[Visualization of neural excitation].
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Animals↗
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Results for “Computer vision”
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Orbital dermoid cysts: clinicopathologic correlations, classification, and management. The 1997 Josephine E. Schueler Lecture.
The dermoid cyst is one of the most common space-occupying orbital lesions, but there has been no large series that details the clinical, pathologic, and therapeutic aspects of this condition. Furthermore, despite the various presentations and types of dermoid cysts, there is no clinically applicable classification of these lesions. We performed a retrospective histopathologic study of 197 consecutive orbital and periorbital dermoid cysts excised at Wills Eye Hospital during a 32-year period, correlated the histopathologic findings with the recorded clinical and radiographic observations, and devised a clinically applicable classification of orbital dermoid cysts. The mean age at excision was 17 years (range, 5 months to 85 years), and the most frequent clinical finding was a painless subcutaneous mass, present in 89% of cases. In 72% of patients, the mass was located in the superotemporal orbital region and produced no abnormalities of vision or intraocular pressure. Computed tomography and magnetic resonance imaging, performed mainly in the more recent cases, disclosed a characteristic round to ovoid cystic lesion with a well-defined lining. Histopathologically, 165 of the cysts (84%) were lined by keratinizing, stratified squamous epithelium. Ten (5%) were lined by nonkeratinizing epithelium resembling conjunctival epithelium. Hair shafts were present in the wall or lumen of the cyst in 195 (99%) of specimens, sebaceous glands in 148 (75%), and sweat glands in 39 (20%); inflammation was present in 75 cases (38%). Based on these personal observations and a review of the literature, a classification of orbital dermoid cysts is proposed that we believe will provide guidance for the ophthalmologist in the management of these lesions.
Adolescent↗
[Diagnostic possibilities of magnetic resonance (MR) tomography in visual system diseases].
Magnetic Resonance (MR) is a method of the whole visual system imaging, including orbit and visual tract. The advantages of MR over CT are: better contrast resolution, possibility of multiplanar imaging and elimination of ionizing radiation. The main indications and limitations of MR in the evaluation of visual system pathology are presented.
Cerebellar Diseases↗
A model for quantitative assessment of visual field changes in primary open-angle glaucoma with a computerized perimeter DICON TKS 4000.
PURPOSE: To evaluate the feasibility of using the grading algorithm utilized by the Advanced Glaucoma Intervention Study (AGIS) on a Humphrey Field Analyser with program 9 (76/30 degrees Threshold Grid) of a computerized perimeter DICON TKS 4000 and find whether the obtained score can be used to determine the stage of glaucoma. METHODS: Computerized perimetry was performed on 205 eyes with proven or suspected glaucoma. Visual field changes were assessed first subjectively, and then with the scoring method used in AGIS: the size, depth, and location of the visual field defects, and the nasal step were determined using a stencil and then the final score was calculated. RESULTS: Of 205 eyes examined 79 had perimetric changes. These were allocated subjectively into four groups corresponding to four stages of glaucoma: initial, evoluted, advanced and terminal. The mean scores for each group were calculated. There was a statistically significant correlation between the score and the stage of glaucoma. The mean scores for the first 3 stages differed significantly from each other. For stages 3 and 4 the difference was not statistically significant. CONCLUSION: The AGIS scoring method, developed originally for program 30-2 of the Humphrey Field Analyzer, can be applied with the 30 degrees Threshold Grid program of DICON TKS 4000 Perimeter for objective assessment of the glaucoma stage.
Feasibility Studies↗
[Wegener's granulomatosis with meningeal involvement: clinic-radiological correlations].
INTRODUCTION: Wegener's granulomatosis is a systemic vasculitis which, in its classical form, is characterized by involvement of the superior and inferior respiratory tract and the kidneys. The vasculitis may be multisystemic. Ophthalmic and neurological involvement are common (22% and 54% of those affected respectively). When considering involvement of the nervous system, the commonest finding is peripheral neuropathy, particularly in the form of multiple mononeuritis. Meningeal involvement is exceptional. CLINICAL CASE AND CONCLUSIONS: We present a case of Wegener's granulomatosis with meningeal involvement, studied using CT and MR. The findings using imaging techniques are described, and conditions which should be considered in the differential diagnosis are discussed.
Adult↗
Theory and implementation of infomax filters for the retina.
