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At least 1,747 records · Page 97Linked to original sources
PubMed2006

Comparative study of cerebral blood flow in patients with normal-tension glaucoma and control subjects.

PURPOSE: To evaluate regional cerebral blood flow (rCBF) in normal-tension glaucoma patients (NTGs) compared with normal volunteers (controls) in a pilot study. DESIGN: Observational cohort study. METHODS: The Iodine-123-IMP single photon emission computed tomography (SPECT) scans were acquired in 31 NTGs and 18 age-matched controls. The SPECT images in NTGs were classified and the quantitative rCBF data were compared with controls. RESULTS: Seven of 31 NTGs (22.6%) exhibited an Alzheimer's disease (AD)-like perfusion pattern although none of them were clinically diagnosed with AD. The visual field defect of NTGs with an AD-like pattern progressed more rapidly than NTGs with a normal pattern (P=.132). The rCBF in left parietal regions of NTGs with senile sclerotic or focal ischemic disk was significantly lower than controls (P<.05). CONCLUSIONS: A number of NTGs exhibited an AD-like perfusion pattern, suggesting that some of NTGs and AD patients might have a common pathologic mechanism.

Aged↗
PubMed2006

Delayed neuropsychiatric syndrome in a child following carbon monoxide poisoning.

Here, we report the case of a five-year-old boy with carbonic monoxide (CO) poisoning. The patient initially recovered after the initiation of hyperbaric oxygen (HBO) therapy, but lethargy as well as visual and gait disturbances appeared two days later. Left hemiparesis and mood lability also subsequently appeared. Slow frontal activity was noted on electroencephalography, while fluid-attenuation inversion recovery and diffusion-weighted magnetic resonance imaging (MRI) revealed high signal-intensity lesions in the hippocampus and deeper layers of the occipital and frontal cerebral cortex. The neurological symptoms subsided gradually during the 10-day course of HBO therapy, but the left-hand paresis and quadrantic hemianopsia persisted, in association with impaired attention, slow mental processing, and incontinence. Lesions in the globus pallidum were noted on follow-up MRI at 14 days, and cortical lesions became evident as linear, low signal-intensity areas on T1-weighted imaging 4 months after presentation. Delayed neuropsychiatric syndrome in CO poisoning is rare in childhood, although children should be carefully monitored after CO exposure. The finding of cortical laminar necrosis in this patient is quite atypical in CO poisoning, and suggests a broader and previously nonpredicted pathomechanism in this condition.

Carbon Monoxide Poisoning↗
PubMed2006

Discrete bandwidth visual feedback increases structure of output as compared to continuous visual feedback in isometric force control tasks.

BACKGROUND: Performance variability measures provide a partial picture of force control ability. Nonlinear analyses can reveal important information related to the randomness and complexity of the data, providing a more complete picture of the physiological process. METHODS: We investigated the effects of visual feedback on the structure and performance of the force output from isometric force control tasks. Twelve young volunteers completed isometric force control tasks using two types of visual feedback: discrete bandwidth (+/-4% maximal voluntary contraction) and continuous line matching. We determined force signal variability (standard deviation), self-similarity (fractal dimension), and complexity (approximate entropy). Analyses of variance (feedback x muscle group x force level) were conducted and P values less than 0.05 were considered significant. FINDINGS: The force signal in discrete bandwidth feedback, compared to continuous line matching, had significantly a higher standard deviation (P=.000): 2.18 Nm (SD 1.98) vs. 0.99 Nm (SD 0.91); lower fractal dimension (P=.000): 1.07 (SD 0.04) vs. 1.16 (SD 0.04); and lower approximate entropy (P=.000): 0.12 (SD 0.07) vs. 0.26 (SD 0.09). INTERPRETATION: The greater self-similarity (lower fractal dimension) and greater regularity (lower approximate entropy) of the discrete bandwidth, compared to the continuous line matching, may indicate a process that required more kinesthetic (intrinsic) feedback to modulate force. Clinicians may choose to employ visual feedback paradigms that target the use of intrinsic feedback during rehabilitation. Discrete bandwidth feedback may be useful for delineating impairments in motor skill and measuring outcomes of intervention programs.

Adult↗
PubMed2005

Recurrent Candida tropicalis meningitis.

