Liquid crystal goggles for vision science applications

Spectral and switching characteristics of two manufacturer liquid crystal goggles are tested, and a contrast ratio for the computer display phosphors wavelengths is determined. Goggles are used in vision science experiments for random dot stereo stimuli phase separation. The human stereovision acuity and threshold was studied for case, when one eye random dot stereo stimulus simulated on the display is cotinuously blurred or the stimulus contrast is decreased.

PLZT Electro-optic Q-switch for Er:Cr:YSGG laser

Q-switching of the Er:Cr:YSGG laser at 2.79 micrometers is realized using electrooptic modulators of PLZT X/65/35 ceramics. The high (but slow as compared with single crystals) electrooptical effect in PLZT allowed to construct Q-switches with an aperture larger than 4 X 4 mm 2 , small lengths of 3 - 6 mm, with a control voltage of 1000 - 1500 V. Q-switching is realized using modulators in two modes--as a (lambda) /2 switch placed into the laser cavity at the Brewster angle avoiding reflection losses and as a (lambda) /4 switch with higher single pass losses due to Fresnel reflections. A higher laser output was obtained using (lambda) /2 switching. The obtained pulses had a halfwidth of 150…

<title>Modified crossed-cylinder aberroscope</title>

We report a technique to estimate eye aberrations, based mainly on the subjective crossed-cylinder method. In order to obtain accurate coordinates of cross sections of the aberration distorted grid image on the retinal plane, needed in subjective methods, fusion of two images is used. The image seen by the eye under investigation is fused by the patient with a similar grid generated and reshaped in the appropriate way on the computer screen. The computer simulated image is viewed either by the second eye (in order to avoid eye rivalry and suppression processes, that are typical for such conditions, stimuli for both eyes are discontinuous and are displayed sequentially with a frequency of 50…

Phase retrieval of vitreous floaters: simulation experiment

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…

Eye Cataract Simulation Using Polymer Dispersed Liquid Crystal Scattering Obstacles

Polymer dispersed liquid crystals with electrically induced variations of light scattering extent similar to that of transparent PLZT ceramics are used for simulation of different development stages of eye cataract. Wavelength dependencies of scattering are determined in the visible spectral range, and human visual response looking through the scattering obstacle to the onset of various spatial frequency stimuli is determined psychophysically and electrophysiologically in order to find correlation between the scattering extent, visual acuity and visual evoked potential VEP chromatic characteristics.

Dependence of Perceived Purity of a Chromatic Stimulus on Saturation Adaptation

Background and Objective. The purpose of sensory adaptation of the visual system is to adjust sensitivity of the photoreceptors to optimize the dynamic range of response of the visual system. It has been shown in numerous research papers that chromatic adaptation influences both color appearance and color discrimination. However, there are almost no studies in which the influence of chromatic adaptation on perceived purity has been investigated. Therefore, the aim of this study was to investigate how chromatic adaptation to stimuli with certain saturation influences perceived purity of test stimuli with the same hue but different saturation. Material and Methods. As the stimuli were modulat…

<title>Assessment of ocular stereovision prevalence and eye dominance stability</title>

The paper reports on the development of the equipment for studies of the eye dominance and ocular stereoprevalence by using black-and-white and color stereostimuli. The stereostimuli are separated either by color-filter goggles or phase separating liquid-crystal-shutter goggles. The stability of the stereoprevalence is studied by artificial step-by-step deterioration of the retinal image quality, particularly in the dominant eye. The stimuli are blurred using spatial Gaussian filtering. The polymer-dispersed-liquid-crystal cell placed in front of the dominant eye induces a controllable light scattering. The stimuli-blurring and light-scattering methods exhibit different influence on the eye…

PLZT laser beam modulator

Abstract Laser beam modulator on transparent electrooptic PLZT ceramics are developed for the use in teaching process in schools and universities. Characteristics of the modulator and its electronic control unit are given.

