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The computer-based patient record (CPR), or electronic patient record, is an outgrowth of early medical information system (MIS) and hospital information system (HIS) efforts. However, significant additional requirements must be met to achieve the CPR vision. Contrasts between CPR and HIS/MIS are described. Factors key to completing the transitions are identified.
Single Landolt Cs were presented in one of four positions on a monitor. Subjects responded by pressing one of four buttons (forced choice). A computer selected the size of the Landolt Cs on a logarithmic scale using the "Best PEST" algorithm (Best Parameter Estimation by Sequential Testing), a modern procedure to measure psychophysical thresholds. For comparison, conventional measurements according to DIN 58220 (Deutsche Industrie Norm) were performed with Landolt Cs projected in eight positions, using three out of five correct responses as the threshold criterion. Examination of 23 patients (most of them with senile cataract) did not show any significant difference between the two tests in either visual acuity or reproducibility on two consecutive days. The coefficients of variation between sessions were 22% for the Freiburg test and 26% for the DIN test and 18% between the two tests, pooled over two sessions. The Freiburg acuity test thus appears to be numerically equivalent to the DIN 58220 procedure. In addition, it has a number of advantages: (1) examiner-dependent variability is reduced; therefore, the test can be used by inexperienced examiners; (2) the forced choice technique is used rigorously; (3) mistakes in confounding oblique directions are largely avoided; (4) the procedure is about twice as fast.
Based on the Varioscope, a commercially available head-mounted operating binocular, we have developed the Varioscope AR, a see through head-mounted display (HMD) for augmented reality visualization that seamlessly fits into the infrastructure of a surgical navigation system. We have assessed the extent to which stereoscopic visualization improves target localization in computer-aided surgery in a phantom study. In order to quantify the depth perception of a user aiming at a given target, we have designed a phantom simulating typical clinical situations in skull base surgery. Sixteen steel spheres were fixed at the base of a bony skull, and several typical craniotomies were applied. After having taken CT scans, the skull was filled with opaque jelly in order to simulate brain tissue. The positions of the spheres were registered using VISIT, a system for computer-aided surgical navigation. Then attempts were made to locate the steel spheres with a bayonet probe through the craniotomies using VISIT and the Varioscope AR as a stereoscopic display device. Localization of targets 4 mm in diameter using stereoscopic vision and additional visual cues indicating target proximity had a success rate (defined as a first-trial hit rate) of 87.5%. Using monoscopic vision and target proximity indication, the success rate was found to be 66.6%. Omission of visual hints on reaching a target yielded a success rate of 79.2% in the stereo case and 56.25% with monoscopic vision. Time requirements for localizing all 16 targets ranged from 7.5 min (stereo, with proximity cues) to 10 min (mono, without proximity cues). Navigation error is primarily governed by the accuracy of registration in the navigation system, whereas the HMD does not appear to influence localization significantly. We conclude that stereo vision is a valuable tool in augmented reality guided interventions.
Above threshold, two superimposed sinusoidal gratings of the same spatial frequency (eg 1 cycle deg-1) and equal contrasts, and with orientations balanced around vertical, usually look like a compound structure containing vertical and horizontal edges. However, at large plaid angles (ie large differences between component orientations) and low plaid contrasts there is a tendency for the stimulus to appear as two overlapping gratings (component structure) with obliquely oriented edges. These dependencies of perceived spatial structure in plaids are incompatible with an edge-coding scheme that uses only circular filters to compute zero-crossings, but instead support the idea that different oriented filters can (compound percept) or cannot (component percept) be combined before edges are represented. Here, further evidence is presented in support of this hypothesis. Two-component plaid stimuli had plaid angles of 45 degrees or 90 degrees, and a range of plaid orientations (ie a range of orientations around which the plaid components were balanced). Observers indicated whether each stimulus was perceived as a compound or component structure for a range of plaid contrasts. In addition to angle and contrast effects, perceived spatial structure was also found to depend on plaid orientation: compound structures were perceived more often when the plaid components were balanced around the cardinal axes of the retina. It is suggested that the principles governing the combination of oriented-filter outputs might be learnt during the development of the visual system by using a Hebb-type rule: coactivated filters are more likely to combine their outputs when activated on future occasions. Given the prominence of vertical and horizontal orientations in a carpentered environment, this simple rule promotes a network that combines filters balanced around cardinal axes more readily than oblique axes, in agreement with the results.