Candida meningitis, a previously rare occurrence, has been increasing in prevalence and often is a result of complications of neurosurgery. We describe the case of a 49-year-old man who presented with headache, vertigo, intermittent blurred vision, and multiple episodes of nausea and vomiting. Computed tomography (CT) showed a left cerebellar hemorrhage with obliteration of the fourth ventricle causing hydrocephalus. He had an occipital craniotomy with transcondylar evacuation of the hemorrhage and placement of a temporary ventriculostomy. The hospital stay was prolonged because of postsurgical complications, and Candida tropicalis meningitis developed. Treatment was started with 400 mg of fluconazole administered intravenously every 12 h. In vitro susceptibility testing showed a minimum inhibitory concentration (MIC) to fluconazole of 1 microg/mL. Fluconazole was therefore continued orally for a total of 60 days, and the patient remained asymptomatic for 2 years. He then presented with increased vertigo and ataxia. Cerebrospinal fluid cultures grew C. tropicalis, which again showed susceptibility to fluconazole with a MIC of 1 microg/mL, identical to that in the previous infection. However, a second course of fluconazole failed to control the infection despite adequate cerebrospinal fluid levels.

Antifungal Agents↗
PubMed2000

The effect of visual targeting on ground reaction force and temporospatial parameters of gait.

BACKGROUND: Visual targeting has been cited as a confounding factor for gait analysis in which measures of ground reaction force and plantar pressure are obtained. OBJECTIVE: To investigate the effect of visual targeting on temporospatial and kinetic aspects of gait when small targets, such as pressure platforms, have to be used. DESIGN: A within subjects repeated measure design was used to measure step parameters and ground reaction forces of 11 healthy volunteers. METHODS: Subjects were required to walk over a 10 m walkway at a self-selected pace. A 30x24 cm(2) target area was superimposed over a hidden Kistler force plate (60x90 cm(2)) mounted at the midpoint of the walkway. Step parameters and ground reaction forces were measured with and without the presence of the target. Ground reaction forces were analysed within the time-domain. RESULTS: Subjects used visual control strategies when approaching targets of similar dimensions to a pressure platform. These strategies were manifested by an increase in the variability of the step length onto the target (P<0.05). However, targeting was observed to have no affect on the magnitude, timing and variability of ground reaction forces when measured within the time-domain and averaged over five trials (P>0.05). CONCLUSIONS: Visual control strategies employed while walking toward a target area have no affect on ground reaction force parameters when measured within the time-domain. RELEVANCE: These findings demonstrate that targeting a 30x24 cm(2) target does not affect ground reaction force parameters, when a gait protocol that fine-tunes the start position is employed. The findings are relevant to gait research in which small force or pressure platforms are used to assess gait kinetics.

Adult↗
PubMed1999

Diurnal fluctuations in corneal topography 10 years after radial keratotomy in the Prospective Evaluation of Radial Keratotomy Study.

PURPOSE: To correlate clinically observed fluctuations in manifest refraction, visual acuity, keratometry, and intraocular pressure (IOP) with changes in the anterior corneal surface as measured by videokeratography in patients 10 years after radial keratotomy (RK). SETTING: Four clinical centers in the United States that participated in the Prospective Evaluation of Radial Keratotomy (PERK) study. METHODS: Thirty-two eyes of 20 PERK patients who noted diurnal fluctuations in vision had clinical examination and videokeratography (TMS-1, Computed Anatomy Inc.) in the morning and evening of the same day a mean of 10.3 years (range 7.8 to 11.7 years) after RK. The videokeratographs were analyzed in terms of various indexes generated by custom-designed software. Morning-to-evening changes in the means of the various clinical and videokeratographic values were assessed using pairwise methods. RESULTS: The mean increase in myopia was 0.36 diopters (D) +/- 0.58 (SD) from morning to evening (P < .01). Analysis of the videokeratographs showed a corresponding increase in average corneal power (ACP), reflecting a steepening of 0.52 +/- 0.45 D (P < .001). The change in ACP was correlated with a change in the manifest spherical equivalent refraction (R = 0.39, P = .03) and a change in best spectacle-corrected visual acuity (R = 0.38, P = .03) over the same period. Similarly, simulated keratometry (SimK) readings correlated with the change in the manifest spherical equivalent refraction (R = 0.38, P = .03 for SimK1; R = 0.37, P = .35 for SimK2; R = 0.4, P = .02 for average SimK), although the standard clinical keratometric data did not (P = .26 for K1, P = .11 for K2, and P = .09 for the mean K). The elevation depression magnitude, a measure of the low-frequency irregularities of the cornea, showed a decrease of 0.32 +/- 1.59, which also correlated with the change in the manifest spherical equivalent refraction (R = 0.37, P = .04). Intraocular pressure tended to decrease from morning to evening (mean change of -0.97 +/- 3.29 mm Hg), but the difference was not significant. Variations in IOP in individual patients, however, were correlated with changes in the manifest spherical equivalent refraction (R = 0.37, P = .04). CONCLUSIONS: Diurnal fluctuations in corneal topographic indexes can be used to evaluate the diurnal fluctuations in refraction and visual acuity after RK. The study findings provide statistical support for the idea that IOP contributes to the diurnal fluctuation in visual acuity after RK.