<title>Estimation of stereovision in conditions of blurring simulation</title>

The aim of this study was to evaluate the simulation of eye pathologies, such as amblyopia and cataracts, to estimate the stereovision in artificial conditions, and to compare the results on the stereothreshold obtained in artificial and real- pathologic conditions. Characteristic of the above-mentioned real-life forms of a reduced vision is a blurred image in one of the eyes. The blurring was simulated by (i) defocusing, (ii) blurred stimuli on the screen, and (iii) occluding of an eye with PLZT or PDLC plates. When comparing the methods, two parameters were used: the subject's visual acuity and the modulation depth of the image. The eye occluder method appeared to systematically provide h…

<title>PLZT ceramics as optical phantom for simulation of light scattering in eye segments and other biological tissues</title>

ABSTRACT Coefficients of light absorption ta and scattering for biological tissues lie within a broad range - minimum ones forhealthy eye tissues up to higher values (fe. t a 0.3 cm and i = 40 cm' at 633 nm for muscle tissues ) for other andmainly turbid tissues. The specific feature of the transparent PLZT ceramics (having absorption t a > 0. 1 cm in the visible and in the near infrared spectrum range) is electrically controlled light scattering. The present work reports onexperimental results of the light transport and backscattering for PLZT 9/65/35 (Pb091La009Zr065Ti035O3). We proposePLZT ceramics with fast and continuously controllable light scattering as an optical phantom for photon …

Scattering and Depolarization in a Polymer Dispersed Liquid Crystal Cell

An imaging polarimeter in transmission has been used to explore the effects of scatter and depolarization induced by a polymer dispersed liquid crystal cell. The experiment was carried out for three visible wavelengths. Both a directional and a scattered component can be distinguished in the light transmitted by this material. Whereas the directional component increased with voltage, the scattered portion decreased. This was a common behaviour for all three wavelengths. The polarimetric analysis revealed that the degree of polarization was also affected by changes in the voltage applied to the cell. Depolarization effects in the scattered component were usually high and decreased with volta…

Warming of water in a glass

The article focuses on the process of water warming from 0 °C in a glass. An experiment is performed that analyses the temperature in the top and bottom layers of water during warming. The experimental equipment is very simple and can be easily set up using devices available in schools. The temperature curves obtained from the experiment help us to understand the process of convection in the glass and to determine the temperature at which the density of water is maximum. In addition, computational fluid dynamics—CFD modeling is carried out to facilitate better comprehension of the phenomenon observed in the experiment.

Dynamics and accuracy of eye aberration measurements

Merits of vision in presence of light scattering using Tiffen ProMist filters

Light scattering caused by Tiffen ProMist photographic filters of various grades at different laser radiation 640 nm, 532 nm and 405 nm was objectively studied and compared. The lack of removal of speckles from the scene of laser radiation scattering did not allow an accurate assessment of the effect of scattering on the decrease in image contrast. Subjective deterioration in visual acuity using various contrast optotypes and contrast sensitivity was assessed by scattering induction using filters up to grade #5. Vision contrast sensitivity diminishes within all studied spatial frequency range 0.5-18 cpd. The degradation of the impact factor to visual acuity without scattering filters when t…

SPECTRAL AND TEMPORAL CHARACTERISTICS OF LIQUID CRYSTAL GOGGLES FOR VISION RESEARCH

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.

Photorefraction demonstrations using electrooptic PLZT ceramics modulators

PLZT ceramics electrooptic (EO) modulator was designed for demonstrations and student's laboratory works to study photorefraction using Ar+ laser (λ = 514 nm). PLZT element had an aperture of 1.5 x 8 mm2 and thickness of 1.5 mm. Reading of recorded patterns was realized by applying to the element the biasing electric field. The most efficient writing took place for ceramics composition PLZT 8.75/65/35. The total intensity of two writing beams was up to 300 mW, the applied electric field during writing -- up to 20 kV/cm. The diffraction efficiency depended on the applied biasing reading electric field EBR . For the reading He-Ne laser the diffraction efficiency η ≈ 0.48 was obtained at the b…

Modelling the appearance of chromatic environment using hyperspectral imaging

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…

Light scattering in artificial fog and simulated with light scattering filter.

Disability glare, affecting e.g. road safety at night, may result either from intraocular light scattering or from external conditions such as fog. Measurements were made of light scattering in fog and compared with intraocular straylight data for normal eyes and eyes with simulated cataract. All measurements were made with a direct compensation flicker method. To estimate light scattering levels in fog, straylight measurements were carried in a fog chamber for different densities of fog. Density was characterized by the meteorological term visibility V and ranged from 7 to 25. Test distance for measurements in the fog was constant at 5 m. Cataract eye conditions were simulated by placing a…

