The aberrations demonstrate the changes in light direction when it passes through the eye’s optical system. Our study goal was to evaluate the impact of keratoconus apex’s localization on eye aberration. 79 eyes were analysed in our study by keratoconus stage and by apex localization. Vertical coma had a statistically significant difference p=0.03 (Mann-Whitney test) between first (1.4 μm) and third (3.9 μm) keratoconus stage. The mean spherical aberration in case of central apex was 0.6 μm and in case of peripheral apex was 1.0 μm (p=0.01). The keratoconic eyes have increased corneal aberrations comparing to normal eyes.
Both in medicine and optometry, clinical guidelines have become a relevant part of clinical practice decision making process. In our study, we aimed to refer to potential limitations related to specific undefined guidelines used in optometry that suggest near addition (add) values based on patient age. We measured near add binocularly at 40 cm distance with plus build up technique in 216 adults aged 35 to 80 years. Baseline subjective refraction, near visual acuity with and without add was analysed in a relation to age and the amount of near add. For further analysis, we randomly selected 30 patients and performed five different near add estimation techniques. Our results support that there is a positive, linear relationship of moderate strength between age and amount of near add (r = 0.73, P < 0.05). Relationship is positive and fairly strong (r = -0.78, P < 0.05) between near visual acuity without add and near add amount and moderate (r = -0.51, P < 0.05) between near visual acuity without add and patient age. Differences between plus build up technique is not statistically significant if compared with other clinical near add estimation techniques (P > 0.05). Guideline based technique (P < 0.01) provided 0.29 D higher near add while technique based on calculations from amplitude of accommodation (P < 0.01) provided 0.65 D lower near add. Based on our results, we highlight that usability of age expected near add in clinical environment is limited because of large individual differences.
Our aim was to analyze viewing distance for smartphone users (aged 18-45 y.) in terms of passive or active task, relation to heterophoria, type of refractive error and smartphone font size. Participants were asked to read out loud text message (passive task) and afterwards rewrite the same text and send back (active task). For the text message we used sentence consisting of 23 words and 200 characters (with spaces). Participants used their own smartphones (font size monitored). For both passive and active task we measured task time and viewing distance at the end of the task. We found significantly shorter viewing distance for digital active task compared to passive task (29.3 ± 4.7 and 32.3 ± 6.0 cm) and also for digital passive task compared to hardcopy passive task (32.3 ± 6.0 and 34.4 ± 5.9 cm). There was no difference between viewing distance with and without low plus lenses (low add) for digital active task (29.9 ± 5.4 and 29.3 ± 4.7 cm) and for digital passive task (31.4 ± 6.4 and 32.3 ± 6.0 cm). Viewing distance and reading/writing speed was not influenced by type of refractive error and heterophoria type. The interaction between task type and heterophoria type was not significantly associated neither with viewing distance (P = 0.77), nor relative viewing distance (P = 0.54). Writing speed decreased significantly with age (P < 0.001), while reading speed was not influenced by the age (P > 0.05). The explanation, why some people prefer closer viewing distance when using smartphone, seems to be more related to task type and relatively shorter length of forearm not type of refractive error or near heterophoria type.
The visual search abilities of radiologists are systematically trained due to the specifics of their professional tasks. We investigated whether the visual-motor performance of radiologists, residents and students varied when searching non-medical targets on the volumetric display. As a result, no significant differences were found in the correct response rate among three groups. However, the total number of interactions was considerably higher for the resident radiologists and medical students comparing to the experienced radiologists. Our results suggest that the radiological experience does not interfere with the outcome in the developed visual search task, but may be reflected in motor behavior.
In natural viewing, numerous depth cues are available to the visual system, but their significance varies considerably depending on the viewing distance. How is it reflected in the outcome of depth judgements? We have designed a psychophysical experiment with a limited number of depth cues to examine distance-related changes in the correct response rate and time. Twenty young adults evaluated relative depth of stimuli in physical space. Each time four constant angular size achromatic stimuli were presented on a volumetric multi-planar display. One of these stimuli was demonstrated closer to the observer comparing to others. The experiment followed the four-interval forced-choice procedure. On any given trial, observers determined which one of four stimuli was located closest to them. The nine viewing distances ranged from 0.5 m to 2.5 m. Overall, the depth judgements were correct and fast at the close viewing distances. However, the correct response rate dropped markedly at 1.0 m distance and continued declining gradually at larger distances. The average response time experienced the linear growth with increasing distance. In total, we showed that the relative depth judgements based on binocular depth cues changed the most at the viewing distances that exceeded 1.0 m, as well as the response time and correctness were affected to varying degrees.
In diagnostics, radiologists search for anatomical abnormalities through generated three-dimensional data on flat displays. Professionals are required to scroll repeatedly through image stacks forth and back, as well as remember a broad amount of visual information. This process leads to working memory overload and decreased search outcome. In contrast, a volumetric multi-planar display includes many planes, which makes possible to visualize data in a true physical depth. Thus, theoretically, it can facilitate the visual search performance in diagnostics and lessen the necessity for repeated scrolling. Therefore, our work aims to explore practically the extent to which the visual search is effective, as well as deliver evidence on the scrolling strategy through image stacks when data are shown on many display planes. Visual search set consisted of constant angular size stimuli presented on ten out of twenty display planes in two depth segments. Participants searched for a target with varying target-distractor similarity within trials. All ten images were presented simultaneously in the beginning of each trial and participants scrolled freely through them. In the result, target discriminability affected significantly the correct response rate and time, as well as search behavior was consistent with the physical design of stimuli set. In more detail, the number of moves through image stack almost doubled when the target-distractor similarity increased and, overall, participants skipped searching repeatedly already seen images. The developed visual search task is suggested for implementation in studies of visual perception and search behavior in threedimensional displays.