In the first part of this paper we discuss a technical visual sensory system, which--in analogy with the retina--includes some preprocessing of visual information. In so doing, we use an information-theoretic criterion, the infomax ansatz, to optimize the response of the sensory system. In particular, it is shown that the lattice structure of the photoreceptor array has to be taken into account. By a discrete Fourier transformation on a triangular lattice we derive the frequency response of the infomax filter within the first Brillouin zone. To illustrate the response properties, infomax filters adapted to different noise levels are applied to images with different signal-to-noise ratios. This clearly demonstrates the necessity of adaptation of the filter properties to the given noise level. Furthermore, it is shown how to efficiently implement infomax-like filters by simple networks with only nearest-neighbour interactions. A two-layered network topology proves to be very advantageous in implementing the desired high-pass or low-pass properties. The network topology allows for adaption of the network to low and high noise levels by simply adjusting the nearest-neighbour couplings. In the second part of this paper, we compare the previously described information-theoretic requirements on a visual sensory system with biological facts known from the vertebrate retina. The substantial physiological response properties of the vertebrate retina are in agreement with the main features of the infomax filter. Since available experimental data lacks information which is necessary for a more quantitative comparison, we present suggestions for future experiments. Some key anatomical features of the retina of many vertebrates compare well with our two-layered implementation of the infomax filter. The analogy, in particular, concerns the adaption mechanism. To illustrate this point, we summarize some recent experiments which demonstrate that in the retina of some species adaption is based on the release of the neuromodulator dopamine by the interplexiform cells. This causes the horizontal cells to decouple. On the basis of recently gained understanding of the outer plexiform layer of the retina some further hypotheses about the functionality of the retina become obvious and possible future experiments to verify or refute them are suggested. Finally, we discuss the infomax approach from a more general point of view. In particular, we show that redundancy is essential to obtaining noise robustness of an internal representation of the environment as it is produced by a sensory system such as the retina.
Animals↗
[Computer eyeglasses--aspects of a confusing topic].
With the coming into force of the new Austrian Employee Protection Act the issue of the so called "computer glasses" will also gain added importance in our country. Such glasses have been defined as vision aids to be exclusively used for the work on computer monitors and include single-vision glasses solely intended for reading computer screen, glasses with bifocal lenses for reading computer screen and hard-copy documents as well as those with varifocal lenses featuring a thickened central section. There is still a considerable controversy among those concerned as to who will bear the costs for such glasses--most likely it will be the employer. Prescription of such vision aids will be exclusively restricted to ophthalmologists, based on a thorough ophthalmological examination under adequate consideration of the specific working environment and the workplace requirements of the individual employee concerned.
Accommodation, Ocular↗
Detection of bilateral symmetry using spatial filters.
When bilaterally symmetric images are spatially filtered and thresholded, a subset of the resultant 'blobs' cluster around the axis of symmetry. Consequently, a quantitative measure of blob alignment can be used to code the degree of symmetry and to locate the axis of symmetry. Four alternative models were tested to examine which components of this scheme might be involved in human detection of symmetry. Two used a blob-alignment measure, operating on the output of either isotropic or oriented filters. The other two used similar filtering schemes, but measured symmetry by calculating the correlation of one half of the pattern with a reflection of the other. Simulations compared the effect of spatial jitter, proportion of matched to unmatched dots and width or location of embedded symmetrical regions, on models' detection of symmetry. Only the performance of the oriented filter + blob-alignment model was consistent with human performance in all conditions. It is concluded that the degree of feature co-alignment in the output of oriented filters is the cue used by human vision to perform these tasks. The broader computational role that feature alignment detection could play in early vision is discussed, particularly for object detection and image segmentation. In this framework, symmetry is a consequence of a more general-purpose grouping scheme.
Computer Simulation↗
Computerized colour vision testing.
There are many advantages to the computerization of colour vision tests. However, previous computerized colour vision tests have involved equipment and methods not commonly used in clinical practice. We created computer emulations of the City University Colour Vision Test (CUT), Ishihara plates and American Optical Hardy-Rand-Rittler (AO-HRR) plates using a commonly available 24-bit colour Macintosh computer. Our colour monitor was calibrated to standard display white (D65), and colour plates were imaged with a colour scanner. The computerized colour images were compared with the standard test plates in a sample of 21 subjects with normal colour vision, 10 patients with congenital red-green defect and 1 patient with an acquired mixed colour defect. The computer images of the three tests correlated well with their conventional counterparts on kappa statistic analysis (p < 0.001), for both the colour normal and colour defective groups. We conclude that our computer emulations of the CUT, Ishihara and AO-HRR tests screen subjects with normal colour vision with high specificity and delineate congenital colour defects with a sensitivity comparable to that of their conventional counterparts.
Adult↗
Dynamics of antagonistic neural processing elements.
