Depertment of Optometry and Vision Science

Disparity-difference between the locations of the two retinal projections of a given point in the space, relative to the corresponding points Hypermetropia LC shutters (goggles)-liquid crystal goggles Myopia PDLC plate-light scattering polymer dispersed liquid crystal cells plate that becomes transparent when voltage is applied PLZT plate-Pb 0.905 La 0.095 Zr 0.35 Ti 0.65 O 3 ceramic plate with semitransparent gold electrodes that it becomes uniformly blurred when voltage is applied Presbyopia Stereoacuity-the lowest disparity value, measured in angle units, by which subjects perceive stereostimuli as a spatial image; this term is used more in clinics to evaluate the quality of stereovision Stereogram Stereothreshold, stereovision threshold-the lowest disparity value by which subjects perceive stereostimuli as a spatial image, a term having the opposite meaning to stereoacuity, by high stereoacuity the stereothreshold is low, both measured in angle units

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 1 (B.Julesz 1974). 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.

Background / Purpose: Global motion perception is the perception of coherent motion in a noisy motion stimulus. This task strongly involves extrastriate brain areas, were the dorsal stream dominates. The aim of our study was to determine global motion perception thresholds of typically developing children with different reading skills. Main conclusion: Global motion thresholds decreased with age for all dot velocities (2 deg/sec, 5 deg/sec and 8 deg/sec) and were significantly higher at 8 deg/sec. Motion perception for poor and good readers differed only for velocity of 2 deg/sec.

When measuring fixation disparity (an oculomotor vergence error), the question arises as to whether a monocular or binocular calibration is more precise and physiologically more appropriate. In monocular calibrations, a single eye fixates on a calibration target that is taken as having been projected onto the center of the fovea; the corresponding vergence state represents the heterophoria (the resting vergence position), which has no effect on the calibration procedure. In binocular calibrations, a vergence error may be present and may affect the subsequent measurement of the fixation disparity during binocular recordings. This study includes a test of the precision of both monocular and binocular calibrations and an evaluation of the impact of the calibration procedure on the measurement of fixation disparity during a dot scanning task. Our results show that 11 participants (out of 19) each exhibited a significant difference in fixation disparity with the two types of calibration ...

Illusory depth sense observing colour planar image such as images presented on computer screen is studied. The effect is binocular and is based on human stereovision, i.e., stereopsis. The colour difference threshold needed to induce the depth sense is determined. The effect polarity reversal-the source image red plane in front of blue plane is observed by partial covering of eye pupils medially or laterally. It is explain by the changes of eye point spread function taking into account coloured ray source and longitudinal chromatic eye aberrations. Image lightness affects the inducing of colour stereopsis due to changes of eye pupil size. Illusory depth sense is essential when designing colour graphical output on computer screen.

The aim of our study was to determine DEM test performance norms for school-aged children in Latvia, assess how DEM test results correlate with children's reading rates, compare test performance between strong and weak readers. A modified DEM test and a newly developed reading test were administered to 1487 children during a screening survey. Our study provides norms for adjusted DEM scores for children from 7 to 18 years of age. A high correlation exists between a child's reading rate and her DEM speed scores for both parts of the test. Weak readers performed significantly more slowly on the DEM test than strong readers. Overall, 6 % of the subject population scored 1 standard deviation below the mean value on both the DEM and reading tests. We conclude that these individuals may be at a higher risk for developing reading impairments.

When examining the fundus of the eye with an ophthalmoscope, the intensity of the retinal reflex depends on the refractive state of the eye. In this study, application of this phenomenon for measuring the refractive state of the eye is demonstrated. First, a calibration curve relating the intensity of the retinal reflex and the refractive state was obtained using a model eye. Next, the intensity of the retinal reflex was measured while subjects were viewing a checker-board pattern, the distance of which was varied within the range from 0.17 to 1 m. Further, the relation between the refractive state and the optical power of the stimulus could be determined based on the measured light intensity and the calibration curve. Generally, the measured refractive state increased with the optical power of the stimulus. However, blinking and fluctuations in accommodation had undesired effects on the results.

