-Recent advances in 3D technology have been accompanied by increasing complaints of visual fatigue. The usual explanation for such fatigue is that accommodation and convergence are mismatched during stereoscopic vision.The aim of this study was to measure fixation distances between lens accommodation and convergence in young subjects while they viewed real objects and 3D video clips. Measurements were made using an original instrument. The 3D video clips were presented to subjects using a liquid crystal shutter glass system. The results showed that when viewing real objects, the diopter values of subjects' accommodation and convergence were similar and changed periodically. This measurement method was thus considered to be appropriate for the measurement of stereoscopic vision. We also investigated lens accommodation and convergence when subjects viewed 3D video clips. Both accommodation and convergence were found to move along with the virtual position of 3D video clips. Therefore, there was little discrepancy between accommodation and convergence during the viewing of 3D images.

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At present, a general belief is that viewing and 3-D images causes eye fatigue and discomfort because of the inconsistency between accommodation and convergence. However, our previous research found that both accommodation and convergence follow the position of virtual 3D objects synchronously. This was especially true in the case of young subjects aged in their 20s.In this study, we simultaneously measured variation of accommodation and convergence and their dependence on pupil diameter by changing the intensity of illumination as well as the brightness of the viewing screen.As a result, in the strongly lit environment, both accommodation and convergence nearly focused on the position of vertical objects. In a weakly lit environment, accommodation tends to focus on a position slightly father than that of convergence which is explained by the variation of pupil diameter.

In recent years, e-readers have spread to many countries. Most of e-readers have a reflective type of display called e-paper. The general view is that under conditions of low illuminance, readability of the e-paper display is poor. However, most recent e-readers have a built-in light system. This system would improve the readability of the e-paper display under low illuminance conditions. We carried out experiments to evaluate the readability e-paper devices using different systems. In the experiments, we conducted subjective evaluations under staged illuminance conditions by using English words. This study found that e-paper devices with built-in light under low illuminance condition were superior in terms of readability.

We carried out experiments to evaluate the readability of reading e-books under staged illuminance conditions (minimum : 10 lx, maximum : 5,000 lx). In the experiments, we conducted subjective evaluations and measured viewing distance. This study found a dependency between readability and illuminance for each device.