In medical imaging, large sets of two-dimensional images are used for evaluating anatomical structures. Observers experience high cognitive load due to necessity of memorizing information and data is not seen in a real volume. A volumetric multi-planar display is a promising technology that can eliminate above mentioned issues by producing images in a real three-dimensional space. Therefore, the goal of our study was to investigate how well individuals perceived a difference in spatial localization of visual stimuli and describe its impact on visual search performance in three-dimensional digital space. Participants searched for a target stimulus which was located closer to the observer comparing to other stimuli in different depth segments of a display and provided subjective evaluation of the task difficulty. The results revealed that on average visual attention could be deployed without significant differences on all four depths segments in terms of response time and quality. But at the same time, eccentricity of stimuli influenced considerably the performance which can be related to higher cognitive load due to limitation of visual acuity and attention in the peripheral visual field. To be added, subjective evaluation of perceived task difficulty matched well response time and accuracy in visual search. The obtained results leaded to the conclusion that spatial layout of stimuli in horizontal and vertical dimension had a bigger impact on visual search performance comparing to the third dimension on a volumetric multi-planar display.
To date, there is no assessment of more than one survey used for a clinical research study that address subjects with and without symptoms related to accommodative or binocular vision disorders. Thus, the purpose of this study was to investigate two different surveys – CISS and Conlon for the same subject group and analyse also critical visual function parameters. Monocular and binocular accommodative response for 20 subjects was measured for dominant eye with openfield infrared autorefractometer (Shin-Nippon SRW-5000) at three distances (24 cm, 30 cm and 40 cm). Subjects were divided into symptomatic and asymptomatic group using cut off score 21 for CISS and 20 for Conlon survey. We found positive exponential growth relationship between CISS and Conlon scores (R² = 0.7), but separation between symptomatic and asymptomatic group differed significantly depending on which survey was used. We found positive correlation between Conlon score and exophoria at 30 cm (r=0.41, p=0.01) and 24 cm (r=0.27, p=0.03). Relationship between subjective symptoms and following clinical parameters - accommodation lag (r < 0.2, p < 0.05), positive relative accommodation (r < 0.15, p < 0.05) and convergence near point (r = 0.26, p < 0.05) were not significant. Our results confirmed that using different subjective symptom surveys can provide different results within the same subject group, therefore we recommend to use surveys as a part of case history and tool to measure patient satisfaction and results of treatment effectiveness instead of using them for clinical trials as a criteria to divide symptomatic and asymptomatic group.
Instead of selecting arbitrary elements our visual perception prefers only certain grouping of information. There is ample
evidence that the visual attention and perception is substantially impaired in the presence of mental fatigue. The question
is how visual grouping, which can be considered a bottom-up controlled neuronal gain mechanism, is influenced. The
main purpose of our study is to determine the influence of mental fatigue on visual grouping of definite information –
color and configuration of stimuli in the psychophysical experiment. Individuals provided subjective data by filling in
the questionnaire about their health and general feeling. The objective evidence was obtained in the specially designed
visual search task were achromatic and chromatic isoluminant stimuli were used in order to avoid so called pop-out
effect due to differences in light intensity. Each individual was instructed to define the symbols with aperture in the same
direction in four tasks. The color component differed in the visual search tasks according to the goals of study. The
results reveal that visual grouping is completed faster when visual stimuli have the same color and aperture direction.
The shortest reaction time is in the evening. What is more, the results of reaction time suggest that the analysis of two
grouping processes compete for selective attention in the visual system when similarity in color conflicts with similarity
in configuration of stimuli. The described effect increases significantly in the presence of mental fatigue. But it does not
have strong influence on the accuracy of task accomplishment.
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.
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 isoluminant
coloured stimuli (white symbols on a yellow background, grey symbols on blue, green or red background). Thus
isoluminant tests had colour contrast only but had no luminance contrast. Visual acuity evaluated with the standard
method and colour tests were studied for subjects with good visual acuity, if necessary using the best vision correction.
The same was performed for subjects with defocused eye and with true amblyopia. Defocus was realized with optical
lenses placed in front of the normal eye. The obtained results applying the isoluminant colour charts revealed worsening
of the visual acuity comparing with the visual acuity estimated with a standard high contrast method (black symbols on a
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 ocular prevalence.
Blurring causes a smooth change of the prevalence towards the nonblurred stimuli eye. The influence of moderate
scattering depends heavily on stimuli color. At a sufficiently high scattering level the instable switching from the
prevalence of one eye to the prevalence of the other occurs.
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 higher stereothreshold
values than the rest of the methods. The PLZT and PDLC plates scattered more in the blue and decreased the contrast of
the stimuli when the blurring degree was increased. In the eye occluder method, the stereothreshold increased faster than
in the defocusation and monitor stimuli methods when the visual acuity difference was higher than 0.4. It has been
shown that the PLZT and PDLC plates are good optical phantoms for the simulation of a cataract, while the defocusation
and monitor stimuli methods are more suitable for amblyopia.
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.
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 images are analyzed with regard to modulation depth, Fourier frequencies and by cross-correlation.
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 disparities simulating the random dot stereotests on a computer monitor with a variable contrasts of one-color stimuli. The applied test differ by stimuli geometry, separation of vision channels, and by data processing. Tests have been appraised and may be used in stereovision studies.
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 impact of eye movements and due to accumulation of the imaging digital data.