Phase retrieval of vitreous floaters: simulation experiment

2020

Knowledge of the structure of vitreous floaters is crucial to evaluate the need for surgical removal of these floaters. We simulated the phase retrieval of microstructures simulating vitreous floaters by an algorithm PhaseLift and investigate the effects of various parameters on the retrieved phase. The object under test was modulated and the coded diffraction patterns were calculated. Next, PhaseLift was used to retrieve the phase. In the current study, we simulate the effect of Gaussian and Poison noise on the phase retrieval of pure phase objects. We apply an iterative algorithm PhaseLift for phase retrieval as this algorithm requires a very few modulating masks and is able to retrieve t…

Rayleigh Equation Anomaloscope from Commercially Available LEDs

2012

Most precise classification of CVD (color vision deficits) can be provided by using anomaloscope. Today anomaloscopes are available, which can evaluate red-green (Rayleigh) and blue-green (Moreland) color defects.DOI: http://dx.doi.org/10.5755/j01.ms.18.2.1928

Color Vision 2020: Introduction by the feature editors

2020

SPECTRAL AND TEMPORAL CHARACTERISTICS OF LIQUID CRYSTAL GOGGLES FOR VISION RESEARCH

2008

ABSTRACT Spectral and switching characteristics of two manufacturer liquid crystal goggles are tested. Experimentally the human stereovision acuity and threshold were studied for the case, when one eye random dot stereo stimulus simulated on the display is continuously blurred or the stimulus contrast is decreased. In order to determine the artefacts of two eye channel crosstalk on the stereostimuli separation the contrast ratio limits for the computer display phosphors wavelengths are determined.

Modelling the appearance of chromatic environment using hyperspectral imaging

2013

Color of objects is a spectral composition of incident light source, reflection properties of the object itself, and spectral tuning of the eye. Light sources with different spectral characteristics can produce metameric representation of color; however most variable in this regard is vision. Pigments of color vision are continuously bleached by different stimuli and optical density of the pigment is changed, while continuous conditions provide an adaptation and perception of white. Special cases are color vision deficiencies which cover almost 8 % of male population in Europe. Hyperspectral imaging allows obtaining the spectra of the environment and modelling the performance of the dichrom…

Cilvēka fizioloģijas un uztveres aktuālie pētījumi 2019.gadā : rakstu krājums

2019

Izdevumā apkopoti LU FMOF Optometrijas un redzes zinātnes nodaļas, kā arī citu struktūrvienību aktuālie pētījumi par cilvēka fizioloģiju un uztveri. 2019. gads Optometrijas un redzes zinātnes nodaļā ir zīmīgs ar nodaļas ilggadējo profesoru jubilejām. Savu apaļo dzimšanas dienu jau ir nosvinējis LU emeritus profesors Ivars Lācis, kurš ir devis lielu ieguldījumu Latvijas Universitātes attīstībā, kā arī viens no Latvijas optometrijas stūrakmeņiem. Šajā izdevumā bez zinātniskiem rakstiem ir īss ieskats viņa biogrāfijā, kura tapusi sadarbībā ar Latvijas Universitātes bibliotēku.

Multispectral colour analysis for quantitative evaluation of pseudoisochromatic color deficiency tests

2010

Multispectral color analysis was used for spectral scanning of Ishihara and Rabkin color deficiency test book images. It was done using tunable liquid-crystal LC filters built in the Nuance II analyzer. Multispectral analysis keeps both, information on spatial content of tests and on spectral content. Images were taken in the range of 420-720nm with a 10nm step. We calculated retina neural activity charts taking into account cone sensitivity functions, and processed charts in order to find the visibility of latent symbols in color deficiency plates using cross-correlation technique. In such way the quantitative measure is found for each of diagnostics plate for three different color deficie…

Multispectral analysis of color vision deficiency tests

2011

Color deficiency tests are usually produced by means of polygraphy technologies and help to diagnose the type and severity of the color deficiencies. Due to different factors, as lighting conditions or age of the test, standard characteristics of these tests fail, thus not allowing diagnosing unambiguously the degree of different color deficiency. Multispectral camera was used to acquire the spectral images of the Ishihara and Rabkin pseudoisochromatic plates in the visible spectrum. Spectral data was converted to cone signals, and successive mathematics applied to provide a simple simulation of the test performance. Colorimetric data of the each pixel of the test image can be calculated an…

The Sun Is no Fun without Rain

2019

Across cultures, people associate colours with emotions. Here, we test the hypothesis that one driver of this cross-modal correspondence is the physical environment we live in. We focus on a prime example – the association of yellow with joy, – which conceivably arises because yellow is reminiscent of life-sustaining sunshine and pleasant weather. If so, this association should be especially strong in countries where sunny weather is a rare occurrence. We analysed yellow-joy associations of 6625 participants from 55 countries to investigate how yellow-joy associations varied geographically, climatologically, and seasonally. We assessed the distance to the equator, sunshine, precipitation, a…

<title>Photoinduced AsSeS thin film phase plates as adaptive optics mirrors for eye aberration correction</title>

2008

Amorphous chalcogenide thin films are excellent materials for holographic recordings. AsSeS thin film coating is a useful optical material for it's thickness to be easily corrected with the use of exposure to light and consecutive chemical etching. Following properties allow to treat the surface of AsSeS chalcogenide films and to use them in adaptive optics systems for correction of the optical wavefront. Hereby, we characterize AsSeS film properties to be used for correction of optical aberrations of the human eye. The thickness of the film is characterized with the method of spectrodensitometry and the surface profile depth with a Hartman- Shack waveform analyzator.

