SEARCH · PubMed Health
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Work associated with visual strain results in visual fatigue. Laser radiation in red part of spectrum relieves visual fatigue, activating reduction-oxidation thiol disulfide system in eyes.
PURPOSE/METHODS: To report the occurrence of complex visual hallucinations in a 69-year-old female with bilateral age-related macular degeneration and unilateral cataract. Her orientation and cognition were normal and she showed no evidence of psychiatric symptoms. RESULTS/CONCLUSIONS: A case of a patient who presented with visual symptoms characteristic of the Charles Bonnet syndrome is reported. Various conditions associated with visual hallucinations must be kept in mind by the ophthalmologist (Arch Soc Esp Oftalmol 2003; 78: 327-330).
Those studying biological systems are often interested in the morphology of the various microscopic organelles. The three dimensional reconstruction and visualization of objects provide a powerful tool to understand the nature of each object, and its relationship to other objects. Segmentation is the key to 3D analysis and study of objects that have been recorded with a series of sectioned images, such as from a confocal laser scanning microscope (CLSM). Segmentation is the process of completely separating or isolating the individual objects in an image. A seed-based semi-automatic segmentation tool has been developed to aid in the process of 3D visualization of objects recorded with serial sectioned images, including a boundary creation method that maintains the separate identity of contacting objects. This segmentation tool also allows the user to retain background information as a separate object, providing important reference and landmark information for the object of interest. This paper summarizes the main parts of the segmentation algorithm and presents 3D reconstructions of visual neurons of the housefly, Musca domestica. These reconstructions are compared to typical 3D images produced from other widely used software packages, including standard CLSM imaging software and the popular ImageJ supported by National Institute of Health (NIH). Efforts are underway to develop a user-friendly graphical user interface (GUI) for the segmentation algorithm to entice broader used in research settings.
The visualization of non-ionic contrast medium (Omnipaque 300) in the excretory urography by bolus injection was examined with regard to the normal sided urinary tract in patients with urolithiasis using a densitometer and further compared with that of ionic contrast medium (60% Urografin). In relation to the photographing method, both contrast media showed an increasing frequency of high opaque site in the order of Tomo, A-P and P-A images, which tended to shift from the upper to the lower urinary tract. In relation to the site of determination, both agents showed a good image in the upper urinary tract by the each photographings, while P-A image was better than A-P image in the lower urinary tract, suggesting their high usefulness for the imaging diagnosis. The visualization in relation to the contrast medium used was better in Omnipaque 300 groups than in 60% Urografin group with a significant difference (P less than 0.05-0.01) in the calyx and pelvis of the kidney by the each photographings, suggesting a high usefulness of non-ionic contrast medium. A densitometer seemed to be a useful means for evaluation and examination of the visualization with excellent objectivity as compared with conventional macroscopic methods.
These standards are a revised and updated version of the Guidelines and Standards for Visual Science Libraries Serving Optometric Institutions, a paper first issued by the Association of Visual Science Librarians (AVSL) in 1976. Their purpose is to provide minimum standards as an aid to accreditation bodies and to institutions initiating library service. In this revision, the Standards and Guidelines have been separated physically so that current information can be updated more frequently and easily. The Standards are a qualitative statement about the minimum levels of staff, collections, and services that should be expected from visual science libraries; the Guidelines contain suggested lists of journals and other quantitative data subject to frequent change. The Guidelines are available separately from the AVSL.
Visualization is a major aspect of overall consciousness and human information processing. This paper attempts to establish some of the common elements that lie behind the diverse ways that the terms visualization and visual imagery are used.
The physical characteristics of a visual display unit (VDU) are compared to those of paperwork, through a review of the literature. Certain display characteristics are shown to enhance visual performance using a VDU whilst others significantly decrease it when compared to using hard copy. Overall, display characteristics do not necessarily render VDU use more difficult than if doing similar visual tasks without using a VDU.
In cyclorrhaphan flies, giant tangential neurons in the lobula plate are supplied by isomorphic arrays of evolutionarily conserved achromatic elementary motion detecting circuits originating in the retina. The arrangements among giant tangential neurons is characteristic of a taxon and can differ between taxa having different visual performances. Observations of 12 brachyceran and 4 nematoceran species have identified different behaviors associated with visually stabilized flight. Neuroanatomical comparisons between closely related species having different behaviors and phylogenetically distant species that have similar behaviors suggest that such differences relate to differences of giant tangential cell architecture in the lobula plate. These functionally related differences contrast to anatomical features that reflect phylogenetic affinities. For example, the lobula plates of robber flies, typified by ballistic flight behavior, all differ from other taxa in lacking cyclorrhaphan-type vertical motion-sensitive neurons; instead, they possess an extra complement of horizontal cells in their place. The results suggest that, although circuits that compute elementary motion are conserved across the Diptera, selective pressure has resulted in modifications of their target neurons, thus contributing to the wide variety of visual behaviors observed within this group of insects.
