Subjective fixation disparity affected by dynamic asymmetry, resting vergence, and nonius bias.

2011

PURPOSE This study was undertaken to investigate how subjectively measured fixation disparity can be explained by (1) the convergent-divergent asymmetry of vergence dynamics (called dynamic asymmetry) for a disparity vergence step stimulus of 1° (60 arc min), (2) the dark vergence, and (3) the nonius bias. METHODS Fixation disparity, dark vergence, and nonius bias were measured subjectively using nonius lines. Dynamic vergence step responses (both convergent and divergent) were measured objectively. RESULTS In 20 subjects (mean age, 24.5 ± 4.3 years, visual acuity, ≥1.0; all emmetropic except for one with myopia, wearing contact lenses), multiple regression analyses showed that 39% of the v…

Binocular function measures as predictors of user performance in stereoscopic augmented reality

2021

Inconsistency between the binocular and focus cues in stereoscopic augmented reality overburdens the visual system leading to its stress. However, a high individual variability of tolerance for visual stress makes it difficult to predict and generalize the user gain associated with the implementation of alternative visualization technologies. In this study, we investigated the relationship between the binocular function and perceptual judgments in augmented reality. We assessed the task completion time and accuracy of perceptual distance matching depending on the consistency of binocular and focus cues in the stereoscopic environment of augmented reality. The head-mounted display was driven…

Performing visual tasks by children with amblyopia.

2021

Changes in physiological astigmatism of human eye during accommodation in emmetropes (Conference Presentation)

2017

Introduction: Most young emmetrope eyes are far from ideal and have some degree of minor spherocylindrical error including also physiological astigmatism. Because of the changes in the shape of optical interfaces, pupil size, eyelid pressure, tear film, body posture, binocularity and accommodation astigmatism is considered as constantly dynamic phenomenon (Cheng et al, 2004). The purpose of this study was to evaluate and quantify changes in physiological astigmatism during accommodation. Method: Twenty young emmetropes with mean age 24 ± 4 years were selected for the study. Refraction and accommodative response were measured monocularly for dominant eye with an open-field infrared autorefract…

<title>Additional usage possibilities for the computerized Hess screen</title>

2003

The purpose of the study was to work out a method how to use the computerized Hess screen in proximal vergence measurements. Proximal vergence or vergence due to knowledge of nearness is one of four independent components making up the total vergence response. Proximal vergence is expressed as a ratio - proximal convergence/test distance (PC/T). The computerized Hess screen is usually used to detect and to measure an ocular misalignment in patients with paralytic strabismus in different directions of gaze. The computerized Hess screen can be used to assess PC/T ratio in different directions of gaze, providing the open-loop disparity vergence and accommodation systems and assuming that tonic…

Ocular performance evaluation

2019

Real and virtual three-dimensional (3D) imaging has found useful applications across different areas of health sciences and with the current rapidly progressive development stage we can expect that the use of 3D imaging soon will be a part of a daily visual load for medical personnel. To better understand the possible impact of prolonged work with 3D content on eye accommodative response and pupil size we compared two 3D imaging techniques - volumetric display that is real voxel-based system and anaglyph technique that is virtual pixel-based system. We have investigated accommodative lag and pupil responses in 38 emmetropic young adult after prolonged visual task with volumetric 3D display …

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.

Monocular Versus Binocular Calibrations in Evaluating Fixation Disparity With a Video-Based Eye-Tracker

2015

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 …

Smartphone viewing distance during active or passive tasks and relation to heterophoria

2019

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.…

Focusing in Depth: Post-Task Accommodation Shifts After Sustained Near Work with Volumetric Multi-Planar Display

2018

Post-task refraction shifts were evaluated with eccentric photorefraction technique to better understand response of visual system and eye accommodation to sustained near work with 3D image formed by volumetric display.

Relation between fixation disparity and the asymmetry between convergent and divergent disparity step responses

2007

Abstract The neural network model of Patel et al. [Patel, S. S., Jiang, B. C., & Ogmen, H. (2001). Vergence dynamics predict fixation disparity. Neural Computation, 13 (7), 1495–1525] predicts that fixation disparity, the vergence error for a stationary fusion stimulus, is the result of asymmetrical dynamic properties of disparity vergence mechanisms: faster (slower) convergent than divergent responses give rise to an eso (exo) fixation disparity, i.e., over-convergence (under-convergence) in stationary fixation. This hypothesis was tested in the present study with an inter-individual approach: in 16 subjects we estimated the vergence step response to a 1 deg disparity stimulus with a subje…

Measuring the refractive state of an eye based on the intensity of the retinal reflex

2017

AbstractWhen 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…

When virtual and real worlds coexist: Visualization and visual system affect spatial performance in augmented reality

2021

New visualization approaches are being actively developed aiming to mitigate the effect of vergence-accommodation conflict in stereoscopic augmented reality; however, high interindividual variability in spatial performance makes it difficult to predict user gain. To address this issue, we investigated the effects of consistent and inconsistent binocular and focus cues on perceptual matching in the stereoscopic environment of augmented reality using a head-mounted display that was driven in multifocal and single focal plane modes. Participants matched the distance of a real object with images projected at three viewing distances, concordant with the display focal planes when driven in the mu…

Eccentric fixation measurements using visuoscopy and Macula Integrity Tester (MIT) in children with amblyopia

2021

The aim of the work was to compare measurements of eccentric fixation in children with amblyopia using two different methods, a traditional visuoscopy and MIT. Monocular fixation was evaluated using visuoscopy and MIT in 16 patients (from 5 to 9 years old). Measurements were started with the better seeing eye to compare the results obtained with the amblyopic eye. All study participants were selected with anisometropic and refractive amblyopia. Visuoscopy is simpler than MIT and less dependent on patient responses, so visioscopy can be used for young children who have not yet acquired verbal skills. Children over the age of 5 can more easily understand the MIT method and get more reliable r…

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…

Accommodative Amplitude in School-Age Children

2017

Abstract In children, intensive near-work affects the accommodation system of the eye. Younger children, due to anatomical parameters, read at smaller distance than older children and we can expect that the accommodation system of younger can be affected more than that of older children. We wanted to test this hypothesis. Some authors showed that the norms of amplitude of accommodation (AA) developed by Hofstetter (1950) not always could be applied for children. We also wanted to verify these results. A total of 106 (age 7-15) children participated in the study. Distance visual acuity was measured for all children and only data of children with good visual acuity 1.0 or more (dec. units) we…

Effect of specialized applications on the visual functions of amblyopic eye in Latvian children

2021

The classical treatment option of amblyopia is occlusions of non-amblyopic eye. The newest methods involve specialized computer and phone games, applications that involve both eyes in visual processing during treatment as well as stimulate binocularity. The aim of the work was to assess the efficiency of specialized phone application ‘Duovision’ in the treatment of amblyopia in preschool-age children. There were 30 participants (5-8 years old): 16 participants had occlusion therapy; 14 participants played the specialized phone application Duovision®. The visual acuity of amblyopic eye, as well as stereopsis was evaluated at near and far distances before the treatment, 2 and 4 months after t…