Two coupled nonlinear first-order systems whose dynamic behavior reflects the neural states exhibited by a spatially localized population of excitatory and inhibitory nerve cells are described. The dynamics of each constituent neural subpopulation represents a fundamental neural information processing element (PE) of a complex neural system. Phase plane analysis is used in this paper to show how such antagonistic positive acting (excitatory) and negative acting (inhibitory) PEs can generate diverse steady-state and temporal phenomena when the nonlinear system parameters of the PEs are altered. By modifying a selected set of parameters, it is possible to program the positive and negative PEs to exhibit various dynamic attributes such as multiple stable states, transient response behavior and limit-cycle oscillations. These dynamic attributes may be used to perform a variety of useful computational tasks in signal processing and vision systems such as short-term memory (STM), temporal filtering (TF) and pulse frequency modulation (PFM). Computer simulations are presented throughout this paper in order to illustrate these dynamic attributes.
Algorithms↗
Sparse coding and decorrelation in primary visual cortex during natural vision.
Theoretical studies suggest that primary visual cortex (area V1) uses a sparse code to efficiently represent natural scenes. This issue was investigated by recording from V1 neurons in awake behaving macaques during both free viewing of natural scenes and conditions simulating natural vision. Stimulation of the nonclassical receptive field increases the selectivity and sparseness of individual V1 neurons, increases the sparseness of the population response distribution, and strongly decorrelates the responses of neuron pairs. These effects are due to both excitatory and suppressive modulation of the classical receptive field by the nonclassical receptive field and do not depend critically on the spatiotemporal structure of the stimuli. During natural vision, the classical and nonclassical receptive fields function together to form a sparse representation of the visual world. This sparse code may be computationally efficient for both early vision and higher visual processing.
Action Potentials↗
Can we get our minds around remote eye and vision consultation?
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Computer Communication Networks↗
Optimization of 125I ophthalmic plaque brachytherapy.
Episcleral plaques containing 125I sources are often used in the treatment of ocular melanoma. Within four years post-treatment, however, the majority of patients experience some visual loss due to radiation retinopathy. The high incidence of late complications suggests that careful treatment optimization may lead to improved outcome. The goal of optimization would be to reduce the magnitude of vision-limiting complications without compromising tumor control. We have developed a three-dimensional computer model for ophthalmic plaque therapy which permits us to explore the potential of various optimization strategies. One simple strategy which shows promise is to maximize the ratio of dose to the tumor apex (T) compared to dose to the macula (M). By modifying the parameters of source location, activity distribution, source orientation, and shielding we find that the calculated T:M ratio can be varied by a factor of 2 for a common plaque design and posterior tumor location. Margins and dose to the tumor volume remain essentially unchanged.
Biophysical Phenomena↗
Low-vision software & strategies.
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Computer Peripherals↗
Beam-deflection method of diagnosing impaired vision.
We describe a simple method to assign a diagnosis of cataract to patients with obscurely impaired vision as well as to those with mild lens opacities. When the narrowest slit is used in a slitlamp examination, a small beam of light appears on the macula. Routine fundoscopy with the 78.0 diopter lens or a 3-mirror glass is appropriate. If a cataract is present, the beam of light is scattered into several straight lines, distorted lines, or both. This has proved a useful diagnostic tool when the lens appears clear but the patient's vision is impaired, and extensive examinations such as computer tomography or nuclear magnetic resonance tomography for impaired vision may be avoided. The beam-deflection method uses devices that are generally available and can detect cataract in the early stages of development.
Adolescent↗
A clear policy: eyesight testing.
Like it or not employers are now required to provide employee eye and eyesight tests on request. Following last month's article on the Display Screen Equipment Regulations Hazel Montague looks at this specific duty and describes how one company has taken a proactive approach to setting up a vision screening programme.
Computer Terminals↗
On raising our sights.
There are some very strong traditions in contemporary research on spatial vision that have arisen, in large measure, through advances in technology. This is especially true of research on the neurophysiology of vision, e.g. in recording from single cells, and in developments in computing that have promoted the study of machine vision. No one would dispute that these are major advances in the field, but one may ask whether they have unduly constrained the sorts of question that we ask about the visual processes. It is argued that they have, and that it is timely to stand back to see what other problems and questions have suffered neglect. Two items seem to be quite ripe for reconsideration: the question of how to understand the enormous adaptability of visual systems to sensory rearrangement (by means of distorting lenses, for example); and the very broad matter of keeping our perceptual processing in close and coherent touch both with stimulation, and with the properties of the physical/biological environment--what Gibson called the problem of veridical perception. It is argued that the two items are closely allied, and can be approached from a single theoretical stance. The one I favour is outlined, and I claim that it is one that has little to do, in the first instance, with either neurophysiology or computation. In that sense tackling the two questions involves raising our sights above the current traditions of vision research, but that of course does not in any way mean attempting to belittle the immense advances that those traditions have brought about.(ABSTRACT TRUNCATED AT 250 WORDS)
Adaptation, Ocular↗