Passive and active light scattering obstacles

Simulation of vision pathologies and adverse viewing conditions in laboratory conditions requires optical phantoms with different level of light scattering. Such obstacles are designed as passive or active elements applying several technologies. We used for studies two kinds of solid state smart materials with electrically controllable light scattering - electrooptic PLZT ceramics, polymer dispersed liquid crystals PDLC and obstacles with fixed light scattering - composite of polymer methylmethaacrilat PMM together with grinded glass microparticles. Report analyzes optical characteristics of such obstacles - attenuation, scattering, depolarization of different wavelength light at various sc…

Electro-optic control of photographic imaging quality through ‘Smart Glass’ windows in optics demonstrations

An experimental setup allowing the modeling of conditions in optical devices and in the eye at various degrees of scattering such as cataract pathology in human eyes is presented. The scattering in cells of polymer-dispersed liquid crystals (PDLCs) and 'Smart Glass' windows is used in the modeling experiments. Both applications are used as optical obstacles placed in different positions of the optical information flow pathway either directly on the stimuli demonstration computer screen or mounted directly after the image-formation lens of a digital camera. The degree of scattering is changed continuously by applying an AC voltage of up to 30–80 V to the PDLC cell. The setup uses a camera wi…

Applicability of a binary amplitude mask for creating correctors of higher-order ocular aberrations in a photoresistive layer

Ocular aberrations can be corrected with wavefront correctors created in a photoresist layer. The simplest type of the mask used in optical lithography is a binary amplitude mask. It is known that such a mask has a periodic hole pattern. The purpose of this research was to assess applicability of a binary amplitude mask for creating ocular wavefront correctors. The photoresist was applied to the substrate by using the dip-coating method. The photoresist layer was illuminated through a mask printed on a transparent film by using a laser printer. The surface of the wavefront correctors was evaluated by aberrometry, scanning electron microscopy and profilometry method. The dip-coating method c…

Mesopic vision characteristics at decreased contrast in fog

Perception of different color contrast stimuli was studied in the presence of light scattering in a fog chamber in Clermont-Ferrand and in laboratory conditions where light scattering of similar levels was obtained. Blue (shortest wavelength) light is scattered in fog to the greatest extent, causing deterioration of vision quality especially for the monochromatic blue stimuli. We have done spectral measurements of the light source in different density fog conditions and no spectral changes were found produced by the fog. Psychophysical measurements of the acuity in fog were done for two subjects with optotypes analyzed for red and blue stimuli.

Howard–Dolman stereovision test at different opponent colour stimuli

The purpose of this study was to investigate visual depth perception of real physical colour stimuli with red-green and blue-yellow opponency. We modified the Howard–Dolman stereotest where subjects should determine the closer of two bars emitting the light of definite colour placed in front of a CRT monitor served as colour background. Two-alternative forced-choice paradigms were used to determine depth perception threshold values. Thresholds close to 5–10 arcsec for luminance and colour contrast stimuli were revealed both for red-green and blue-yellow stimuli. A term, stereosensitivity – a reciprocal magnitude of the stereothreshold – was introduced to separately analyse luminance and col…

Effect of Light Scattering Simulation in the Eye on Different Color Stimuli Perception

One of the factors which influences visual functions is intraocular light scattering. To assess the effect of light scattering and stimulus color on visual functions, visual acuity and retinal straylight were measured with and without light scattering occluder. For visual acuity measurements black Landolt optotypes on red, green and blue background were used. Retinal straylight was measured with a direct compensation method using the same colors stimuli. For one subject straylight was measured with 5 different light scattering levels of eye occluder.

Multispectral colour analysis for quantitative evaluation of pseudoisochromatic color deficiency tests

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…

Er:YAG laser giant-pulse generation

Three possibilities of mid-infrared Er:YAG lasers Q-switching were investigated: mechanical and two electro-optical ones. The mechanical method of Q-switching was proved by using of a rotating mirror placed inside the resonator; Pockels or Kerr cells were used for the electro-optical Q-switching. The Pockels cell was constructed on the basis of the Brewster angle cut LiNb03 crystal; the Kerr cell used a ceramic PLZT material. In all the three cases the Er:YAG laser resonator was plan parallel and it consisted of the rear copper mirror and output coupler with 50-70% reflectivity. The Er:YAG crystal was pumped by one xenon flashlamp in a single elliptical silver coated cavity. The generated g…

Retinal image quality and visual stimuli processing by simulation of partial eye cataract