The repeatabilities of both the visual analogue scale (VAS) and numerical rating scale (NRS) as methods of assessing visual quality (VQ) were estimated by obtaining three replicated responses from each of a group of nine normal subjects who viewed a standardized scene under conditions of controlled refractive blur. In both cases, repeatability was highest in the absence of blur but fell markedly as increasing amounts of visual decrement were induced. Coefficients of reproducibility ranged from 4.1 to 36.0 for VASs; and from 1.2 to 34.9 for NRSs. Except where VQ was high, both types showed generally poor repeatability. When the data were used to compare the two methods, no consistent bias was found and agreement was good for high VQ levels. The NRS offers a reasonable alternative to the VAS as a method of assessing subjective VQ.
The second part of the Bennett Lecture for 1975 by Denny-Brown examined the subcortical representation of the dissociation of function described by Denny-Brown and Chambers. Complete removal in the macaque monkey of the corticomesencephalic fibers where they pass from pulvinar to colliculus, and of the colliculus, resulted in the same loss of visual object identification, binocular fixation, and visuosocial behavior that followed removal of area 17. Vision for peripheral movement and spatial orientation ("panoramic vision") remained excellent, with release of catatonia. Conversely, unilateral electrolytic lesions of the mesencephalic tegmentum produced visuospatial distortion, asymmetry of optic righting, and directional difficulties in eye movement (Parinaud syndrome and skew deviation). When bilateral, tegmental lesions produced great constriction of visual field with release of convergence and fixation spasm. Suppression of peripheral attention resulted from perceptual rivalry.
Seventeen children, born of severely diabetic mothers, exhibited segmental optic nerve hypoplasia with normal visual acuity and altitudinal or sector field defects corresponding to the hypoplastic areas of the disc. This is the first group of patients with optic nerve hypoplasia in which a possible cause has been identified. Optic nerve hypoplasia is neither a rare abnormality usually associated with serious central nervous system defects, nor is it always accompanied by decreased visual acuity.
Intraocularly injected colchicine suppresses axonal transport within the developing rat's optic nerve throughout the critical period of visual system development. This results in a stunting of retinofugal terminals and relay neurons in the lateral geniculate nucleus. The present study focuses upon the effects of this unique form of developmental deprivation on the maturation of the visual cortex. Colchicine, in concentrations of from 10(-5) to 10(-2) M, was injected into the eyes of albino rats at birth or at 5, 10, or 15 days of age. Litters were killed at 5 to 50 days after this single injection, and the brains were processed for Nissl, rapid Golgi, histochemical, or electron microscopic analysis. The following results were obtained: Planimetry of coronal sections of the striate cortex revealed a reduction in the thickness of the cortex and in the ratio of neuropil area to neuronal soma area contralateral to the injected eye which was confined principally to layer IV, lower layer III, and upper layer V. This effect was inversely related to postnatal age at injection and directly proportional to colchicine concentration. A rapid Golgi analysis of 51 pairs of layer V pyramidal neurons in control and experimental cortex demonstrated a reduction in the number and size of spines along the portion of the apical dendrite passing through lower layer III and IV following colchicine administration at birth or 5 or 10 days of age but no significant change in the branching pattern of the entire dendritic arbor. Electron microscopy revealed a reduction in the number of small, asymmetric synaptic complexes with the result that the average size of remaining profiles was increased in layers III and IV. Histochemical analysis of cortical succinic dehydrogenase and cytochrome oxidase revealed a distinct band of intense enzyme activity in lower layers III and IV in normal cortex at 20-30 days of age. This band was significantly reduced in intensity after neonatal injection of colchicine as shown by densitometric measurements and comparison of experimental and control cortex. It is concluded that the geniculocortical projection, while not affected directly by colchicine administration, is altered by the secondary effects of axonal transport suppression, leading to an alteration in the establishment of cortical synaptic patterns and arborizations of their postsynaptic neurons whose dendrites are located in those layers recipient to this projection.