The aim of this study was to assess the visual acuity of myopes with standard and reversed contrast optotypes and to determine how the visual acuity of myopes is affected by optical defocus and the type of optical correction, either contact lenses or spectacles. Twenty-three myopic subjects (18 and 23 years old) with uncorrected vision had their visual acuity assessed with both standard and reversed contrast optotypes. The study also included 10 myopes with contact lens as well as habitual spectacle correction. The visual acuity for myopes with uncorrected vision was better with reversed than standard contrast optotypes. Better reversed contrast than standard contrast visual acuity was obtained also with spectacle and contact lens correction. This result could be due in part to low order aberrations (optical defocus) in myopes spectacle or contact lenses correction.

Volumetric display shows promising implications for healthcare related applications as an innovative technology that creates real three-dimensional (3D) image by illuminating points in three-dimensional space to generate volumetric images without image separation. We used eccentric photorefractometry to objectively study ocular performance in a practical environment by evaluating near work-induced refraction shift, accommodative microfluctuations, and pupil size for 38 young adults after viewing anaglyph, and volumetric 3D content for prolonged time. The results of our study demonstrate that participants who performed relative depth estimation task on volumetric 3D content were less likely to experience task-induced myopic refraction shift. For both 3D content types, we observed pupil constriction, that is possibly related to visual fatigue. For anaglyph 3D pupil constriction, onset was observed significantly sooner, compared to volumetric 3D. Overall, sustained work with 3D content...

The visual search performance of radiologists is systematically challenged due to the use of flat-panel displays when viewing multi-slice images. Three-dimensional visualization of information is expected to facilitate visual search for radiologists. However, as the differences in user performance, depending on radiologist experience, have not yet been assessed for real three-dimensional images, it is difficult to estimate the usability of new visualization systems for radiologists with different amounts of professional search experience. In this study, we aimed to determine how three-dimensional visual search is affected by radiologist experience and the physical properties of stimuli. Radiologists, residents, and medical students accomplished visual search tasks with varying set sizes and target-distractor similarities. Search items were presented on multiple display planes and image manipulation was conducted using a computer keyboard. We compared the search outcome and strategy ...

Background: The image optical quality is affected by changes in corneal shape of patients with keratoconus. The goal of this study was to explore which corneal parameters determine the visual quality in keratoconus subjects, which corneal slope parameter has the strongest correlation with visual quality and contrast sensitivity. Methods: The study covered eyes of 77 subjects, graded from the first to third keratoconus stages. To characterize the shape of cornea, we obtained measurements in two ways: (a) projected two perpendicular axes onto a cornea – the main axis passed through the central point of the cornea (visual axis projection) and keratoconus apex, while the second axis was perpendicular to the main axis – and read elevation values at points on theses axis; (b) projected circles with different diameters around the central part of the cornea (1, 2 and 3 mm) and read elevation values at points equally displaced on these circles. The measurements were used to calculate various...

Background: To understand which irregular corneal parameters determine the visual quality in keratoconus subjects. Methods: The cross-sectional study examined thecovered eyes of 44 subjects, graded from the first to third keratoconus stages by Amsler-Krumeich classification. To characterize the shape of cornea, wWe obtained measurements in two ways: (a) by projectinged two perpendicular axes onto a cornea (– the main axis passed first, through the central point of the cornea (visual axis projection) and keratoconus apex; second, as , while the second axis was perpendicular to the main axis) to – and read the elevation values at points on theses axeis as parameters characterising the corneal surface; (b) by projectinged circles with different diameters around the central part of the cornea (1, 2, and 3 mm) and reading elevation values at points equally displaced on these circles as parameters characterising an anterior surface slope. Irregular corneal shape parameters’ correlations w...