The left and right eyes receive subtly different images from a visual scene. Binocular disparities of retinal image locations are correlated with variation in the depth of objects in the scene and make stereoscopic depth perception possible. Disparity stereoscopically specifies a stimulus; changing the stimulus in a way that conserves its disparity leaves the stimulus stereoscopically unchanged. Therefore, a person's ability to use stereo to see the depth separating any two objects should depend only on the disparities of the objects, which in turn depend on where the objects are, not what they are. However, I find that the disparity difference between two stimuli by itself predicts neither stereoacuity nor perceived depth. Human stereo vision is shown here to be most sensitive at detecting the relative depth of two gratings when they are parallel. Rotating one grating by as little as 10 degrees lowers sensitivity. The rotation can make a perceptible depth separation invisible, although it changes neither the relative nor absolute disparities of the gratings, only their relative orientations. The effect of relative orientation is not confined to stimuli that, like gratings, vary along one dimension or to stimuli perceived to have a dominant orientation. Rather, it is the relative orientation of the one-dimensional components of stimuli, even broadband stimuli, that matters. This limit on stereoscopic depth perception appears to be intrinsic to the visual system's computation of disparity; by taking place within orientation bands, the computation renders the coding of disparity inseparable from the coding of orientation.
Hyperacuity is demonstrated in a neuromorphic model of the early visual system. The model incorporates Bayesian principles which are embodied in the dynamics of reentrant and recurrent feedback processes. Each retinotopically mapped area in the model represents a transformation of data from the visual field. Sensory information propagates in a bottom-up direction from one area to the next, while information based on Bayesian priors propagates in a top-down direction through reentrant connections. The 'bottom-up' and 'top-down' information maintain a separate existence in distinct layers of the model, but they interact through local connections within each area. Transformations between one area and the next are defined by the reentrant synaptic connections between areas, while local prior probability maps are defined by local recurrent connections within layers. The representation of hyperacuity is accomplished using a model of functional multiplicity: the large ratio of neurons in striate cortex compared with the number of afferent fibers projecting from the lateral geniculate nucleus. High functional multiplicity, in conjunction with hierarchical reentrant processing, allows the model to represent a fine-grained restoration of the line structure of visual input.
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Many computational models of normal vernier acuity make predictions based on the just-noticeable contrast difference. Recently, Hu, Klein and Carney [(1993) Vision Research, 33, 1241-1258] compared vernier acuity and contrast discrimination (jnd) in normal foveal viewing using cosine gratings. In the jnd stimulus the test grating was added in-phase to the (sinusoidal) pedestal, whereas in the vernier stimulus the same test grating was added with an approx. 90 deg phase shift to the pedestal. In the present experiments, we measured thresholds for discriminating changes in relative position and changes in relative contrast for abutting, horizontal cosine gratings in a group of amblyopes using the Hu et al., test-pedestal approach. The approach here is to ask whether the reduced vernier acuity of amblyopes can be understood on the basis of reduced contrast sensitivity or contrast discrimination. Our results show that (i) abutting cosine vernier acuity is strongly dependent on stimulus contrast. (ii) In both anisometropic and strabismic amblyopes, abutting cosine vernier discrimination thresholds are elevated at all contrast levels, even after accounting for reduced target visibility, or contrast discrimination. (iii) For both strabismic and anisometropic amblyopes, the vernier Weber fraction is markedly degraded, while the contrast Weber fraction is normal or nearly so. (iv) In anisometropic amblyopes the elevated vernier thresholds are consistent with the observers' reduced cutoff spatial frequency, i.e. the loss can be accounted for on the basis of a shift in spatial scale. (v) In strabismic amblyopes and in the normal periphery, there appears to be an extra loss, which can not be accounted for by either reduced contrast sensitivity and contrast discrimination or by a shift in spatial scale. (vi) This extra loss cannot be quantitatively mimicked by "undersampling" the stimulus. (vii) Surprisingly, in some strabismics, and in the periphery, at relatively high spatial frequencies, vernier thresholds appear to lose their contrast dependence, suggesting the possibility that there may be qualitative differences between the normal fovea and these degraded visual systems. (viii) This contrast saturation can be mimicked by "undersampling" the target, or by introducing strips of mean luminance between the two vernier gratings, thus mimicking a "scotoma". Taken together with the preceding paper, our results suggest that the extra loss in position acuity of strabismic amblyopes and the normal periphery may be a consequence of noise at a second stage of processing, which selectively degrades position but not contrast discrimination.