Intracellular recordings accompanied by dye fills were made from neurons associated with optic glomeruli in the lateral protocerebrum of the brain of the blowfly Phaenicia sericata. The present account describes the morphology of these cells and their electrophysiological responses to oriented bar motion. The most dorsal glomeruli are each supplied by retinotopic efferent neurons that have restricted dendritic fields in the lobula and lobula plate of the optic lobes. Each of these lobula complex cells represents a morphologically identified type of neuron arranged as an ensemble that subtends the entire monocular visual field. Of the four recorded and filled efferent types, three were broadly tuned to the orientation of bar stimuli. At the level of optic glomeruli a relay neuron extending centrally from optic foci and a local interneuron that arborizes among glomeruli showed narrow tuning to oriented bar motion. The present results are discussed with respect to the behavioral significance of oriented motion discrimination by flies and other insects, and with respect to neuroanatomical data demonstrating the organization of deep visual neuropils.
Subjects participated in perceptual and imagery tasks while their brains were scanned using positron emission tomography. In the perceptual conditions, subjects judged whether names were appropriate for pictures. In one condition, the objects were pictured from canonical perspectives and could be recognized at first glance; in the other, the objects were pictured from noncanonical perspectives and were not immediately recognizable. In this second condition, we assume that top-down processing is used to evaluate the names. In the imagery conditions, subjects saw a grid with a single X mark; a lowercase letter was presented before the grid. In the baseline condition, they simply responded when they saw the stimulus, whereas in the imagery condition they visualized the corresponding block letter in the grid and decided whether it would have covered the X if it were physically present. Fourteen areas were activated in common by both tasks, only 1 of which may not be involved in visual processing (the precentral gyrus); in addition, 2 were activated in perception but not imagery, and 5 were activated in imagery but not perception. Thus, two-thirds of the activated areas were activated in common.
A recurrent system is constructed in order to investigate the role of the backward neural connections found in the primate visual system. The system incorporates a layer to perform localized spatial frequency analysis of input images, a function which has been assumed to take place in the primary visual cortex. The function of the system is examined by simulation. The results show that the system can separate an object pattern from its background, irrespective of its precise position. The acceptable displacement range for input images is determined from the width of the window function used to calculate the local Fourier transform. A multilayer version of the above recurrent system is also constructed.
Cataract patients suspected of having disease which might interfere with good postoperative visual function were referred for evaluation. Monocular steady-state luminance visual evoked potentials (VEPs) were elicited with closed eyes at a stimulus rate of 10 flashes/sec. VEPs were rated as either normal or abnormal. Patients with normal VEPs were predicted to have an acuity of 6/15 (20/50) or better. Patients with abnormal VEPs were predicted to have acuities of 6/18 (20/60) or worse. Postoperative acuities were determined for all patients who underwent surgery and who had no intraoperative or early postoperative complications. The association of preoperative VEPs and observed postoperative acuities were quantitatively compared by a 2 x 2 contingency table for the 59 eyes which met these criteria. The chi-square was significant (p less than 0.001). The overall accuracy of prediction was 76%. Accuracy was 80% for patients with a preoperative acuity of 6/60 (20/200) or better and 75% for those whose postoperative acuity was 6/120 (20/400) or worse. This difference was not statistically significant.
The functional organization of visual cortical cells was studied in two groups of five week old kittens: one group normally reared, the other reared in total darkness from the third day after birth. The following results were obtained: 1. The cells of the normally reared kittens were similar to adult cells except for some aspects of immaturity. In contrast, the cells of the dark-reared kittens were totally non-specific. Their receptive field showed neither orientational nor directional properties. 2. The distribution of cells according to the ocular dominance was not different in either group and was similar to that previously described for "adult" cells. 3. A few hours of visual experience was sufficient to provide specific receptive field properties to the cortical cells of a dark-reared kitten. 4. Conditioning exposure with an oriented grating induced changes in orientational sensitivity in normally reared kittens but not in dark-reared kittens.
MRI was used to study possible morphological changes in the visual system in 12 patients suffering from congenital blindness of peripheral (ocular) origin. While their optical pathways showed degeneration, hypoplasia or atrophy in 7 out of 12 cases, the occipital cortex appeared normal in all cases. This dissociation between afferent pathways and the cortex is contrary to the assumption that visually deprived cortex may undergo degeneration. The finding is congruent with evidence that the occipital cortex is used for other, nonvisual functions.