Visual stimuli were demonstrated on a 4.3’’ mobile phone screen inside a “Virtual Reality” adapter that allowed separation of the left and right eye visual fields. Contrast of the retina image thus can be controlled by the image on the phone screen and parallel to that at appropriate geometry by the AC voltage applied to scattering PDLC cell inside the adapter. Such optical pathway separation allows to demonstrate to both eyes spatially variant images, that after visual binocular fusion acquire their characteristic indications. As visual stimuli we used grey and different color (two opponent components to vision – red-green in L*a*b* color space) spatially periodical stimuli for left and ri…

Spectral scattering dependencies of controllable PLZT occluder for vision science applications

Summary form only given. PLZT ceramics have an unique property - a facility to change the light scattering efficiency with the applied electric field. This effect is well manifested especially in the visible, just where the transparency windows of PLZT begins. Formerly we developed eye occlusion devices for vision science applications to introduce a dynamic decrease of the image contrast in stereovision tests. In future we plan to construct, using controllable scattering in PLZT, an eye simulator to study cataract caused retinal image quality reduction. The present work reports on spectral dependencies of such an eye occluder studied with the double optical integrated sphere technique.

<title>Polarization-optical visualization of eye inhomogeneities</title>

Polarization sensitive technique is reported for visualization of eye scattering and birefringent inhomogeneities using digital subtracting of eye images captured by a CCD camera for two orthogonal polarizations of light forming images in the CCD camera. For fast capturing of images the polarization plane of the backscattered light is periodically switched at 90 degrees by an electro-optical PLZT phase plate. This plate is placed close to the CCD camera together with a sheet polarizer inserted between camera and the phase plate. Polarization plane is switched applying the voltage 1200 V to the phase plate at a rate of 7.5 Hz. The technique improves visualization due to diminishing of the im…

Multicolour LEDs in educational demonstrations of physics and optometry

LED light sources are used to design experimental setup for university courses teaching human color vision. The setup allows to demonstrate various vision characteristics and to apply for student practical exercises to study eye spectral sensitivity in different spectral range using heterochromatic flicker photometry. Technique can be used in laboratory works for students to acquire knowledge in visual perception, basics of electronics and measuring, or it can be applied as fully computer control experiment. Besides studies of the eye spectral sensitivity students can practice in trichromatic color matching and other visual perception tasks

Tunable liquid lens equipped virtual reality adapter for scientific, medical, and therapeutic goals

We adapted virtual reality appliances to use them in scientific medical diagnostics and therapeutic aims by incorporated as part of appliance ocular system two electrically tunable Optotune liquid lenses, controllable by computer USB ports within 20D range. In present time we used the appliance to investigate the mono- and/or binocularly illusory perception dominances (Shapiro and al;2008), nonlinearities caused by controversial Gestalt recognition of motion. Back layer of stimuli elements contained internal motion sources - clockwise spinning disk on neutral background. Disk consisted of centrosymmetric radial rays which luminance was sinus mode modulated along the disc circumference. Spin…

Multispectral analysis of color vision deficiency tests

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…

Color stimuli perception in presence of light scattering.

Perception of different color contrast stimuli was studied in the presence of light scattering: in a fog chamber in Clermont-Ferrand and in laboratory conditions where light scattering of similar levels was obtained, using different light scattering eye occluders. Blue (shortest wavelength) light is scattered in fog to the greatest extent, causing deterioration of vision quality especially for the monochromatic blue stimuli. However, for the color stimuli presented on a white background, visual acuity in fog for blue Landolt-C optotypes was higher than for red and green optotypes on the white background. The luminance of color Landolt-C optotypes presented on a LCD screen was chosen corresp…

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

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

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…

<title>Factors affecting intraocular light scattering from different color straylight sources</title>

Important optical parameter of the eye is intraocular light scattering. Straylight can reduce visual acuity, contrast sensitivity. It is one of the main factors for glare, especially for drivers at night, when there is light source some distance away from the fixation point. There are many factors, which can affect amount of light scattering in the eye. To assess the effect of the color of the straylight source on retinal image quality at different light scattering levels, retinal straylight was measured with and without light scattering occluder. Red, green and blue colors were choosed for straylight source. Psychophysical and electrophysiological methods were used to evaluate light scatte…

“SmartGlass” Obstacles for Dynamic Inducing of Light Scattering in Vision Research Experiments

