Tsuneto Iwasaki

Stereoscopic 3‐D display with optical correction for the reduction of the discrepancy between accommodation and convergence

— This paper describes a method for reducing the discrepancy between accommodation and convergence when viewing stereoscopic 3-D images. The method uses a newly developed stereoscopic 3-D display system with a telecentric optical system and a mobile LCD. The examination of a mono-focal lens showed that a correction lens having the appropriate refractive power and conditions for presenting stereoscopic 3-D images clearly reduces the discrepancy between accommodation and convergence. The authors also developed a stereoscopic 3-D display that uses dynamic optical correction to reduce the discrepancy between accommodation and convergence. The display equalizes the theoretical points of accommodation and convergence. The purpose of the development was to expand the regeneration range of a stereoscopic 3-D image having the appropriate accommodation. An evaluation of the developed display showed that it resolves the discrepancy between convergence and accommodation.

Objective evaluation of eye strain using measurements of accommodative oscillation

Accommodative oscillations occurring during eye strain induced by two different types of experimental visual search task—visual display terminal (VDT) work and conventional hard-copy (paper) work— were objectively measured using infrared optometry. The low-frequency component (0 to 1-5 Hz) of the accommodative oscillation was found to be significantly increased after the VDT work, but not after the paper work. At other frequencies there were no significant differences between the two work types and no significant effect of the task itself. In a questionnaire survey the subjects using the VDT complained more than the subjects given paper work of ocular symptoms such as eye strain and blurred vision. These results suggest that measurement of changes in accommodative oscillation, particularly the low-frequency component (0 to 15 Hz), may provide an objective parameter of eye strain.

The tolerance range of binocular disparity on a 3D display based on the physiological characteristics of ocular accommodation

Abstract This study investigates the permissible value of horizontal binocular disparity when gazing at a three-dimensional (3D) display based on ocular accommodation function. For the closely perceived image on the 3D display screen, the crossed disparity of +1.0° and of +0.5° were given and for the far image, which gave the image far away from the screen, the uncrossed disparities of −1.0° and of −0.5° were taken. The disparity was 0° when the image was displayed on the screen. When the disparity was +1.0° and the stereoscopic image had been perceived, the accommodative response became significantly larger in comparison to that at 0°. An accommodation lead was observed significantly at a disparity +1.0°. The tolerance of binocular disparity on the 3D display based on the physiological aspect of ocular accommodation is thus suggested to be less than +1.0°.

The change in colour critical flicker fusion (CFF) values and accommodation times during experimental repetitive tasks with CRT display screens

Two groups of normal subjects were loaded an experimental visual task, or a calculating and discriminating task, on a CRT display screen under different work speeds and amounts. The colour (red, green and yellow) CFF values of the subjects were measured every 15 min during the task and their accommodative function, represented by the accommodation time, was measured before and after the task. The two groups of subjects showed no significant differences in the pattern of change in the colour CFF values. The green and yellow CFF deteriorated significantly at 30 min after the start of the task. The red CFF values decreased significantly at 15 min after the start of the task and this conditions continued to the end of the task. Both groups showed a lengthening accommodation relaxation time but no change in the accommodation relaxation time after the task. This increase in the relaxation time was larger in the group of subjects who were loaded a larger amount of work at a higher speed. The results suggest that the decrease in the CFF value of the subject, particularly when the subject sees light directly using a CRT display screen, does not signify the decline in the activity or consciousness level of the brain centre alone.

Eye-strain and changes in accommodation of the eye and in visual evoked potential following quantified visual load

The measurements were made of the muscular contractions and relaxations of accommodation (infrared optometer) and of visual evoked potential (VEP) (photic stimulation) before and after one hours visual load, checking calculations (1800 questions/hour and 900 questions/hour). The results showed that the relaxation time in accommodation lengthened and the latency of the positive wave appearing at about 100 ms in VEP increased with the increase in visual load. In addition, the complaint rate for eye-strain was higher in the group given heavier visual work. In this group, there was no significant difference in amplitude of VEP before and after the visual task. The difference in the relaxation time before and after the visual task tended to be negatively correlated to the difference in amplitude of VEP and positively related to that in the latency. In the group given lighter visual work there were significant differences in the latency and the amplitude of VEP before and after the visual task, neither were co...