A 39-year-old man had bilateral proptosis and blurred vision for I week. Computed tomography and magnetic resonance imaging showed signs of bilateral orbital pseudotumor, a suprasellar mass, and pulmonary infiltration. Biopsies from retrobulbar and bronchial sites showed similar inflammatory tissue. His disease resolved with pulsed corticosteroid therapy.
Computer simulation of the molecular dynamics of retinal during its photoisomerisation inside a restrictive active site gives a detailed model for the sequence of events in the first step of the vision process. It is proposed that the prelumirhodopsin intermediate contains a strained all-trans retinal molecule produced directly and rapidly from the 11-cis, 12-s-trans conformation in rhodopsin by a bicycle-pedal isomerisation. The model reproduces the main experimental observations and explains how the protein makes the photoisomerisation path unique.
We have used a computable model of human spatial vision to make predictions for phase-discrimination experiments. This model is being developed to deal with a broad range of problems in vision and was not specifically formulated to deal with phase discrimination. In the model, cross correlation of the stimuli with an array of sensors produces feature vectors that are operated on by a position-uncertain ideal observer to simulate detection and discrimination experiments. In this report the stimuli are compound sinusoidal gratings composed of a fundamental and a higher-frequency component added in various phases. We compare model predictions with three key results from the literature: the effect of the contrast of the fundamental on phase discrimination, threshold phase difference as a function of the fundamental frequency, and the contrast required for phase discrimination as a function of the frequency ratio of the two grating components. In the first two cases, the predictions capture the main features of the data, although quantitative discrepancies remain. In the third case, the model fails, and this failure suggests additional restrictions on the combination of information across sensors.
A 34-year-old white male presented with a previous diagnosis of optic atrophy secondary to multiple sclerosis, seeking low vision rehabilitation. This case report is presented to illustrate the importance of prescribing both conventional optical low vision devices, as well as computer low vision aids in order to provide comprehensive low vision rehabilitation for a young visually impaired adult.
A computational model is proposed to account for the adaptive properties of the fly motion system. The response properties of motion-sensitive neurons in the fly are modelled using an underdamped adaptive scheme to adjust the time constants of delay filters in an array of Reichardt detectors. It is shown that the increase in both temporal resolution and sensitivity to velocity change observed following adaptation to constant motion can be understood as a consequence of local adaptation of the filter time constants on the basis of the outputs of elementary motion detectors.
A 50-year-old male presented with a very unusual case of a calcified anterior communicating artery (AComA) aneurysm associated with a tuberculum sellae meningioma. Until 10 years previously, the patient had been a professional soccer player for 15 years. He noticed a slight decrease in visual acuity in the right eye 7 years before. The patient was in the care of an oculist throughout this period. Two months before admission, a significant and rapid decrease of vision in the right eye occurred. Computed tomography and magnetic resonance imaging showed a round-shaped, partially calcified tumorous lesion. Four-vessel angiography revealed a large AComA aneurysm. During surgery, a tuberculum sellae. meningioma was found in combination with an AComA aneurysm with a completely calcified wall. The meningioma was resected totally. The AComA aneurysm with a calcified wall could not be clipped or resected and was left alone. His visual deficit improved postoperatively.
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