FERROELECTRIC LIQUID CRYSTAL GLASSES FOR AMBLYOPIA RESEARCH

2008

ABSTRACT Ferroelectric Liquid Crystal (FLC) filters offer the speed of electronic light shutters and the vibration free operation. These characteristics make them ideal for applications requiring short exposure times and minimal blur, offering switching times of 0.0002 of a second. FLC filters can be used as the optical shutters for machine vision purposes, also in vision research. On the basis of FLC filters we have developed ferroelectric glasses, allowing temporal separation of optical information for both eyes. In the case of amblyopia (“lazy eye”) the only way to oblige the “lazy” eye to work is to close the other better-seeing eye. We advice an appliance for dynamic visual system trai…

Colour vision experimental studies in teaching of optometry

2005

Following aspects related to human colour vision are included in experimental lessons for optometry students of University of Latvia. Characteristics of coloured stimuli (emitting and reflective), determination their coordinates in different colour spaces. Objective characteristics of transmitting of colour stimuli through the optical system of eye together with various types of appliances (lenses, prisms, Fresnel prisms). Psychophysical determination of mono- and polychromatic stimuli perception taking into account physiology of eye, retinal colour photoreceptor topography and spectral sensitivity, spatial and temporal characteristics of retinal receptive fields. Ergonomics of visual perce…

Influence of ocular aberrations on the diameter of retinal blood vessels

2011

Lower-order and higher-order ocular aberrations influence not only visual perception but also appearance of retinal images. We suggest that the diameter of blood vessels may differ for various patterns of aberrations based on how the maps of point spread functions are orientated to these vessels. We tested our hypothesis by a star chart simulation method and by using simulating aberrations in a real image of a living retina. We observed that broadening of the blood vessels due to ocular aberrations depends not only on the relative orientation of the wavefront but also on their actual width. The change in the diameter ratio is clinically significant and is comparable to changes in the arteri…

Algorithms for skiascopy measurement automatization

2014

Automatic dynamic infrared retinoscope was developed, which allows to run procedure at a much higher rate. Our system uses a USB image sensor with up to 180 Hz refresh rate equipped with a long focus objective and 850 nm infrared light emitting diode as light source. Two servo motors driven by microprocessor control the rotation of semitransparent mirror and motion of retinoscope chassis. Image of eye pupil reflex is captured via software and analyzed along the horizontal plane. Algorithm for automatic accommodative state analysis is developed based on the intensity changes of the fundus reflex.

A/V ratio as predicted by full width at half maximum and by blood vessel tracking in presence of ocular aberrations

2011

Aberrations impact A/V ratio calculated from full width at half maximum. We investigated whether aberrations affect A/V ratio calculated by tracking the vessels. Aberrations changed the A/V ratio. We conclude that aberrations impact A/V ratio.

Phase retrieval for studying the structure of vitreous floaters simulated in a model eye

2021

We simulate vitreous floaters in a model eye and apply a phase retrieval algorithm to recover the structure of the vitreous floaters. The algorithm requires modulating the object under study by a r...

Multispectral analysis and cone signal modelling of pseudoisochromatic test plates

2013

The aim of the study is to determine the consistency of the desired colour reproduction of the stimuli using calibrated printing technology available to anyone (EpsonStylus Pro 7800 printer was). 24 colour vision assessment plates created in the University of Latvia were analysed right after their fabrication on august 2012 and after intense use for 7 months (colour vision screening on 700 people). Multispectral imagery results indicate that the alignment of the samples after seven months of use has maintained on the CIExy confusion lines of deutan deficiency type, but the shift towards achromatic area in the diagram indicate decrease in the total colour difference (ΔE*ab) of test backgroun…

Smaguma punktu metodes un reāls novērotājs, izmantojot multi-spektrālās bildes

2006

Darbs ir uzrakstīts latviešu valodā uz 55 lapām, satur 37 att., 1.pielikumu un 44 literatūras avotus. Darba mērķis. Izstrādāt uzmanības modeli, ņemot vērā monitora spektrālo starojumu. Darba uzdevumi. Raksturot monitora spektrālas īpašības. Izstrādāt stimulu vadītas uzmanības modeli, kurā ir ņemtas vērā no objekta nākošas gaismas spektrālās īpašības. Pielietot modeli eksperimenta stimuliem un atrast saistības ar acu kustību raksturlielumiem. Raksturot uzmanības uzvedību atkarībā no stimula īpašībām. Subjekti. Kopā eksperimentos piedalījās 6 subjekti vecumā no 22 līdz 54 gadiem. 3 no tiem meklēšanas eksperimentā un 3 reakcijas laika eksperimentā. Rezultāti un secinājumi. Izstrādātais stimulu…

Krāsu un formas nozīme attēlu atpazīšanā

2011

Elektroniskā versija nesatur pielikumus