Surmised state of accommodation to stereoscopic three-dimensional images with binocular disparity

Three-dimensional image (3-D image) was experimentally generated by the binocular disparity principle, and psychological tests were performed in relation to the state of accommodation. An image of a square formed by the time-sharing system using liquid crystal (LC) shutter glasses was displayed before the CRT screen (forward image) by the crossed visual-line method and behind the monitor screen (backward image) by the non-crossed visual-line method. The subjects were requested to subjectively compare each image with the original image on the CRT screen in relation to the size. The forward image displayed by the crossed visual lines looked smaller than the original image, while the backward image displayed by the non-crossed visual lines looked larger. In consideration of the developmental mechanism of micropsia occurring in patients with accommodative palsy or paresis of accommodation and macropsia occurring in patients with accomodative spasm, it was surmised that, in the generation of 3-D image due to binocular disparity, accommodation works so that the original image position is maintained.

Effects of a visual task with cognitive demand on dynamic and steady‐state accommodation

Dynamic accommodative response before and after, and steady‐state accommodation during, a visual task were measured using an infrared optometer to investigate the effects of psychological stress on accommodative facility. Increase in the post‐task dynamic accommodation response time (for a near‐to‐far condition) was greater for a group of subjects given a mental task at a higher presentation speed. In addition the steady‐state accommodation showed an inward shift under a closed‐loop condition which was enhanced when computation time was decreased. However, an inward shift was not evident when the performance level of subjects increased following training. The relationship between psychological stress. cognitive demand and accommodative function is discussed.

A study on visual characteristics of binocular 3-D images

To put the binocular 3-D image system into practical use, it is necessary to investigate the relationship between the system and human subjects in order to make an ergonomic evaluation of the system. In this study, a comparative analysis is made of the changes in the accommodation and pupil functions before and after observing binocular 3-D images as the visual distance varies. The results suggest that: (1) the discordance in the distance information on the accommodation and pupil functions when observing 3-D images is compensated by the miosis and altering the focal depth, (2) from the consideration of the effect of the visual distance condition on the visual functions, it is believed that the visual functions are stabilized at the dark focus in the sense that the changes in the contraction and relaxation after observing the 3-D images are minimized.

Examination of a stereoscopic 3D display system using a correction lens

This paper describes an examination of a stereoscopic 3-D display system using a correction lens. The purpose of the system is to reduce the accommodation and convergence difference during viewing stereoscopic 3-D images by using simple technique. This correction lens is a mono-focal lens, and added to the polarized filter glasses. In this study, the authors carried out three experiments in order to examine the appropriate utilization conditions and effects of the correction lens. In experiment 1, the refractive power of correction lens was examined under six conditions in which distances of accommodation and convergence were theoretically equal. In experiment 2, the presenting condition of stereoscopic 3-D images suitable for the correction lens was examined by measurement of refractions during viewing visual target that moved in depth direction. In experiment 3, the effectiveness of the correction lens was examined by using the utilization conditions obtained in experiment 1 and 2. From the results of the experiments, the following conclusions were drawn. (1) Correction lenses shift the accommodation distance. (2) Using a correction lens with the appropriate refractive power and setting the appropriate conditions for presenting stereoscopic 3-D images reduced the difference between accommodation and convergence. (3) The use of a correction lens affected the subjective symptoms of asthenopia.

Potential Preventive Effects of a New Visual Intervention for Accommodative Insufficiency and Asthenopia due to Sustained Near Task

Background: The objective of this study was to experimentally investigate whether a new visual intervention with optical and binocular vergence demands prevents accommodative insufficiency and asthenopia after sustained periods of visual task. Methods: Fourteen female students were given the intervention with optical and binocular vergence demands for 1.5 min immediately after 20 min of a sustained task on a three-dimensional display. Before and after the trial, their ocular functions were measured and their symptoms assessed. A new type of intervention was developed that can vary optical and binocular vergence demands. For control, the subjects rested with eyes closed for 1.5 min after the task instead of the intervention. Results: In the control group, accommodative contraction time (from far to near) and accommodative relaxation time (from near to far) was delayed from 1.13 to 1.68 s and from 1.36 to 1.60 s, respectively, and the symptom of asthenopia increased after rest. In the intervention group, however, changes in those functions were smaller than those in the control group. Conclusions: These results suggest that the new intervention with optical and binocular vergence demands is effective for the treatment of accommodative insufficiency that follows sustained periods of visual task, and consequently, the symptom of asthenopia induced by accommodative insufficiency may decrease.