We describe a technique that allows control of visual stimuli quality through the use of a setup with a polymer dispersed liquid crystal (PDLC) film positioned in the optical pathway of one or both human eyes. Nowadays, PDLC films allow alteration of the resolution and contrast limits of the transmitted light due to continuous change in the light scattering that is obtained by the application of an AC electrical field. In our experimental setup, the use of a wide-aperture up to area of 20 x 15 cm2 PDLC sheet is combined with a flat-screen PC display or with a modified display emission block without its interference filter unit and with an installed individually controllable colored light-em…

<title>Stereoacuity determination at changing contrast of colored stereostimuli</title>

Studies are focused on design and appraisal of an objective test for assessment of the stereovision quality in unfavorable conditions. Stereostimuli of different colors are used while the contrast of one of the stimulus being varied. Tests are based on principles of black-and-white and two primary color random dot stereotests. Experiments are divided by the method of stimuli display and separation: 1) stereoeffect is obtained haploscopically - by use of spectacles with color filters (blue and red) or prisms, 2) stimuli separation is obtained by liquid crystal shutters when both eye stimuli are demonstrated with a different delay. The stereovision threshold is determiend at different stimuli…

Colour vision experimental studies in teaching of optometry

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…

Phase transitions and properties of perovskite ferroelectric ceramics and films for certain applications

Abstract The structure-properties relationships and phase transitions in perovskite ceramics, and films of PLZT, PLZST, PST, PSN, PMNT compounds are discussed with regard to ordering, relaxor behaviour, pronounced ferroelectric, electromechanical and electrocaloric properties. The theoretical approach is extended to the time dependent Ginsburg-Landau model. The evolution of dielectric properties in relaxors after the change of temperature and electric field creating an increase of dielectric permittivity is found to follow a logarithmic law of decay. A strong electromechanical response is observed in a number of thin films of different compositions.

LED Based Dual Wavelength Heterochromatic Flicker Method for Separate Evaluation of Lutein and Zeaxanthin in Retina

The decrease of density and consequentially optical density of macular pigment serves as a diagnostic mean for a number of ophthalmological pathologies, particularly as a risk factor for age related macular degeneration. Macular pigment absorbs light in short wavelength blue spectral range. Thus the optical density of macular pigment can be detected by various optical – both objective and subjective psychophysical techniques. Latter techniques use eye and brain visual pathways as spectral sensitive optical detector and decision maker, and exploit perception facility to process information flow in a unique manner to create various perception illusions. The psychophysical methods of detection…

Chromostereopsis in "virtual reality" adapters with electrically tuneable liquid lens oculars

Chromostereopsis can be sight and feel in “Virtual Reality” adapters, that induces the appearance of color dependant depth sense and, finally, combines this sense with the source conceived depth scenario. Present studies are devoted to investigation the induced chromastereopsis when using adapted “Virtual Reality” frame together with mobile devices as smartphones. We did observation of composite visual stimuli presented on the high spatial resolution screen of the mobile phone placed inside a portable “Virtual Reality” adapter. Separated for the left and right eyes stimuli consisted of two areas: a) identical for both eyes color chromostereopsis part, and b) additional conventional color ne…

Influence of ocular aberrations on the diameter of retinal blood vessels

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…

Optical phase retrieval using four rotated versions of a single binary amplitude modulating mask

In recent years, phase retrieval methods recovering the phase of an object from coded diffraction patterns have gained popularity. A numerical phase retrieval method called PhaseLift that recovers the phase of an object from a very limited number of coded diffraction patterns was recently proposed. Performance of PhaseLift has been analyzed for different types and the number of masks modulating an object. We present a unique application of PhaseLift that uses four rotations of a single mask, modulating only the amplitude of an object. In simulations, a phase screen with the root-mean-square (RMS) value 0.294  μm was used as the test object. The RMS value of the retrieved phase screen after …

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

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.

