Search results for " Vision"
showing 10 items of 2709 documents
Blue-yellow deficiencies in young moderate smokers.
2021
Purpose To evaluate whether tobacco affects color vision in young moderate smokers. Methods Chromatic mechanisms of 13 moderate smokers (10–20 cigarettes/day and at least 5 years smoking) and 17 non-smokers in the 18–35 age range were assessed with the Farnsworth-Munsell 100-hue (FM100h) test and short wavelength automated perimetry (SWAP). Results FM100h Total Error Scores (TES) were higher for smokers, and although differences were not significant (p = 0.14), a linear model with principal component analysis was able to explain 95% of the variance in TES and red-green partial error scores, though not in blue-yellow partial error scores (p = 0.07), using the number of years as smokers and t…
Phase information of time-frequency transforms as a key feature for classification of atrial fibrillation episodes
2015
[EN] Patients suffering from atrial fibrillation can be classified into different subtypes, according to the temporal pattern of the arrhythmia and its recurrence. Nowadays, clinicians cannot differentiate a priori between the different subtypes, and patient classification is done afterwards, when its clinical course is available. In this paper we present a comparison of classification performances when differentiating paroxysmal and persistent atrial fibrillation episodes by means of support vector machines. We analyze short surface electrocardiogram recordings by extracting modulus and phase features from several time-frequency transforms: short-time Fourier transform, Wigner-Ville, Choi-…
Relation between fixation disparity and the asymmetry between convergent and divergent disparity step responses
2007
Abstract The neural network model of Patel et al. [Patel, S. S., Jiang, B. C., & Ogmen, H. (2001). Vergence dynamics predict fixation disparity. Neural Computation, 13 (7), 1495–1525] predicts that fixation disparity, the vergence error for a stationary fusion stimulus, is the result of asymmetrical dynamic properties of disparity vergence mechanisms: faster (slower) convergent than divergent responses give rise to an eso (exo) fixation disparity, i.e., over-convergence (under-convergence) in stationary fixation. This hypothesis was tested in the present study with an inter-individual approach: in 16 subjects we estimated the vergence step response to a 1 deg disparity stimulus with a subje…
Temporal Structure of Human Gaze Dynamics Is Invariant During Free Viewing.
2015
We investigate the dynamic structure of human gaze and present an experimental study of the frequency components of the change in gaze position over time during free viewing of computer-generated fractal images. We show that changes in gaze position are scale-invariant in time with statistical properties that are characteristic of a random walk process. We quantify and track changes in the temporal structure using a well-defined scaling parameter called the Hurst exponent, H. We find H is robust regardless of the spatial complexity generated by the fractal images. In addition, we find the Hurst exponent is invariant across all participants, including those with distinct changes to higher or…
Monocular versus binocular pupillometry.
2004
Purpose To quantify differences between monocular and binocular pupil size measurement under scotopic and mesopic conditions. Setting Department of Ophthalmology, Johannes Gutenberg-University, and Department of Medical Biometry, Epidemiology and Informatics, University of Mainz, Mainz, Germany. Methods Computerized dynamic pupillometry (P2000 SA, Procyon Instruments Ltd.) was used at 3 illumination levels: scotopic at 0.03 lux, mesopic low at 0.82 lux, and mesopic high at 6.4 lux. One hundred forty eyes of 70 healthy volunteers without ocular pathology were examined. The subjects were divided into 2 groups. In the first group, the pupil diameter was measured binocularly first. In the secon…
Changes in colour discrimination during the menstrual cycle.
2006
A group of normal women of reproductive age were recruited to investigate colour discrimination during the various phases of the menstrual cycle. Colour vision was tested with the Farnsworth-Munsell 100-hue arrangement test, and the test was administered at 3 time points: the beginning of the cycle, ovulation, and the end of the cycle. We found that colour discrimination was better at ovulation than at the other 2 time points. It is possible that psychological as well as hormonal factors could contribute to improved colour vision performance at ovulation.
Simulating Images Seen by Patients with Inhomogeneous Sensitivity Losses
2012
PURPOSE We aim to simulate how colored images are perceived by subjects with local achromatic and chromatic contrast sensitivity losses in the visual field (VF). METHODS The spatiochromatic corresponding pair algorithm, introduced in a previous article (J Opt Soc Am (A) 2004;21:176-186), has been implemented with a linear model of the visual system. Spatial information is processed separately by the chromatic and achromatic mechanisms by means of a multiscale model, with sensors selective to frequency, orientation, and spatial position, whose mechanism-dependent relative weights change with the spatial location of the image. These weights have been obtained from perimetric data from a patie…
Visual performance with simultaneous vision multifocal contact lenses.
2011
Purpose: The aim was to assess visual performance after PureVision high addition multifocal contact lens (PM) fitting through contrast sensitivity measured under different illumination levels for both distance and near. Methods: In a cross-over study, 20 presbyopic patients were randomly assigned to PM or spectacles. Near contrast sensitivity was measured with the Vistech VCTS 6500 system. Distance contrast sensitivity and distance visual acuity (VA) were measured with the Functional Vision Analyser under photopic (85 cd/m2) and mesopic (3.0 cd/m2) conditions, the latter also under two levels of induced glare: 1.0 lux and 28 lux. Near VA was measured by logMAR charts under approximately 8…
Prevalence of general binocular dysfunctions in a population of university students.
1997
Although some authors report that the prevalence of general binocular dysfunctions (nonstrabismic) for nonpresbyopes in the clinical population is greater than any condition except refractive error, limited research is available to support this statement. This clinical study determined the presence and clinical implications of these conditions in a population of university students with heavy near visual demands.From a group of second year students who were given a thorough eye examination, 65 students were selected. The criteria for selection were the absence of significant uncorrected refractive error, healthy eyes, and no strabismus or amblyopia.32.3% of the subjects showed general binoc…
Chromatic and achromatic visual fields in relation to choroidal thickness in patients with high myopia: A pilot study
2018
Purpose. - To analyse the relationship between the choroidal thickness and the visual perception of patients with high myopia but without retinal damage. Methods. - All patients underwent ophthalmic evaluation including a slit lamp examination and dilated ophthalmoscopy, subjective refraction, best corrected visual acuity, axial length, optical coherence tomography, contrast sensitivity function and sensitivity of the visual pathways. Results. - We included eleven eyes of subjects with high myopia. There are statistical correlations between choroidal thickness and almost all the contrast sensitivity values. The sensitivity of magnocellular and koniocellular pathways is the most affected, an…