N3 Z -1.859 -0.192 -0.019 -2.273 -2.257 -2.882 p 0.063 0.848 0.985 0.023 0.024 0.004 N5 Z -0.284 -1.026 -2.533 -2.512 -0.246 -0.844 p 0.776 0.305 0.011 0.120 0.805 0.399 N6 Z -0.101 -0.675 -2.999 -1.922 -0.856 0.259 p 0.919 0.500 0.003 0.055 0.392 0.796 N7 Z -1.188 -0.993 -0.083 -0.046 -0.215 -2.159 p 0.235 0.320 0.933 0.964 0.830 0.031 Table 4. Results of Mann-Whitney U test for fixation time in first and repeated experiment. Table 5. Results of Mann-Whitney U test for saccades in first and repeated experiment.

High-speed saccadic eye movements serve the function of moving the fovea on to the part of array that we want to process in detail. The contribution of peripheral vision is essential in planning and controlling saccadic eye movements. For this reason, central information analysis and selection of next saccadic targets can affect saccades, fixation duration and time needed to complete the visual search task [1]. Methods are developing to train saccades, fixations and effective information processing via magnocelullar flow using visual search task [2, 3]. Moreover, only one target is chosen to be found amongst other distractors in a visual search task. Therefore the aim of the present study was to define whether influence of peripheral information could be traced in the parameters of eye movements and fixations. Apart from this, the efficiency of the performance of visual search task was investigated.

High-speed saccadic eye movements serve the function of moving the fovea on to the part of array that we want to process in detail. The contribution of peripheral vision is essential in planning and controlling saccadic eye movements. For this reason, central information analysis and selection of next saccadic targets can affect saccades, fixation duration and time needed to complete the visual search task [1]. Methods are developing to train saccades, fixations and effective information processing via magnocelullar flow using visual search task [2, 3]. Moreover, only one target is chosen to be found amongst other distractors in a visual search task. Therefore the aim of the present study was to define whether influence of peripheral information could be traced in the parameters of eye movements and fixations. Apart from this, the efficiency of the performance of visual search task was investigated.

It is known that brightness of the retinal reflex depends on the refractive state of an eye. This phenomenon is often faced by optometrists and ophthalmologists. Thus accommodation of an eye also contributes to the retinal brightness. This means that the retinal brightness could be used to measure the accommodative lead and lag characteristic to the accommodative response [1]. There is a wide variety of techniques for measuring the dynamic accommodation, i.e., the characteristics of accommodation while the gaze is fixated onto moving targets.Among these methods the following methods can be mentioned: infrared photorefraction [2], measurement of anterior chamber depth, MEM dynamic retinoscopy, 3-D OCT, autorefraction etc. However, brightness of the retinal reflex has never been used previously for measuring the accommodative response. The goal of this study was to design a method and device for measuring the accommodative response to stimuli with various spectral distribution and det...

We randomly presented trial images using two colored light sources (red and blue luminophores) on a DELL U2412M display with pixel pitch 0.27 mm. The distance to display was 0.8 m. Therefore displaying 1px comprises an angle around the visual limit of 1’. We used a series of trials – up to 30 presentations of each color difference pair (Fig.1). The observers’ positive responses to the query “Is the center part closer?” were counted as “1” and summed. The psychometric curves were fit with a sigmoidal function (where the trial sample set number N was used as the ordinate). The sigmoidal function slope parameter was used to calculate the effect threshold NTh.

Many children have undetected vision problems or insufficient visual information processing that may be a factor in lower academic outcomes. The aim of this paper is to contribute to a better understanding of the importance of vision screening for school-aged children, and to investigate the possibilities of how eye-tracking (ET) technologies can support this. While there are indications that these technologies can support vision screening, a broad understanding of how to apply them and by whom, and if it is possible to utilize them at schools, is lacking. We review interdisciplinary research on performing vision investigations, and discuss current challenges for technology support. The focus is on exploring the possibilities of ET technologies to better support screening and handling of vision disorders, especially by non-vision experts. The data orginate from a literature survey of peer-reviewed journals and conference articles complemented by secondary sources, following a rapid ...