<title>Stereovision studies by disbalanced images</title>

Studies are focused on design and appraisal of an objective test of the quality of stereovision depending on optical stimuli blurring and detecting of the stereovision threshold at various stimuli blur degree. The method is based on the principles of grayscale and color random dot stereotests. Experiments may be divided with respect to the principle of demonstration: 1) the blur is modeled by defocusing an optical lens - the strength of the optical system is varied at a constant quality of the stimulus, or 2) the blur is simulated on the computer screen - here the quality of the stimulus varies. To obtain an independent description and to measure blurring the experimentally demonstrated ima…

Pseudoisochromatic test plate colour representation dependence on printing technology

The aim of the study is to determine best printing technology for creation of colour vision deficiency tests. Valid tests for protanopia and deuteranopia were created from perceived colour matching experiments from printed colour samples by colour deficient individuals. Calibrated EpsonStylus Pro 7800 printer for ink prints and Noritsu HD 3701 digital printer for photographic prints were used. Multispectral imagery (by tunable liquid crystal filters system CRI Nuance Vis 07) data analysis show that in case of ink prints, the measured pixel colour coordinate dispersion (in the CIExy colour diagram) of similar colour arrays is smaller than in case of photographic printing. The print quality i…

PLZT ceramics Fabry-Perot interferometers for visible and mid-infrared lasers

Abstract Phenomena characteristic for thermo-optically and electro-optically tunable PLZT ceramics Fabry-Perot interferometers are analyzed, when these devices are used with Ar+ ion and solid state erbium lasers. A new original technique of Q-switching of mid-infrared solid state pulse lasers using a Fabry-Perot output coupler with integrated Q-switch function is reported.

Color difference threshold of chromostereopsis induced by flat display emission

The study of chromostereopsis has gained attention in the backdrop of the use of computer displays in daily life. In this context, we analyze the illusory depth sense using planar color images presented on a computer screen. We determine the color difference threshold required to induce an illusory sense of depth psychometrically using a constant stimuli paradigm. Isoluminant stimuli are presented on a computer screen, which stimuli are aligned along the blue–red line in the computer display CIE xyY color space. Stereo disparity is generated by increasing the color difference between the central and surrounding areas of the stimuli with both areas consisting of random dots on a black backgr…

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

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...

Time response of the vision binocularity by use of dynamic suppression of retinal images

We present a novel technique for determination the stereopsis dynamic response, using as stimulus a random dot stereopair. Stereopsis can be evoked or depressed by continuous or flash illumination of the stimulus with simultaneous control of a special light scattering obstacle build in the visual path of one eye. The obstacle--a thin plate of electrooptical PLZT ceramics-- exposes (by applying of the voltage to semitransparent gold electrodes deposited on both surfaces of the plate) light scattering so blurring the retinal image, similar as for an eye with a cataract, depressing stereopsis. The random dot stereopair contains contours of images with a different stereodisparity. The PLZT plat…

<title>The perception of isoluminant coloured stimuli of amblyopic eye and defocused eye</title>

In routine eye examination the visual acuity usually is determined using standard charts with black letters on a white background, however contrast and colour are important characteristics of visual perception. The purpose of research was to study the perception of isoluminant coloured stimuli in the cases of true and simulated amlyopia. We estimated difference in visual acuity with isoluminant coloured stimuli comparing to that for high contrast black-white stimuli for true amblyopia and simulated amblyopia. Tests were generated on computer screen. Visual acuity was detected using different charts in two ways: standard achromatic stimuli (black symbols on a white background) and isoluminan…

<title>Eye model with controllable lens scattering</title>

A model of human eye for experiments in vision research has been developed using PLZT ceramics. This ``artificial eye{''} allows to simulate light scattering caused by cataract in the eye lens. Light scattering of a composite eye lens of the model depends on the electric field applied to a transparent electrooptic PLZT ceramics plate that is attached directly to the lens. The image degradation in such a model eye at various degrees of scattering is studied observing and recording the contrast of images on the ``retinal plane{''} created by standard test objects with different spatial frequency or by a He-Ne laser source passing a diffractive transparent placed before the eye.

Multispectral analysis and cone signal modelling of pseudoisochromatic test plates

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…

Improvement of solid state Er:YAG pulse laser performance for use in medicine

The large quadratic electro-optic effect of PLZT ceramics allows to design small size modulators for the solid state infrared Er:YAG laser (lasing at (lambda) equals 2.94 micrometers - the most pronounced absorption band of water), which has found application in medicine for efficient ablation of hard and soft tissues. In the free-running mode, the Er:YAG laser emits spikes that form the pulse envelope with duration of 150 - 800 microsecond(s) . An extracavity PLZT 8.5/65/35 ceramics modulator (aperture of 4 X 6 mm2 and length of 18 mm) was used to obtain (Pi) -shaped segments with the rise and decay times less than 5 microsecond(s) . That allows to reduce considerably the fraction of the p…