Adult↗
PubMed2004

Single-photon emission computed tomography in a patient with ictal metamorphopsia.

Metamorphopsia is a type of visual illusion, which has been reported as a rare ictal manifestation. The patient presented with a simple partial status epilepticus characterised by continuous facial metamorphopsia, intermittently accompanied by elementary visual hallucinations or other types of visual illusions. Subtraction single-photon emission computed tomography images showed an increased perfusion in the ventrolateral aspect of the right temporo-occipital junction (middle and inferior occipital, and inferior temporal gyri). The result suggests that the anatomical substrate involved in the generation of ictal facial metamorphopsia is located in the visual association areas at the right temporo-occipital junction.

Brain↗
PubMed2002

Palinopsia and perilesional hyperperfusion following subcortical hemorrhage.

We report a patient who exhibited transient palinopsia and visual hallucinations. Disturbances initially included an auditory component and increasingly were localized to the left visual field. These events occurred during recovery from a right subcortical hematoma with left homonymous hemianopia. Single-photon emission computed tomography (SPECT) demonstrated extensive perilesional hyperperfusion involving parts of the right parietal, temporal, and occipital cortex. Perilesional hyperperfusion disappeared as the visual abnormalities diminished. We believe that excitatory neuronal activation in perilesional cortex during recovery contributed importantly to the transient abnormal perceptions.

Cerebral Hemorrhage↗
PubMed2003

Investigating the effects of a set of intercorrelated variables on eye fixation durations in reading.

The present experiment investigated the influence of 5 intercorrelated variables on word recognition using a multiple regression analysis. The 5 variables were word frequency, subjective familiarity, word length, concreteness, and age of acquisition (AoA). Target words were embedded in sentences and eye tracking methodology was used to investigate the predictive power of these variables. All 5 variables were found to influence reading time. However, the time course of these variables differed. Both word frequency and familiarity showed an early but lasting influence on eye fixation durations. Word length only significantly predicted fixation durations after refixations on the target words were taken into account. This is the 1st experiment to demonstrate concreteness and AoA effects on eye fixations.

Attention↗
PubMed2004

Recording spikes from a large fraction of the ganglion cells in a retinal patch.

To understand a neural circuit completely requires simultaneous recording from most of the neurons in that circuit. Here we report recording and spike sorting techniques that enable us to record from all or nearly all of the ganglion cells in a patch of the retina. With a dense multi-electrode array, each ganglion cell produces a unique pattern of activity on many electrodes when it fires an action potential. Signals from all of the electrodes are combined with an iterative spike sorting algorithm to resolve ambiguities arising from overlapping spike waveforms. We verify that we are recording from a large fraction of ganglion cells over the array by labeling the ganglion cells with a retrogradely transported dye and by comparing the number of labeled and recorded cells. Using these methods, we show that about 60 receptive fields of ganglion cells cover each point in visual space in the salamander, consistent with anatomical findings.

Action Potentials↗
PubMed2002

Current status of screening for diabetic retinopathy in the UK.

This article reviews the current status of retinopathy screening schemes in the UK. There is evidence that high-quality diabetic retinopathy screening schemes are in existence but provision is patchy. Many health authorities have ad hoc screening programmes reaching only about 60% of patients, with unacceptable or undocumented efficacy and minimal quality control. Several models of screening are currently in use with the current preferred option being camera-based screening. Digital imaging systems offer the best prospects for image acquisition, although at present evidence of adequate effectiveness only exists for 35 mm film-based systems. The final report of the National Diabetic Retinopathy Screening Programme commissioned by the UK National Screening Committee for inclusion into the national service framework for diabetes, is thus eagerly awaited and should set standards for screening programmes, in order to improve the care of all those with diabetes. Quality assurance will be the main driver in the immediate future of improvements in screening programmes. Research data will provide the evidence to refine techniques and set targets in the longer term, with the emphasis on cost-effectiveness and quality of life.

Cost-Benefit Analysis↗
PubMed1998

[Measuring the effect of eyeglasses on determination of squint angle with Purkinje reflexes and the prism cover test].

