Search results for "Spatial frequency"
showing 10 items of 92 documents
Accommodative stimulus-response curves to low-pass filtered natural images
2018
To assess how the monocular steady-state accommodative stimulus-response curve is modified when viewing low-pass filtered natural images. Eighteen adult subjects participated in the study. The accommodative stimulus-response curve was objectively assessed by means of a Hartmann-Shack wavefront sensor. Measurements were taken at different accommodative demands. Target images were low-pass filtered versions of a natural image that were obtained applying different digital spatial filters that limited the spatial frequency content of the natural image. Cutoff spatial frequencies were set at 30, 21, and 15 cycles per degree (cy/deg). Mean data obtained for each target were fitted to linear model…
Effect of luminance on photopic visual acuity in the presence of laser speckle
1988
Visual acuity in coherent and incoherent light has been determined by using square-wave gratings of 100% contrast. Luminance was varied from 3 to 400 cd/m2. Coherent illumination resulted in a 40% loss of visual acuity. This is probably due to the masking effect of coherent spatial noise (speckle). However, the most interesting finding is the change in shape of the photopic visual-acuity-luminance function. With coherent illumination, the function is vertically displaced and of a different gradient. An increase in luminance produces a decrease in visual acuity. This indicates that the masking effect of the speckle is dependent on luminance. Two observers were used, and similar results were …
On-eye optical quality of daily disposable contact lenses for different wearing times
2012
Purpose To quantify the optical quality of various daily disposable contact lenses in vivo and to ascertain its variation in terms of wearing time by means of objective non-invasive determination of wavefront patterns. Methods The crx1 adaptive-optics system was used to measure the wavefront aberrations in 15 myopic eyes before and at 2-h intervals after contact lens fitting, over a 12-h wearing period. Seven types of contact lenses having different material, water content and lens design were evaluated in this study: Dailies Total1, Dailies AquaComfort Plus, Proclear 1 Day, 1-Day Acuvue TruEye, 1-Day Acuvue moist, SofLens daily disposable and Clariti 1-Day. The aberration data were analyse…
Diseño de una nueva prueba para medir la función de sensibilidad al contraste con iPad
2015
[EN] Purpose: To introduce a new application (ClinicCSF) to measure Contrast Sensitivity Function (CSF) with tablet devices, and to compare it against the Functional Acuity Contrast Test (FACT). Methods: A total of 42 subjects were arranged in two groups of 21 individuals. Different versions of the ClinicCSF (.v1 and .v2) were used to measure the CSF of each group with the same iPad and the results were compared with those measured with the FACT. The agreements between ClinicCSF and FACT for spatial frequencies of 3, 6, 12 and 18 cycles per degree (cpd) were represented by Bland---Altman plots. Results: Statistically significant differences in CSF of both groups were found due to the change…
Choice of spatial frequency for contrast sensitivity evaluation after corneal refractive surgery.
2002
ABSTRACT PURPOSE: To study the utility of measurements of contrast sensitivity at different spatial frequencies as an index of visual recovery following refractive surgery. METHODS: Contrast sensitivity at 1.5, 3, 6, 12, and 18 c/deg was measured with the Stereo Optical FACT chart in 20 patients after photorefractive keratectomy (PRK) using the Nidek EC-5000 excimer laser system, and in 18 patients following laser in situ keratomileusis (LASER). Contrast sensitivity was measured preoperatively and 1, 3, 6, and 12 months after surgery. RESULTS: Results showed a statistically significant reduction (P<01) in contrast sensitivity at all spatial frequencies in PRR patients during the first an…
Differences in visual performance of AcrySof ReSTOR IOL in high and low myopic eyes.
2009
PURPOSE To determine the differences in refractive and visual results obtained in eyes with high and low myopia after multifocal intraocular lens (IOL) implantation. METHODS Monocular visual acuity for distance and near, with and without distance correction, and photopic and mesopic contrast sensitivity were measured at 6 months after surgery in 152 myopic eyes implanted with the AcrySof ReSTOR Natural (SN60D3) IOL. Two groups were created: high and low myopia (76 eyes in each). RESULTS Monocular best distance-corrected visual acuity was 0.02+/-0.06 logMAR for low myopes and 0.05+/-0.09 logMAR for high myopes. Monocular best distance-corrected near visual acuity was 0.04+/-0.05 and 0.07+/-0…
Synergy of spatial frequency and orientation bandwidth in texture segregation
2021
Defining target textures by increased bandwidths in spatial frequency and orientation, we observed strong cue combination effects in a combined texture figure detection and discrimination task. Performance for double-cue targets was better than predicted by independent processing of either cue and even better than predicted from linear cue integration. Application of a texture-processing model revealed that the oversummative cue combination effect is captured by calculating a low-level summary statistic (\(\Delta CE_m\)), which describes the differential contrast energy to target and reference textures, from multiple scales and orientations, and integrating this statistic across channels wi…
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…
The effect of simulated normal and amblyopic higher-order aberrations on visual performance.
2012
Purpose To study the effect of simulated amblyopic and normal higher-order aberrations on visual performance of normal eyes. Methods To assess visual function, an adaptive optics visual simulator was used to compensate volunteers' ocular aberrations and simulate the wavefront aberration patterns found in healthy and amblyopic eyes in 7 healthy individuals. Visual acuity for high (100%), medium (50%), and low (10%) contrast and contrast sensitivity at 10, 20, and 25 cycles per degree (cpd) were measured after simulation of both pattern aberrations. The modulation transfer function and the point spread function were computed based on the aberration data. All measures were taken for 3 and 5.5 …
Forced Rayleigh scattering from non-harmonic gratings applied to complex diffusion processes in glass-forming liquids
1999
Abstract Tracer diffusion of 9,10-phenanthrenequinone (PQ) and its photoproduct in super-cooled phenolphthalein-dimethyl-ether (PDE) was studied by forced Rayleigh scattering. In order to investigate the spatial frequency dependence of the grating dynamics, several spatial harmonics of the grating with non-sinusoidal phase profile produced by non-linear recording were monitored. An optical scheme with a diverging reading beam is proposed for simultaneous reconstruction of the harmonic components.