (b) stakes placed in a 3-D virtual space (range = 330 mm); and (c) stakes in a 3-D outdoors open field (range = 45 m). Observers made matching judgments of distances between all possible pairs of stimuli, obtained from 16 stimuli (in a regular squared 4 x 4 matrix). Two parameters from Stevens' power law informed us about the distortion of visual space: its exponent and its coefficient of determination (R2). The results showed a ranking of the magnitude of the distortions found in each experimental environment, and also provided information about the efficacy of available visual cues of spatial layout. Furthermore, our data are in agreement with previous findings showing systematic perceptual errors, such as the further the stimuli, the larger the distortion of the area subtended by perceived distances between stimuli. Additionally, we measured the magnitude of distortion of visual space relative to physical space by a parameter of multidimensional scaling analyses, the RMSE. From these results, the magnitude of such distortions can be ranked, and the utility or efficacy of the available visual cues informing about the space layout can also be inferred.

Adult↗
PubMed2003

Controlling steering and judging heading: retinal flow, visual direction, and extraretinal information.

The contribution of retinal flow (RF), extraretinal (ER), and egocentric visual direction (VD) information in locomotor control was explored. First, the recovery of heading from RF was examined when ER information was manipulated; results confirmed that ER signals affect heading judgments. Then the task was translated to steering curved paths, and the availability and veracity of VD were manipulated with either degraded or systematically biased RF. Large steering errors resulted from selective manipulation of RF and VD, providing strong evidence for the combination of RF, ER, and VD. The relative weighting applied to RF and VD was estimated. A point-attractor model is proposed that combines redundant sources of information for robust locomotor control with flexible trajectory planning through active gaze.

Automobile Driving↗
PubMed1999

Weighted combination of size and disparity: a computational model for timing a ball catch.

How do we time hand closure to catch a ball? Binocular disparity and optical looming provide two sources of information about an object's motion in depth, but the relative effectiveness of the two cues depends on ball size. Based on results from a virtual reality ball-catching task, we derive a simple model that uses both cues. The model is sensitive to the relative effectiveness of size and disparity and implicitly switches its response to the cue that specifies the earliest arrival and away from a cue that is lost or below threshold. We demonstrate the model's robustness by predicting the response of participants to some very unusual ball trajectories in a virtual reality task.

Cues↗
PubMed2001

Optic flow is used to control human walking.

How is human locomotion visually controlled? Fifty years ago, it was proposed that we steer to a goal using optic flow, the pattern of motion at the eye that specifies the direction of locomotion. However, we might also simply walk in the perceived direction of a goal. These two hypotheses normally predict the same behavior, but we tested them in an immersive virtual environment by displacing the optic flow from the direction of walking, violating the laws of optics. We found that people walked in the visual direction of a lone target, but increasingly relied on optic flow as it was added to the display. The visual control law for steering toward a goal is a linear combination of these two variables weighted by the magnitude of flow, thereby allowing humans to have robust locomotor control under varying environmental conditions.

Models, Biological↗
PubMed2006

Modified virtual reality technology for treatment of amblyopia.

PURPOSE: The conventional patching/occlusion treatment for amblyopia sometimes gives disappointing results for a number of reasons: it is unpopular, prolonged, frequently resulting in poor or noncompliance, and also disrupts fusion. The aim of this research was to develop a novel virtual-reality (VR)-based display system that facilitates the treatment of amblyopia with both eyes stimulated simultaneously. METHODS: We have adopted a multidisciplinary approach, combining VR expertise with a team of ophthalmologists and orthoptists to develop the Interactive Binocular Treatment (I-BiT) system. This system incorporates adapted VR technology and specially written software providing interactive 2D and 3D games and videos to the patient via a stereo (binocular) display, and a control screen for the clinician. RESULTS: We developed a prototype research system designed for treatment of amblyopia in children. CONCLUSIONS: The result is a novel way to treat amblyopia, which allows binocular treatment. It is interactive, and as it is partially software based, can be adapted to suit the age/ability, and needs of the patient. This means that the treatment can be made captivating and enjoyable. Further research is on-going to determine the efficacy of this new modality in the treatment of amblyopia.

Amblyopia↗
PubMed2000

[An automated and spectral differentiating dark adaptometer--initial results of a clinical study].

BACKGROUND: Routine measurement of dark adaptation is a lengthy process and the presence of a qualified operator is required. MATERIALS AND METHODS: Our dark adaptometer uses either a red or a green light-emitting diode to produce the threshold stimulus. Through an electronic circuit arrangement the dark adaptation curve is automatically measured. A computer stores the resulting data and renders the statistical analysis possible. To obtain the normal adaptation curve, 33 healthy volunteers were tested. We subsequently examined 32 patients in the clinical assay. RESULTS: The adaptation for the green test light results in an overlapping photopic/scotopic graph and is used as an analogy for the curve resulting from a white test light. The red LED produces the scotopic graph later on with a more elevated threshold. Of the patients examined, 14 with night blindness show the expected pathological results. Correlating to the type of disease, the other 18 patients without night blindness show normal dark adaptation. CONCLUSIONS: In 150 examinations the dark adaptometer proved to be easy to handle, yielding valid and reliable results. The automatic recording allows operator-independent measurements. The dark adaptation rate for red and green and the final cone and rod threshold can be evaluated. The computer control provides statistical analysis and the possibility to delegate the examination.

Adolescent↗
PubMed2003

[Shutter-glasses haploscope with eye-tracking control for fusion therapy].

BACKGROUND: Common haploscopes require a manual input of the presented disparity and particularly prepared images; moreover, they can be used predominantly by orthoptists. We developed a device that makes possible a haploscope on the basis of a computer monitor with shutter-glasses. The presented disparity is determined with help of an eye-tracker. MATERIALS AND METHODS: A patient looks at a monitor through shutter-glasses, the eyes being recorded by a camera. An eye-tracking software determines the fixation points and the angle of strabismus. Images are presented at the monitor with a disparity that is regulated according to these measurements. This is controlled by means of a software so that the disparity is gradually decreased according to the patients abilities. Diagnostic data are recorded permanently. RESULTS: Any monitor contents, such as videos, TV or computer applications, can be used for fusion training or diagnostic purposes with the new apparatus. Initial investigations of patients with heterophoria or intermittent exophoria indicate a decrease of the subjective angle of strabismus by compensation and an increase of the fusional range. CONCLUSIONS: The developed shutter-glass-haploscope with eye-tracking control provides several methods for diagnosis. The appliance provides automated fusion training adapted to the patient that can be done at the working place or at home.

Adolescent↗
PubMed1994

[Electroretinography study of unanesthetized young children].

BACKGROUND: The electroretinogram (ERG) ist an important examination method for the evaluation of retinal dysfunction in children. However it is often difficult and sometimes almost impossible to examine especially younger children with usual methods. Because of its risks, general anesthesia is rarely used. METHODS: ERG examinations were performed without general anesthesia or sedation with DTL (Dawson-Trick-Litzkow) electrodes. These are conjunctival electrodes made of thin microfibers. Several additional modifications of the standard examination technique were utilized, which enabled us to examine children of almost any age. 10 volunteers and 34 children between 6 month and 9 years of age were examined. RESULTS: 62 eyes of 34 children were evaluated. The diagnostic problem could be solved in three quarters of the patients with the ERG. CONCLUSION: With the DTL electrode and some methodical changes in the standard ERG technique it is possible to perform ERG's in little children without anesthesia or sedation. This method can be applied in children over 2 years of age. Below this age an sedation of any kind is necessary.

Child↗