BACKGROUND: The alternating prism and cover test is the conventional test for the measurement of the angle of strabismus. The error induced by the prismatic effect of glasses is typically about 27-30%/10 D. Alternatively, the angle of strabismus can be measured with methods based on Purkinje reflex positions. This study examines the differences between three such options, taking into account the influence of glasses. MATERIALS AND METHODS: The studied system comprised the eyes with or without glasses, a fixation object and a device for recording the eye position: in the case of the alternate prism and cover test, a prism bar was required; in the case of a Purkinje reflex based device, light sources for generation of reflexes and a camera for the documentation of the reflex positions were used. Measurements performed on model eyes and computer ray traces were used to analyze and compare the options. RESULTS: When a single corneal reflex is used, the misalignment of the corneal axis can be measured; the error in this measurement due to the prismatic effect of glasses was 7.6%/10 D, the smallest found in this study. The individual Hirschberg ratio can be determined by monocular measurements in three gaze directions. CONCLUSIONS: The angle of strabismus can be measured with Purkinje reflex based methods if the fundamental differences between these methods and the alternate prism and cover test, and if the influence of glasses and other sources of error are accounted for.

Blinking↗
PubMed1994

Striate cortex extracts higher-order spatial correlations from visual textures.

Spatial correlations define the statistical structure of any visual image. Two-point correlations inform the visual system about the spatial frequency content of an image. Higher-order correlations can capture salient features such as object contours. We studied "isodipole" texture discrimination in V1 to determine if higher-order spatial correlations can be extracted by early stages of cortical processing. We made epicortical, local field potential, and single-cell recordings of responses elicited by isodipole texture interchange in anesthetized monkeys. Our studies demonstrate that single neurons in V1 can signal the presence of higher-order spatial correlations in visual textures. This places a computational mechanism, which may be essential for form vision at the earliest stage of cortical processing.

Animals↗
PubMed2004

Detection of 1st- and 2nd-order temporal-envelope cues in a patient with left superior cortical damage.

This psychophysical study explores the extent to which the auditory cortex is necessary for various aspects of temporal-envelope perception, that is, perception of the slow temporal modulations in amplitude known to be crucial for sound identification. The ability to detect 1st- and 2nd-order sinusoidal amplitude modulation (AM) is evaluated in a single patient showing left-hemisphere damage encroaching the primary and secondary auditory cortices. Here, 1st- and 2nd-order AM refer to (1) sinusoidal variation in the amplitude of a 2 kHz pure tone, and (2) sinusoidal variation in the depth of a 64 Hz AM applied to the 2 kHz pure tone, respectively. The results replicate previous findings by showing that damage to the left auditory cortex results in a selective deficit in auditory sensitivity to the lowest 1St-order AM (i.e., 1st-order AM frequencies < 16 Hz). Moreover, a dissociation is apparent between the ability to detect 1st- and 2nd-order temporal-envelope cues. The patient shows poorer than normal ability to detect 2nd-order AM at low frequencies ranging from 4-23 Hz, but normal ability to detect the high (64 Hz) 1st-order AM carrying these 2nd-order modulations. This result indicates that damage to the left primary and secondary auditory cortices affects the ability to detect temporal variations in the local properties of sounds(such as AM depth). It is also consistent with the idea that, as in vision, central nonlinear mechanisms are involved in the computation of such local (or 2nd-order) temporal properties.

Acoustic Stimulation↗
PubMed2004

Neural attractor network for application in visual field data classification.

The purpose was to introduce a novel method for computer-based classification of visual field data derived from perimetric examination, that may act as a 'counsellor', providing an independent 'second opinion' to the diagnosing physician. The classification system consists of a Hopfield-type neural attractor network that obtains its input data from perimetric examination results. An iterative relaxation process determines the states of the neurons dynamically. Therefore, even 'noisy' perimetric output, e.g., early stages of a disease, may eventually be classified correctly according to the predefined idealized visual field defect (scotoma) patterns, stored as attractors of the network, that are found with diseases of the eye, optic nerve and the central nervous system. Preliminary tests of the classification system on real visual field data derived from perimetric examinations have shown a classification success of over 80%. Some of the main advantages of the Hopfield-attractor-network-based approach over feed-forward type neural networks are: (1) network architecture is defined by the classification problem; (2) no training is required to determine the neural coupling strengths; (3) assignment of an auto-diagnosis confidence level is possible by means of an overlap parameter and the Hamming distance. In conclusion, the novel method for computer-based classification of visual field data, presented here, furnishes a valuable first overview and an independent 'second opinion' in judging perimetric examination results, pointing towards a final diagnosis by a physician. It should not be considered a substitute for the diagnosing physician. Thanks to the worldwide accessibility of the Internet, the classification system offers a promising perspective towards modern computer-assisted diagnosis in both medicine and tele-medicine, for example and in particular, with respect to non-ophthalmic clinics or in communities where perimetric expertise is not readily available.

Diagnosis, Computer-Assisted↗